Patent Application
20220409887
The invention relates to neuromodulation of a nerve supplying the spleen, more particularly to devices, systems and methods that stimulate neural activity in the nerve, and even more particularly to signal parameters and electrode design. The invention also relates to devices, systems and methods that stimulate neural activity in the nerve for the treatment of inflammatory disorders.
Inflammation plays a fundamental role in host defenses and the progression of immune-mediated diseases (reviewed in [1]). The inflammatory response is initiated in response to an injury and/or an infection by chemical mediators (e.g. cytokines and prostaglandins) and inflammatory cells (e.g. leukocytes). A controlled inflammatory response is beneficial, for example, in the elimination of harmful agents and the initiation of the repair of damaged tissue providing protection against infection. However, the inflammatory response can become detrimental if dysregulated, leading to a variety of inflammatory disorders such as rheumatoid arthritis, osteoarthritis, asthma, allergies, septic shock syndrome, atherosclerosis, and inflammatory bowel disease, Crohn's disease, ulcerative colitis, and other clinical conditions mediated by chronic inflammation.
The spleen contains half of the body's monocyte population making this organ the main contributor in inflammation. This organ is known to be innervated by different nervous branches (reviewed in [2]). The parasympathetic innervation of the spleen is a matter of debate since Dale's isolation of acetylcholine (ACh) from the spleen [2]. Buij and co-workers have suggested a parasympathetic innervation of the spleen in rodents [3,4], but human correlation to this nerve is not known. The traditional view of splenic innervation is proposed to be 98% sympathetic as demonstrated by neuroanatomical and neurochemical evidences [2].
From a functional point of view, vagus nerve stimulation (reviewed in [5]) as well as the nerve plexus surrounding the splenic artery, referred to herein as the splenic arterial nerve, inhibit LPS-induced TNF release in mice [6]. According to Tracey and coworkers, the splenic arterial nerve activity is directly controlled by the cholinergic anti-inflammatory pathway (CAP) originating from the efferent branch of the vagus [5]. While vagal regulation of inflammatory tone and inflammatory reflex has received much attention, others have disputed the connections between vagus and splenic arterial nerve. Some authors have shown that denervation of the splenic arterial nerve in mice led to the inhibition of the CAP [6]. However, Martelli et al. have challenged this view by showing that the splenic arterial nerve was not directly connected to the vagus [7] but rather emerged as an independent branch of the greater splanchic nerve which controls splenic arterial nerve activity [8,9]. These authors also counter the view that neural sensing of inflammatory markers is humoral and not neural [10]. Furthermore, it is disputed whether the efferent arm of the inflammatory reflex response is sympathetic or parasympathetic.
Electrostimulation of the vagus nerve has been shown to relieve symptoms of rheumatoid arthritis in a clinical trial [11]. However, there are concerns that stimulation of the vagus nerve can produce undesired, non-specific side effects because the vagus nerve is comprised of approximately 100,000 nerve fibres with 80% going to the brain and 20% innervating most of the organs, including the heart, liver and gastrointestinal tract.
Electrical stimulation of the splenic nerves is associated with vascular responses of the spleen [12]. References [6,13,14,15] describe electrical stimulation of the splenic arterial nerves for the treatment of inflammatory disorders. However, the electrical parameters used in these references to cause stimulation of neural activity may lead to off-target effects such as a change in splenic artery and vein blood flow as well as changes in systemic arterial blood pressure and heart rate.
Thus, there is a need for further and improved ways of stimulating neural activity in a nerve supplying the spleen for treating inflammatory disorders, including autoimmune disorders (e.g. rheumatoid arthritis, osteoarthritis, psoriatic arthritis, spondyloarthropathy, ankylosing spondylitis, psoriasis, lupus, multiple sclerosis, Inflammatory Bowel Disease, Crohn's disease, and ulcerative colitis) and sepsis.
Stimulation of neural activity in a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve), can be achieved using electrical signals. When using electrical signals for such purposes, stimulation of neural activity is caused by the influence of electrical currents of the electrical signal on the distribution of ions across the nerve membrane.
The amount of electrical current that is required for stimulation of neural activity is typically characterized by the pulse height that is supplied to the nerve by the electrical signal, which may vary depending on the waveform of the electrical signal. Through experimental studies, the inventors have found improved waveforms of the electrical signal which decrease the pulse height required in order to stimulate neural activity in a human nerve supplying the spleen, thereby optimizing the biological efficacy and reproducibility of stimulation parameters of the electrical signal for use in humans whilst reducing the burden on the signal generator.
Thus, the invention provides a system for stimulating the neural activity of a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle, preferably a splenic arterial nerve. The system comprises at least one electrode in signaling contact with the nerve, and at least one controller electrically coupled to the at least one electrode. The at least one controller configured to control the operation of the least one electrode to apply an electrical signal to the nerve. The electrical signal either has a frequency of 300 Hz and is applied in a periodic on-off pattern, or has a frequency of ≤50 Hz and is applied continuously. On-off pattern stimulation may also be referred to as burst stimulation or periodic stimulation. The electrical signal comprises a pulse train having a pulse width >1 ms.
The invention also provides a method for treating inflammatory disorders in a subject. The method comprises providing a system of the invention, positioning at least one electrode in signaling contact with a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve), and controlling the operation of the least one electrode with at least one controller to apply an electrical signal to the nerve to stimulate neural activity.
The invention also provides a method of reversibly stimulating neural activity in a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve). The method comprises providing a system of the invention, positioning the at least one electrode in signaling contact with the nerve, and controlling the operation of the least one electrode with at least one controller to apply an electrical signal to the nerve to stimulate neural activity.
The invention also provides a method for determining whether a neural interface is correctly placed in signaling contact with a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve). The method comprises providing the system of the invention, positioning the neural interface in signaling contact with the nerve, controlling the operation of the least one electrode with at least one controller to apply an electrical signal to the nerve, determining that a change in blood flow rate in the spleen, splenic artery, splenic vein, a decrease in spleen volume, an increase in neural activity in the nerve, or a change in impedance of the at least one electrode has been detected, and indicating to an operator that the neural interface had been placed correctly in signaling contact with the nerve.
In other words, the invention provides stimulation parameters for different functions. More specifically, continuous stimulation may be used to induce blood flow changes within the splenic vasculature that can be detected and used as on-table or pen-surgically as an indicator of successful electrode placement and/or amplitude determination; and periodic stimulation may be used as a preferred treatment paradigm, whereby such blood flow change and/or other possible systemic effects are avoided whilst maintaining efficacy as a treatment.
Thus, the electrical signal either has a frequency of ≤300 Hz and is applied in a periodic on-off pattern for treatment, or has a frequency of ≤50 Hz and is applied continuously for indication of electrode placement and/or amplitude determination. In view of these different functions, the continuous application may be used first for indication of electrode placement and/or amplitude determination, and then the periodic on-off pattern stimulation may be used once the electrode placement and/or amplitude has been determined.
For example, a continuous stimulation ≤10 Hz may be used for efficacy and/or treatment; and/or a continuous stimulation ≤30 Hz and ≥5 Hz may be used for blood flow detection; and/or a periodic stimulation ≥10 Hz may be used for efficacy and/or treatment.
The invention also provides a computer-implemented method for treating inflammatory disorders in a subject. The method comprises controlling the operation of at least one electrode of the system of the invention to apply an electrical signal to a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve) to stimulate neural activity. The invention also provides a computer-implemented method of reversibly stimulating neural activity in a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve). The method comprises controlling the operation of at least one electrode of a system of the invention to apply an electrical signal to the nerve to stimulate neural activity.
The invention also provides a computer-implemented method of determining whether a neural interface is correctly placed in signaling contact with a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve). The method comprises controlling the operation of the at least one electrode of the system of the invention to apply an electrical signal to the nerve, determining that a change in blood flow rate in the spleen, splenic artery, splenic vein, a decrease in spleen volume, an increase in neural activity in the nerve, or a change in impedance of the at least one electrode has been detected, and indicating to an operator that the neural interface had been placed correctly in signaling contact with the nerve.
The invention also provides a neurostimulatory electrical signal for use in treating an inflammatory disorder in a subject, wherein the electrical signal is the electrical signal any electrical signal according the invention.
The invention also provides a modified nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. splenic arterial nerve) to which a system of the invention is in signaling contact, wherein the at least one electrode is in signaling contact with the nerve and so the nerve can be distinguished from the nerve in its natural state, and wherein the nerve is located in a subject who suffers from, or is at risk of, an inflammatory disorder.
The invention also provides a modified nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve) bounded by a nerve membrane, comprising a distribution of potassium and sodium ions movable across the nerve membrane to alter the electrical membrane potential of the nerve so as to propagate an action potential along the nerve in a normal state; wherein at least a portion of the nerve is subject to the application of a temporary external electrical field which modifies the concentration of potassium and sodium ions within the nerve, causing depolarization of the nerve membrane, thereby, in a disrupted state, temporarily generating an action potential de novo across that portion; wherein the nerve returns to its normal state once the external electrical field is removed.
The invention also provides a modified nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve) obtainable by stimulating neural activity of the nerve according to a method of the invention.
The invention also provides a neural interface suitable for placement around a plurality of splenic arterial nerves, where the neural interface fully circumvents the plurality of splenic arterial nerves and comprises at least one electrode.
The invention also provides a neural interface suitable for placement around at least one splenic arterial nerve and the splenic artery, where the neural interface circumvents the splenic artery and the at least one splenic nerve by at least 50%, preferably at least 75%, and comprises at least one electrode.
The invention also provides a method of controlling a system of the invention which is placed in signaling contact with a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve), comprising a step of sending control instructions to the system, in response to which the system applies an electrical signal to the nerve.
The Nerves Surrounding the Spleen
Innervation of the spleen is primarily sympathetic or noradrenergic, with peptide neurons likely representing the bulk of the remaining neurons. The human spleen is traditionally considered to be innervated by the splenic plexus surrounding the splenic artery only. The splenic artery is covered with nervous tissue, which is derived from the coeliac plexus and continues with the splenic artery to the spleen as the splenic plexus. The splenic plexus enters the spleen at the hilum where the splenic artery diverges in terminal branches and the splenic plexus continues with these branches into the parenchyma of the spleen.
The splenic plexus includes several nerve fascicles which circumvent the main splenic artery from celiac artery to spleen, each nerve fascicle comprising a small bundle of nerve fibers. A nerve fascicle (or known as a pen-arterial nerve fascicle) that circumvents the splenic nerve is referred to herein as a splenic arterial nerve.
The invention involves applying an electrical signal to, and thereby modulating the neural activity of, a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle. Preferably, the nerve is a splenic arterial nerve.
In some embodiments, the nerve is a sympathetic nerve.
In some embodiments, the invention may involve applying a signal to one splenic arterial nerve. In other embodiments, the invention may involve a plurality (i.e. a bundle) of splenic arterial nerves.
In other embodiments, the invention may involve applying an electrical signal to at least one splenic arterial nerve and the splenic artery. In other embodiments, the invention may involve applying an electrical signal to all splenic arterial nerves and the splenic artery.
Stimulation of a Nerve Supplying the Spleen
The invention involves applying an electrical signal to a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve) to stimulate neural activity in the nerve. Stimulation refers to where signaling activity at least part of the nerve being increased compared to baseline neural activity in that part of the nerve, where baseline neural activity is the signaling activity of the nerve in the subject prior to any intervention. Put another way, stimulation results in the creation of neural activity which increases the total neural activity in that part of the nerve.
“Neural activity” of a nerve refers to the signaling activity of the nerve, for example the amplitude, frequency and/or pattern of action potentials in the nerve. The term “pattern”, as used herein in the context of action potentials in the nerve, is intended to include one or more of: local field potential(s), compound action potential(s), aggregate action potential(s), and also magnitudes, frequencies, areas under the curve and other patterns of action potentials in the nerve or sub-groups (e.g. fascicules) of neurons therein.
Stimulation typically involves increasing neural activity e.g. generating action potentials beyond the point of the stimulation in at least a part of the nerve. At any point along the axon, a functioning nerve will have a distribution of potassium and sodium ions across the nerve membrane. The distribution at one point along the axon determines the electrical membrane potential of the axon at that point, which in turn influences the distribution of potassium and sodium ions at an adjacent point, which in turn determines the electrical membrane potential of the axon at that point, and so on. This is a nerve operating in its normal state, wherein action potentials propagate from point to adjacent point along the axon, and which can be observed using conventional experimentation.
One way of characterizing a stimulation of neural activity is a distribution of potassium and sodium ions at one or more points in the axon, which is created not by virtue of the electrical membrane potential at adjacent a point or points of the nerve as a result of a propagating action potential, but by virtue of the application of a temporary external electrical field. The temporary external electrical field artificially modifies the distribution of potassium and sodium ions within a point in the nerve, causing depolarization of the nerve membrane that would not otherwise occur. The depolarization of the nerve membrane caused by the temporary external electrical field generates de novo action potential across that point. This is a nerve operating in a disrupted state, which can be observed by a distribution of potassium and sodium ions at a point in the axon (the point which has been stimulated) that has an electrical membrane potential that is not influenced or determined by the electrical membrane potential of an adjacent point.
Stimulation of neural activity is thus understood to be increasing neural activity from continuing past the point of signal application. Thus, the nerve at the point of signal application is modified in that the nerve membrane is reversibly depolarized by an electric field, such that a de novo action potential is generated and propagates through the modified nerve. Hence, the nerve at the point of signal application is modified in that a de novo action potential is generated.
When the signal is an electrical signal, the stimulation is based on the influence of electrical currents (e.g. charged particles, which may be one or more electrons in an electrode in signaling contact with the nerve, or one or more ions outside the nerve or within the nerve, for instance) on the distribution of ions across the nerve membrane.
Stimulation of neural activity encompasses full stimulation of neural activity in the nerve—that is, embodiments where the total neural activity is increased in the whole nerve.
Stimulation of neural activity may be partial stimulation. Partial stimulation may be such that the total signaling activity of the whole nerve is partially increased, or that the total signaling activity of a subset of nerve fibers of the nerve is fully increased (i.e. there is no neural activity in that subset of fibers of the nerve), or that the total signaling of a subset of nerve fibers of the nerve is partially increased compared to baseline neural activity in that subset of fibers of the nerve. For example, an increase in neural activity of ≤20%, ≤25%, ≤30%, ≤35%, ≤40%, ≤45%, ≤50%, ≤60%, ≤70%, ≤80%, ≤90% or ≤95%, or an increase of neural activity in a subset of nerve fibers of the nerve.
Neural activity may be measured by methods known in the art, for example, by the number of action potentials which propagate through the axon and/or the amplitude of the local field potential reflecting the summed activity of the action potentials.
Stimulation of neural activity may be an alteration in the pattern of action potentials. It will be appreciated that the pattern of action potentials can be modulated without necessarily changing the overall frequency or amplitude. For example, stimulation of neural activity may be (at least partially) corrective. As used herein, “corrective” is taken to mean that the modulated neural activity alters the neural activity towards the pattern of neural activity in a healthy subject, and this is called axonal modulation therapy. That is, upon cessation of signal application, neural activity in the nerve more closely resembles (ideally, substantially fully resembles) the pattern of action potentials in the nerve observed in a healthy subject than prior to signal application. Such corrective stimulation can be any stimulation as defined herein.
For example, application of a signal may result in an increase on neural activity, and upon cessation of signal application the pattern of action potentials in the nerve resembles the pattern of action potentials observed in a healthy subject. By way of further example, application of the signal may result in neural activity resembling the pattern of action potentials observed in a healthy subject and, upon cessation of the signal, the pattern of action potentials in the nerve remains the pattern of action potentials observed in a healthy subject.
Stimulation of neural activity may comprise altering the neural activity in various other ways, for example increasing a particular part of the baseline neural activity and/or stimulating new elements of activity, for example: in particular intervals of time, in particular frequency bands, according to particular patterns and so forth.
One advantage of the invention is that stimulation of neural activity is reversible. Hence, the modulation of neural activity is not permanent. For example, upon cessation of the application of a signal, neural activity in the nerve returns substantially towards baseline neural activity within 1-60 seconds, or within 1-60 minutes, or within 1-24 hours (e.g. within 1-12 hours, 1-6 hours, 1-4 hours, 1-2 hours), or within 1-7 days (e.g. 1-4 days, 1-2 days). In some instances of reversible stimulation, the neural activity returns substantially fully to baseline neural activity. That is, the neural activity following cessation of the application of a signal is substantially the same as the neural activity prior to a signal being applied. Hence, the nerve or the portion of the nerve has regained its normal physiological capacity to propagate action potentials.
In other embodiments, stimulation of neural activity may be substantially persistent. As used herein, “persistent” is taken to mean that the neural activity has a prolonged effect. For example, upon cessation of the application of a signal, neural activity in the nerve remains substantially the same as when the signal was being applied—i.e. the neural activity during and following signal application is substantially the same. Reversible modulation is preferred.
Suitable Forms of an Electrical Signal
The invention uses an electrical signal applied via at least one electrode which placed in signaling contact with a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve). As used herein, “signaling contact” is where at least part of the electrical signal applied via the at least one electrode is received at the nerve.
Electrical signals applied according to the invention are ideally non-destructive. As used herein, a “non-destructive signal” is a signal that, when applied, does not irreversibly damage the underlying neural signal conduction ability of the nerve. That is, application of a non-destructive signal maintains the ability of the nerve or fibers thereof, or other nerve tissue to which the signal is applied, to conduct action potentials when application of the signal ceases, even if that conduction is in practice artificially stimulated as a result of application of the non-destructive signal.
Electrical signals applied according to the invention may be a voltage or a current waveform.
The electrical signal may be characterized by one or more electrical signal parameters. The electrical signal parameters include waveform, frequency, and amplitude.
Alternatively or additionally, the electrical signal may be characterized by the pattern of application of the electrical signal to the nerve. The pattern of application refers to the timing of the application of the electrical signal to the nerve. The pattern of application may be continuous application or periodic application, and/or episodic application.
Episodic application refers to where the electrical signal is applied to the nerve for a discrete number of episodes throughout a day. Each episode may be defined by a set duration or a set number of iterations of the electrical signal.
Continuous application refers to where the electrical signal is applied to the nerve in a continuous manner. Where the electrical signal is applied continuously and episodically, it means that the signal is applied in a continuous manner for each episode of application. In embodiments where the electrical signal is a series of pulses, the gaps between those pulses (i.e. between the pulse width and the phase duration) do not mean the signal is not continuously applied.
Periodic application refers to where the electrical signal is applied to the nerve in a repeating pattern (e.g. an on-off pattern). Where the electrical signal is applied periodically and episodically, it means that the signal is applied in a periodic manner for each episode of application.
The inventors have found improved waveforms of the electrical signal which decrease the pulse height required in order to stimulate neural activity in a human nerve supplying the spleen, whilst reducing the burden on the signal generator. The improved waveforms are discussed in detail below.
Waveform
Modulation (e.g. stimulation) of a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve), can be achieved using electrical signals which serve to replicate the normal neural activity of the nerve. Thus, the waveform of the electrical signal comprises a pulse train.
A pulse train comprises a plurality of sequential pulses, which may be characterized by pulse width, pulse height and/or interphase delay. Pulse width refers to the time duration between the start of a pulse and the end of the same pulse. Interphase delay refers to the time period from the end of a pulse to the start of the next pulse. Pulse height, which is also referred to as pulse amplitude, refers to the amplitude of current of the pulse, typically measured in amps.
Pulse width and pulse height are preferably constant for all of the pulses in the pulse train. Likewise, interphase delay is preferably constant between all of the pulses in the pulse train.
The inventors found that for pulse widths of >1 ms (i.e. greater than 1 ms, not including 1 ms) a decrease in the pulse height required to stimulate neural activity in a human splenic nerve is observed. The pulse height required to stimulate neural activity in a nerve is also referred to herein as the ‘stimulation threshold’ and the ‘pulse height threshold’. A decrease in the pulse height threshold is advantageous because the biological efficacy of the electrical signal is improved for use in humans. Moreover, implantable signal generators can have a limitation of the maximum pulse height they can output and in some cases higher amplitudes can have safety concerns. Therefore, with some signal generators a decrease in the pulse height threshold can be advantageous as it translates to a higher degree of nerve activation at a lower amplitude achievable by the signal generator. Therefore, the pulse width of the pulse train may have a lower limit of >1 ms.
The inventors also found that for pulse widths over 5 ms there is an increase in both the pulse height threshold and the amount of charge density required in order to stimulate neural activity in a human splenic nerve. As a consequence, the biological efficacy is significantly reduced for pulse widths above 5 ms. Moreover, at these values of pulse height and charge density, the likelihood of tissue scarring in the nerve is increased significantly. Therefore, a pulse width above 5 ms is not desirable for use in humans. Accordingly, the pulse width of the pulse train may have an upper limit of ≤5 ms.
Moreover, the inventors found that for pulse widths greater than 3 ms there is a negligible decrease in the pulse height threshold beyond that experienced by pulse trains having a pulse width of >1 ms. However, for pulse widths greater than 3 ms the amount of charge density per phase required increases. Therefore, the biological efficacy is reduced for pulse widths greater than 3 ms such that diminishing benefits are seen whilst potentially compromising electrochemical integrity of the electrodes, thereby reducing reproducibility of stimulation parameters. More importantly, at pulse widths of around 3 ms tissue scarring starts to be observed. Therefore, the pulse width of the electrical signal may have an upper limit of ≤3 ms.
The inventors also found that for pulse widths around 2 ms both the pulse height threshold required is minimised. Accordingly, the pulse width may be between 1.5 and 2.5 ms, preferably between 1.75 ms and 2.25 ms, more preferably between 1.9 ms and 2.1 ms, even more preferably between 1.95 ms and 2.05 ms, even more preferably between 1.99 ms and 2.01 ms, even more preferably 2 ms.
The inventors additionally found that the inclusion of an interphase delay reduces the threshold of pulse height required to stimulate neural activity in a human splenic nerve. Therefore, in some examples, the pulse train may have an interphase delay.
The inventors further found that longer interphase delays produce greater reductions in pulse height threshold. Accordingly, the interphase delay may have a lower limit of ≥0.1 ms, more preferably ≥0.15 ms, even more preferably ≥0.19 ms, even more preferably still ≥0.2 ms. At interphase delays greater than 0.3 ms it was found that there is no further reduction in pulse height threshold. Accordingly, the upper limit of interphase delay of the pulse train may be ≤0.3 ms, more preferably ≤0.25 ms. Any combination of the upper and lower limits of interphase delay is possible. Preferred ranges of interphase delay include between 0.1 ms and 0.3 ms, and between 0.2 ms and 0.25 ms.
The pulses are preferably square pulses. However, other pulse waveforms such as sawtooth, sinusoidal, triangular, trapezoidal, quasitrapezodial or complex waveforms may also be used with the invention.
The pulses may be biphasic in nature. The term “biphasic” refers to a pulse which applies to the nerve over time both a positive and negative charge (anodic and cathodic phases). For biphasic pulses, the pulse width includes the time duration of a primary phase of the waveform, for example the anodic phase or the cathodic phase.
The pulses may be charge-balanced. A charge-balanced pulse refers to a pulse which, over the period of the pulse, applies equal amounts (or thereabouts) of positive and negative charge to the nerve. The biphasic pulses are preferably charge-balanced.
The pulses may be symmetric or asymmetric. A symmetric pulse is a pulse where the waveform when applying a positive charge to the nerve is symmetrical to the waveform when applying a negative charge to the nerve. An asymmetric pulse is a pulse where the waveform when applying a positive charge to the nerve is not symmetrical with the waveform when applying a negative charge to the nerve.
If the biphasic pulse is asymmetric, but remains charged balanced, then the areas of the opposing phases must equal. Amplitude (see below) can be reduced, but the pulse width would need to be extended to ensure the area under the curve is matched.
In an exemplary embodiment, the waveform is a pulse train with biphasic, asymmetric, charge balanced square pulses.
Amplitude
For the purpose of the invention, the amplitude is referred to herein in terms of charge density per phase. Charge density per phase applied to the nerve by the electrical signal is defined as the integral of the current over one phase (e.g. over one phase of the biphasic pulse in the case of a charge-balanced biphasic pulse). Thus, charge density per phase applied to the nerve by the electrical signal is the charge per phase per unit of contact area between at least one electrode and the nerve, and also the integral of the current density over one phase of the signal waveform. Put another way, the charge density per phase applied to the nerve by the electrical signal is the charge per phase applied to the nerve by the electrical signal divided by the contact area between at least one electrode (generally the cathode) and the nerve.
The charge density per phase required by the invention represents the amount of energy per cm2 required to stimulate neural activity in a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve) to increase immunesuppressive effects.
The charge density per phase required to stimulate neural activity in a porcine splenic arterial nerve is between 5 μC to 150 μC per cm2 per phase or in some cases between 5 μC to 180 μC per cm2 per phase using an extravascular cuff (values may be slightly affected by electrode design). For example, the charge density per phase applied by the electrical signal may be ≤10 μc per cm2 per phase, ≤15 μc per cm2 per phase, ≤20 μC per cm2 per phase, ≤25 μC per cm2 per phase, ≤30 μC per cm2 per phase, ≤40 μC per cm2 per phase, ≤50 μC per cm2 per phase, ≤75 μC per cm2 per phase, ≤100 μC per cm2 per phase, ≤125 μC per cm2 per phase, ≤150 μC per cm2 per phase, or ≤180 μC per cm2 per phase. Additionally or alternatively, the charge density per phase applied by the electrical signal may be ≥5 μC per cm2 per phase, ≥10 μC per cm2 per phase, ≥15 μC per cm2 per phase, ≥20 μC per cm2 per phase, ≥25 μC per cm2 per phase, ≥30 μC per cm2 per phase, ≥40 μC per cm2 per phase, ≥50 μC per cm2 per phase, ≥75 μC per cm2 per phase, ≥100 μC per cm2 per phase, ≥125 μC per cm2 per phase, or ≥150 μC per cm2 per phase. Any combination of the upper and lower limits above is also possible.
The charge density per phase required to stimulate neural activity in a human splenic arterial nerve is between approximately 70-1300 μC per cm2 per phase. For example, the charge density per phase applied by the electrical signal may be ≤80 μC per cm2 per phase, ≤140 μC per cm2 per phase, 170 μC per cm2 per phase, ≤230 μC per cm2 per phase, ≤250 μC per cm2 per phase, ≤300 μC per cm2 per phase, ≤350 μC per cm2 per phase, ≤400 μC per cm2 per phase, ≤450 μC per cm2 per phase, ≤500 μC per cm2 per phase, ≤1100 μC per cm2 per phase, or ≤1300 μC per cm2 per phase. Additionally or alternatively, the charge density per phase applied by the electrical signal may be ≥70 μC per cm2 per phase, ≥140 μC per cm2 per phase, ≥170 μC per cm2 per phase, ≥230 μC per cm2 per phase, ≥250 μC per cm2 per phase, ≥300 μC per cm2 per phase, ≥350 μC per cm2 per phase, ≥400 μC per cm2 per phase, ≥450 μC per cm2 per phase, ≥500 μC per cm2 per phase, ≥1100 μC per cm2 per phase, or ≥1300 μC per cm2 per phase. Any combination of the upper and lower limits above is also possible.
The charge density per phase required to stimulate neural activity in a human splenic arterial nerve may depend on the pulse width being used. The inventors found that the charge density per phase required to stimulate neural activity in a human splenic arterial nerve with a pulse width of 2 ms may to be up to 835 μC per cm2 per phase. Accordingly, the charge density per phase applied by the electrical signal when the pulse width is 2 ms may be ≤80 μC per cm2 per phase, ≤140 μC per cm2 per phase, ≤170 μC per cm2 per phase, ≤230 μC per cm2 per phase, ≤250 μC per cm2 per phase, ≤300 μC per cm2 per phase, ≤350 μC per cm2 per phase, ≤400 μC per cm2 per phase, ≤450 μC per cm2 per phase, ≤500 μC per cm2 per phase, ≤600 μC per cm2 per phase, ≤700 μC per cm2 per phase, or ≤800 μC per cm2 per phase.
The charge density per phase may be ≥5 μC per cm2 and ≤850 μC per cm2, also referred to as between 5 μC per cm2 and 850 μC per cm2 Additionally, the charge density per phase may be ≥5 μC per cm2 and ≤550 μC per cm2, ≥5 μC per cm2 and ≤250 μC per cm2, ≥50 μC per cm2 and ≤250 μC per cm2 or ≥100 μC per cm2 and ≤200 μC per cm2.
The total charge applied to the nerve by the electrical signal in any given time period is a result of the charge density per phase of the signal, in addition to the frequency of the signal, the pattern of application of the signal and the area in contact between at least one electrode and the nerve. The frequency of the signal, the pattern of application of the signal and the area in contact between at least one electrode and the nerve are discussed further herein. It will be appreciated by the skilled person that the amplitude of an applied electrical signal necessary to achieve the intended stimulation of the neural activity will depend upon the positioning of the electrode and the associated electrophysiological characteristics (e.g. impedance). It is within the ability of the skilled person to determine the appropriate current amplitude for achieving the intended modulation of the neural activity in a given subject.
It would be of course understood in the art that the electrical signal applied to the nerve would be within clinical safety margins (e.g. suitable for maintaining nerve signaling function, suitable for maintaining nerve integrity, and suitable for maintaining the safety of the subject). The electrical parameters within the clinical safety margin would typically be determined by pre-clinical studies.
Episodic Application
Episodic application refers to where the electrical signal is applied to the nerve for a discrete number of episodes throughout a day. The electrical signal according to the invention may be applied for up to a maximum of twenty-four episodes per day, up to a maximum of eighteen episodes per day, up to a maximum of twelve episodes per day or up to a maximum of six episodes per day. For example, the number of episodes of signal application per day may be one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, twenty-one, twenty-two, twenty-three or twenty-four. In another embodiment, the number of episodes per day may be up to a maximum of twenty-four times per day, up to a maximum of thirty times per day, up to a maximum of thirty-six times per day, up to a maximum of forty-two times per day or up to a maximum of forty-eight times per day.
The electrical signal may be applied episodically every 2 to 3 hours. For example, the electrical signal may be applied episodically once every 2 hours, 2 hour 15 min, 2 hour 30 min, 2 hour 45 min, 3 hours.
In an additional embodiment, the electrical signal may be applied episodically one to five times per hour. In a further embodiment, the electrical signal may be applied episodically up to a maximum of five times per hour, up to a maximum of ten times per hour, up to a maximum of fifteen times per hour or up to 20 times per hour.
Each episode may be defined by a set duration or a set number of iterations of the electrical signal. In some embodiments, each episode comprises applying to the nerve between 50 and 22000 or between 50 and 10000, e.g. between 60 and 3000 pulses of the electrical signal, between 100 and 2400 pulses of the electrical signal, between 200 and 1200 pulses of the electrical signal, between 400 and 600 pulses of the electrical signal, etc. For example, each episode may comprise applying ≤400, ≤800, ≤1200, ≤1600, ≤2000, ≤2400, ≤3000, ≤10000, ≤15000, ≤18000, ≤20000 or ≤22000 pulses of the electrical signal. In another example, each episode may comprise applying ≤200, ≤400, ≤600, ≤800, ≤1000, or ≤1200 pulses of the electrical signal. In a further example, each episode may comprise applying ≤400, ≤425, ≤450, ≤475, ≤500, ≤525, ≤550, ≤575, or ≤600 pulses of the electrical signal.
In other embodiments, each episode comprises between 20 and 450 iterations, between 20 and 400 iterations, between 20 and 200 iterations, between 20 and 100 iterations, between 20 and 80, or between 20 and 40 iterations of the periodic pattern. For example, each episode comprises applying 20, 25, 30, 35, or 40 iterations of the periodic pattern, or any number therebetween. As another example, each episode may comprise applying 20, 25 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 90, 100, 150, 200, 250, 300, 350, 400 or 450 iterations of the periodic pattern, or any number therebetween. As further example, each episode comprises at least (≥) 50 iterations, ≥75 iterations, ≥100 iterations or ≥150 iterations. Each episode may comprise ≤200 iterations, ≤150 iterations, ≤75 iterations or ≤50 iterations. Any combination of the upper and lower limits is also possible. For example, each episode may comprise ≥50 iterations and ≤200 iterations. The higher the frequency, the lower the number of iterations.
In an additional embodiment, the total charge delivered per day may be up to and including (≤) 900 millicolumbs per 30 minutes. For example, the total charge delivered per day may ≤21,600 millicolumbs per day. In another example, the total charge delivered per day may be less than or equal to 600 millicolumbs per day, less than or equal to 500 millicolumbs per day, less than or equal to 400 millicolumbs per day, less than or equal to 300 millicolumbs per day, less than or equal to 200 millicolumbs per day, less than or equal to 100 millicolumbs per day, less than or equal to 75 millicolumbs per day, or less than 55 millicolumbs per day. The total charge delivered per day may be greater than or equal to 0.5 millicolumbs greater than or equal to 0.6 millicolumbs. greater than or equal to 0.7 millicolumbs, greater than or equal to 0.8 millicolumbs, greater than or equal to 1.0 millicolumb, greater than or equal to 10 millicolumbs, greater than or equal to 20 millicolumbs, greater than or equal to 30 millicolumbs, greater than or equal to 40 millicolumbs, greater than or equal to 50 millicolumbs, greater than or equal to 60 millicolumbs, or greater than or equal to 70 millicolumbs per day. The total charge may be delivered episodically during different pulse burst paradigms. Any combination of the upper and lower limits for the total charge delivered per day is also possible. For example, the total charge delivered per day may be greater than or equal to 0.5 millicolumbs and less than or equal to 600 millicolumbs.
In some embodiments, the episodes may be based on the subject's sleep-wake cycle, in particular the episodes may be whilst the subject is asleep. In some such embodiments, the episodes may be applied between 10 μm and 6 am. The sleep-wake cycle may be measured via known methods by detecting the subject's circadian rhythm phase markers (e.g. cortisol level, melatonin level or core body temperature), and/or a detector for detecting the subject's movements. In some embodiments, the episodes may be applied whilst the subject is awake, for example between 6 am and 10 pm.
Alternatively or additionally, the electrical signal may be applied episodically in regular intervals or in an irregular intervals. For example, 6 episodes may be delivered per day, once every 2 hours, during the wake cycle of a patient. Different episodic intervals may be used between each episode, for example a first episodic interval may be used between first and second episodes and a second episodic interval different from the first episodic interval may be used between the second and third episodes. Different combinations of the upper and lower limits of the following are possible: number of episodes and/or, episodic intervals and/or, sleep-wake cycle and/or forms of electrical signal may be used to achieve a total charge delivered per day discussed above.
Periodic Application
Periodic application refers to where the electrical signal is applied to the nerve in a repeating pattern. The preferred repeating pattern is an on-off pattern, where the signal is applied is applied for a first duration, referred to herein as an ‘on’ duration, then stopped for a second duration, referred to herein as an ‘off’ duration, then applied again for the first duration, then stopped again for the second duration, etc.
The periodic on-off pattern preferably has an on duration of between 0.1 and 10 s and an off duration of between 0.5 and 30 s. For example, the on duration (referred as the time during which pulses at a certain frequency and amplitude are delivered to the nerve) may be ≤0.2 s, ≤0.5 s, ≤1 s, ≤2 s, ≤5 s, or ≤10 s. Alternatively or additionally, the on duration may be ≥0.1 s, ≥0.2 s, ≥0.5 s, ≥1 s, ≥2 s, or ≥5 s. Any combination of the upper and lower limits above for the on duration is also possible. For example, the off duration (referred to the time between on periods, during which no pulses are delivered to the nerve) may be ≤1 s, ≤3 s, ≤5 s, ≤10 s, ≤15 s, ≤20 s, ≤25 s, or ≤30 s. Alternatively or additionally, the off duration may be ≥0.5 s, ≥1 s, ≥2 s, ≥5 s, ≥10 s, ≥15 s, ≥20 s, or ≤25 s. Any combination of the upper and lower limits above for the off duration is also possible. In an exemplary embodiment, the periodic on-off pattern has an on duration of 0.5 s on, and 4.5 sec off. In another example, the periodic on-off pattern has an on duration of 0.5s on, and 5 sec off for up to 10 Hz pulses. For frequency higher than 10 Hz (for example 30 Hz) an example periodic on-off pattern has an on duration of or 0.1s on, and an off duration of 3s. In other words, a ratio of the on duration to the off duration may be 1:5, further preferably wherein the ratio is 1:6, 1;7, 1:8, 1:9, 1:10, 1:20 or 1:30. A ratio of the on duration to the off duration may be 1:10 for pulse frequency up to 10 Hz, and a ratio of the on duration to the off duration may be 1:30 for pulse frequency higher than 10 Hz.
Where the electrical signal is applied periodically and episodically, it means that the signal is applied in a periodic manner for each episode of application.
Periodic application may also be referred to as a duty cycled application. A duty cycle represents the percentage of time that the signal is applied to the nerve for a cycle of the periodic pattern. For example, a duty cycle of 20% may represent a periodic pattern having an on duration of 2 s, and an off duration of 10 s. Alternatively, a duty cycle of 20% may represent a periodic pattern having a on duration of 1 s, and an off duration of 5 s. In other words, periodic application may also be referred to as on-off pattern stimulation, or burst stimulation.
Duty cycles suitable for the present invention are between 0.1% and 100%.
Frequency
Frequency is defined as the reciprocal of the phase duration of the electrical waveform (i.e. 1/phase).
The preferred frequencies for stimulating a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve), are disclosed. In particular, preferred frequencies for embodiments where the electrical signal is applied periodically and for embodiments where the electrical signal is applied continuously are disclosed.
As previously noted, embodiments where the electrical signal is applied periodically and embodiments where the electrical signal is applied continuously provide different functions using different stimulation parameters. A continuous stimulation may be used to induce blood flow changes within the splenic vasculature that can be detected and used as on-table or pen-surgically as an indicator of successful electrode placement and/or amplitude determination; and a periodic stimulation may be used as a preferred treatment paradigm, whereby such blood flow change and/or other possible systemic effects are avoided whilst maintaining efficacy as a treatment.
In embodiments where the electrical signal is applied periodically, the electrical signal has a frequency of ≤300 Hz, preferably ≤50 Hz, more preferably ≤10 Hz. For example, the frequency of the electrical signal may be ≤50 Hz, ≤100 Hz, ≤150 Hz, ≤200 Hz, ≤250 Hz or ≤300 Hz. In other examples, the frequency of the electrical signal may be ≤10 Hz, ≤15 Hz, ≤20 Hz, ≤25 Hz, ≤30 Hz, ≤35 Hz, 40 Hz, ≤45 Hz, or ≤50 Hz. In further examples, the frequency may be ≤1 Hz, ≤2 Hz, ≤5 Hz, or ≤10 Hz. Additionally or alternatively, the frequency of the electrical signal may be ≥10 Hz, ≥15 Hz, ≥20 Hz, ≥25 Hz, ≥30 Hz, ≥35 Hz ≥40 Hz, ≥45 Hz, or ≥50 Hz. In other examples, the frequency of the electrical signal may be ≥0.1 Hz, ≥0.2 Hz, ≥0.5 Hz, ≥1 Hz, ≥2 Hz, or ≥5 Hz. Any combination of the upper and lower limits above is also possible.
In embodiments where the electrical signal is applied continuously, the electrical signal has a frequency of ≤50 Hz, preferably ≤10 Hz, more preferably ≤2 Hz, even more preferably ≤1 Hz. For example, the frequency may be ≤1 Hz, ≤2 Hz, ≤5 Hz, or ≤10 Hz. In other examples the frequency may be 0.1 Hz, ≤0.2 Hz, ≤0.3 Hz, ≤0.4 Hz ≤0.5 Hz, ≤0.6 Hz ≤0.7 Hz, ≤0.8 Hz, or ≤0.9 Hz. Additionally or alternatively, the frequency of the electrical signal may be ≥0.1 Hz, ≥0.2 Hz, ≥0.5 Hz, ≥1 Hz, 2 Hz, or ≥5 Hz. Any combination of the upper and lower limits above is also possible.
Where the signal waveform comprises a pulse train, the pulses are applied to the nerve at intervals according to the above-mentioned frequencies. For example, a frequency of 50 Hz results in 50 pulses being applied to the nerve per second.
Electrode and Neural Interface Design
The electrical signal is applied to a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve), via at least one electrode in signaling contact with the nerve. The at least one electrode may be positioned on a neural interface 10.
In some embodiments, the electrode and/or neural interface is configured for placement around at least one splenic arterial nerve and/or around the splenic artery. In such embodiments, the neural interface may be a cuff type interface, but other interfaces which partially or fully circumvent the nerve may be used.
In other embodiments, the neural interface 10 is configured for placement on the at least one splenic arterial nerve and/or on the splenic artery. In such embodiments, the neural interface 10 may be a patch or clip type interface.
In other embodiments, the neural interface 10 is configured for placement in the splenic artery. In such embodiments, the neural interface may be a catheter or a probe type interface.
In other embodiments, the neural interface 10 is configured for placement in at least one splenic arterial nerve. In such embodiments, the neural interface may be a pin type interface.
The neural interface comprises at least one electrode. The electrodes may fabricated from, or be partially or entirely coated with, a high charge capacity material such as platinum black, iridium oxide, titanium nitride, tantalum, poly(elthylenedioxythiophene) and suitable combinations thereof.
The at least one electrode may be a flat interface electrode which is flexible, particularly in embodiments where the neural interface is configured for placement on or around the at least one splenic arterial nerve and/or the splenic artery so as to circumvent the nerve, and/or the splenic artery when the neural interface 10 is secured on the nerve. However, other electrode types are also suitable for use in the invention.
Other electrode types suitable for the present invention include cuff electrodes (e.g. spiral cuff, helical cuff or flat interface); hemi-cuff electrodes; a mesh, a linear rod-shaped lead, paddle-style lead or disc contact electrodes (including multi-disc contact electrodes); hook electrodes; sling electrodes; intrafascicular electrodes; glass suction electrodes; paddle electrode; and percutaneous cylindrical electrodes.
The at least one electrode may comprise a first electrode 11 and a second electrode 12, referred to herein as a bipolar electrode configuration.
As shown in
In other embodiments, the at least one electrode may comprise a first electrode, a second electrode, and a third electrode, referred to herein as a tripolar electrode configuration.
As with the bipolar configuration, the first, second and third electrodes may be positioned along the longitudinal axis of the nerve, and in one example the second electrode may be positioned between the first electrode 11 and the third electrode 13.
The electrodes may be at least in part insulated from one another by a non-conductive biocompatible material. To this end, a neural interface may comprise a non-conductive biocompatible material which is spaced transversely along the nerve when the device is in use.
The preferred electrode sizes for applying an electrical signal to at least one splenic arterial nerve are disclosed. The total surface area of the electrodes may be 0.1-0.3 cm2. Preferably the total surface area of the electrodes is less than 0.2 cm2. For example, the total surface area of the electrodes may be 0.12 cm2. In another example, the total surface area of the electrodes may be 0.18 cm2.
In preferred electrode configurations, the width of each of the first electrode 11 and the second electrode 12 may be between 1 and 4 mm. For example, the width may be between 1 mm and 3 mm, or between 2 mm and 4 mm, or between 2 mm and 3 mm.
The following coatings and/or surface treatments may be used to modify the capacitance of the electrodes: Iridium oxide; Titanium nitride; PEDOT/PEDOT-PSS; Platinum black; Laser roughened; Electrical dissolution etching; Chemical etching; Silicon Carbide.
Controller
Referring to
The at least one controller may be configured to operate in an open-loop fashion, wherein a predefined signal (as described above) is delivered to the nerve in a predefined pattern of application (also as described above) with or without an external trigger, and without any control or feedback mechanism. Alternatively, the at least one controller may be configured to operate in a closed-loop fashion, wherein a signal is applied based on a control or feedback mechanism.
The at least one controller is preferably constructed so as to generate, in use, a preconfigured and/or operator-selectable signal that is independent of any input in the system 50. The preconfigured and/or operator-selectable signal may be any one of the electrical signals previously described. In other embodiments, the at least one controller is responsive to an external signal, more preferably information (e.g. data) pertaining to one or more physiological parameters of the subject, but still within the confines of the signals previously described.
The at least one controller may be a microprocessor 60 in the system 50, suitable to be implanted in the subject.
Alternatively or additionally, the at least one controller may be a controller external to the subject.
The at least one controller may be triggered upon receipt of a signal generated by an operator, such as a physician or the subject in which the device 106 is implanted. To that end, the system 50 may additionally comprise an external system 80 comprising a controller 101. An example of such a system is described below with reference to
External system 80 of wider system 100 is external the system 50 and external to the subject, and comprises controller 101. Controller 101 may be used for controlling and/or externally powering system 50. To this end, controller 101 may comprise a powering unit 102 and/or a programming unit 103. The external system 80 may further comprise a power transmission antenna 104 and a data transmission antenna 105, as further described below.
The least one controller, including microprocessor 60 and controller 101, may be a processor connected to a memory (i.e. a non-transitory computer readable storage medium) carrying an executable computer program comprising code portions which, when loaded and run on the processor, cause the processor to at least control operation of the at least one electrode. By control the operation is it meant that the at least one controller causes the at least one electrode to apply an electrical signal to the nerve using any of the signal parameters and patterns of application previously described.
Neural Stimulation System
In addition to the neural interface 10 and the at least one controller 60, the system 50 may comprise a signal generator 113 which is configured to deliver the electrical signal described above to the at least one electrode in response to a control operation from the at least one controller. The signal generator may comprise at least one current or voltage source.
The signal generator 113 may be electrically coupled to the at least one controller and to the at least one electrode. In some embodiments, at least one electrode may be coupled to the signal generator 113 via electrical leads 107. In some embodiments, the electrical leads may be coupled to the interconnectors previously described. Alternatively, the signal generator 113 may be directly integrated with the at least one electrode without leads. In any case, the system 50 may comprise a device 106, which may be implanted in the subject, and which may comprise DC current blocking output circuits (or AC current blocking output circuits), optionally based on capacitors and/or inductors, on all output channels (e.g. outputs to the at least one electrode, or physiological sensor 111).
In addition to the neural interface 10, the at least one electrode, the at least one controller, and the signal generator 113, the system 50 may comprise one or more of the following components: implantable transceiver 110; power source 112; memory 114 (otherwise referred to as a non-transitory computer-readable storage device); physiological sensor 111; and physiological data processing module 115. The physiological sensor 111 and physiological data processing module 115 are referred to herein as a detector.
The various components of the system 50 are preferably part of a single physical device, either sharing a common housing or being a physically separated collection of interconnected components connected by electrical leads, as shown in
For example, in some embodiments, one or more of the following components may be contained in the implantable device 106: power source 112; memory 114; and a physiological data processing module 115.
The power source 112 may comprise a current source and/or a voltage source for providing the power for the signal generator 113. The power source 112 may also provide power for the other components of the implantable device 106 and/or system 50, such as the microprocessor 60, memory 114, and implantable transceiver 110. The power source 112 may comprise a battery, the battery may be rechargeable.
It will be appreciated that the availability of power is limited in implantable devices, and the invention has been devised with this constraint in mind. The implantable device 106 and/or system 50 may be powered by inductive powering or a rechargeable power source.
Memory 114 may store power data and data pertaining to the one or more physiological parameters. For instance, memory 114 may store data pertaining to one or more signals indicative of the one or more physiological parameters detected by detector (e.g. via physiological sensor 111, and/or the one or more corresponding physiological parameters determined via physiological data processing module 115). In addition or alternatively, memory 114 may store power data and data pertaining to the one or more physiological parameters from external system 80 via the implantable transceiver 110. To this end, the implantable transceiver 110 may form part of a communication subsystem of the wider system 100, as is further discussed below.
Physiological data processing module 115 is configured to process one or more signals indicative of one or more physiological parameters detected by the physiological sensor 111, to determine one or more corresponding physiological parameters. Physiological data processing module 115 may be configured for reducing the size of the data pertaining to the one or more physiological parameters for storing in memory 114 and/or for transmitting to the external system via implantable transceiver 110. Implantable transceiver 110 may comprise an one or more antenna(e). The implantable transceiver 100 may use any suitable signaling process such as RF, wireless, infrared and so on, for transmitting signals outside of the body, for instance to wider system 100 of which the system 50 is one part.
Alternatively or additionally, physiological data processing module 115 may be configured to process the signals indicative of the one or more physiological parameters and/or process the determined one or more physiological parameters to determine the evolution of the disease in the subject. In such case, the system 50, in particular the implantable device 106, will include a capability of calibrating and tuning the signal parameters based on the one or more physiological parameters of the subject and the determined evolution of the disease in the subject.
The physiological data processing module 115 and the at least one physiological sensor 111 may form a physiological sensor subsystem, also known herein as a detector, either as part of the system 50, part of the implantable device 106, or external to the system.
There may be at least one detector configured to detect one or more physiological parameters relating to the treatment of an inflammatory disorder. For example, reduction in pro-inflammatory cytokines and chemokines, an increase in anti-inflammatory cytokines (e.g. IL-10) and/or resolving mediators (such as resolvins, lipoxins, eicosanoids, maresins and protectins), an increase in catecholamines and acetylcholine, changes in haematology and cell counts; such as changes in immune cell population or immune cell surface co-stimulatory molecules, a reduction in factors involved in the inflammation cascade, and/or a reduction in immune response mediators, as is further discussed below. For example, the detector may be configured for detecting biomolecule concentration using electrical, RF or optical (visible, infrared) biochemical sensors.
There may be at least one detector configured to detect other physiological parameters such as blood flow rate in the spleen, blood flow rate in the splenic artery, blood flow rate in the splenic vein, spleen volume, neural activity in at least one splenic arterial nerve, or impedance of the at least one electrode.
For example, the detector may be configured for detecting blood flow using intra- or pen-vascular flow tubes in or around the artery or vein. Alternatively, detector may detect splenic artery contraction and blood flow changes using electrical impedance tomography, electrical impedance, stimulator voltage compliance, Doppler flow, splenic tissue perfusion, ultrasound, strain measurement, or pressure.
In other examples, the detector may be configured for detecting neural activity of at least one splenic arterial nerve using an electrical sensor. When the detector is configured for detecting neural activity of a single splenic arterial nerve, the detector may detect action potentials. When the detector is configured for detecting neural activity of a plurality of splenic arterial nerve, the detector may detect compound action potentials.
In further examples, the detector may be configured for detecting spleen volume using ultrasound.
In other examples, the detector may be configured to detect impedance of the at least one electrode using an impedance meter, preferably a low-current AC (e.g. 1 kHz) impedance meter. In particular, the detector may detect impedance between the at least one electrode and ground, and/or between pairs of electrodes of the at least one electrodes (where there is a plurality of electrodes). In such examples, the at least one electrode is suitable for placement on or around the nerve.
In other examples, the detector may be configured for detecting the subject's movement using an accelerometer. The accelerometer determines when the subject is asleep by determining if the subject is lying down, i.e. if there has been an extended period (e.g. >70 min) in which the subject has maintained a substantially lying down position. This determination is based on the orientation and acceleration of experienced and measured by the accelerometer.
The physiological parameters determined by the detector may be used to trigger the microprocessor 60 to deliver a signal of the kinds described above to the nerve using the at least one electrode. Upon receipt of the signal indicative of a physiological parameter received from physiological sensor 111, the physiological data processor 115 may determine the physiological parameter of the subject, and the evolution of the disease, by calculating in accordance with techniques known in the art. For instance, if a signal indicative of excessive cytokine (e.g.TNF) concentration in the circulation is detected, the processor may trigger delivery of a signal which dampens secretion of the respective signaling molecule, as described elsewhere herein.
The memory 114 may store physiological data pertaining to normal levels of the one or more physiological parameters. The data may be specific to the subject into which the system 50 is implanted, and gleaned from various tests known in the art. Upon receipt of the signal indicative of a physiological parameter received from physiological sensor 111, or else periodically or upon demand from physiological sensor 111, the physiological data processor 115 may compare the physiological parameter determined from the signal received from physiological sensor 111 with the data pertaining to a normal level of the physiological parameter stored in the memory 114, and determine whether the received signals are indicative of insufficient or excessive of a particular physiological parameter, and thus indicative of the evolution of the disease in the subject.
The system 50 and/or implantable device 106 may be configured such that if and when an insufficient or excessive level of a physiological parameter is determined by physiological data processor 115, the physiological data processor 115 triggers delivery of a signal to the nerve by the at least one electrode, in the manner described elsewhere herein. For instance, if physiological parameter indicative of worsening of any of the physiological parameters and/or of the disease is determined, the physiological data processor 115 may trigger delivery of a signal which dampens secretion of the respective biochemical, as described elsewhere herein. Particular physiological parameters relevant to the present invention are described above. When one or more signals indicative of one or more of these physiological parameters are received by the physiological data processor 115, a signal may be applied to the nerve via the at least one electrode.
In some embodiments, controller 101 may be configured to make adjustments to the operation of the system 50. For instance, it may transmit, via a communication subsystems (discussed further below), physiological parameter data pertaining to a normal level of signaling molecules secreted from the spleen. The data may be specific to the subject into which the device is implanted. The controller 101 may also be configured to make adjustments to the operation of the power source 112, signal generator 113 and processing elements 60, 115 and/or electrodes in order to tune the signal delivered to the nerve by the neural interface 10.
As an alternative to, or in addition to, the ability of the system 50 and/or implantable device 106 to respond to physiological parameters of the subject, the microprocessor 60 may be triggered upon receipt of a signal generated by an operator (e.g. a physician or the subject in which the system 50 is implanted). To that end, the system 50 may be part of a wider system 100 which comprises external system 80 and controller 101, as is further described below.
Beyond the Neural Stimulation System
The neural stimulation system 50 may be part of a wider system 100 that includes a number of subsystems, for example the external system 80, see
The external subsystem 80 may comprise, in addition to controller 101, one or more of: a powering unit 102, for wirelessly recharging the battery of power source 112 used to power the implantable device 106; and, a programming unit 103 configured to communicate with the implantable transceiver 110. The programming unit 103 and the implantable transceiver 110 may form a communication subsystem. In some embodiments, powering unit 102 is housed together with programing unit 103. In other embodiments, they can be housed in separate devices.
The external subsystem 80 may also comprise one or more of: power transmission antenna 104; and data transmission antenna 105. Power transmission antenna 104 may be configured for transmitting an electromagnetic field at a low frequency (e.g., from 30 kHz to 10 MHz). Data transmission antenna 105 may be configured to transmit data for programming or reprogramming the implantable device 106, and may be used in addition to the power transmission antenna 104 for transmitting an electromagnetic field at a high frequency (e.g., from 1 MHz to 10 GHz). The temperature in the skin will not increase by more than 2 degrees Celsius above the surrounding tissue during the operation of the power transmission antenna 104. The at least one antennae of the implantable transceiver 110 may be configured to receive power from the external electromagnetic field generated by power transmission antenna 104, which may be used to charge the rechargeable battery of power source 112.
The power transmission antenna 104, data transmission antenna 105, and the at least one antennae of implantable transceiver 110 have certain characteristics such a resonant frequency and a quality factor (Q). One implementation of the antenna(e) is a coil of wire with or without a ferrite core forming an inductor with a defined inductance. This inductor may be coupled with a resonating capacitor and a resistive loss to form the resonant circuit. The frequency is set to match that of the electromagnetic field generated by the power transmission antenna 105. A second antenna of the at least one antennae of implantable transceiver 110 can be used in system 50 for data reception and transmission from/to the external system 80. If more than one antenna is used in the system 50, these antennae are rotated 30 degrees from one another to achieve a better degree of power transfer efficiency during slight misalignment with the with power transmission antenna 104.
External system 80 may comprise one or more external body-worn physiological sensors 121 (not shown) to detect signals indicative of one or more physiological parameters. The signals may be transmitted to the system 50 via the at least one antennae of implantable transceiver 110. Alternatively or additionally, the signals may be transmitted to the external system 50 and then to the system 50 via the at least one antennae of implantable transceiver 110. As with signals indicative of one or more physiological parameters detected by the implanted physiological sensor 111, the signals indicative of one or more physiological parameters detected by the external sensor 121 may be processed by the physiological data processing module 115 to determine the one or more physiological parameters and/or stored in memory 114 to operate the system 50 in a closed-loop fashion. The physiological parameters of the subject determined via signals received from the external sensor 121 may be used in addition to alternatively to the physiological parameters determined via signals received from the implanted physiological sensor 111.
For example, in a particular embodiment a detector external to the implantable device may include a non-invasive blood flow monitor, such as an ultrasonic flowmeter and/or a non-invasive blood pressure monitor, and determining changes in physiological parameters, in particular the physiological parameters described above. As explained above, in response to the determination of one or more of these physiological parameters, the detector may trigger delivery of signal to a splenic arterial nerve by the at least one electrode, or may modify the parameters of the signal being delivered or a signal to be delivered to the nerve by the at least one electrode in the future.
The system 100 may include a safety protection feature that discontinues the electrical stimulation of the nerve in the following exemplary events: abnormal operation of the system 50 (e.g. overvoltage); abnormal readout from an implanted physiological sensor 111 (e.g. temperature increase of more than 2 degrees Celsius or excessively high or low electrical impedance at the electrode-tissue interface); abnormal readout from an external body-worn physiological sensor 121 (not shown); or abnormal response to stimulation detected by an operator (e.g. a physician or the subject). The safety precaution feature may be implemented via controller 101 and communicated to the system 50, or internally within the system 50.
The external system 80 may comprise an actuator 120 (not shown) which, upon being pressed by an operator (e.g. a physician or the subject), will deliver a signal, via controller 101 and the respective communication subsystem, to trigger the microprocessor 60 of the system 50 to deliver a signal to the nerve by the at least one electrode.
The external system 80 may comprise a display 109 for the microcontroller 60 or the controller 101 to alert the operator (e.g. a physician or the subject) to a state of the system or of the subject. The display 109 may be a monitor such as an LED monitor, or may be a visual indicator such as an LED.
System 100 of the invention, including the external system 80, but in particular system 50, is preferably made from, or coated with, a biostable and biocompatible material. This means that the system is both protected from damage due to exposure to the body's tissues and also minimizes the risk that the system elicits an unfavorable reaction by the host (which could ultimately lead to rejection). The material used to make or coat the system should ideally resist the formation of biofilms. Suitable materials include, but are not limited to, poly(p-xylylene) polymers (known as Parylenes) and polytetrafluoroethylene.
The implantable device 106 of the invention will generally weigh less than 50 g.
Determining Correct Placement of the Neural Interface
The invention also provides a method for determining whether a neural interface 10 is correctly placed in signaling contact with a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle (e.g. a splenic arterial nerve). The method comprises the following steps:
Referring to step A of the method, the system of the invention provided may comprise a neural interface with at least one electrode, at least one controller, and at least one detector. Any other feature of the system described herein may also be provided.
In step B, the electrode and/or neural interface is preferably positioned in signaling contact with the nerve. In some embodiments of the method, step B may be omitted. For instance, step B may be omitted when determining whether an electrode and/or neural interface which was previously implanted has moved over time.
In step C, the at least one controller controls the operation of the at least one electrode to apply the electrical signal to the nerve. The electrical signal may be similar to an electrical signal used to stimulate neural activity described above in that it may have the same waveform, and also apply the same charge density per phase to the nerve. However, the overall charge applied to the nerve is preferably higher. This can be achieved by using continuous signal application instead of periodic signal application, and/or by using a higher frequency than the frequencies described for continuous signal application above.
In particular, the signal may be applied continuously with a frequency of the rate previously described for periodic signal application. Thus, the electrical signal may have a frequency of ≤300 Hz, preferably 50 Hz, more preferably ≤10 Hz. For example, a continuous stimulation ≤10 Hz may be used for efficacy and/or treatment; and/or a continuous stimulation ≤30 Hz and ≥5 Hz may be used for blood flow detection; and/or a periodic stimulation ≥10 Hz may be used for efficacy and/or treatment. For example, the frequency of the electrical signal may be ≤50 Hz, ≤100 Hz, ≤150 Hz, ≤200 Hz, 250 Hz or ≤300 Hz. In other examples, the frequency of the electrical signal may be ≤10 Hz, ≤15 Hz, ≤20 Hz, ≤25 Hz, ≤30 Hz, ≤35 Hz, ≤40 Hz, ≤45 Hz, or ≤50 Hz. In further examples, the frequency may be ≤1 Hz, ≤2 Hz, ≤5 Hz, or ≤10 Hz. Additionally or alternatively, the frequency of the electrical signal may be ≥10 Hz, ≥15 Hz, ≥20 Hz, ≥25 Hz, ≥30 Hz, ≥35 Hz ≥40 Hz, ≥45 Hz, or ≥50 Hz. In other examples, the frequency of the electrical signal may be ≥0.1 Hz, ≥0.2 Hz, 0.5 Hz, ≥1 Hz, ≥2 Hz, or ≥5 Hz. Any combination of the upper and lower limits above is also possible.
The electrical signal may be applied continuously for one of the application episodes previously described (e.g. 400 to 600 pulses). Alternatively, the electrical signal may be applied continuously for an episode defined by a set duration. Preferably the set duration for applying the electrical signal is 3 hours. For example, the set duration may be ≤1 min, ≤2 min, ≤5 min, ≤10 min, ≤20 min, ≤30 min, ≤1 h, ≤2 h, or ≤3 h. Additionally or alternatively, the set duration may be 1 min, ≥2 min, 5 min, ≥10 min, ≥20 min, ≥30 min, ≥1 h, or ≥2 h. Any combination of the upper and lower limits above is also possible.
In step D, the at least one detector may detect one or more of: blood flow rate in the spleen, blood flow rate in the splenic artery, blood flow rate in the splenic vein, spleen volume, neural activity in the nerve, or impedance of the at least one electrode. Suitable detectors for detecting these physiological parameters are described above.
When the detector is configured to detect blood flow rate in the spleen, blood flow rate in the splenic artery, and/or blood flow rate in the splenic vein, the electrode and/or neural interface may be determined to be placed in signaling contact with the nerve correctly when the detected blood flow is different than baseline blood flow.
When the detector is configured to detect neural activity in at the nerve, the electrode and/or neural interface may be determined to be placed in signaling contact with the nerve correctly when the detected neural activity is higher than baseline neural activity.
When the detector is configured to detect spleen volume, the electrode and/or neural interface may be determined to be placed in signaling contact with the nerve correctly when the detected spleen volume is lower than baseline spleen volume. In other words, when the spleen has contracted.
When the detector is configured to detect impedance of the at least one electrode, the electrode and/or neural interface may be determined to be placed in signaling contact with the nerve correctly when the detected impedance is different from baseline impedance. The detected impedance is an impedance between a first electrode and a second electrode of the at least one electrode measured whilst applying the signal to the nerve. “Baseline impedance”, is the impedance between the first electrode and the second electrode before applying the signal to the nerve.
According to step E, once the at least one controller has established that the neural interface has been placed correctly on the nerve, the at least one controller may indicate this to an operator. Indication to an operator may take the form of a notice on a display 109 of the system, a blinking LED, or the like.
If the detector determines that the electrode and/or neural interface is not placed in signaling contact with the nerve correctly, the at least one controller may indicate to an operator, via the display 109, that the neural interface is not correctly placed in signaling contact with the nerve.
If the neural interface has not been placed correctly, then steps B to E can be repeated until the neural interface is correctly placed in signaling contact with the nerve.
Steps C, D and E of the method may be executable by the at least one controller. The at least one controller comprises a processor connected to a memory (i.e. a non-transitory computer readable storage medium) carrying an executable computer program comprising code portions which, when loaded and run on the processor, cause the processor to perform steps C, D and E.
The method for determining placement of the neural interface may also be used to follow up the success of a system of the invention (i.e. one which is implanted in the subject) post operatively through the patient's lifetime (for example using external transcutaneous splenic blood flow measurement or systemic arterial blood pressure as a marker of successful nerve-electrode intercation). Thus, in addition to way of ensuring correct placement, the method provides a way to determine suitable efficacy (in cases where cytokine readouts will not be possible).
Inflammatory Disorders
The invention is useful for treating conditions associated with an imbalance of pro- and anti-inflammatory cytokine profiles compared to the physiological homeostatic state, such as inflammatory disorders (e.g. chronic inflammatory disorders).
Inflammatory disorders are typically characterized by an imbalance of pro- and anti-inflammatory cytokine profiles compared to the normal physiological homeostatic state, e.g. increased pro-inflammatory cytokines levels and/or decreased anti-inflammatory cytokines levels compared to the normal physiological homeostatic state.
Thus, the invention is useful for treating subjects suffering from, or are at risk in developing, inflammatory disorders. The invention may treat or ameliorate the effects of the inflammatory disorders by reducing inflammation. This may be achieved by decreasing the production and release of pro-inflammatory cytokines, and/or increasing the production and release of anti-inflammatory cytokines and/or resolving mediators (e.g. pro-resolvins), from the spleen by reversibly electrically stimulating a nerve supplying the spleen, wherein the nerve is associated with a neurovascular bundle.
Inflammatory disorders include autoimmune disorders, such as arthritis (e.g. rheumatoid arthritis, osteoarthritis, psoriatic arthritis), myasthenia gravis, thryoiditis, systemic lupus erythematosus, Goodpasture's syndrome, Behcets's syndrome, allograft rejection, graft-versus-host disease, ankylosing spondylitis, Berger's disease, diabetes including Type I diabetes, Berger's disease, Retier's syndrome, spondyloarthropathy, ankylosing spondylitis, psoriasis, lupus, multiple sclerosis, Inflammatory Bowel Disease, Crohn's disease, and ulcerative colitis.
Further examples of inflammatory disorders include diseases involving the gastrointestinal tract and associated tissues, such as appendicitis, peptic, gastric and duodenal ulcers, peritonitis, pancreatitis, ulcerative, pseudomembranous, acute and ischemic colitis, inflammatory bowel disease, diverticulitis, cholangitis, cholecystitis, Crohn's disease, and enteritis.
Further examples of inflammatory disorders include diseases of the bones, joints, muscles and connective tissues, such as the various arthritides and arthralgias, osteomyelitis, gout, periodontal disease, rheumatoid arthritis, spondyloarthropathy, ankylosing spondylitis and synovitis.
Further examples include systemic or local inflammatory diseases and conditions, such as asthma, allergy, anaphylactic shock, immune complex disease, sepsis, septicemia, endotoxic shock, eosinophilic granuloma, granulomatosis, and sarcoidosis.
Other examples include diseases involving the urogential system and associated tissues, such as diseases involving the respiratory system and associated tissues, such as bronchitis, cystic fibrosis, adult respiratory distress syndrome, pneumonitis, alvealitis, or bronchiolitis.
Further examples are dermatological diseases and conditions of the skin (such as burns, dermatitis, dermatomyositis, sunburn, urticaria warts, and wheals); diseases involving the cardiovascular system and associated tissues (such as vasulitis, angiitis, endocarditis, arteritis, atherosclerosis, thrombophlebitis, pericarditis, myocarditis, myocardial ischemia, congestive heart failure, periarteritis nodosa, and rheumatic fever); as well as various cancers, tumors and proliferative disorders (such as Hodgkins disease), nosicomal infection; and, in any case the inflammatory or immune host response to any primary disease.
Other examples of inflammatory disorders include diseases involving the central or peripheral nervous system and associated tissues, such as Alzheimer's disease, depression, multiple sclerosis, cerebral infarction. Inflammatory disorders also include conditions associated with immune or inflammatory response (i.e. acute inflammatory episodes) include injury to nerves or other tissue and pain associated with nerve or other tissue. Injury may be due to a physical, chemical or mechanical trauma. Non-limiting examples of injury include acute trauma, burn, and whiplash. Conditions associated with a particular organ such as eye or ear may also include an immune or inflammatory response.
Another example of an inflammatory disorder is post-operative ileus (POI). POI is experienced by the vast majority of patients undergoing abdominal surgery. POI is characterized by transient impairment of gastro-intestinal (GI) function along the GI tract as well pain and discomfort to the patient and increased hospitalization costs. The impairment of GI function is not limited to the site of surgery, for example, patients undergoing laparotomy can experience colonic or ruminal dysfunction. POI is at least in part mediated by enhanced levels of pro-inflammatory cytokines and infiltration of leukocytes at the surgical site. Neural inhibitory pathways activated in response to inflammation contribute to the paralysis of secondary GI organs distal to the site of surgery. Stimulation of neural activity as taught herein may thus be effective in the treatment or prevention of POI.
The invention is particularly useful in treating autoimmune disorders (e.g. rheumatoid arthritis, osteoarthritis, psoriatic arthritis, spondyloarthropathy, ankylosing spondylitis, psoriasis, lupus, multiple sclerosis, Inflammatory Bowel Disease, Crohn's disease, and ulcerative colitis) and sepsis.
Treatment of Inflammatory Disorders
Treatment of the inflammatory disorder can be assessed in various ways, but typically involves determining an improvement in one or more physiological parameters of the subject.
Useful physiological parameters of the invention may be one or more of the group consisting of: the level of a pro-inflammatory cytokine, the level of an anti-inflammatory cytokine and/or resolving mediator, the level of a catecholamine, the level of an immune cell population, the level of erythrocytes, the level of an immune cell surface co-stimulatory molecule, the level of a factor involved in the inflammation cascade, the level of an immune response mediator, and clinical observations and scoring systems (e.g. Disease activity scores or other appropriate methods).
As used herein, an “improvement in a determined physiological parameter” is taken to mean that, for any given physiological parameter, an improvement is a change in the value of that parameter in the subject towards the normal value or normal range for that value—i.e. towards the expected value in a healthy subject. As used herein, “worsening of a determined physiological parameter” is taken to mean that, for any given physiological parameter, worsening is a change in the value of that parameter in the subject away from the normal value or normal range for that value—i.e. away from the expected value in a healthy subject.
Improvement in a determined physiological parameter according to the invention is indicated by one or more of the group consisting of: a reduction in a pro-inflammatory cytokine, an increase in an anti-inflammatory cytokine and/or resolving mediator, an increase in a catecholamine, the level of erythrocytes, a change in an immune cell population, a change in an immune cell surface co-stimulatory molecule, a reduction in a factor involved in the inflammation cascade, and a change in the level of an immune response mediator. The invention might not lead to a change in all of these parameters.
By stimulating a splenic arterial nerve, the spleen may: (a) decrease the secretion of a pro-inflammatory cytokine compared to baseline secretion; and/or (b) increase the secretion of an anti-inflammatory cytokines and/or resolving mediators compared to baseline secretion. For example, the decrease in a pro-inflammatory cytokine secretion may be by: ≤10%, ≤15%, ≤30%, ≤35%, 40%, ≤50%, ≤60%, ≤70%, ≤80%, ≤90% or ≤95%. The increase in an anti-inflammatory cytokine secretion may be by: ≤5%, ≤10%, ≤15%, ≤20%, ≤25%, ≤30%, ≤35%, 50%, ≤60%, ≤70%, ≤80%, ≤90%, ≤95%, ≤100%, ≤150%, ≤200%, or ≤500-1000%.
Once the cytokine is secreted into the circulation, its concentration in circulation is diluted. Stimulation of the splenic arterial nerve may result in: (a) a decrease in the level of a pro-inflammatory cytokine in the plasma or serum by ≤5%, ≤10%, ≤15%, ≤20%, ≤25%, 30%, ≤35%, ≤50%, 60%, ≤70%, ≤80%, ≤90%, or ≤95%; and/or (b) an increase in the level of an anti-inflammatory cytokine and/or resolving mediator in the plasma or serum by ≤5%, ≤10%, ≤15%, ≤20%, ≤25%, 30%, ≤35%, ≤50%, ≤60%, ≤70%, ≤80%, ≤90%, ≤95%, ≤100%, ≤150% or ≤200%.
Preferably the level in the serum is measured.
By stimulating the splenic arterial nerve, the level of catecholamine (e.g. norepinephrine or epinephrine), e.g. its level in the spleen or splenic vein, may increase, for example, by: ≤5%, ≤10%, 15%, ≤20%, ≤25%, ≤30%, ≤35%, ≤50%, ≤60%, ≤70%, ≤80%, ≤90%, ≤95%, 100%, ≤150% or ≤200%.
For example, stimulating a splenic arterial nerve can decrease the level of a pro-inflammatory cytokine (e.g. TNFα) in the serum by 30%-60%.
Pro-inflammatory cytokines are known in the art. Examples of these include tumor necrosis factor (TNF; also known as TNFα or cachectin), interleukin (IL)-1α, IL-1β, IL-2; IL-5, IL-6, IL-8, IL-15, IL-18, interferon γ (IFN-γ); platelet-activating factor (PAF), thromboxane; soluble adhesion molecules; vasoactive neuropeptides; phospholipase A2; plasminogen activator inhibitor (PAI-1); free radical generation; neopterin; CD14; prostacyclin; neutrophil elastase; protein kinase; monocyte chemotactic proteins 1 and 2 (MCP-1, MCP-2); macrophage migration inhibitory factor (MIF), high mobility group box protein 1 (HMGB-1), and other known factors.
Anti-inflammatory cytokines are also known in the art. Examples of these include IL-4, IL-10, IL-17, IL-13, IL-la, and TNFα receptor.
Pro-resolving mediators are also known in the art. In particular, specialized pro-resolving mediators are a class of molecules produced during metabolism of polyunsaturated fatty acids via the action of several enzymes (e.g. lipoxygenase, cycloxygenase, cytochrome P450 and others). They orchestrate the resolution of acute and chrionic inflammation. Examples include Lipoxins, Resolvins, Protectins and Maresins.
It will be recognized that some of pro-inflammatory cytokines may act as anti-inflammatory cytokines in certain circumstances, and vice-versa. Such cytokines are typically referred to as pleiotropic cytokines.
Factors involved in immune responses may be useful measurable parameters for the invention, for example, TGF, PDGF, VEGF, EGF, FGF, I-CAM, nitric oxide.
Chemokines may also be useful measurable parameters for the invention, such as 6cKine and MIP3beta, and chemokine receptors, including CCR7 receptor.
Changes in immune cell population (Langerhans cells, dendritic cells, lymphocytes, monocytes, macrophages), or immune cell surface co-stimulatory molecules (Major Histocompatibility, CD80, CD86, CD28, CD40) may also be useful measurable parameters for the invention. Applying a signal to the nerves according to the invention can cause reduction in total counts of circulating or tissue-specific (e.g. joint-specific in the case of rheumatoid arthritis) leukocytes (including monocytes and macrophages, lymphocytes, neutrophils, etc.).
Factors involved in the inflammatory cascade may also be useful measurable parameters for the invention. For example, the signal transduction cascades include factors such as NFκ-B, Egr-1, Smads, toll-like receptors, and MAP kinases.
Methods of assessing these physiological parameters are known in the art. Detection of any of the measurable parameters may be done before, during and/or after modulation of neural activity in the nerve.
For example, a cytokine, chemokine, or a catecholamine (e.g. norepinephrine or epinephrine) may be directly detected, e.g. by ELISA. Alternatively, the presence or amount of a nucleic acid, such as a polyribonucleotide, encoding a polypeptide described herein may serve as a measure of the presence or amount of the polypeptide. Thus, it will be understood that detecting the presence or amount of a polypeptide will include detecting the presence or amount of a polynucleotide encoding the polypeptide. Specialized pro-resolving mediators can also be directly measured and quantified used methods described and available in the art. Such methods include liquid chromatograpohy and trandem mass spectrometry.
Quantitative changes of the biological molecules (e.g. cytokines and pro-resolving mediators) can be measured in a living body sample such as urine or plasma. Detection of the biological molecules may be performed directly on a sample taken from a subject, or the sample may be treated between being taken from a subject and being analyzed. For example, a blood sample may be treated by adding anti-coagulants (e.g. EDTA), followed by removing cells and cellular debris, leaving plasma containing the relevant molecules (e.g. cytokines and pro-resolving mnediators) for analysis. Alternatively, a blood sample may be allowed to coagulate, followed by removing cells and various clotting factors, leaving serum containing the relevant molecules (e.g. cytokines and pro-resolving mediators) for analysis. In the embodiments where the signal is applied whilst the subject is asleep, the invention may involve determining the subject's circadian rhythm phase markers, such as the level of cortisol (or its metabolites thereof), the level of melatonin (or its metabolites thereof) or core body temperature. Cortisol or melatonin levels can be measured in the blood (e.g. plasma or serum), saliva or urine. Methods of determining the levels of these markers are known in the art, e.g. by enzyme-linked immunosorbent assay (ELISA) or radioimmunoassay. If measurements of the subject's circadian rhythm phase markers indicate circadian oscillations of inflammatory markers which may beneficially be regulated by application of a signal with a system of the invention, then application of the signal at late night/early morning (when cortisol levels begin to rise) at a suitable periodicity according to the subject's circadian rhythm may be appropriate.
As used herein, a physiological parameter is not affected by the modulation (e.g. stimulation) of the splenic neural activity if the parameter does not change (in response to nerve modulation) from the normal value or normal range for that value of that parameter exhibited by the subject or subject when no intervention has been performed i.e. it does not depart from the baseline value for that parameter. Such a physiological parameter may be arterial pressure, heart rate or glucose metabolism. Suitable methods for determining changes in any these physiological parameters would be appreciated by the skilled person.
The skilled person will appreciate that the baseline for any neural activity or physiological parameter in an subject need not be a fixed or specific value, but rather can fluctuate within a normal range or may be an average value with associated error and confidence intervals. Suitable methods for determining baseline values are well known to the skilled person.
As used herein, a physiological parameter is determined in a subject when the value for that parameter exhibited by the subject at the time of detection is determined. A detector (e.g. a physiological sensor subsystem, a physiological data processing module, a physiological sensor, etc.) is any element able to make such a determination.
Thus, in certain embodiments, the invention further comprises a step of determining one or more physiological parameters of the subject, wherein the signal is applied only when the determined physiological parameter meets or exceeds a predefined threshold value. In such embodiments wherein more than one physiological parameter of the subject is determined, the signal may be applied when any one of the determined physiological parameters meets or exceeds its threshold value, alternatively only when all of the determined physiological parameters meet or exceed their threshold values. In certain embodiments wherein the signal is applied by a system of the invention, the system further comprises at least one detector configured to determine the one or more physiological parameters of the subject.
In certain embodiments, the physiological parameter is an action potential or pattern of action potentials in a nerve of the subject, wherein the action potential or pattern of action potentials is associated with the condition that is to be treated.
It will be appreciated that any two physiological parameters may be determined in parallel embodiments, the controller is coupled detect the pattern of action potentials tolerance in the subject.
A predefined threshold value for a physiological parameter is the minimum (or maximum) value for that parameter that must be exhibited by a subject or subject before the specified intervention is applied. For any given parameter, the threshold value may be defined as a value indicative of a pathological state or a disease state. The threshold value may be defined as a value indicative of the onset of a pathological state or a disease state. Thus, depending on the predefined threshold value, the invention can be used as a treatment. Alternatively, the threshold value may be defined as a value indicative of a physiological state of the subject (that the subject is, for example, asleep, post-prandial, or exercising). Appropriate values for any given physiological parameter would be simply determined by the skilled person (for example, with reference to medical standards of practice).
Such a threshold value for a given physiological parameter is exceeded if the value exhibited by the subject is beyond the threshold value—that is, the exhibited value is a greater departure from the normal or healthy value for that physiological parameter than the predefined threshold value.
A subject of the invention may, in addition to having an implant, receive medicine for their condition. For instance, a subject having an implant according to the invention may receive an anti-inflammatory medicine (which will usually continue medication which was occurring before receiving the implant).
Such medicines include, nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, 5ASAs, disease-modifying-anti-inflammatory drugs (DMARDs) such as azathioprine, methotrexate and cyclosporin, biological drugs like infliximab and adalimumab, and the new oral DMARDs like Jak inhibitors. Thus the invention provides the use of these medicines in combination with a system of the invention.
General
The methods described herein may be performed by software in machine readable form on a tangible storage medium e.g. in the form of a computer program comprising computer program code means adapted to perform all the steps of any of the methods described herein when the program is run on a computer and where the computer program may be embodied on a computer readable medium. Examples of tangible (or non-transitory) storage media include disks, thumb drives, memory cards etc. and do not include propagated signals. The software can be suitable for execution on a parallel processor or a serial processor such that the method steps may be carried out in any suitable order, or simultaneously. This acknowledges that firmware and software can be valuable, separately tradable commodities. It is intended to encompass software, which runs on or controls “dumb” or standard hardware, to carry out the desired functions. It is also intended to encompass software which “describes” or defines the configuration of hardware, such as HDL (hardware description language) software, as is used for designing silicon chips, or for configuring universal programmable chips, to carry out desired functions.
Those skilled in the art will realize that storage devices utilized to store program instructions can be distributed across a network. For example, a remote computer may store an example of the process described as software. A local or terminal computer may access the remote computer and download a part or all of the software to run the program. Alternatively, the local computer may download pieces of the software as needed, or execute some software instructions at the local terminal and some at the remote computer (or computer network). Those skilled in the art will also realize that by utilizing conventional techniques known to those skilled in the art that all, or a portion of the software instructions may be carried out by a dedicated circuit, such as a DSP, programmable logic array, or the like.
Unless otherwise indicated each embodiment as described herein may be combined with another embodiment as described herein. The term “comprising” encompasses “including” as well as “consisting” e.g. a composition “comprising” X may consist exclusively of X or may include something additional e.g. X+Y.
It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages.
It will be understood that the above description of a preferred embodiment is given by way of example only and that various modifications may be made by those skilled in the art. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention.
Embodiments of the invention will be described, by way of example, with reference to the following drawings, in which:
Porcine Data
Electrical Stimulation of the Splenic Arterial Nerve in Pig
Materials and Methods
A total of 8 pigs (body weight between 40-50 Kg) were used for the histological and electrophysiological characterization of the splenic nerve.
On the experimental day, the animal was sedated with ketamine (1.5 mg/kg) and midazolam (0.5 mg/kg) administered by intramuscular injection. An intravenous catheter was placed in one auricular vein, and anesthesia was induced by propofol (2 mg/Kg) administered intravenously. An endotracheal tube was placed, and anesthesia was maintained with sevoflurane inhalant combined with continuous rate infusion (CRI) of fentanyl (0.2 μg/Kg/min).
After induction of general anesthesia, the animal was positioned in dorsal recumbency for placement of bilateral indwelling jugular vein catheters and one femoral arterial catheter under ultrasonographic guidance. Animals undergoing SpN cuff implantation were then repositioned into right lateral recumbency.
The surgical approach to SpN cuff implantation was as follows. The thoracolumbar junction was supported and slightly elevated using a sand bag. After appropriate surgical preparation (clipping and aseptic scrub with chlorhexidine gluconate and alcohol), the left flank was aseptically draped exposing a 20×25 cm area centered on the second to last rib. A 15 cm skin incision was made in the second to last intercostal space using monopolar electrocautery. The incision was continued through the subcutaneous tissues and intercostal musculature until the peritoneum was exposed. Two Finochietto rib retractors were placed retroperitoneal, taking care to engage the ribs. Over the next few minutes, the retractors were gradually opened, resulting in exposure of the left lateral abdomen measuring approximately 10×8 cm. The retractor blades were covered with gauze sponges soaked in carboxymethyl cellulose (CMC). The peritoneum was longitudinally incised and sutured to the skin (Vicryl 2-0; Ford interlocking suture pattern) covering the retractors blades in order to minimize risk of splenic tears during handling. Using careful digital manipulation, the spleen was exteriorized and the splenic artery (SpA) was identified along its visceral surface. At the mid portion of the spleen, proximal to the SpA branching into the left gastroepiploic artery, a short segment of the SpA was carefully dissected free of surrounding soft tissue for placement of a 1 mm ultrasonic flow probe (Transonic). After probe placement, the spleen was repositioned into the abdomen.
By slight rotation of the splenic visceral base towards the operator, and placing gentle ventral traction on the spleen, the gastrosplenic ligament at the splenic hilum was incised using Metzembaum scissors, exposing the SpA. The artery was followed in a dorsal direction to its origin (i.e. the bifurcation of the celiac artery into the left gastric artery (LGA) and the SpA). Immediately distal to this bifurcation, an approximately 1 cm segment of the SpA with the peri-arterial SpN network intact, was circumferentially isolated by blunt dissection using Metzenbaum scissors. A curved Mixter artery forceps was inserted under the artery from caudal to cranial, grasping one flap of the 2.5 mm diameter CorTec cuff introduced into the surgical field using straight Microdissection forceps. The cuff was placed around the SpA and the intact pen-arterial SpN network by reversing the motion of the Mixter forceps, taking care to appose the two flaps of the cuff when properly placed. The tension on the spleen and artery was then released. SpA blood flow readings were tested and finally the rib retractors were partially closed and the exposed incision covered with saline-soaked gauze sponges.
Electrophysiological experiments generally entailed dissecting and cuffing (using a 500 μm diameter bipolar or tripolar CorTec cuff) one or several discrete SpN fascicles few centimeters distal (closer to the spleen) to the stimulating cuff to enable evoked compound action potential (eCAP) recording during stimulation of the whole SpN plexus or of few fascicles (see
Recorded eCAP were amplified and filtered (100-1000 Hz) using an 1800 2-Channel Microelectrode AC Amplifier (A-M system). Nerve activity was monitored continuously using an oscilloscope and recorded to a computer using a 16 channels PowerLab (AD Instruments) acquisition system and LabChart 8 software using a sampling rate of 20 kHz. eCAP were generally averaged (8-10 pulses) and peak to peak or area under the curve (AUC) of the averaged response quantified. The conduction velocity of the eCAP components of the SpN were calculated from the distance between stimulation and recording site and the latency of the eCAP signal.
Electrocardiogram (ECG), Heart rate (HR), arterial blood pressure, respiratory rate (RR), pulse oximetry, capnography, spirometry were monitored throughout the surgery. Body temperature was recorded continuously with an intranasal probe. Arterial blood gasses were analyzed throughout the experiment to monitor pH, Glucose, pO2 and pCO2, K+levels. All physiological parameters as well as the level of used sevoflurane were recorded (every 5-10 minutes) on the record sheet. Physiological data were also digitalized using Powerlab acquisition system and LabChart software. All parameters were generally sampled at a frequency between 0.1 and 2 kHz.
The depth of anesthesia was assessed by palpebral reflex, corneal reflex, medioventral eye ball position, and jaw tone.
Moreover, physiological parameters as well as a bispectral index monitoring system (levels between 30 and 60) were used to adjust anesthetic levels. In some cases, boluses of propofol were used.
In some cases intra-operative ultrasonography of the spleen was used for real-time monitoring of SpA blood flow changes during SpN stimulation. For this procedure, an intra-operative probe (i12L-RS linear intraoperative transducer 4-10 MHz, 29×10 mm footprint, 25 mm field of view; GE Vivid-i) was used.
SpA blood flow changes was assessed by color Doppler and continuous wave spectral tracing. After color Doppler identification of the SpA within the splenic parenchyma 2-3 cm distal to the splenic hilum, continuous wave spectral tracing of the SpA flow was obtained by directing the windowing cursors to the center of the SpA lumen. After obtaining a representative signal, the ultrasonography probe and cursor window was left in position while SpN stimulation commenced.
All statistical analyses were performed with commercially available statistical software (JMP Pro 13.0.0 or GraphPad Prism 5.0).
Results
Recording of the eCAP generated during SpN stimulation, either of the whole SpN plexus with the pen-arterial cuff, or stimulation of few fascicles with a smaller cuff, generated an eCAP with a specific latency dependent on the distance between stimulating and recording sites (
SpN biphasic stimulation for 1 minute at 10 Hz and 400 μs PW above a specific current threshold consistently caused transient blood flow reduction within the distal SpA as measured via a perivascular flow probe. There was a clear dose-response relationship between delivered current and flow reduction: the higher the amplitude the stronger was the observed reduction in blood flow (
In parallel, recording of the blood flow within the splenic vein (SpV) was recorded by using a Doppler flow probe placed at the splenic base, where the vein leaves the splenic hilum. Interestingly, stimulation (symmetric biphasic pulses, 400, 10 Hz for 1 minute) caused an increase in the mean SpV blood flow (mSpV BF) that was current amplitude dependent. Stimulation with 12 mA and 400 μs PW (36.9 μC/cm2/phase) caused a maximum increase of about 200% when compared to baseline mSpV BF. The transient reduction of mSpA BF was also accompanied by a transient increase in systemic mean arterial blood pressure (sMABP). This increase (in average between 1-6 mmHg) from baseline correlated again with the stimulation intensity (
The changes observed in mSpA BF, sMABP, HR, RR during a 1-minute stimulation (symmetric biphasic pulses, 10 Hz, 400 μs PW) at different current amplitudes (1-50 mA, corresponding to 3.076-153.8 μC/cm2/phase) are summarized in
Direct stimulation of discrete SpN bundles dissected off the SpA (using a 500 μm diameter cuff) evoked similar changes in the mSpA BF, sMABP and HR. These changes, occurring during a 1 minute (symmetric biphasic pulses, 1 Hz, 400 μs PW) and different current amplitudes (0.1-2.5 mA, corresponding to 3.86-96.61 μC/cm2/phase), are summarized in
Blood flow changes in the mSpA were also affected by different frequencies of stimulation. When stimulating (symmetric biphasic pulses, 400 μs PW for 1 minute at about 36.9 μC/cm2/phase) at different frequencies (between 0.25 and 100 Hz), 30-50 Hz reliably caused the strongest blood flow reduction in the SpA (
This was once again observed when maximally (around 70 μC/cm2/phase) stimulating only few fascicles dissected off the artery. A stronger reduction in mSpA BF occurred already at lower frequencies (1 Hz and below), because of the higher recruitment of nerve fibers compared to the stimulation amplitude used for the whole plexus during the frequency analysis. Consistently however, the maximal reduction was observed between 30-50 Hz (
In order to further confirm that the observed changes in SpA BF were due to direct neuronal activation (rather than stimulation of smooth muscles) Lidocaine (2% lidocaine hydrochloride solution) was applied locally around the implanted SpN cuff (either the pen-arterial cuff or the cuff for dissected fascicles). Lidocaine is a specific blocker of fast voltage gated Na+channels. Lidocaine was able to block the changes in SpA BF. Further, mechanical occlusion of the SpA, able to reduce the BF up to 80%, did not cause any change in sMABP or HR. In addition, transection of the central end of the SpN (proximal to the cuff) did not abolish stimulation effects on SpA blood flow, sMABP and HR. Also the transection of the SpN within the GEP and SG segments did not prevent these changes. Interestingly, all these effects were only abolished when the peripheral end of the SpN (distal to the cuff) was cut. All these data suggest that the changes in SpA BF and SpV BF were neuronal driven and related to the constriction of the SpA as well as the contraction of the spleen capsule. On the other hand, the changes in sMABP and HR were probably not due to the activation of a neuronal pathway towards the brain but to the increase outflow of blood from the spleen towards the heart.
In few animals, SpA blood flow changes during stimulation was also monitored using intra-operative ultrasonography at the splenic hilum. After identifying the SpA by color Doppler, the change in BF was monitored as Doppler signal as shown in
Splenic nerve stimulation was associated with transient local changes in mSpA BF and mSpV BF as well as splenic contraction. These changes were due to the direct activation of the SpN, rather than direct stimulation of the smooth muscles of the SpA. Spleen contraction during SpN stimulation has been previously reported also in other species [16]. The observed change in mSpA BF was very consistent between animals. The variation was probably mainly due to different fitting of the cuff around the SpN plexus in different animals. Changes in SpA BF could be easily monitored via non-invasive ultrasound and therefore could be used as a marker to assess effective stimulation of the SpN also in a clinical setting.
The transient changes observed during SpN stimulation were shown to be amplitude and frequency dependent. During a minute of stimulation at different current amplitudes, the strongest mSpA BF reduction was observed at the highest current amplitude tested that also corresponded to the peak of the recorded eCAP. This was true when stimulating the whole SpN plexus (with a peri-arterial cuff) or when stimulating only few fascicles placed within a smaller cuff. The difference in the total charge density needed to obtain maximum eCAP from the SpN plexus and from SpN fascicles could be explained by the partial coverage of the plexus with the 2.5 mm cuff used. In most of the pigs in fact this cuff resulted only in a 270-300 degrees of circumferential coverage. When cuffing only few fascicles of the SpN dissected off the artery the coverage was almost total. Therefore, in order to limit charge density needed to obtain optimal recruitment of SpN fascicles, optimal circumferential coverage of the artery will be needed.
The strongest changes (in mSpA BF and sMABP) were observed at frequency between 30 and 50 Hz. Although the total number of pulses delivered could be an important factor in determining the magnitude of this changes, it is true that when comparing changes occurring with the same number of pulses delivered at different frequencies, 30-50 Hz range still caused the strongest changes. This could be explained with previously reported data showing that maximum release of NA from the cat spleen was observed at 30 Hz [17,18]. Higher release of NA could explain the higher magnitude of the changes observed in this stimulation range.
Optimization of the Signal Parameters
Materials and Methods
In order to develop an optimized stimulation paradigm, several signal parameter settings were tested in the pigs mentioned above using the materials and methods described above.
The optimization of parameters was focused at reducing off target effects and increasing efficiency of the SpN response. In particular, since the systemic changes caused by SpN stimulation were related to the local constriction of the SpA and contraction of the spleen, parameters able to minimize these changes could represent optimal paradigm to be transferred in chronic studies and clinical studies where systemic effects (e.g. changes in sMABP and HR) are not ideal.
Results
Repetitive stimulation of the SpN was found to cause fatigue in the nerve fibers at certain frequencies. This effect consisted of two characteristics: i) a reduction of SpN eCAP amplitude and ii) slowing of SpN conduction velocity. Both these characteristics were observed at frequencies higher than 1 Hz, with fatigue effects increasing with increasing frequency. Stimulation of the SpN at 10 Hz continuously for 1 minute caused, in fact, adaptation in the recorded response, resulting in a decreased amplitude of the eCAP over time (
In addition, when stimulating at 10 and 30 Hz continuously, a rapid increase in eCAP amplitude was observed within the first 5-20 pulses. This phase preceded the successive reduction in amplitude and velocity (
As described previously the frequency of the stimulation not only impacted the response of the nerve but it also affected differently the physiology. Frequencies between 30 and 50 Hz caused the strongest changes in mSpA BF that drives the changes in sMABP. Frequencies 1 Hz caused, in comparison, little changes in mSpA BF. Frequencies between 1 and 30 Hz caused changes of mSpA BF of increasing magnitude. By selecting a high current amplitude (in order to recruit most of the SpN fibres), a 10 Hz, biphasic, symmetric 60 s stimulation is sufficient to cause, at least, a 50% maximum reduction in the mSpA BF. The stimulation of the SpN with the same biphasic symmetric pulses and current amplitude but with 1 Hz frequency, caused a reduction in mSpA BF about 40% lower (decrease from around 70% to around 50%) than the one generated with the 10 Hz stimulation (
The same was observed when applying a burst stimulation (5 pulses at 10 Hz every 5 s) using biphasic pulses and the same current amplitude (
Herein lies a description of the opportunity space to provide optimised neural activation, in the absence of ‘nerve fatigue’, while provide options for effectively stimulating physiological changes (high frequency), or to avoid them (low frequency or burst frequency), depending on the target profile of the therapy. During surgery it may be very effective to use blood flow changes to induce easily visualised target engagement profiles, to prove the device and therapy are appropriately positioned and of suitable amplitude. Then a switch to burst or low frequency stimulation will ensure ideal nerve engagement for efficacy in splenic engagement, while avoiding clinically consequential effects of continual changes in blood flow in awake patients.
Parameters for optimal stimulation (and therefore efficacy) should in principle i) generate a very consistent and maintained amplitude response of the nerve, ii) deliver as many pulses as needed (to obtain the therapeutic effect) in the shortest possible time window in order to reduce energy requirement and discomfort to patients and iii) have the lowest spectrum of off target effects. The stimulation of the SpN at frequencies higher than 1 Hz showed a clear activity-dependent variations in response (eCAP) amplitude and conduction velocity. This effect has been previously observed in other unmyelinated nerves, in both rodents and humans [19,20,21,22]. During regular stimulation at 0.25 Hz, conditioning pulses intermittently interposed at varying inter-stimulus intervals, unmyelinated fibers showed a progressive reduction of conduction velocity dependent on the number of interposed stimuli [20]. The same effect was observed with stimulation of the SpN, where repetitive stimulation caused reduction in conduction velocity as well as reduction in eCPA amplitude. This effect has been previously called “subnormality” of action potential conduction.
When the SpN was stimulated continuously at 10 Hz, a short period of increased response has been observed followed by the slowing and reduction of the response phase. This other period has been also described before and termed “supernormality”. Supernormality and subnormality of action potential conduction are probably due an after-depolarization and a subsequent period of hyperpolarization of the membrane when pulses are delivered within a short time window (below 1000 ms from one another) [20,21,22]. When recording eCAP, this membrane changes in the axons that cause an increase in the current activation threshold, resulted in a lower amplitude of the recorded signal. This was not simply an effect of the slowing of the conduction velocity: the recorded eCAP shifted to longer latencies and decreased in amplitude without spreading in total width. In fact the measured AUC was smaller over time. However, it still possible that the observed reduction in eCAP amplitude was due to a de-synchronization of the action potentials that then cancel each other when recording a compound response. Single unit recording would be ideal to demonstrate that the SpN is really subjected to this activity-dependent changes.
It has been shown here that low frequency stimulation (1 Hz or below) or burst stimulation (5 pulses at 10 Hz, every 5 s) caused limited or no fatigue on the SpN as well as caused the lowest off target effects. To date these two paradigms, delivered with biphasic, asymmetrical pulses, represent the optimal stimulation pattern for the SpN for treatment of immune-mediated conditions (e.g. inflammatory disorders). Frequencies higher than 1 Hz, induce changes in blood flow and pressure, and could be useful in identifying nerve-target engagement during electrode positioning.
Effects of Continuous Electrostimulation in In Vivo LPS Porcine Model
Materials and Methods
Animals
A total of 23 pigs (weight 65-70 Kg) were used for this section of the study.
General Design
Pigs were terminally anesthetized and split into the following five groups: sham (implanted with electrodes but not stimulated), Dexamethasone (the SpN was accessed and then animals were injected with Dexamethasone at −2 and 0h), LVNS (pigs were implanted on the cervical LVN), eLVNS (pigs were implanted on the cervical LVN, that was ligated and cut distal to the cuff electrode and the efferent stump only stimulated), and SpNS (pigs were implanted on the pen-arterial SpN).
The implanted devices of the LVNS, eLVNS and SpNS pigs were stimulated continuously from −2h to +1h (relative to the injection of LPS) at 1 Hz. E. coli-derived LPS was administered at a dose of 0.25 mg/Kg to all groups at 0 h. Dexamethasone was used as positive control.
Peripheral venous blood was collected for 2 h prior to LPS injection (baseline), and then every half hour up to 4 hours post injection. For all of these time points, cytokine analysis (TNFα and IL-6), was performed by commercially available ELISAs.
Results
Cytokine quantification. For all groups, LPS injection resulted in a significant increase in TNFα levels in all post-injection samples compared to baseline (pre-LPS injection), with the peak response observed at approximately 1 hour post injection (
Cytokine levels were compared between groups by calculating the area under the curve (AUC) from between −2h to +4h post-injection. TNFα levels were reduced around 30% at 1.5 hours in SpN as well as LVNS and eLVNS groups when compared to Sham. For IL-6, there was a reduction in both the peak response value (
The administration of LPS in vivo to mimic an inflammatory response provided a good model to test the efficacy of SpN stimulation. The administration of LPS (0.25 mg/Kg) in 65-70 kg pigs caused upregulation of cytokines (TNFα and IL-6) in the blood of all the animals tested. In particular, TNFα reached a peak value of about 5 ng/ml at 1h post injection while IL-6 peaked at around 0.5 ng/ml at 2.5h post LPS injection.
Therefore, this model provides the proof that SpN stimulation is able to modulate the response to an inflammatory stimulus, and shows that prolonged stimulation of SpN reduces the levels of pro-inflammatory cytokines, as seen in particular by the reduction of IL-6. This is likely to be beneficial for reducing inflammatory responses in subjects, particularly in light of recent evidence showing the vagus nerve stimulation is beneficial in the treatment of autoimmune disorders.
In summary, it was found that neural stimulation of a nerve supplying the spleen, and in particular, the splenic arterial nerve, showed pro-survival effects in an in vivo LPS animal model. Hence, stimulation of the neural activity of splenic nerves can be particularly useful for treating inflammatory disorders.
Characterization of the Splenic Arterial Nerves in Pig
Materials and Methods
Gross anatomical studies of the spleen with related organs were performed in 12 female pig cadavers (body size 22 to 120 kg) within 1 hour of euthanasia. The following measurements were made: length and width of the spleen; length of the celiac artery (from the aorta to the branching in to the left gastric and splenic arteries); length of the splenic artery (SpA) (from the branching of the celiac artery to entering the splenic parenchyma); SpA diameter measured 1 cm distal to the celiac artery and at the splenic hilum; distance from pancreas to the spleen; distance from pancreas to the splenic lymph nodes. Also, the number and course of the abdominal vagal branches, celiac ganglion, splanchnic nerves and splenic nerves were recorded. The SpA with associated splenic nerves were processed for Haematoxylin and Eosin (H&E) histology.
The spleen with intact vasculature and innervation was harvested from 12 female pig cadavers (body weight 22 kg, n=6; body weight 45 kg, n=6). All tissues were harvested within 1 hour of euthanasia, and were immediately fixated in 10% neutral-buffered formalin. The SpA with an intact perivascular neuronal network was sectioned every 5 mm from the origin at the bifurcation of the celiac artery, to the splenic hilum. This resulted in 5 sections, defined as the Bifurcation; the Proximal SpA; the Middle SpA; the Distal SpA and the Hilum location. The proximal SpA section corresponds to the location for cuff placement in the following electrical stimulation study discussed above.
At each of these five locations, sections were processed for routine H&E staining. The Proximal, Middle and Distal SpA sections were also processed for immunohistochemistry and for semi-thin sectioning and staining with osmium tetroxide and toluidine blue.
Digital images of the H&E stained sections were acquired at 2× magnification and appropriate software (Image J 1.50i) was used for histomorphometric analysis as detailed below. After manually selecting every single nerve fascicle by using the ROI manager function, the number of pen-arterial nerve fascicles were counted and the fascicle sizes assessed by measuring minimum Feret's diameter (μm).
The total nerve area (in μm2) was calculated, and the pen-arterial fascicle distribution was quantified by assessing the percentage of the arterial circumference in which fascicles were identified, defining 360 degree distribution as 100%. The distance from each fascicle to the external arterial wall was measured by drawing the shortest possible perpendicular line from each fascicle to the arterial wall. Splenic artery external and internal diameters were measured at the proximal, middle and distal SpA locations.
Double staining with tyrosine hydroxylase (TH) and acetylcholine transferase (ChAT) was used for assessing neuronal phenotype. By counterstaining with neurofilament 200 (NF200) and the nuclear stain 4′,6-diamidino-2-phenylindole (DAPI), NF200-TH double positive nerves were considered sympathetic, while NF200-ChAT double positives were considered parasympathetic nerves. In order to determine the proportion of efferent versus afferent nerves, the same locations were double stained with the efferent marker TH and the afferent marker calcitonin gene-related peptide (GCRP). Two different digital images were randomly captured at 20× magnification from each nerve, and pseudocolored composites generated using appropriate software (AxioVision LE64).
Myelination of SpN axons was assessed by immunofluorescent staining as well as from semi-thin sections. Different portions of the SpA and SpN were stained with antibodies against Neurofilament and β-III Tubulin and Myelin Basic Protein (MBP). Pseudocolored composite images were generated using appropriate software as described above. Semi-thin sections were stained with osmium and toluidine blue. Digital images were acquired at 100× magnification and the number of myelinated and unmyelinated axons were manually counted in an area of 100×100 μm. This procedure was repeated 3 times per nerve, and the mean of these were used for further analysis. Also, this procedure was used for deriving axon density (number of axons/mm2).
All statistical analyses were performed with commercially available statistical software (JMP Pro 13.0.0). Due to non-normal distribution, all histomorphometric measurements were compared between the different pig sizes and SpA locations using the Wilcoxon rank-sum test. Statistical significance was defined as P<0.05.
Results
Neurovascular structures enters and leaves the spleen along the visceral surface only. Specifically, the first major abdominal branch of the aorta, the celiac artery, bifurcates into the hepatic artery, the SpA and the LGA (
At the splenic base, the dorsal SpA branch divide into several smaller arteries identified as the short gastric arteries, which courses towards the greater curvature of the stomach. Although these arteries are considered terminal branches of the SpA, they are capable of providing collateral blood supply to the spleen by anastomoses with branches of the LGA and the left gastroepiploic arteries. The SpV runs parallel to the SpA along the visceral surface of the spleen, from the apex to the hilum. After leaving the splenic hilum, the SpV courses closely adhered to the SpA for a short distance until it travels in a medial direction to drain into the hepatic portal vein, which in turn drains into the caudal vena cava. This leaves a small space in which the artery and the vein run separated by a few millimeters of soft tissue. This area, which is immediately distal to the bifurcation of the celiac artery into the SpA and LGA, has been identified as the optimal interface point for the following functional studies. At this location, the SpA diameter is 1.5-3 mm in the 30 kg animal; 2-4 mm in the 60 kg animal and 5-8 mm in the 110 kg animal.
The SpN consist of a plexus of fibers running along the SpA towards the splenic hilum. It is difficult to establish the origin of these nerves, although fibers can be seen arising from the CG which is located immediately caudal to the bifurcation of the celiac artery into the SpA and the LGA. Data from previous studies conducted mainly in rodents, established that most of the SpN originates from the celiac and suprarenal ganglia. This has yet to be proven in large animal species.
It has also been hypothesized that a direct connection exists between the Vagus nerve (VN) and the SpN, though the celiac ganglion. The subdiaphragmatic VN was seen crossing the lateral aspect of the celiac artery, and coursing towards the CG and the left adrenal gland. Some fibers coming from the subdiaphragmatic VN was also seen merging with fibres within the SpN plexus. Although these fibers might continue on to innervate the pancreas, a direct connection between the VN and the spleen cannot be excluded based on these observations. In rodents, it has been demonstrated that a direct connection exists between the VN and the SpN, and also between the splanchnic nerves and the SpN via the CG. In the pig, part of the splanchnic nerves was seen running towards the adrenal gland and CG.
In rodent species, other nerves have been described to innervate the spleen in addition to the peri-arterial SpN; more specifically, an apical nerve has been described within the gastro-splenic ligament of rats and mice. This is a sympathetic nerve (TH+) possibly originating from the paravertebral sympathetic nerves, and runs towards the apex of the spleen within the gastrosplenic ligament.
All histological measurements are presented in Table 1. The SpN-SpA distance was the only measurement significantly larger in the 45 kg pigs versus the 22 kg pigs (at the middle SpA and distal SpA locations; P<0.001); therefore, for all the other measurements, data from all pigs were combined for statistical analysis. There was a reduction in number of pen-arterial nerve fascicles along the SpA from proximal to distal; there were statistically significantly more fascicles at the bifurcation versus all other locations (P<0.0001). At the splenic hilum, nerve fascicles were significantly larger than at the other locations (P<0.0001). The SpA external diameter was significantly larger at the proximal SpA location versus the middle and the distal SpA locations (P=0.0162 and P=0.0158, respectively). The SpN/SpA distance also decreased from proximal to distal; in the 45 kg pigs, the distance was significantly larger at the Bifurcation versus all other locations (P<0.001). Also in the 45 kg pigs, the SpN/SpA distance was significantly larger at the Hilum versus the Proximal, Middle and Distal SpA locations (P<0.008).
1185 ± 616.2*
284.6 ± 166.4¥
382.9 ± 247.4¥
¥Significantly larger in the 45 kg vs. the 22 kg pigs.
ΔSignificantly different from the Middle and Distal SpA. Significance P < 0.05.
The circumferential SpN distribution was significantly higher at the Proximal versus the Middle and Distal SpA locations (P=0.02 and P=0.15, respectively). Also, fascicles were more uniformly circumferentially distributed around the SpA at the proximal location whereas at the middle and distal SpA, the distributional pattern was more bimodal with fascicle clustering on opposite sides of the artery.
In the pig nerves are found along both the short gastric and gastro-epiploic arteries within the gastrosplenic ligament (
The number of nerve fascicles and fascicle size observed in these two regions is much smaller compared to those observed along the main SpA. The quantification of the number and relative diameter of the nerve fascicles along the main SpA and along the other different anatomical locations in 45-50 Kg farm pigs is shown in
Further histochemical and immunohistochemical analysis showed that the SpN is composed by >99.9% of unmyelinated fibers. Toluidine blue staining of semi-thin sections, in fact, did not show myelinated axons. In line with this, staining for Myelin Basic Protein (MBP) revealed a very little number of positive axons (<0.01%). Both of the techniques assessing myelination revealed almost complete absence of myelin in the investigated sections of the SpN as illustrated in
The histological analysis performed here showed that the SpN constitutes a neurovascular plexus along the main SpA as well as short gastric and gastroepiploic arteries. The number of fascicles is unexpectedly high. Considering the average size of a SpN axon (ca. 2 μm in diameter) it is possible to calculate that the SpN plexus should contain (at maximum) a total of about 150K axons at the level of the main SpA (middle section). Part of these axons will innervate the SpA endothelium and part of these axons will instead enter the spleen and forms synaptic connections with either smooth muscles or immune cells at the level of the marginal zone between white and red pulp as well as within the white pulp as previously described in other species [23,24,25,26,27]. The number of axons seems high if it is considered that the human vagus nerve (that has the same size of the pig vagus nerve), which targets several organs in the body, is supposed to contain about 100 k axons. The high number of axons in the SpN could be related to the size of the spleen in the pig, which has a volume approximately 2-3 times bigger than the human spleen, and the length of the artery that the SpN is supposed to innervate. The number of fascicles and axons in the human SpN might be different.
The spleen of pigs (and other mammals, such as dogs) is also thought to contain a higher proportion of smooth muscle cells compared to the human spleen [28]. However, several papers have also shown that the human spleen is able to contract during stressful conditions, such as apnea and physical exercise [29,30].
The vascular organization of the splenic artery and vein is slightly different between pigs and humans. In the pig the SpA and SpV run in close approximation towards and from the spleen. Moreover, SpV and SpA do not present loops or convolutions like those observed in humans. Therefore, only a short (approximately 1-1.5 cm) segment of the SpA, close to the trifurcation point of the celiac artery, is better separated from the SpV. This segment of the artery was chosen as best intervention point in the stimulation studies above. The access to the neurovascular bundle at this location is, in fact, safer, thus reducing the chances to damage the nerves as well as artery and vein during dissections.
Human Data
Electrophysiological Characterization of Human Splenic Nerves:
Materials and Methods
Human SpN specimens One fresh harvested tissue from a donor patient containing the splenic neurovascular bundle NVB was preserved in organ transplant-suitable solution on ice for transportation. Upon arrival the specimen was placed in ice-cold Kreb's solution under a dissecting microscope, and a minimum of one discrete SpN fascicle per sample was carefully separated from the SpA and subsequently instrumented with two bipolar circumferential cuff electrodes (0.65 mm diameter, 5.5 mm length; CorTec GmbH) placed approximately 10 mm apart, to evoke and record CAPs. Fascicle electrode coverage was estimated to be 100% in all implantations.
Recordings Nerve activity was continuously monitored using an oscilloscope, and digitally recorded via a 1401 digital acquisition system and Spike2 software (Cambridge Electronic Design Ltd), with the sampling rate set at 20 kHz. Evoked CAPs were averaged (8 pulses) and the peak-to-peak amplitude of the averaged response quantified. The conduction velocity of the eCAP components was calculated from the measured distance between the stimulation site and the recording site and the latency of the eCAP signal (measured from the peak of the stimulation artefact to the peak of the eCAP).
Results Compared to the porcine samples, the human SpA presented with a more convoluted course as previously described (Michels 1942). Furthermore, the splenic NVB was embedded in extensive amounts of connective tissue and fat (
Calculated conduction velocities demonstrated typical values for unmyelinated fibres, where the range and average conduction velocity was 0.49 m/s, compared to porcine (0.7 m/s) and rat (0.72 m/s) SpN (
The human SpN has anatomical, morphological and electrophysiological characteristics similar to other mammals (porcine and rodent). The human SpN are composed of unmyelinated axons as confirmed by conduction velocities. It is therefore appropriate to assume that the stimulation parameters (frequency and waveform) optimized in the pig will be also suitable for the human splenic nerve. However, requirements for charge need to be calculated from the entire NVB.
Histomorphometric Characterisation of Human Splenic Anatomy
The objective of this study was to develop an understanding of the human splenic anatomy and estimate the approximate values of splenic neurovascular bundle (NVB) using histology (see Table 2). The study was performed on the splenic tissue received from transplant patients. Histomorphometric estimations for lumen diameter, arterial wall, fascicle diameter (mean Feret diameter) and the approximate distance of each fascicle from adventitia (outer splenic arterial wall) were calculated.
Materials and Methods
Five human splenic NVBs were provided from transplant patients at Addenbrooke's hospital, Cambridge, UK. The tissue was immersed in 10% neutral buffered formalin (NBF) as soon as possible post-excision. Photographs of the tissue were taken, with a ruler present for gross measurements (see
For quantification purposes, the splenic tissue was divided into three parts: proximal, middle and distal. Each of these parts consisted of several sections. The proximal end is close to the celiac indicated with a suture in
To summarise, as shown in
Translational Charge Requirements from Porcine to Human Splenic Neurovascular Bundle
Materials and Methods
3D Finite Element Model computer simulations were created using histology data from porcine and human splenic histology. This essentially comprised of splenic artery (lumen+arterial wall) and extravascular tissue. The ‘extravascular tissue’ is composed of ‘adipose tissue’ and ‘connective tissue’, with nerves embedded in the tissue. For porcines, a model with a split in the Cortec cuff (representing the in-vivo cuff) was used. For human models, cuffs with three arms structure were used. The diameter of the used cuff was 9 mm.
Considering the differences between porcine and human histology: the fascicles in porcine are evenly distributed around the artery and are in close proximity, whereas the fascicles in humans appear more dispersed; and b) the histology in porcine indicates negligible adipose tissue extravascularly, converse to substantial amounts in humans.
To translate the estimation of stimulation parameters from porcine to human, modeling was performed in the following two phases:
Phase (a): Development of 3D Finite Element Models (FEM) in Sim4Life simulation tool.
Sim4Life was used to develop representative nerve and artery models (based on histology and image quantification), cuff and electrodes (specifications defined by CAD) and 3D voltage fields.
Phase (b): Analysis of FEM solutions in the same tool. Sim4Life was used to interpolate voltage along axons using Sundt nerve model [31], and axon simulations estimated the strength-duration and population recruitment curves.
Results
It is estimated that the charge requirements in human acute models for a recruitment of 100% can potentially vary from approximately 80-1300 μC/cm2 (using 400 uS pulse widths, 12 mm2 surface area) and 70-1100 μC/cm2 (using 1 ms pulse widths). Approximately 70% of the recruitment is indicated under 350 μC/cm2. The additional 30% recruitment requires exponential increase in charge requirements beyond what is likely accommodated for by an implantable device. For example, it can be seen that a recruitment of 100% can potentially vary between 70-1300 μC/cm2, between 70-450 μC/cm2 for 80% recruitment, between 70-250 μC/cm2 for 50% recruitment, and between 70-170 μC/cm2 for 30% recruitment.
The nerves fibres in the humans are more dispersed in comparison to porcines. The range of the fascicle spread around splenic artery as indicated by histology profiling can be in the range of approximately 1-3 mm. The histomorphomteric data was further used to optimise the stimulation parameters and translate the charge requirements from porcines to humans using computatational modelling tools. Using Sundt c-fibre model the charge requirements for humans is indicated to be in range of approximately 70-1000 μC/cm2 for hundred percent recruitment.
Ex-vivo electrophysiological study of human splenic nerves
The objective of this study was to estimate indicative stimulation parameters of human splenic nerves in order to de-risk and optimize the biological efficacy and reproducibility of stimulation parameters of the electrical signal for use in humans, in particular for stimulation of a human splenic nerve. The study was performed using ex-vivo using human splenic samples.
Materials and Methods
An isolated fascicle was used as a control and cuffed with a smaller diameter Cortec Cuff electrode (500 μm diameter) for recording and stimulation, as shown in
Results
The nerve viability on isolated nerves was verified with a smaller 500 μm cuff electrodes, used as a control. The current strength-pulse width results from stimulation in eight human SNVB samples stimulated with 6 mm cuff demonstrates that the use of a 2 ms pulse width permits a 2.5- to 3-fold reduction of the stimulation threshold of pulse height for a 2.5-fold increase of pulse width i.e. from 0.4 to 2 ms (see
Interestingly, 400 μs pulse width, which seems to be an optimum stimulation parameter in the porcine in-vivo study, did not experimentally prove optimum in the case of human ex-vivo and in-silico tissue preparations. The mean pulse height from N=6 in acute porcine study was approximately 3.5 mA (see
An increase in frequency from 1 Hz to 10 Hz indicates a reduction in eCAP amplitude and is indicative of nerve fatigue (see
It was found that for increasing pulse width, particularly pulse widths greater than 1 ms, a decrease in the pulse height threshold needed to trigger an action potential in a human splenic nerve is observed.
This is a surprise based on the porcine model which showed the optimum pulse width to be far lower, at 0.4 ms. Lower pulse height thresholds are generally desirable because the biological efficacy and reproducibility of the stimulation parameters for use in humans is improved.
It has also been found that at a pulse width of 3 ms or above (3-5 ms shown in data) there is no further decrease in pulse height, whereas there is an increase in charge density. Therefore, the strain of the electrodes outweighs the benefits seen in the IPG beyond a pulse width of 3 ms. Between 2 ms and 3 ms, there is a negligible decrease in pulse height threshold but the amount of charge density required increases. Therefore it may be desirable to use a pulse width of less than 3 ms in humans. Pulse width around 2 ms offer an optimal trade-off between ensuring a low charge density being required, and a low pulse height being required for the stimulation of a human splenic nerve.
It is estimated that the charge density per phase requirements in human ex-vivo sample for 100% nerve recruitment can be as high as 400 μC/cm2. However, it is expected that for chronic stimulation, the formation of scar tissue may reduce the nerve recruitment by a factor of between 1.5 and 3.
Human Chronic Model Stimulations
The purpose of this study was to determine the biological effect varying of interphase delay and pulse width. The study was conducted using a human chronic model simulation.
Materials and Methods
Hybrid electromagnetic (EM) and neuronal simulations were used to predict axonal recruitment in two representative image-based and 3D computational neurostimulation models of human and porcine splenic neurovascular bundle, for multiple variations of dielectric parameters of the nerve bundles, stimulus waveforms (0.4 ms, 1 ms and 2 ms biphasic pulses), and fibre diameters (0.5-1 mm). One representative cross section histological image of splenic neurovascular bundle for each species was segmented using iSEG within Sim4Life platform. Tissues were differentiated to identify vessel wall, blood, extra fascicular medium—internal and external to the electrode—and the endoneurium tissue within fascicles. The segmented tissue surfaces were extruded in 3D using extrusion functionalities. The bundle models were combined with cuff electrodes geometries, were surrounded by saline solution tissue to mimic experimental conditions, and fascicles were populated with multiple parallel axonal trajectories randomly distributed within each fascicle cross section.
EM simulations were performed using a FEM solver in the quasi-static approximation that handles anisotroμC electric tensors conductivity and support thin layer settings. FEM calculations were executed on unstructured meshes created on the model geometries, built within Sim4Life using adaptive criteria and mesh quality adjustment. The meshes were edited to extract patches at the electrode surface to assign flux density boundary conditions, and at the interfaces between fascicles and interfascicular tissues to define thin layers mimicking the perineurium. In order to execute transient neuroelectric simulations for a given set of stimulation conditions (fibre diameters, pulse waveform, temperature), the range of parametrised axon electrophysiology in Sim4Life was extended by a c-fibre model (Sundt Model) completing the functionality required to stimulate nerves featuring distribution of unmyelinated c-fibres with arbitrary fibre diameters. Sim4Life functionalities such as the automatic sweeping and titration procedure were used to quantify stimulation thresholds (e.g. the pulse height threshold), investigate strength-duration (SD) curves and perform sensitivity analysis e.g. with respect to dielectric properties of tissues or pulse parameters. The creation of neuroelectric models, the creation and the setup of hybrid EM-neuronal simulations, and the post-processing of the results was assisted by 1) Python scripts facilitating the flexible, parametrised generation of functionalised nerve models, 2) the assignment of heterogeneous tissue properties and anisotroμC electrical conductivities, 3) the creation of mesh and its editing, 4) the distribution of fibre models within fascicles, 5) the assignment of electrophysiological behaviour as well as for automised post-processing analysis, e.g. the quantification of stimulation thresholds, extraction of recruitment curves, identify location of spike initiation and latencies (time of first spikes) with respect to stimulus pulse-shape.
The image-based models of neurovascular bundles developed were adapted to include fibrotic tissue surrounding the electrodes and the insulating silicone to mimic the presence of a post-implantation fibrotic tissue. Hybrid EM-neuronal simulations were used to calculate the neuroelectric responses of electrophysiological models of individual unmyelinated C-fiber axons inserted within the fascicles of the bundles to quantify the stimulation thresholds (e.g. pulse height threshold) for initiation of the action potentials. From the calculated thresholds, recruitment curves were plotted for both acute and the chronic scenarios based on biphasic waveforms with different pulse durations (rdur) and interphase delays (Tinter). The results are based on the following principal assumptions: (i) the dielectric properties, the structure, and the composition of the fibrotic tissue are uniform across all simulations; (ii) the fibrotic tissue is homogeneous and isotropic; (iii) there is no distinction between the fibrotic tissue formed around the electrodes vs. the silicone; (iv) the position of the fascicles is kept constant moving from acute to chronic scenario. The diameter of the neurovascular bundle is also kept constant and 0.5 mm of interfascicular tissue has been replaced by fibrotic tissue layer.
Results
The findings on pulse width in the ex-vivo preparations are further supported by this in-silico modelling data, as shown in
It was found that effects of interphase delay and pulse width are prominent. In particular, the interphase delay of 0.2 ms demonstrated a potential advantage of 5-10% over 0 ms interphase delay.
It is noted that these findings are supported by in-silico modelling data, as shown in
Other ex-vivo studies in unmyelinated fibers have found that for interphase delays greater than 300 μs, no further reduction in pulse amplitude threshold is found. This is depicted in
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2020/051458 | 6/17/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62863792 | Jun 2019 | US |
