Patent Application
20240016404
The invention relates to a measuring device for non-invasively detecting the intracranial pressure of a patient.
Numerous neurointensive care conditions can be associated with a life-threatening increase in intracranial pressure (ICP). Because the volume inside the skull is constant, an increase in volume of one or more compartments can lead to an increase in ICP. These compartments include the brain tissue (e.g., due to hemorrhage, swelling, inflammation), the CSF space (e.g., due to hydrocephalus, hemorrhage), and the vascular compartment (e.g., change due to hyper- or hypoventilation). The relationship between intracranial volume and intracranial pressure is termed intracranial compliance. ICP increases exponentially with volume increase, because initially an ICP increase can be compensated by so-called reserve spaces (CSF space, vascular compartment) (Monroe-Kellie doctrine). Conditions that can lead to an increase in pressure include traumatic brain injury, epi- and subdural hematomas, space-occupying ischemic strokes, intracerebral hemorrhage, subarachnoid hemorrhage, sinus and cerebral vein thrombosis, meningitis, encephalitis, global cerebral hypoxia, and other entities such as brain tumors, intoxications, and metabolic disorders.
In order to permanently monitor the ICP in critical cases such as severe traumatic brain injury, a measurement catheter can be inserted invasively through the cranial dome. However, invasive measurement procedures are a great burden for many patients, so that monitoring is often dispensed with.
Non-invasive measurement methods have already been proposed based on the measurement of the elongation of the skull. Blood volume fluctuations due to the heartbeat cause the skull to stretch, especially across the connective tissue closed cranial sutures. The resulting pressure pulse fluctuations in the brain are approximately 3-4 mmHg. These cause a minimal pulse-synchronous expansion of the skull.
Document WO 2013/041973 A2 proposes a measuring device for non-invasive measurement of intracranial pressure, comprising a sensor designed to detect the deformation of the skull. The sensor is connected to an amplifier, an ND converter, a processor, a display, and a memory. The measuring device enables the intracranial pressure to be determined by evaluating the sensor signals, based on which the deformation of the skull can be determined.
A similar measuring device is known from WO 2019/087148 A1, in which data acquired by a sensor is sent wirelessly to a receiver after processing.
With these measuring devices, however, there is the disadvantage that a dominant influence of the pulsation of the external carotid artery cannot be excluded due to a lack of decoupling. The cranial pulsation caused by the pulsatile internal pressure, which is significantly less than the arterial pulsation, is of little importance without discrimination of the arterial pulsation. The strain gauge arrangements proposed in the cited printed materials are operated at their measurement limit. This also means that no padding of the measuring device on the skull is possible, so that prolonged use is very uncomfortable for the patient with increasing duration.
The invention is based on the task of providing a measuring device for non-invasive detection of intracranial pressure pulsation that eliminates the aforementioned disadvantages and enables simple yet reliable measurement of vital data such as static intracranial pressure.
To solve this task, a measuring device having the features of claim 1 is provided.
The measuring device according to the invention comprises a holding device which can be detachably attached to the outside of the patient's skull in a force-locking and/or form-locking manner, at least one bimorph bending sensor which is arranged in or on the holding device, an analog signal amplifier and/or an analog signal filter for amplifying and/or filtering the measurement data supplied by the bimorph bending sensor, an ND converter for converting the analog measurement data into digital data, and a computing unit for preprocessing the digital data and for calculating and/or deriving vital parameters such as intracranial pressure on the basis of the digital data.
The measuring device according to the invention is characterized by the fact that it largely eliminates the influence of pulsating arterial vessels, i.e. the intracranial pressure pulsation is actually measured. In addition to conditioning the digital data, the computing unit is also used to perform corrections and calculate characteristic curve parameters and values that can be derived from them, such as intracranial pressure (ICP). In addition, systolic or diastolic characteristic values or vital parameters can be derived from the digital data. Optionally, the measuring device according to the invention comprises a display so that amplitude curves, a measurement curve, determined parameters or derived values or warnings can be output.
The invention is based on the realization that a bimorph bend sensor can be used to provide a particularly simple yet reliable and precise measurement of intracranial pressure pulsation. The principle of the invention is based on the deflection of a bimorph bending sensor attached to a head cuff or to a contact surface on the head due to the pulse-synchronous cranial volume expansion caused by the pulsating intracranial pressure (ICP).
A piezoelectric bending sensor can measure the smallest deformations or vibrations of the skull due to the heartbeat. The pressure of the blood pumped through the heart into the brain decreases gradually during the heartbeat due to the transmission pathways through the brain tissue. The transfer function sometimes depends on the intracranial pressure and related autoregulation mechanisms, so that the dynamic course of the pressure drop can be used to infer the intracranial pressure and autoregulation status, among other things.
Preferably, the holding device is designed as a headband or head cuff. However, the holding device can alternatively also be attached by placing, gluing or clamping the bending sensor by means of a cap or bandage. The exclusive or additional use of a suitable elastic coupling medium such as a skin-friendly double-sided adhesive film is also conceivable.
The measuring device comprises the headband or cuff, which is at least partially flexurally flexible and can also be at least partially elastically stretchable. The tensioning force of the headband or cuff is adjustable. The at least one bending sensor is part of a bend-flexible portion of the headband or cuff and can bend statically or dynamically due to static or dynamic volume expansion of the skull directly or due to an associated change in tensile stress of the support attached thereto, in particular a headband. The cuff can be applied to the patient's head and secured via a tensioning device with a constant tensioning force.
Preferably, the bend sensor is a bimorph piezoelectric bend sensor. It may be a bimorph bending sensor with antiparallel polarity. In this case, use is made of the effect that the pressure pulse-induced dynamic volume deflection of a skull on which the measuring device according to the invention is arranged causes a dynamic tensile stress on the measuring device according to the invention, which is designed as a headband, and a dynamic bending at the position of the bending sensor. In this way, even extremely weak pressure-induced volume changes of the skull can be detected.
A bimorph bend sensor consists of two sensor layers symmetrically arranged around the neutral fiber. When this arrangement is bent in one direction, one of the sensory active bending sensor layers is stretched while the other is equally compressed. When bending in the other direction, the behavior is exactly the opposite. Due to an antiparallel polarity of the two sensor layers, the signals of these opposing loads, since they have the same sign, add up in terms of magnitude and increase the overall signal. Coincident effects, on the other hand, such as interfering temperature effects or pyroelectric effects, are largely cancelled out and thus compensated.
In addition to a bimorph piezoelectric bending sensor, a multimorph bending sensor can also be used, which is composed of several pairs of sensors with alternating antiparallel polarity.
It can be provided that the bending sensor is arranged like a rocker on a support which can be attached to the outside of the patient's skull. In this embodiment, the bending sensor is arranged on a support that is arranged in the region of a cranial suture of the patient. The bimorph piezoelectric bending sensor can move around a pivot point under the effect of the volume deflections of the skull like a rocker. The holding device, which is designed as a headband, generates a counter (bearing) force on the bending sensor via a defined pretensioning force, which is necessary for the bending.
In an alternative embodiment, the bend sensor is disposed on a central portion of a C-shaped holder disposed between two end portions. The C-shaped holder is placed on a patient's skull such that the two end sections are located on either side of the skull suture. Pulsatile volume deflection of the skull causes the two end sections (legs) of the C-shaped holder to move in opposite directions, resulting in bending of the middle section of the bend sensor, The attachment of the bend sensor(s) is always done in such a way that no or negligible pulsations are transmitted to the bend sensor through external arteries or veins. This can be achieved by ensuring that pulsating arteries or veins have no or only strongly damped mechanical contact with the bend sensor or its attachment, i.e. with the headband. The C-shaped holder of the measuring device according to the invention allows strongly pulsating external vessels such as large arteries to be effectively and easily bridged for this purpose. This can additionally be done at other locations by using recesses in the support. By using foam padding, the influence of smaller and thus weaker pulsating external vessels can also be effectively damped below the influence limit. A direct or insufficiently damped contact to a pulsating artery would be immediately visible in the time signal by means of the typical “arterial curve shape” and the significantly higher amplitude.
Another alternative embodiment provides for the C-shaped holder to be fastened around the head with a cuff or strap like a headband, so that the pulsating volume deflection is transmitted to the tensile stress of the cuff or strap and this in turn causes a corresponding bending via the legs of the C-shaped holder, which is detected by the bending sensor. Via such a cuff, the smallest volume deflections of the skull can be transmitted in the form of a tensile stress to the C-legs of the sensor holder. This also results in a bending of the C-arm, which is detected by the bending sensor.
A defined pretensioning force is generated by such a headband. The change in volume of the skull caused by the pulsations of the intracranial pressure cause a bending of the piezoelectric bending sensor, which can be detected by means of the measuring device according to the invention. Using the measured values obtained in this way, the intracranial pressure pulsation and thus its pressure pulse shape can be monitored and vital state variables such as intracranial pressure can be calculated from the pressure pulse shape characteristics and its characteristic values. The C-shaped holder can also be arranged inverted on the patient's skull, i.e., so that the two end sections extend away from the skull. In this case, the headband also creates a pretensioning force. The bimorph bending sensor can be placed on either side or symmetrically on both sides of the middle section. Alternatively, in this example as in all other examples, a bimorph bend sensor may be placed in the neutral fiber of the center section. It is also possible for multiple piezoelectric bend sensors to be arranged inside the middle section symmetrically with respect to the neutral fiber. A soft, elastic support pad can also be placed on the outside of the skull, onto which the C-shaped holder is attached. Alternatively, the pad may be attached to the headband in such a way that it can be quickly replaced.
Preferably, the holding device designed as a headband can have a device for generating and adjusting a pretensioning force acting on the patient's skull. Preferably, the device for generating the pretensioning force may comprise a force sensor or a strain sensor. The pretensioning force may be adjusted by a user via a hand wheel or the like, or alternatively by means of a motor. For this purpose, the device may include a linear-elastic strain element such as a tension spring. In a further embodiment, this linear-elastic expansion element can be fixed, i.e. blocked, with respect to a further deflection after a constant tensile stress has been set.
In this context, it is preferred that the device for generating the pretensioning force has an indicator for the pretensioning force or for a tensions assigned to it. In this way, the user can set and control a specific pretensioning force that is transmitted to the piezoelectric bending sensor via the headband.
To further simplify the use of the measuring device according to the invention, the device for generating the pretensioning force can be designed to automatically set a predefined pretensioning force. An electromechanical or a pneumatic mechanism may be provided for this purpose. Manual or automatic control of the pretensioning force can be achieved by pneumatic tensioning force adjustment using an integrated air cushion in combination with an air pressure sensor.
Optionally, the headband may have padding over at least part of its length. The padding may also consist of several separate padded support points. The padding is located on the inside of the support device configured as a headband. The padding may comprise an elastic foam or a viscoelastic memory foam. The headband or cuff may be in full contact or only in defined contact areas or contact points to minimize interference from pulsatile soft tissues such as peripheral blood vessels and muscle activity, or to avoid contact with injuries.
It can also be provided that the measuring device according to the invention has one or more structure-borne sound sensors and/or one or more acceleration sensors, one or more position sensors and/or one or more pulse sensors and/or one or more blood pressure sensors and/or a temperature sensor, and that the computing unit is designed to detect external disturbing influences by at least one of the sensors mentioned. These external disturbing influences can be eliminated by calculation after detection so that they do not adversely affect the measurement of the intracranial pressure.
Preferably, the bending sensor can be removed from the holder designed as a headband and replaced. Retaining devices such as recesses and/or retaining clips are provided at the preferred sensor position of the headband or the cuff for fastening the sensor so that a form fit and/or a force fit is made possible. However, the bend sensor may also be bonded and/or screwed to the headband or cuff. The headband can be reused for another patient after sterilization. It is also possible that the headband has different positions for attaching the bend sensor. It is also possible that several bend sensors are attached to the headband.
One embodiment of the measuring device according to the invention provides that the bimorph bending sensor and the analog signal amplifier are integrated in a single component. Optionally, the following components may also be integrated in the single component: ND converter, a transmitting device, a transmitting-receiving device for wireless data transmission, a battery, a rechargeable battery. This reduces the number of components and the measuring device requires only a small installation space.
It may also be provided that the measuring device has a data logger connected to the A/D converter or the computing unit. The data logger stores either the measured values of the bending sensor and/or the data derived therefrom, such as the intracranial pressure. The data stored in the data logger can thus also be evaluated at a later time. The measuring device according to the invention can thus also be designed as a mobile device.
The holding device arranged as a headband may include an energy storage device, preferably a battery or a rechargeable battery, thereby enabling use as a mobile device.
Further possible applications arise if the piezoelectric bending sensor and/or the analog signal amplifier and/or the A/D converter is/are connected to a transmitting device or a transmitting/receiving device for wireless data transmission. In this case, data acquired by the sensor can be transmitted to a receiver, optionally after amplification or after conversion to digital data. In the case of wireless data transmission, the holding device designed as a headband does not require any cable connections, which simplifies and facilitates handling.
A variant of the measuring device according to the invention provides that several piezoelectric bending sensors are arranged on the headband. This makes it possible to measure the intracranial pressure pulsation and thus the intracranial pressure at several points.
In addition, the invention relates to a method for non-invasively detecting the intracranial pressure pulsation of a patient with a measuring device of the type described having the features of claim 17. The method according to the invention comprises the following steps: force-locking and/or form-locking attachment of the holding device, which has the at least one bimorph bending sensor and is in the form of a headband, to the outside of the patient's skull, dynamic detection of deformations and/or oscillations of the skull caused by the person's heartbeat by means of the at least one bending sensor, and calculation of characteristic curve parameters on the basis of the deformations and/or oscillations of the skull detected by means of the bending sensor and on the basis of a measured pulse curve, and derivation of vital state variables such as the intracranial pressure (ICP).
The method may also include the following steps: Digitization, signal preprocessing, determination of characteristic parameters. In the method according to the invention, it is preferred that the dynamically recorded deformations and/or oscillations of the skull are used to measure the “pressure response function” due to the cardiac pulsation excitation and to calculate therefrom an intracranial pressure and other parameters that are related to various vital state variables. For example, the procedure can be performed for the following diseases or conditions: head trauma, vasospasm, infarction, occlusions, reperfusion, revascularization, tension headache, migraine, embolus detection with carotid stenosis, dementia, hydrocephalus, brain tumor, sickle cell anemia, vascular malformations, meningitis, encephalitis, coma, heart failure, Aortic stenosis, aortic regurgitation, aortic valvuloplasty, carotid revascularization, aortic dissection, cardiopulmonary bypass, anesthesia, hyperventilation, catecholamines, volume management, hemofiltration, hemodialysis, pulmonary arterial hypertension, renal insufficiency, hemodialysis, peritoneal dialysis.
A variant of the method according to the invention provides that the detection of the pulsation of the cranial deflection due to the intracranial pressure pulsation and/or its effects is performed with two or more bending sensors arranged frontally at the base of the skull.
Alternatively or additionally, the detection of intracranial pressure can be performed with two or more bending sensors located occipitally at the base of the skull.
Preferably, the method according to the invention is carried out permanently, with vital parameters and intracranial pressure being recorded or derived at fixed intervals. In this way, long-term monitoring of a patient is also possible.
In the method according to the invention, the at least one bending sensor can be attached to the skull by placing, gluing or clamping. Preferably, the holding device designed as a headband is used for this purpose.
It is also possible that the at least one bending sensor is connected to the skull as an inlay of an exoskeleton or a helmet. This ensures a uniform contact pressure of the sensor or sensors.
The invention also includes a computer program suitable for the following functions:
P2/P1, P2/P1, Atotal, P12-P32|, P1/P3, |P12-P32|, Atotal, Asys/Adia,
Due to the extraordinarily high signal quality, especially the diastolic pressure curve range can be evaluated for itself and derivations to the entire field of application can be performed.
Clear curve characteristics can be obtained from the diastolic pressure curve area using the measuring device of the invention, in contrast to other methods such as transcranial Doppler, from which, for example, a diastolic flow velocity profile is obtained. These contain important information about effects of changes, diseases, etc., that can be attributed to microcirculatory disturbances, increased tissue resistance, intracranial pressure elevation, chronic inflammation, arteriosclerosis, diabetes, and inadequate O2 or CO2 exchange, hypotension, or hypovolemia.
Thus, pathological changes in these areas can be detected early without an invasive procedure and progressive changes can be monitored easily. In addition, treatment effects in such areas can be assessed much more easily and therapies can be directed more specifically.
The invention is explained below by means of embodiment examples with reference to the drawings. The drawings are schematic representations and show:
The left part of
With continuous recording, intracranial pressure (ICP) shows a multipeak pulse-synchronous periodic course: The first peak P is caused by the main arterial pressure wave. A second peak T is caused by filling of the cerebral arteries with blood and depends on intracranial compliance. A third peak or even several further peaks are related to diastolic-induced pulsations, e.g., closure of the aortic valves.
With increasing ICP, T increases relative to P as well as the total pulse pressure amplitude, so that the curve shape becomes increasingly pyramidal. From the dynamic course, it is thus possible to draw a conclusion about an increased static intracranial pressure.
By detecting the deflection of a bimorph piezoelectric bending sensor attached to a head cuff, headband, or support surface on the head due to pulse-synchronous cranial volume expansion caused by intracranial pressure pulsating at approximately 3-4 mmHg, mean static intracranial pressure (ICP) can be indirectly determined from the pulse shape. Absolute measured blood pressure values can be added to increase the accuracy of this procedure.
Essential components of the measuring device or steps of the measuring procedure are explained with reference to
In an alternative embodiment, the cuff can be provided on its inside with a viscoelastic memory foam. This has the property that it becomes hard under rapid loading, especially in the event of a rapid impact.
The described embodiments each show closed cuffs that extend over the entire circumference of a patient's skull. However, a cuff may also extend and be clamped over only a portion of the circumference of the skull. For this purpose, the cuff can be made of a flexible material, a bendable material or a spring-elastic material.
In a modified embodiment, a non-stretchable tension strap may be used instead of an expandable rubber band. In this case, a short stretchable element is required to attach the cuff to a skull with some pretension.
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By selectively mechanically coupling the ribbon or padding to one or more arteries (e.g., carotid artery), the arrangement can also be used to measure blood pressure pulsation and thus blood pressure measurement at the head. In this configuration, the signal from external blood pressure pulsation is significantly higher than the signal from cranial deflection caused by intracranial pulsation. Such “transient” coupling can be achieved by rotating the head cuff, i.e., the ribbon, by 90° so that the carotid artery is below the bearing surfaces of the ribbon. However, the same could be done without rotating the ribbon by inserting a foam under the locking mechanism and/or the C-shaped support. Advantageously, the head cuff formed as a ribbon contains a coupling element at the position of the C-shaped holder and/or the locking mechanism, which can be reversibly coupled to the carotid artery. This can be done, for example, via a thread or a deployable coupling mechanism analogous to a snap-action switch. The coupling force can be adjusted with the existing locking device, preferably to a value at which the system has been calibrated.
The described features of the measuring device and the associated method can be combined in any way.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 133 776.0 | Dec 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/086314 | 12/16/2021 | WO |
