Patent Application
20090024017
The present invention generally relates, in a first aspect, to an electrophysiological sensor, i.e., an electrode assembly for electrophysiological applications—and particularly to a sensor adapted for electrophysiological applications which do not require conducting substances acting as an interface between the sensor and the signal taking area.
The invention likewise relates to an electrophysiological sensor operating in dry conditions particularly applicable to transmitting weak electrical signals (such as biological potential or biopotential signals) with low noise, through the skin, based on nanotechnology.
The present invention also generally relates, in a second aspect, to a weak electrical signal, generally biological potential signal, conditioning circuit, and, in a third aspect, to a method for controlling such circuit, and particularly to a circuit and a method adapted for conditioning weak electrical signals coming from a medium, compensating possible interferences and direct current offsets experienced by such signals without inducing an additional current flow through the medium.
The invention is particularly applicable to obtaining and conditioning biopotential electrical signals from any part of the body of a patient, such as those obtained by means of electroencephalograms (EEG), electrocardiograms (ECG), electro-oculograms (EOG) or electromyograms (EMG).
The demand for electrophysiological sensors applied on the skin is currently increasing in modern clinics and in biomedical applications.
Patent application EP-A-1596929 describes a medical device comprising an electrode incorporating a material based on carbon nanotubes and a method for manufacturing the device.
Carbon nanotubes were discovered in approximately 1991 and from then on numerous and very interesting applications such as power storage for batteries, capacitors, etc. have been found for them. The previously mentioned patent application starts from the knowledge of these nanotubes for constructing a medical device. Said medical device is used for perceiving and communicating electrical stimuli in a way similar to that considered in the present invention, but in that patent application it is necessary to apply, in at least one portion of the surface of the medical device, an adhesive layer formed by a conductive polymer for adhering the nanotubes to at least one portion of the electrode. This layer is not necessary in the sensor of the present invention, being able to use techniques such as CVD (Chemical Vapor Deposition) for the direct growth of the nanotubes on a conducting substrate in the device.
The medical device described in patent application EP-A-1596929 does not describe nor suggest that the nanotubes arranged on a portion of the electrode are configured and/or adapted for directly penetrating the skin, it must be deduced therefrom that its application will be the conventional one by means of placing an interface layer between the electrode and the skin, generally a gel type interface layer.
The need to apply an interface layer between the electrode or sensor and the skin or another organic tissue involves some drawbacks: it is necessary to invest a long time preparing the skin and the device (in the order of a few minutes) for each intervention. The gel-skin interface is not a stable interface, which adds noise (electrode-skin, electrode-polymer or gel, gel-skin) to the measurements taken, disrupting its reliability. The conductive gel can further undergo modifications such as drying out (at least to a certain extent) during the process and therefore adding even more noise to the involved information. It is likewise necessary to act on the skin on which the device will be placed by slightly scratching or scraping the epidermal surface in order to unify it and ensure the conductivity with the consequent discomfort for the patient and operating time.
Due to the foregoing, it seems to be necessary to offer an alternative to the state of the art alleviating the discomfort generated in the patient, saving time for the operator, and reducing the disturbances and errors derived from the noise added to the measurements. It is therefore of interest to provide a sensor improving the previously indicated current deficiencies.
The electrophysiological sensor proposed by the first aspect of the present invention provides a particular solution to this need and unlike the device described in the mentioned patent application EP-A-1596929, in said alternative sensor it will be possible to dispense with the mentioned substrate-nanotube adhesive layer, furthermore adding a different operation based on penetrating the skin by the nanotubes, as is described below.
In addition, the circuitry currently used for measuring biopotential signals obtained by means of electrodes or electrophysiological sensors is based on the differential amplification and on the filters. High-gain amplification is carried out by means of a differential amplifier with a high input impedance, a high common-mode rejection ratio (CMRR) and a gain which is adjustable.
An instrumentation amplifier is a closed-loop gain unit which has a differential input and a single output with respect to a reference terminal. The impedances of the two input terminals are generally balanced and have high values, typically 109 K, or greater. The input polarization currents must also be low, normally between 1 nA and 50 nA. As occurs with operational amplifiers, the output impedance is very low, nominally a few milliohms, at low frequencies.
Instrumentation amplifiers are a low-pass filter, in which the bandwidth for a unitary gain for a small signal is typically between 500 kHz and 4 MHz. A gain increase reduces the bandwidth but its response is very flat in the range of biopotential signals (up to a few kHz). For this reason, active low-pass filters are required for improving the frequency range of interest.
An ideal low-pass filter would completely eliminate the signals above the cutoff frequency and would allow the signals below it (within the passband) to perfectly pass. Several undertakings are carried out in the actual filters in order to attempt to approximate the ideal case. Several types of filters are optimized in order to obtain a flat gain response within the passband, others sacrifice gain variation (ripple) in the passband in order to obtain a more sudden drop in the edge of the passband, whereas others sacrifice both, the flat response and the drop ratio, in order to favor the reliability in the pulsatile response.
After the analog signal conditioning, the signal can be digitized with an analog-to-digital converter, or ADC. The Nyquist criterion requires that the sampling frequency be at least two times the highest frequency contained in the signal, or the information on the signal will be lost. If the sampling frequency is less than twice the maximum frequency of the analog signal, a phenomenon known as aliasing or overlapping will occur. It is important to point out that if an input filter is not arranged in the input of the ideal sampler, any frequency component (either a signal or noise) falling outside the Nyquist bandwidth will be overlapped, i.e. will undergo aliasing effects. For this reason a filter is used in almost all the ADC sampling applications for eliminating these unwanted signals.
The main problem in biopotential measurements are the interferences, including the dominant noise of the line frequency of 50 or 60 Hz. In known proposals of weak electrical signals conditioning circuits, specifically biopotential signals obtained by means of a series of electrodes, the active electrodes include a follower close to each of them for intermediately storing the signal of the electrode, such that virtually all interference problems associated with the differential and high impedances of each electrode are eliminated.
Respective examples of the state of the art with regard to ECG systems with their corresponding instrumentation amplifiers AD8220 and INA326 respectively, appear on page 2 of the bulletin “Amplifier ICs Volume 6, Issue 1” of “Analog Devices” and on page 17 of the document “Information for Medical Applications” from “Real World Signal Processing” from Texas Instruments (SLYB108).
The slight imbalances in the lengths and the contacts of the electrodes cause the common-mode signal to be offset in direct current, which forms the main limitation of the differential amplifier of the instrumentation amplifier. The right leg exciter circuit (DRL) attempts to reduce this limitation by applying a voltage close to the common-mode voltage in a voltage supplying reference electrode or DRL electrode. Other alternating current (AC) coupling techniques could be applied for changing the reference voltage of the instrumentation amplifier. The circuit shown in
The lower limit of the noise level in the bioelectrical measurements is determined by the thermal noise of the impedance of the electrodes. Consequently, in order to achieve noise levels in the range of microvolts, the impedance of the electrode, including that existing between the electrode and the skin of the patient, must be less than 100 kΩ.
There are several patent documents describing different systems and methods for carrying out biopotential signal measurements. Several of said documents are set forth below.
Patent document EP1631189A1 discloses a system for carrying out biopotential signal measurements, in which a probe is used with an electrode located adjacent to the patient (in contact or without contact therewith). The use of a ground voltage, the voltage of a second electrode in contact with the patient or the voltage of a second electrode incorporated in the actual probe as the reference voltage of the differential amplifier to which the electrode is connected is proposed. The probe incorporating the electrode can include electronic circuitry with amplifiers, filtering and gain steps, batteries, components for transmitting through cable or wirelessly or components for recording data for a subsequent transmission. The probe includes a conductor separated a fixed distance with respect to the electrode adjacent to the patient for the purpose of insulating it against interference signals, for example coming from the amplifier included in the actual probe.
In addition, U.S. Pat. No. 5,876,351A1 proposes a portable modular device for carrying out electrocardiograms, which for several of its embodiments comprises amplifiers, each of them with a first input connected to each of several electrodes, previous to the instrumentation amplifier, and with a second input connected to a common reference voltage which can be that of the DRL (Wilson) or GND electrode, selected by means of a multiplexer.
U.S. Pat. No. 5,392,785A1 proposes an instrumentation amplifier applied to reducing common-mode voltage in ECG and EEG measurements by means of the application by a compensation circuit a compensation voltage representative of said common-mode voltage in different manners, some with a third DRL electrode and others without this third electrode but with a feedback path for high frequencies between a capacitor included in a compensation circuit and the capacity existing between the patient and the ground, or chassis, through said ground or chassis. The input of the amplifier of the compensation circuit is connected to the outputs of the differential amplifiers of the signals of the electrodes, for the purpose of monitoring the common-mode voltage received through the electrodes.
U.S. Pat. No. 5,713,365A1 proposes dispensing with the DRL electrode by maintaining a good rejection to the electric noise, directly feeding back the common-mode voltage detected in the output of the differential amplifiers of each electrode, in the inputs thereof, for the purpose of obtaining a portable device more than that of improving the performance of the systems which do inject a reference signal through the DRL electrode.
In all the mentioned system proposals including DRL circuits there is an electrical connection between the latter and the circuit conditioning the signals coming from the electrodes, since the voltage applied to the DRL electrode corresponds to the common-mode voltage detected in the differential amplifiers connected to each electrode, which makes the fluctuations in the electrical signals provided by the electrodes and the possible artifacts, or interfering signals, cause changes in the voltage to be applied to the DRL electrode, which results in the occurrence of a current injection in the patient through the DRL electrode-skin-tissue interface, altering the balance in the potentials of the half-cells.
The differential amplifiers of each electrode in the known proposals share one and the same reference voltage.
None of the mentioned proposals describes the electric separation of the DRL circuit from the circuit conditioning the electrical signals coming from the electrodes for the purpose of preventing the mentioned unwanted current injection in the medium, nor that of using individual reference voltages for each electrode for the purpose of comparing each of them with one of the signals supplied by each of the receiver electrodes in respective instrumentation or differential amplifiers.
The present invention relates, in a first aspect, to a electrophysiological electrode assembly or sensor which is basically integrated by an electrode for the skin which can be used in multiple applications such as: electroencephalograms (EEG), electrocardiograms (ECG), electro-oculography (EOG), or electromyography (EMG) among others. The sensor is based on technology with nanostructures and is applied in the transmission of weak electrical signals, with low noise, through the skin. It consists of an assembly formed by a structure of carbon nanotubes (CNT) with a particular arrangement and configuration especially favorable for electrophysiological applications.
More specifically, the proposed electrophysiological sensor is of the type comprising a plurality of conducting nanostructures which can transmit a weak electrical signal captured from the skin or from another part of an organic tissue to a transmitter means formed for example by an electrical connector which continues in a conductor or wiring and is characterized by integrating a structure of multiple carbon nanotubes fixed to a suitable conducting support substrate, said nanotubes emerging from said substrate in the form of substantially rigid and filiform elements, like needles. The fixing does not require a polymer layer for adhering the nanotubes. These rigid and filiform nanostructures are thus chemically connected at one end to said conducting substrate linked to an electrical connector and are operable to at least partially penetrate said organic tissue or skin at their free end like needles, without needing any intermediate gel or interface, i.e., the electrophysiological sensor operates in dry conditions on the skin which must not have been previously subjected to a previous preparation treatment. The contact and partial penetration of the nanotubes in the Stratum Corneum (outer layer of the epidermis with a thickness of 10 to 20 μm and forming a resistive medium) allow a stable electrical contact with low impedance and noise.
In a first embodiment the electrophysiological sensor of the invention comprises an envelopment casing housing said connector and which has associated to an outer wall the mentioned conducting substrate supporting the nanostructures.
According to a second preferred embodiment it has been provided that the sensor includes a local amplifier in association with said connector.
In an even more improved third version the sensor additionally includes a circuit for a treatment (pre-processing or processing) or at least partial adaptation of the weak electrical signals captured from the skin.
In an even more improved fourth version, the incorporation of an electronic circuit for transmitting the data captured by the sensor, by radiofrequency, to a remote management point has been provided.
The transmission and control of the electronic circuit associated to sensor is carried out wirelessly being able to couple, if necessary, other digital communication devices, as can be the case of a USB communications port.
The sensor will generally incorporate a digital electronic circuit carrying out signal conditioning, automatic gain control, automatic drift compensation, digitization and digital filtering functions.
These functions allow considerably reducing the interferences of the signal and form a substantial improvement with respect to the state of the art.
Another function of the mentioned electronic circuit is the possibility of compressing the digitized signals, prior to transmitting said signals to the signal storage and display devices, thus allowing to reduce the rate of information to be transmitted and the consumption of the device.
Differential modulation techniques such as for example Continuously Variable Slope Delta-modulation (CVSD), widely used for voice transmission in Bluetooth devices, are used for compressing the digitized signal.
The measurement and arrangement of the mentioned nanotubes incorporated in the body of the sensor, projecting therefrom grouped like a brush, is such that they can penetrate the stratum corneum, the last layer of the skin, thus offering a better reception of the electrical signal.
This new arrangement for the capturing means of the sensor allows:
In other words, by using the electrophysiological sensor proposed by the present invention, a preparation of the skin before or after transmitting electrical signals through the skin will not required.
Said nanotubes can likewise be incorporated in a mold placed or fixed in different supports such as a garment, a pillow or a mattress, being able to go unnoticed by the patient and not interfering in the measurements taken. Furthermore, the actual tissues will also be able to have integrated communication infrastructures.
An electrophysiological sensor, such as that described herein can be used in communication in the body area by using weak and therefore safe electrical signals. In other words, using the inside of the body as a conductor for transferring information to the so-called Body network area, including communications with implants.
According to the first aspect of the present invention, the use of a technology of carbon nanotubes is highly interesting due to the fact that said nanotubes are extremely small, thus increasing health safety by decreasing the risk of infection. The nanotubes used are good conductors, inert and extremely hard and consistent.
According to an embodiment, a reasonable value for the resistance of the assembly of carbon nanotubes has to be less than 100 kΩ; given that the impedance of a multiple wall carbon nanotube, which are those used herein, is 1000 kΩ, it is sufficient for a few to penetrate the skin or establish a low impedance electrical contact by means of another mechanism (capacitance). From this data and carrying out the appropriate calculations the conclusion is reached that the sensor proposed by the first aspect of the present invention will consists of at least 20 nanotubes considering that all of them have fall contact with the skin.
The present invention also relates to using an electrophysiological sensor as that proposed by the first aspect of the invention, in EEG, ECG, EMG, EOG, or for brain-machine interface applications, biometry applications or systems for detecting fatigue and hypovigilance, as well as to using said sensor for monitoring the wakefulness or sleep state in an individual.
With regard to the circuitry used for conditioning weak signals, generally biopotential signals, in view of the state of the art the main drawbacks of which have been set forth above, it seems to be necessary to offer an alternative which enables solving said drawbacks, and which particularly prevents altering the balance in the potentials of the half-cells occurring in the conventional proposals upon injecting a current into a medium, generally a patient, through a reference electrode, such as that described above as a DRL electrode.
To that end the present invention relates in a second aspect to a weak electrical signal conditioning circuit, of the type comprising:
Unlike the conventional proposals the circuit proposed by the second aspect of the invention is adapted for applying to the voltage supplying electrode, by means of said reference voltage generating device, a continuous electrical signal with a fixed value, the mentioned compensation means being insulated electrically with respect to the constant reference voltage generating device and substantially with respect to the voltage supplying electrode for assuring that there is no current flow through the medium as a result of the action of the compensation means, contrary to what occurred with the previously described conventional conditioning circuits, in which the fluctuations in the electrical signals provided by the receiver electrodes and the possible artifacts, or interfering signals, caused a current injection into the medium through the reference electrode, altering the balance in the potentials of the half-cells.
In the circuit proposed by the second aspect of the invention the mentioned compensation means are electrically independent from the reference voltage generating device, and comprise:
Said control system is generally connected with the output of said instrumentation amplifier for controlling the voltage generating device according to the output signal of the instrumentation amplifier.
For an embodiment the mentioned compensation means are adapted for, for the purpose of complementing said compensation carried out by means of applying said reference voltage, supplying the instrumentation amplifier, through a direct current offset adjustment input, with a direct current compensation adjustment signal at the output of the instrumentation amplifier representative of a variable voltage value determined according to the direct current offset to be compensated experienced by the weak electrical signal received by the first receiver electrode.
The compensation means are also adapted for compensating alternating interfering signals by means of supplying said electrical signal with a reference voltage and/or said adjustment signal, to said second input and to said direct current offset adjustment input of the instrumentation amplifier, respectively.
In the present application weak electrical signals are understood to be signals with low amplitude and/or coming from sources with high output impedances. The AC voltage values of such signals are typically less than 10 mV and can have DC direct components greater than the AC signal.
For a preferred embodiment the conditioning circuit proposed by the second aspect of the invention is applied to conditioning biopotential measurement signals on any part of the body of a patient, such as those obtained by means of electroencephalograms (EEG), electrocardiograms (ECG), electro-oculograms (EOG) or electromyograms (EMG), said medium being a patient, for the purpose of achieving a minimum current flow therethrough.
For said preferred embodiment the voltage supplying electrode is in contact with a contact area of said patient, forming with said constant voltage generating device a right leg circuit DRL for the purpose of achieving that the voltage of the patient is substantially equal to the voltage supplied by the constant voltage generating device.
A third aspect of the present invention relates to a method for controlling a weak electrical signal conditioning circuit, of the type which comprises:
The method proposed by the third aspect of the invention is characterized in that:
For an embodiment the method comprises carrying out said compensation of the direct current offsets experienced by said weak electrical signal received by the first receiver electrode by means of applying said reference voltage and modifying its value in a controlled manner.
The proposed method comprises carrying out said compensation or compensations for compensating the common-mode voltage variations of said instrumentation amplifier.
The method proposed by the third aspect of the invention is applied to conditioning biopotential measurement signals, said medium being a patient, for the purpose of achieving a minimum current flow through the medium.
Although it is not limited to it, the method proposed by the third aspect of the invention is applied to controlling a conditioning circuit according to the second aspect of the invention.
In addition, the circuit proposed by the second aspect of the invention can be applied to conditioning signals obtained by different types of electrodes (wet, dry, etc.), but for a preferred embodiment the electrodes comprise one or more electrophysiological sensors such as that proposed by the first aspect of the invention, in which case the digital electronic circuit described for several embodiments of the sensor proposed by the first aspect, which carries out signal conditioning, automatic gain control, automatic drift compensation, digitization and digital filtering functions, is for the present preferred embodiment the conditioning circuit proposed by the second aspect of the invention.
The interferences of the biopotential signals are considerably reduced, and the offsets experienced by such signals are compensated by means of implementing said preferred embodiment, using the high performance of both the electrophysiological sensor proposed by the first aspect, and the conditioning circuit proposed by the second aspect.
The previous and other advantages and features will be more fully understood from the following detailed description of several embodiments with reference to the attached drawings, which must be considered in an illustrative and non-limiting manner, in which:
a to 7e are different views of a support supporting the circuit proposed by the second aspect of the invention and the electrodes connected thereto applied in the head of a patient, for the embodiment of an encephalogram, and
The electrophysiological sensor 1 according to the first aspect of the invention is integrated by a casing 8 housing an assembly of carbon nanotubes (CNT) 2 supported directly on a conducting substrate 3 from which they emerge like very fine rigid needles, suitable for being able to directly come into contact with the skin 6 without applying an electrolytic gel and at least partially penetrate the stratum corneum, the outermost layer of the skin, as observed in
With the electrophysiological sensor 1 presented by the first aspect of the present invention provided with a structure of inert (i.e., non-polarizable) carbon nanotubes 2, in the form of rigid filiform elements grouped like a brush which can penetrate said outer layer of the skin, a transmission of electrical signals carrying information is achieved, from an organic tissue, with less noise with respect to the sensors of the state of the art and without needing an intermediate interface layer. Said structure of carbon nanotubes (CNT) 2 is further designed so that it penetrates very little, without coming into contact with the nerve cells, thus preventing any sensation of pain in the patient or possible transmission of an infection.
Advantageously the carbon nanotubes 2 used have multiple walls whereby their conductivity is increased and the capture and transmission of the biological potential signals is favored.
The mentioned multiple wall carbon nanotubes 2 have been obtained by growing directly in the substrate 4, which is made of highly doped silicon or titanium.
In another embodiment shown in
The sensor of the invention can be formed such that it can be directly incorporated into different substrates, such as garments, pillows, mattresses or others. In a particular embodiment it has been provided that said conducting substrate is integrated in a material forming part of a surface of said garment or other article providing a substrate.
Taking into account that the electrophysiological sensor of the invention operates as a biological electrode such as a transducer converting an ionic current into an electrical current, it has been provided that in a possible embodiment the sensor of the invention also use a suitable coating for facilitating the Red-Ox reaction in the interface area and for such purpose the mentioned nanotubes 2 are at least partially coated (in the region of their tips), with a suitable coating and particularly with an Ag—AgCl coating.
In another implementation of the invention it has been provided that the described electrophysiological sensor further houses an electronic circuit for processing and treating the signal, and a radio-frequency transmitter.
Unlike the performance of a similar sensor of the state of the art in which there will be at least two RC couplings, with their corresponding associated output and input resistances, corresponding respectively to a first gel-skin interface and to a second gel-electrode interface, in the proposal of the present invention said RC coupling is limited to the skin-sensor coupling, a considerable reduction in the noise introduced in the captured weak signal being derived therefrom due to the smaller charge accumulations in the interface layers, especially upon avoiding the gel-skin interface which is known to provide a component of instability most probably due to the diffusion of the gel in the stratum corneum which is a dynamic non-homogeneous process.
The substitution of known electrophysiological electrodes for EEG, ECG, EMG, EOG, or for brain-machine interface applications, as well as the use of said sensor for communications between devices in the human body (external or implants) using the inside of the body as a conducting means, must be emphasized Among the applications for the electrophysiological sensor of the invention.
Other applications of the described electrophysiological sensor are in the area of research on sleep and particularly for monitoring the wakefulness or sleep state in an individual or for fatigue studies and in the area of biometry based on EEG and ECG.
The invention also relates to the use of an electrophysiological sensor according to the first aspect of the invention in EEG, ECG, EMG, EOG, or for brain-machine interface applications, biometry applications or systems for detecting fatigue and hypovigilance, as well as to the use of said sensor for monitoring the wakefulness or sleep state in an individual.
A person skilled in the art will be able to carry out variations and modifications on the embodiments indicated up to this point and introduce other elements into the capturing chain of the sensor, known in themselves, without departing from the scope of the present invention as it is defined by the attached claims.
With reference to
The circuit of
As has been previously stated the circuit proposed by the second aspect of the invention is adapted for applying to the voltage supplying electrode E3, by means of the reference voltage generating device D, a continuous electrical signal with a fixed value, said reference voltage generating device D being a constant voltage generating device D.
The constant voltage generating device D is formed, for the embodiments shown by
Since the compensation means are insulated electrically with respect to the constant voltage generating device D and substantially with respect to the voltage supplying electrode E3 (between E1 and E3 there is only the impedance of the patient H, which is very high) it is assured that there is no current flow through the medium H as a result of the action of the compensation means, contrary to conventional proposals in which said current flow causing changes in the potentials of the half-cells did occur.
The compensation means of the circuit proposed by the second aspect of the invention comprise, for the embodiment shown by
As has been previously stated, the mentioned compensation means are adapted for supplying the instrumentation amplifier Amp1, through a direct current offset adjustment input DIGIN1, with a direct current compensation adjustment signal Sc1 at the output of the instrumentation amplifier Amp1 representative of a variable voltage value determined according to the direct current offset to be compensated experienced by said weak electrical signal SE1 received by the first receiver electrode E1.
Likewise the compensation means of the circuit proposed by the second aspect of the invention are also adapted to compensate alternating interfering signals by means of supplying said electrical signal with a reference voltage Vref1 and/or said adjustment signal Sc1, according to the necessary compensation.
The compensation means are adapted for, according to the ratio between the output signal of the instrumentation amplifier Amp1 and the dynamic range thereof:
For the embodiments shown by
The mentioned control system is formed by a microcontroller μc (or by a logic circuit for other embodiments not shown), forming part of a local electronic system SCM which also includes said voltage generating devices D, DAC1, said control system being connected to the output of the instrumentation amplifier Amp1 once digitized by a digital-to-analog converter ADC1, for monitoring it and operating accordingly, said operation including the mentioned control of the digital-to-analog converter DAC1 for modifying the value of the reference voltage Vref1.
Continuing with
In said circuit shown by
The compensation means illustrated in
As is seen in
The compensation means are adapted for compensating direct current offsets experienced by the weak electrical signal SE2 received by said second electrode E2 and alternating interfering signals, operating in a manner similar to how they operate with the differential amplifier Amp1, including the supply of a respective direct current compensation adjustment signal Sc2 and the sending of a gain adjustment signal Sg2 to an adjustment input DIGIN2 of the same Amp2.
The local control system SCM shown in
The microcontroller μc of
The polarization voltages of the amplifiers Amp1, Amp2 and of the operational amplifier of the generating device D, and indicated as +V in
A suitable instrumentation amplifier for being used as Amp1 and Amp2 is for example the programmable-gain instrumentation amplifier AD8555, although the circuit shown by
It is necessary to point out that the conditioning circuit of
In fact the actual instrumentation amplifiers Amp1, Amp2, such as the mentioned AD8555, include a circuit for suppressing radio frequency interferences with a low-pass filter with a bandwidth of a few kHz.
A low-pass (RC) filter (not shown) is used before the digitalization, which filter allows the signals within the passband of the filter to pass through while at the same time it limits the bandwidth of the signals which are outside the passband, thus reducing the possible noise in the input signals of the analog-to-digital converters ADC1, ADC2, and therefore obtaining digital signals VAmp1o, VAmp2o representative of interference-free analog signals.
It is necessary to point out that some of the components or elements of the local electronic system SCM have also not been shown so that
As is schematically shown in
For an embodiment, said remote control system SR is adapted for wirelessly receiving, from the local electronic system SCM, the digital values representative of the output signal VAmp1o, VAmp2o of the instrumentation amplifier (
For an embodiment, the remote control system SR is adapted for carrying out, automatically or if necessary with the intervention of an operator (for example for choosing a control program to be applied), at least part of the gain adjustments of the instrumentation amplifiers Amp1, Amp2, and/or the modification of the values of the reference voltages Vref1, Vref2, and/or the modification of the adjustment signals Sc1, Sc2, and for carrying out the corresponding sendings of the digital values of the adjustment signals Sc1, Sc2, Sg1, Sg2 and/or of reference voltages Vref1, Vref2 to the local electronic system SCM.
For another embodiment, the local electronic system SCM is adapted for carrying out the gain adjustments of the instrumentation amplifiers Amp1, Amp2, and/or the modification of the value of the reference voltages Vref1, Vref2 and/or the modification of the adjustment signals Sc1, Sc2.
Such remote control system SR is, for an embodiment, a computerized system in connection with display means, such as a screen, for displaying the output signals VAmp1o, VAmp2o, i.e., for the case of an ECG, the signals representative thereof.
The mentioned remote computerized system SR preferably comprises a series of both input and output peripherals in order to enable its use by an operator for example for the mentioned embodiment in which part of the adjustments are carried out by the remote system SR.
The remote system SR obviously also has a communications module (not shown) which is internal or external (for example connected to a USB port) and which can wirelessly communicate with the communications module M of the local electronic system SCM with the same technology and protocols (for example Zigbee).
The main objective of using wireless communication is eliminating possible signal interferences with the mains frequency (50 or 60 Hz) caused by the use of cables. This is so due to the fact that said wireless interface or communication eliminates the main stray capacitance between the body of the patient and ground which occurred in the mentioned cables of conventional proposals. Said wireless communication obviously also provides great autonomy to the patient which the wiring does not allow.
For an embodiment, the instrumentation amplifiers Amp1, Amp2, associated circuitry, and in general the local electronic system SCM are supported by a support C which also supports all or part of the electrodes E1, E2, E3, together with the instrumentation amplifiers Amp1, Amp2 and associated circuitry ADC1, ADC2, filters (not shown), etc.
The fact that the signals of the receiver electrodes E1, E2 are amplified and digitized in situ, i.e., with the instrumentation amplifiers Amp1, Amp2, and other associated circuitry, arranged very close to the electrodes, considerably eliminates the interfering noise which conventionally occurs when the active electrodes are far from the amplifying steps, due to the high degree of rejection to the common-mode of the instrumentation amplifiers it eliminates the mains frequency noise common to the two electrodes E1, E2, and to the absence of cables between the electrodes E1, E2 and the amplification electronics. After the digitization in situ the digitalized output signal VAmp1o, VAmp2o (see
The reference voltage of the supplying electrode E3 of the DRL circuit has a high immunity to noise, due to the fact that it comes from a dedicated noise cancellation circuit, which in
a to 7e show a case for which (unlike that shown by
For the embodiment shown in said
The intermediate portion Ci of the support C forms a strip Ci running along the head connecting the front portion Cd and a back portion Ct of the support C. Said strip Ci can be extended for the purpose of adapting the support C to different head sizes.
There is a housing Aj defined in the back portion Ct of the support C for the local electronic system SCM, which is in turned housed inside a case T, which is shown with greater detail in
In the case T shown in said
Said case T also has on one of its sides a switch Sw for its handling by an operator for the purpose of activating/deactivating the local electronic system (SCM).
As has been indicated in a previous section, the present invention also relates, in a third aspect, to a method for controlling a weak electrical signal conditioning circuit which, although it is not limited to it, is applied to controlling a conditioning circuit according to the second aspect of the invention.
For the embodiments for which the method is applied to the proposed circuit according to the second aspect of the invention, specifically for the embodiments shown by
As has been previously described with reference to the circuit proposed by the second aspect of the invention, the method proposed by the third aspect also comprises carrying out said compensations performing the mentioned actions for generating, modifying, adjusting and supplying signals Vref1, Vref2, Se1, Sc2, Sg1 and Sg2, according to the ratio between the output signal of the instrumentation amplifier or amplifiers Amp1, Amp2 and the dynamic range thereof.
An embodiment of the method proposed by the third aspect of the invention is described below with reference to an instrumentation amplifier Amp1, although the second Amp2 or even other additional amplifiers are controlled in the same way as that explained below for Amp1.
For said embodiment, shown by means of a flow chart in
a) fixing an initial work point which includes predetermining a value for the gain adjustment signal Sg1, according to the desired gain, and a substantially equal value for the reference electrical signal to be applied to the voltage supplying electrode E3 and for the reference voltage Vref1, i.e., equal to that generated by the constant voltage generating device D (see
Said step a) is shown in the first and second boxes (counting from the top) of the flow chart of
b) monitoring the digitized output of the instrumentation amplifier Amp1 for a predetermined number of samples or period;
Step b) is shown in the third and fourth boxes of the flow chart of
c) checking if the values of the signal VAmp1o obtained in said monitoring of said step b) are within the dynamic range of the instrumentation amplifier Amp1 (fifth box counting from the top), and:
d1) if there are values of the monitored signal VAmp1o above and below the dynamic range of the instrumentation amplifier Amp1, reducing the gain thereof by means of modifying said gain adjustment signal Sg1 (box to the right of the sixth box counting from the top) and its corresponding application (second box); and carrying out said steps b) and c) again;
d2) if there are only values of the monitored signal VAmp1o above the dynamic range of the instrumentation amplifier Amp1 (affirmative response to the dilemma of the seventh box counting from the top), at least increasing the value of the reference voltage Vref1 (box to the right of the seventh box counting from the top), applying it (second box), and carrying out said steps b) and c) again; or
d3) if there are only values of the monitored signal VAmp1o below the dynamic range of the instrumentation amplifier Amp1 (negative response to the dilemma of the seventh box counting from the top), at least decreasing the value of the reference voltage Vref1 (last box of the flow chart of
As is indicated in the flow chart of
said step d2) further comprises modifying the direct current offset adjustment signal Sc1 and applying it to the direct current offset adjustment input DIGIN1 of the instrumentation amplifier Amp11, in order to reduce the direct current level in the monitored signal VAmp1o; and
said step d3) further comprises modifying the direct current offset adjustment signal Sc1 and applying it to the direct current offset adjustment input DIGIN1 of the instrumentation amplifier Amp11, in order to increase the direct current level in the monitored signal VAmp1o.
As has been previously mentioned the method proposed by the third aspect of the invention comprises compensating the direct current offsets experienced by other weak electrical signal or signals received by other receiver electrodes in contact with other areas of the patient H, in a manner similar to how the compensation with the weak electrical signal SE1 received by the first receiver electrode E1 is carried out.
A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| P 200601997 | Jul 2006 | ES | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/ES2007/000390 | Jun 2007 | US |
| Child | 12107392 | US |
