WO2014033117A1

WO2014033117A1 - Electrophysiological analysis system with malfunction detection

Info

Publication number: WO2014033117A1
Application number: PCT/EP2013/067702
Authority: WO
Inventors: Kamel KHALFALLAH; Philippe Brunswick
Original assignee: Impeto Medical
Priority date: 2012-08-28
Filing date: 2013-08-27
Publication date: 2014-03-06
Also published as: FR2994819B1; FR2994819A1

Abstract

The invention relates to an electrophysiological analysis system comprising: a series of electrodes intended to be placed in different regions of the human body; a direct current voltage source; a control device adapted (i) to selectively apply direct current bursts, generated by the voltage source, to a pair of so-called active electrodes, said active electrodes forming an anode and a cathode, and (ii) to connect at least one other so-called passive electrode with high-impedance, said electrode measuring the potential reached by the body; and a measurement device arranged to obtain data representative of the current at the cathode and the potentials on at least some of the electrodes connected with high impedance, in response to the application of the bursts, which data can be used to determine a value for the electrochemical conductance of the skin at the anode and at the cathode. The system is characterised in that it also comprises a system-diagnosis device adapted to detect a system malfunction on the basis of the data representative of the current at the cathode and the potentials on at least some electrodes connected with high impedance.

Description

ELECTROPHYSIOLOGICAL ANALYSIS SYSTEM WITH DETECTION OF

FAULTS

FIELD OF THE INVENTION

The invention generally relates to the field of electrophysiological analysis of the human body, for example to detect pathologies.

The invention is particularly applicable to the evaluation of the sweat function of the human body.

PRIOR ART

The Applicant has already proposed in patent FR 2 912 893 an electrophysiological analysis system comprising a series of electrodes intended to be positioned in different regions of the body of a subject, a source of DC voltage, adapted to generate slots of adjustable DC voltage, and a switching circuit, arranged to selectively connect a pair of so-called active electrodes to the voltage source, said active electrodes constituting an anode and a cathode, and for connecting at least one other high impedance electrode.

The system includes four electrodes: two electrodes for the feet, and two for the hands, on which the patient positions his hands and feet.

The voltage applied by the voltage source on the electrodes makes it possible to generate an electrophysiological current in the outer layer of the skin, the study of certain characteristics of which may indicate the existence of pathologies or pathological predispositions.

In particular, by measuring the current flowing through the body at the cathode, as well as the potentials of the electrodes connected in high impedance, one can evaluate the electrochemical conductance of the skin.

FIG. 1 shows the current generated in the skin in response to the application of a voltage by the anode, as well as the electrochemical conductance of the skin as a function of the voltage at the anode. The electrochemical conductance of the skin corresponds to the slope of the voltage-current curve for the lowest voltages, and it varies according to the state of health of the subject. For example, a low slope of the voltage-current curve may be an indication, in a diabetic subject, of diabetic neuropathy, as described in Gin H, et al. "Non-invasive and quantitative assessment of sudomotor function for peripheral diabetic neuropathy assessment. Diabetes Metab (201 1), doi: 10.1016 / j.diabet.201 1.05.003 ".

However, the measurement may be distorted in the case where the subject changes the position of his hands or feet on the electrodes, or in case of malfunction of one of the components of the system, including the electrodes.

The measurement, which consists in applying to the active electrodes a series of continuous voltage slots, the value of the voltage varying from one slot to the next, can be wrongly pursued in the absence of detection of one of these biases. . This results in a loss of time since it is necessary to take the measurement from the beginning, and a risk of erroneous diagnosis. SUMMARY OF THE INVENTION

The object of the invention is to remedy at least one of the disadvantages described above. In particular, an object of the invention is to allow the detection of the dysfunction of an electrode or an alteration of the position or contact of an electrode with respect to the region of the body on which it is placed.

In this regard, the invention proposes an electrophysiological analysis system, comprising:

a series of electrodes intended to be placed in different regions of the human body,

a source of continuous voltage,

a control device adapted to selectively apply to a pair of so-called active electrodes continuous voltage pulses generated by the voltage source, said active electrodes constituting an anode and a cathode, and for connecting at least one other electrode, so-called passive, high impedance, said electrode for measuring the potential reached by the body, and

a measuring device arranged to record data representative of the current at the cathode and potentials on at least some electrodes connected in high impedance in response to the application of the slots, said data for determining a value of the electrochemical conductance of the skin at the anode and at the cathode,

the system being characterized in that it further comprises a diagnostic device of the system, adapted to detect a malfunction of the system from the data representative of the current at the cathode and potentials on at least some electrodes connected in high impedance.

Advantageously, but optionally, the system according to the invention may further comprise at least one of the following characteristics:

the system further comprises a measurement resistor connected in series between the cathode and the earth, the measuring device being arranged to detect the voltage across the measuring resistor, and the system diagnostic device is adapted to detect a malfunction of the anode if the voltage across the measuring resistor and the potential of the passive electrodes are zero.

the diagnostic device of the system is adapted to detect a malfunction of the cathode if the voltage across the measuring resistor is zero and the potentials of the passive electrodes are non-zero, the diagnostic device of the system is adapted to detect a malfunction a passive electrode if its potential is constant for different voltage values imposed on the anode,

the diagnostic device of the system is adapted to detect a contact failure of the cathode with the skin of the body or a fault of electrical contact between the cathode and the rest of the circuit if the potential of the passive electrodes is equal to the potential imposed on the anode.

the system diagnostic device is further adapted to determine, from the data, the value of the electrochemical conductances of the skin at the anode and at the cathode, and to analyze said values to detect a displacement of at least one electrode relative to the region of the human body on which it has been placed, and to identify said electrode.

The system further includes a display device adapted to display an alert indicating the malfunction of an electrode and identifying each defective electrode. The invention also proposes a method of electrophysiological analysis, implemented in a system according to the invention, the method comprising at least one measurement step during which the control device applies to the anode a series of said slots of DC voltage, and during which the measurement circuit reads the data representative of the current at the cathode and the potentials on at least some electrodes connected in high impedance in response to the application of the slots,

the method being characterized in that it further comprises a diagnostic step of the system, comprising detecting a malfunction of the system from data representative of the current at the cathode and potentials on at least some electrodes connected in high impedance ,

Advantageously, but optionally, the method according to the invention further comprises at least one of the following characteristics:

- The system diagnostic step is performed before or at the same time as the measurement step.

If no dysfunction has been detected during the diagnostic step of the system, the method further comprises, after the step of measuring, an analysis of the values of the electrochemical conductances of the skin at the anode and at the cathode to detect a displacement of at least one electrode relative to the region of the human body on which it has been placed, and to identify said electrode.

if a displacement of an electrode has been detected, a new measuring step is implemented.

The method further comprises displaying the result of the step of analyzing the values of the electrochemical conductances, the indication of each relative displacement between an electrode and the body, and the interruption of a measurement step in case such displacement. DESCRIPTION OF THE FIGURES

Other features, objects and advantages of the present invention will appear on reading the detailed description which follows, with reference to the appended figures, given by way of non-limiting examples and in which: FIG. 1, already described, represents an example of current-voltage and conductance-voltage response of human skin.

FIG. 2 diagrammatically represents an embodiment of the system proposed by the invention,

FIG. 3 schematically illustrates the possible causes of malfunction of the different electrical components of an embodiment of the system of FIG. 2,

FIGS. 4a, 4b and 4c show the malfunctioning of certain electrodes, respectively the anode, a high impedance connected electrode, and, at the same time, the cathode and an electrode connected at high impedance.

FIG. 5 represents an algorithm for detecting a malfunction implemented by a system according to the invention,

Figure 6 shows the impact of a displacement of an electrode (skin / electrode shake) on the value of the electrochemical conductance of the skin. FIG. 7 represents the main steps of the electrophysiological analysis method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Electrophysiological Analysis System

With reference to FIG. 2, there is shown diagrammatically an electrophysiological analysis system 100.

This system comprises a plurality of electrodes 1 10, preferably four electrodes, of which two electrodes extend over a surface large enough for an individual to affix his hands, and the two other electrodes extending on a surface. large enough for an individual to put his feet on it.

For example, these electrodes may have an area greater than 50 cm ² , preferably greater than 100 cm ² .

The system 100 includes a DC voltage source 120, adapted to generate DC voltage slots. The voltage delivered by the source is preferably between 0 and 10 V, advantageously between 0 and 4 V. Voltage slots may have a duration greater than or equal to 0.2. second, and vary in voltage from one slot to another, increasing, decreasing, or other (eg increasing and decreasing).

The system 100 also comprises a control device 130 of the DC voltage source 120 and the electrodes 1 10. This device makes it possible to selectively connect a pair of electrodes, forming an anode and a cathode, to the DC voltage source so that this one applies to them niches of tensions. These electrodes are then called "active".

The other electrodes are then connected in high impedance, and measure the potential reached by the body. They are called "passive" electrodes.

FIG. 2 shows a switching matrix for illustrating the selectively connecting function of the electrodes to the DC voltage source 120 by the control device 130.

The controller 130 may implement measurement cycles by varying the active and passive electrode pairs. Typically, with a four-electrode system as described above, measurements are made with the following pairs of electrodes (abbreviated designation in parentheses):

Cathode Anode

Left Hand (MG) Right Hand (MD)

Right Hand (MD) Left Hand (MG)

Left foot (PG) Right foot (PD)

Right foot (PD) Left foot (PG).

The system 100 also comprises a measuring device 140, which is arranged to record the potentials of the passive electrodes, and to measure the current between the active electrodes. In this respect, the measuring device 140 advantageously comprises a measurement resistor R _ca ii _b connected in series between the cathode and a reference voltage, for example ground. The current through the cathode is determined by measuring the voltage across the resistor, and dividing that voltage by the value of the resistor.

The measured data is displayed on a display 131.

In addition, the system comprises a diagnostic device 150 of the system, for detecting the possible malfunction of one of its components, from the measurements made by the measuring device. This diagnostic device 150 may for example be a processing unit receiving as input the different measurements taken by the measuring device 140, and analyzing these data as described below to deduce a state of operation or malfunction of the system.

The different causes of dysfunction are typically:

- bad contact (equivalent to a wire cut) electrical in the circuit,

electrode connected to the ground, and

poor contact or lack of contact between an electrode and the skin of the subject. Modeling system malfunction cases

To account for these possible causes of malfunction, FIG. 3 shows an equivalent electrical diagram of the system 100. In this equivalent diagram, each electrode e among the set comprising the anode a, the cathode ç, and the electrodes connected in high impedance hi, is modeled as being connected to the rest of its electrical circuit by a connector K _e , and the skin of the subject by a connector K ' _e .

It was also noted Ve the input potential of the corresponding connector K _e , and V ' _e the potential output of the corresponding connector K' _e . The potential V _e corresponds to the potential actually measured in the system, while the potential V _e corresponds to the local potential of the skin at the region of contact with the electrode.

In this scheme, also called _R and the electrochemical resistance of the skin at the electrode e, and C _and the electrochemical skin conductance, equal to the inverse of the resistance at this electrode.

The current flowing through the electrodes connected in high impedance, which is normally zero, is called current so that the current I + i at the anode is equal to the current I at the cathode. We finally note V _x the potential reached by the body at the application of the current by the electrodes.

From this modeling, one can report all the operating states of the system from the behavior of a connector, as follows.

in normal operation, all connectors K _e and K ' _e are closed, in case of poor electrical contact in the system, a connector K _e is open, in case of poor contact of an electrode with the skin, the corresponding connector K ' _e is open,

when an electrode is apparently grounded, the corresponding connector K _e is connected to the ground.

This modeling by the connectors makes it possible to deduce the relations between the potentials and the current recorded by the measurement circuit in the different cases of system operation: In normal operation, V _e = V ' _e for all the electrodes ee {a , c, hi}.

In addition, as R _h i "1, V _h i = V _hi and i = 0.

The electrochemical conductance of the skin is governed by the following relationships:

at the anode:

I + i _ I

C ^{a =} V ' _a - V _x ⁼ V' _a - V _x

V _c 1 ₌ 1

Rcalib V _a - V _hi R _a

- at the cathode:

/

c V _x - V ' _c

v _c i ₌ i

Rcalib V _h i- V _c R _c

In the event of anomaly at the anode, that is to say of bad contact with the source of tension, of absence of contact with the skin, or connection of the anode with the mass, the electrical behavior of the system is as follows:

- the potential V _delivered by the voltage source is not zero, but the potential V _'a is zero,

at the cathode, the potentials V _c and V ' _c are both zero,

for the electrodes connected in high impedance, V _x = V _h i = V ' _h i = 0.

The conductance calculated at the anode is then zero also C _a = 0. At the cathode C _c is undefined.

FIG. 4a shows the measurements obtained in the event of anomaly at the anode. It is noted in fact that the potential Vhi of all electrodes connected in high impedance are zero.

In the event of an anomaly of the system at the cathode level, whatever the anomaly, the following relationships apply:

The potential V _delivered by the voltage source is not zero, and V _a = _V (assuming that the cathode is the only electrode having an abnormality), At the cathode, V _c = 0 because the cathode discharge the earth through the measuring resistor R _ca iib,

- The electrochemical conductance of the skin calculated at the anode is zero Ca = 0.

More specifically, if the anomaly of the cathode is a connection to the earth, the potential V ' _c is zero as well: V' _c = V _c = 0. With regard to the electrodes connected in high impedance, Vx = V ' _h i = V _h i, V _h , is variable as a function of the value of the voltage Va imposed by the voltage source, and V _h i is between 0 and Va . If the anomaly of the cathode is a bad electrical contact or a lack of contact with the skin, the current passing through the cathode is zero, the potential V _c of the cathode is zero, and V ' _C = V _X.

Concerning the electrodes connected in high impedance, V ' _h i = V _h i and in addition we obtain the relation V _hi «V _a « V _x because:

V _a - V _x = R _a . I

Hence V _a = V _hi . (1 + and V _x = V _hi . (1 + with R _hi »1.

^K hl ^K hl

In case of anomaly of the system at an electrode connected at high impedance, whatever this anomaly, the potential Va is non-zero and V ' _a = V _a (assuming that the anode is not defective) .

Moreover, the potential V _h is constant regardless of the value of the voltage imposed on the anode.

FIG. 4b shows the measurements obtained in the event of a malfunction of a V _xG electrode connected at high impedance placed at level of the patient's left foot. Note that the potential of this electrode is constant, regardless of the value of the voltage at the anode.

Finally, there is shown in Figure 4c where two electrodes have failed: the cathode and a V _xG electrode connected to high impedance and placed at the patient's left foot. It can be seen that the potential at the cathode is zero and that at the electrodes connected at high impedance is constant, and that the electrochemical conductance of the skin at the anode is zero as well. System diagnostic process

The above findings are implemented in an algorithm implemented by the diagnostic device 150, to detect a malfunction and to identify one or more faulty electrodes, from the potentials V _h i recorded on the high impedance electrodes, the potential Va delivered by the voltage source, the potential V _c measured across the measuring resistor and the current I traversing the electrodes and measured at the measurement resistor, these quantities being transmitted by the measuring device 140.

The successive steps of this algorithm are shown in FIG.

In the first place, if the potential V _c and the potential V _h i of the electrodes connected at high impedance are zero, the device 150 detects a malfunction of the anode.

Otherwise, if the potential V _c measured at the measurement resistance is zero, while the potential V _h i is not, the device 150 detects a malfunction of the cathode.

More specifically, if the potential V _h i of the electrodes connected in high impedance is equal to the voltage Va imposed by the voltage source, the malfunction of the cathode is poor electrical contact or poor contact of the electrode with the skin of the subject .

If the potential V _h of an electrode connected at high impedance is constant regardless of the voltage Va imposed by the voltage source, then the device 150 also detects a malfunction of this electrode connected at high impedance. In other cases, with a potential V _c zero, the malfunction detected by the device 150 is a connection of the cathode to ground.

In the case where the potential V _c is not zero, then the cathode does not fail. If the potential V _h i of one of the passive electrodes is constant, independently of the value of the voltage Va applied by the voltage source, the device 150 detects a malfunction of this passive electrode.

In the remaining case (non-zero potential V _c , and potential V _h i of the variable passive electrodes as a function of the potential V _a ), no electrode malfunction is detected.

In practice and considering the noise, the equality of two tensions can be verified with respect to an absolute or relative threshold.

Electrophysiological analysis method

By identifying the possible causes of malfunction of the system 100, it can implement an electrophysiological analysis method during which possible failures are detected.

The main steps of this process are shown in FIG.

This method comprises at least one measuring step 200, during which the control device 130 connects two electrodes 1 10 in anode and cathode, and two electrodes 1 10 in high impedance, and controls the voltage source 120 continues to deliver at the anode a series of voltage crenels. The measuring device 140 raises the potential of the electrodes connected in high impedance, and the voltage across the measuring resistor Rcalib to deduce the value of the current at the cathode.

These measurements are used by the diagnostic device 150 or the measuring device 140 to deduce the value of the electrochemical conductance of the skin of the subject at the level of the anode and the cathode, with the formulas described above.

Before or during the measuring step 200, the method further comprises a step 210 of diagnosing the system. This step is analogous to the measuring step in the sense that two electrodes are connected in high impedance, and two electrodes are connected as anode and cathode.

The voltage source 120 delivers DC voltage pulses to the anode, and the measurement device 140 reads the same data as before. It then transmits them to the diagnostic device 150, which implements the algorithm described above to detect a possible failure of one or more electrodes of the system.

By analyzing the values of the potential of the passive electrodes and the voltage across the measuring resistor R _ca ii _b , the diagnostic device 150 can, as has been seen, detect the dysfunction of an electrode and identify said electrode.

If a malfunction is detected, the diagnostic device 150 controls the display 220 of an alert message by the display 131. This alert message includes the indication of the existence of an anomaly and the identification of the faulty electrode (s).

If the system diagnostic step takes place at the same time as the measurement step, the measurement can be interrupted. The measurement step can also be restarted.

If no malfunction has been detected, the diagnostic device 150 implements a step 230 for detecting a "shake", that is to say a relative displacement of an electrode relative to the zone of the body on which it is positioned.

With reference to FIG. 6, a shake disturbs the measurement since it substantially modifies the apparent electrochemical conductance of the subject's skin at the level of the electrode. Indeed, the electrochemical conductance varies according to the surface of the body in contact with the electrode.

The detection of the shake is performed at the end of the measuring step 200, the diagnostic device calculates the electrochemical conductance of the skin for different values of the voltage applied by the voltage source to the anode, and determines by comparison if the variation of the electrochemical conductance between two successive voltages exceeds a predetermined threshold, that is to say if the monotony of the curve is broken or if the conductance itself is "out of range"; that is, does not fall within an interval of predetermined values.

In this case, the diagnostic device controls the display 240 of an alert message by the display device. This warning message indicates that a shake is occurring as well as the electrode concerned.

The measurement can then be repeated.

Claims

1. An electrophysiological analysis system (100), comprising:

a series of electrodes (1 10) intended to be placed in different regions of the human body,

a DC voltage source (120),

a control device (130) adapted to selectively apply to a pair of so-called active electrodes dc pulses generated by the voltage source, said active electrodes constituting an anode and a cathode, and for connecting at least one other said electrode, said passive, in high impedance, said electrode serving to measure the potential reached by the body, and

a measuring device (140) arranged to record data representative of the current at the cathode and potentials on at least some electrodes connected in high impedance in response to the application of the slots, said data making it possible to determine a value of the conductance electrochemical skin at the anode and cathode,

the system being characterized in that it further comprises a system diagnostic device (150), adapted to detect a system malfunction from data representative of the current at the cathode and potentials on at least some electrodes connected at high impedance.

2. The system of claim 1, further comprising a measurement resistor (R _ca ii _b ) connected in series between the cathode and the earth, the measuring device (140) being arranged to record the voltage across the resistor of the resistor. measurement, in which the system diagnostic device is adapted to detect a malfunction of the anode if the voltage across the measuring resistor and the potentials of the passive electrodes are zero.

3. System according to claim 2, wherein the system diagnostic device (150) is adapted to detect a malfunction of the cathode if the voltage across the measuring resistor is zero and the potentials of the passive electrodes are non-zero. .

4. System according to one of claims 2 or 3, wherein the diagnostic device (150) of the system is adapted to detect a malfunction of a passive electrode if its potential is constant for different voltage values imposed on the anode.

5. The system of claim 4, wherein the system diagnostic device (150) is adapted to detect a contact failure of the cathode with the skin of the body or a lack of electrical contact between the cathode and the rest of the circuit if the potential of the passive electrodes is equal to the potential imposed on the anode.

6. System according to one of the preceding claims, wherein the diagnostic device (150) of the system is further adapted to determine, from the data, the value of the electrochemical conductances of the skin at the anode and the cathode , and for analyzing said values to detect a displacement of at least one electrode relative to the region of the human body on which it has been placed, and to identify said electrode.

7. System according to one of the preceding claims, further comprising a display device (131) adapted to display an alert indicating the malfunction of an electrode and identifying each defective electrode.

8. Electrophysiological analysis method, implemented in a system according to one of the preceding claims,

the method comprising at least one measurement step (200) during which the controller applies to the anode a series of said DC voltage slots, and during which the measuring circuit reads the data representative of the current at the cathode and potentials on at least some electrodes connected in high impedance in response to the application of the slots,

the method being characterized in that it further comprises a diagnostic step of the system, comprising detecting a malfunction (210) of the system from the data representative of the current at the cathode and potentials on at least some connected electrodes in high impedance,

9. The method of claim 8, wherein the diagnostic step of the system is performed before or at the same time as the measuring step.

The method of claim 8, wherein, if no malfunction has been detected during the diagnostic step of the system (210), the method further comprises, after the measuring step (200), a analyzing the values of the electrochemical conductances of the skin at the anode and the cathode to detect a displacement of at least one electrode relative to the region of the human body on which it has been placed, and to identify said electrode.

1 1. The method of claim 10, wherein, if a displacement of an electrode has been detected, a new measurement step is implemented.

12. The method of claim 1 1, implemented in a system according to claim 7, further comprising displaying the result of the step of analyzing the values of the electrochemical conductances, the indication of each relative displacement between a electrode and the body, and the interruption of a measuring step in case of such displacement.