WO2007119144A2

WO2007119144A2 - Apparatus and method for measuring the cutaneous electrical impedance op an individual

Info

Publication number: WO2007119144A2
Application number: PCT/IB2007/000949
Authority: WO
Inventors: Gianfranco Coccoli; Claudio Lazzari
Original assignee: Gianfranco Coccoli; Claudio Lazzari
Priority date: 2006-04-14
Filing date: 2007-04-12
Publication date: 2007-10-25
Also published as: WO2007119144A3; ITMI20060756A1

Abstract

An apparatus for measuring the cutaneous electrical impedance of an individual, comprising an oscillator (10) operatively associable with a first skin portion (21) of the individual, and tuning means (11) for carrying out tuning of an oscillation frequency of said- oscillator (10) with a characteristic frequency of the nervous rete innervating the first skin portion (21), thereby obtaining a corresponding tuned frequency (f ). The apparatus (1) further comprises an output block (30) connected to the oscillator (10) to generate, as a function of the tuned frequency (f ), an output signal (31) representative of the electrical impedance (Zeq) of the first skin portion (21). Also described is a method of measuring the electrical impedance of an individual.

Description

"APPARATUS AND METHOD FOR MEASURING THE CUTANEOUS ELECTRICAL IMPEDANCE OF AN INDIVIDUAL"

D e s c r i p t i o n

The present invention relates to an apparatus and method for measuring the cutaneous electrical impedance of an individual.

This measurement aims at interactively determining the cutaneous psychogalvanic reflex and the bioelectric activity of the acupuncture points.

It is known that during the embryo development the skin and the whole nervous system originate from the same cells; the two systems are therefore in mutual and constant operational relationship. For the same reason, skin has a very rich neuron rete interactively connecting it to the central nervous system; therefore it constitutes a very reactive organ having an

"interface" function between the nervous system and the external world.

This assumption allowed neurophysiologists to discover that given skin regions possess a sort of measurable "electrical topography" which is a function both of the psycho-emotional state (psychogalvanic reflex) and of the activity of anatomically-corresponding visceral structures (acupuncture reflex) .

In some skin regions this phenomenon is particularly marked; in these regions a very high density of the nervous tissue has been discovered and it is exactly to this regions and the acupuncture points correspond. Various methods are presently used for study and measurement of the psychogalvanic reflex and the reactive state of the acupuncture points, and one of the most used of them is a method using the electrical impedance meter.

Neurophysiological researches have come to the conclusion that the cutaneous electrical impedance depends on the reactivity of the nervous tissue innervating it. More specifically, the reactive mode of the neuron surface rete, in response to stimuli of the surrounding environment, is the main element capable of dynamically conditioning the value of the cutaneous electrical impedance according to an inverse-ratio law. In other words, the greater the reactivity of the cutaneous nervous tissue in response to stimuli applied thereto, the smaller in proportion the value of the electrical impedance measurable in that skin length is.

This phenomenon depends on complicated biochemical reactions the final effect of which is to vary the electrolytic concentration in the tissue context and, consequently, the electric conductivity thereof.

In addition, the value of the electrical impedance on the acupuncture points depends on the functional state of the anatomically corresponding visceral system the topographic coincidence of which is always mediated by the nervous system.

A correct measurement by an impedance meter of the skin reactivity, be it of the galvanic or acupuncture type, cannot therefore be separated^' from application of a stimulus that is generally of the electric type. A first example of apparatus in accordance with the known art contemplates -use of two electrodes to be positioned in contact with the patient's skin and through which a (direct or alternating) stimulating voltage is applied to the skin itself; by an ammeter series-connected to one of said electrodes, detection of the current flowing in the circuit takes place so that calculation of the cutaneous impedance in the region under examination is made possible.

However, in the case of a direct voltage, measurement is very inaccurate due to the fact that it only detects the electrical resistance of the considered skin portion, while fully neglecting the inductive and capacitive components of the impedance; therefore the electric reactivity of the cutaneous skin system is not taken into account, which makes the detection carried out quite unreliable.

In the case of an alternating voltage, the operating limit of the measurement consists in that the frequency at which detection is carried out -is fixed by the operator a priori, and therefore it is impossible to consider the reactivity of the cutaneous nervous system in a simple and immediate manner.

In this case an empirical mapping of the impedance of the concerned skin portion is required, which mapping is obtained by a series of measurements carried out at different frequencies; thus a curve of the experimental type can be traced, which is representative of the impedance against frequency. In other words, the inductive and capacitive components of the skin portion are taken into consideration as passive elements, while in this case too excluding the reactive mode of the cutaneous nervous system, which will make measurement once again not very accurate and reliable.

A different type of apparatus comprises two pairs of electrodes; the first pair is connected to a pulse generator and allows application of these pulses to the patient's skin. The second pair of electrodes, positioned close to the electrodes of the first pair, is connected to an oscilloscope for detection of the frequency of the signal flowing through the skin so that the impedance of such a region- can be determined.

A disadvantage typical of these apparatus can be found in the manufacture complexity of each of them that must be provided with both a stimulation circuit and an impedance-determining circuit; in addition, it will be understood that the electrodes used for stimulation are in contact with skin portions different from those of the electrodes used for measurement of the skin impedance; therefore an intrinsic inaccuracy in measurement appears, exactly due to the spatial difference between the region that is stimulated and the region where detection is carried out.

A further type of apparatus made available by the known art comprises two electrodes alone, each operatively associated with a double-throw circuit breaker; in a first configuration, the two circuit breakers connect the electrodes (and therefore the patient's skin) to a stimulator for application of a series of stimulation pulses; in- the second configuration, the circuit breakers connect the respective electrodes to an oscilloscope for determining the frequency of the response signal and consequent measurement of the skin impedance. Alternatively, in the second configuration the electrodes can be connected to a ohmmeter for directly calculating the impedance of the concerned skin region.

In the last-mentioned type of apparatus too, an important operating drawback is present; in addition to an important manufacturing complexity, these apparatus are imprecise, since the stimulation and detection steps are carried out at non-coincident time instants, so that the cutaneous impedance can only be determined in an inaccurate manner.

It is an aim of the present invention to make available an apparatus and a method for measurement of the cutaneous impedance of an individual having a significant accomplishment simplicity.

Another aim of the invention is to provide an apparatus and a method enabling the cutaneous electrical impedance of an individual to be measured in a precise and reliable manner, as^" a function of the reactivity of the nervous system.

It is a further aim of the invention to make available an apparatus having limited manufacturing costs and a reduced overall bulkiness.

The foregoing and further aims are substantially achieved by an apparatus and a method for measuring the cutaneous impedance of an individual in accordance with the features recited in the appended claims.

Further features and advantages will become more apparent from the detailed description of a preferred embodiment of the invention taken by way of non- limiting example; this description is set out with reference to the accompanying drawings also given for illustrative purposes, in which:

- Figs. Ia and Ib show block diagrams of two embodiments of an apparatus in accordance with the invention;

- Fig. 2 diagrammatically shows the structure of the apparatus seen in Fig. Ia;

- Fig. 3 shows a possible circuit implementation of the apparatus seen in Fig. Ia;

- Fig. 4 shows a possible circuit implementation of a functional block of the apparatuses seen in Figs. Ia and Ib;

- Fig. 5 shows a possible embodiment of an oscillator to be used in the apparatus of the invention.

With reference to the drawings, an apparatus for measuring the cutaneous impedance of an individual in accordance with the present invention has been generally identified by reference numeral 1.

Apparatus 1 first of all comprises an oscillator 10, operatively associable with the skin 20 of an individual to measure the electrical impedance of the latter; more particularly, oscillator 10 is associable with a first skin portion 21 of said individual.

Preferably, oscillator 10 comprises an amplifier 12 and a feedback branch for feeding back amplifier 12.

Apparatus 1 further comprises tuning means 11 to tune an oscillation frequency of oscillator 10 with a characteristic frequency of the nervous rete innervating the first skin portion 21. In this way it is obtained that the oscillation frequency of oscillator 10, after a certain tuning transient, is substantially equal to the characteristic frequency of the nervous rete innervating the first skin portion 21; therefore a tuned frequency f of oscillator 10 is obtained.

In order to tune the frequency of oscillator 10 with said characteristic frequency, the tuning means 11 is provided with at least one active element 14 connected to oscillator 10 and operatively associable with the first skin portion 21.

By means of the active element 14 the first skin portion 21 is included in the feedback branch 13. In particular, one portion of the output signal of oscillator 10 starts circulating in the first skin portion 21; this electric stimulus activates a reflected nervous mechanism that reaches the spinal cord and therefrom comes to the corresponding brain nucleus located in the central nervous system, where other neuron pathways coming from other organs converge .

The organ correlated with the first skin portion 21 projects nervous fibres to the brain nucleus itself which is reached by the nervous fibres coming from the corresponding reflex skin arch. The afferent signals are then processed so that they subsequently come back again, through the spinal cord, to the skin portion from which the reflex originated, i.e. the first skin portion 21, thereby locally conditioning the impedance thereof.

In this way,^■ the impedance of the first skin portion 21 is inserted in the feedback branch 13 of amplifier 12, so that it can be measured as described in the following; the active element 14 can be an electrode.

Practically, operation of the system takes place following the feedback principle where the output signal of oscillator 10 causes a stimulus on the cutaneous nervous rete that in turn responds with a frequency of neuro-pulses conditioned to the functional state of the corresponding nuclei of the central nervous system, thus producing a variation in the impedance that in turn creates a further variation in the oscillator frequency. The phenomenon goes on until a stability state is achieved between the oscillator frequency . and the frequency of the reflected skin response; corresponding to this value is a well precise value of cutaneous impedance Zeq.

Preferably, the tuning means 11 further comprises an auxiliary element 15 operatively associable with the skin 20 to close said feedback branch 13 on amplifier 12.

In more detail, the auxiliary element 15 can be associated with a second skin portion 22 different from said first skin portion 21. In a first embodiment, the first skin portion 21 is defined by the contact region between the active element 14 and the individual's skin

20; therefore, in this case value Zeq will be representative of the electrical impedance of the contact area between the active element 14 and skin 20

(figure Ia) .

Therefore, • this first case deals with a unipolar technique for determination of the individual's cutaneous impedance.

In a second embodiment, the first skin portion 21 is defined between the contact region between the active element 14 and skin 20, and the contact region between the auxiliary element 15 and skin 20; therefore, in this case value Zeq will be representative of the electrical impedance of the area included between the contact region between the active element ^■ 14 and skin

20, and the contact region between the auxiliary element 15 and skin 20 (Fig. Ib) .

Therefore, in this second case a bipolar technique for determination of the individual's cutaneous impedance is involved.

Apparatus 1 further comprises an output block 30 connected to oscillator 10 to generate an output signal 31 representing the electrical impedance Zeq of the first skin portion 21.

In particular, the output signal 31, i.e. the calculated electric impedance Zeq, is a function of said tuned frequency f; preferably, impedance Zeq is such calculated that it is inversely proportional to the tuned frequency f.

The output block 30 may comprise a display, on which •value Zeq for example is displayed.

Generally, the display means by which the result of measurement is made usable by the operator can be either directly mounted on the housing body 40 of apparatus 1 (to be described in the following) , or positioned at a distance and connected to oscillator 10 following various technologies. Preferably, connection between this display means and oscillator 10 is of the wireless type and obtained using an optoelectronic transmission system, for example .

It is also to be noticed that conversion between the value of the output frequency of oscillator 10 and value Zeq can be locally carried out downstream of oscillator 10; alternatively, the signal incorporating the tuned frequency f can be remotely transmitted, so that conversion can be performed by a device separated from oscillator 10.

Apparatus 1 can be generally interfaced with remote devices through the telematic network, such as mobile telephony, the Internet, or other telecommunications systems .

In addition, apparatus 1 may be integrated into more complicated machinery for diagnostic-therapeutic use, electromedical use, and not.

Advantageously, apparatus 1 further comprises a housing body 40 to at least partly hold oscillator 10 and the output block 30.

Preferably, the housing body 40 is of substantially cylindrical shape, as diagrammatically shown in Fig. 2. In particular, the housing body 40 is made of metal material, such as stainless steel, polished aluminium and/or chromium-plated brass.

Preferably, the auxiliary element 15 comprises said housing body 40; practically, by the metal structure of - li ¬

the housing body 40, the circuit of oscillator 10 is electrically associated with the individual's skin 20, so that the first skin portion 21 can be suitably inserted in the feedback branch 13 and said tuned frequency f can be obtained.

In the preferred embodiment, the active element 14 has a conical or pyramidal structure 14a; the converging end of this structure 14a is designed to be brought into contact with skin 20.

If apparatus 1 is designed to carry out a unipolar measurement, the contact area between the converging end of structure 14a and skin 20 defines the first skin portion 21.

By way of example, the contact area between the active element 14 (and in particular converging end 14a thereof) and skin 20 can be included between 10 mm² and 20 mm².

Advantageously, the active element 14 is mounted to an axial end 40a of the housing body 40. In particular, the diverging end of structure 14a is mounted to the axial end 40a of the housing body 40a, as diagrammatically shown in Fig. 2.

Generally, the active element 14 and/or auxiliary element 15 can comprise either an endermic electrode (e.g. an electrode consisting of a metal plate, a conductive-rubber plate or a self-stick disc, or an electrode in the form of a sphere, a pencil, a clamp, a wire or a strip) or an intradermal electrode (e.g. an electrode consisting of a simple needle, a coaxial needle, a rigid catheter, a flexible catheter) . Preferably, apparatus 1 is provided with activation means 50 (comprising a push-button or a selector, for example) for activation of the impedance-measuring operation; the activation means 50 can be advantageously mounted on the housing body 40.

Conveniently, apparatus 1 may also comprise a feeding unit (not shown) , positioned within the housing body 40; this feeding unit has the function to power oscillator 10, and preferably the output block 30, so as to make apparatus 1 independent of any connection with external feeding networks.

Fig. 3 shows a possible embodiment of the circuit in accordance with the invention. This circuit comprises an integrated circuit 60 of the NE556 type for example, in turn comprising two timer circuits, preferably of the NE555 type.

The first timer circuit is in the configuration of an astable oscillator with 50% duty cycle and is designed to generate a square wave having a frequency included between 0 and 2 KHz.

The second timer circuit is a monostable circuit capable of outputting pulses of a duration equal to 24μs and of substantially the same frequency as that of the astable oscillator.

Pin 65 of the integrated circuit 60 is connected to the housing body 40, i.e. the metal container of apparatus 1.

Resistor R2 (value 1KΩ, by way of example) is a pull- up resistor and its function is to keep the output voltage of the astable oscillator high.

The square-wave frequency is determined by resistor Rl (value included between 30KΩ and 70KΩ, preferably between 33KΩ and 68KΩ, and in particular equal to 56KΩ) , capacitor C2 (value 3.3nF, by way of example) and impedance Zeq of the first skin portion 21, that is in contact with the active element 14. The latter can consist of a spherical cap made of stainless steel and having a base diameter of 4 mm.

The signal is brought from pin 65 of the astable oscillator, through the decoupling capacitor Cl (value InF, by way of example) , to pin 68 of the monostable circuit, that is connected to the positive terminal of the feeding means through resistor R3 (value 10KΩ, by way of example) so as to avoid false triggering.

Resistor R4 (value 22KΩ, by way of example) and capacitor C5 (value InF, by way of example) determine the pulse duration time (preferably equal to 24μs, as mentioned above) that is outputted through pin 69 of the integrated circuit 60.

Capacitors C3 (value 1OnF, by way of example) , C4

(value 1OnF, by way of example) and C6 (value 47μF, by way of example) have the function to protect the circuit against external interferences and prevent accidental self-oscillations.

Diode Dl, preferably of the 1N4004 type, has the function to avoid damages due to accidental polarity reversals in the feeding means. Fig. 4 diagrammatically shows the exemplary structure of a circuit 70 that can be used for displaying the level (or value) of the impedance Zeq of the first skin portion 21.

The circuit can be made in different ways; for instance, alphanumeric indicators consisting of LEDs or liquid crystals, electrodynamic or magnetodynamic analog indicators, displays with animated figures, interfaces with PC, etc.

In the embodiment diagrammatically shown in Fig. 3 ten low-consumption LED bars are provided (seven green and three red, for example) , preferably of the DC-763 EWA type.

The indicator is piloted by a driver, preferably of the LM 3914 N type.

The signal to be measured is picked up by pin 69 of said integrated circuit 60, carried by diode D2

(preferably of the 1N4148 type) and therefrom sent to capacitor C7 (value 2,2μF, by way of example) through the load resistor R5 (value 15KΩ, by way of example) . Resistor R6 (value 15KΩ, by way of example) is used to determine the discharge time of capacitor C7.

In this way voltage at the ends of capacitor C7 is proportional to the output frequency of the integrated circuit 60.

Resistors R8 (value 1.2KΩ, by way of example) and R9 (value 470Ω, by way of example) determine the input sensitivity of driver LM 3914 N and the operating current of the bar LEDs of the DC-763 EWA type. Resistor R7 (value 220Ω, by way of example) and Zener diode DZl determine the switching-on point of the yellow LED 71 acting as switching-on indicator lamp of the circuit and minimum charge value of the battery; under 7.2 V the LED is not lighted which means that the battery is exhausted to such a point that measurement is unreliable.

Fig. 5 shows a circuit diagram of an alternative embodiment of oscillator 10. This embodiment contemplates use of an operational amplifier, of the μA 741 type for example, in the configuration of a square- wave generator with 50% duty cycle.

Capacitor Cl determines the oscillator work frequency, to be tuned to the characteristic frequency of the nervous rete innervating the first skin portion 21; the latter is inserted in the feedback branch 13, connecting the noninverting input and output of the operational amplifier with each other.

The oscillator work frequency can be obtained from the following relation: f=l/(2,197-Cl-Zeq) wherein value 2,197 is given by -2-ln(l/3).

Resistors Ra, Rb have a value of 10KΩ, by way of example.

It will be recognised that any operational integrated circuit can be used in the invention, provided it has a sufficiently high input impedance.

Alternatively, logic integrated circuits or discrete components such a-s transistors for example, can be used.

Generally, it will be recognised that apparatus 1 can be made following several different technologies, among which the following are herein ^'mentioned: ASIC, SMD, Hybrid, Multilayer, programmable microprocessor, etc.

In use, tuning between the frequency of oscillator 10 and the characteristic frequency of the nervous rete innervating the first skin portion 21 is obtained by electrically connecting oscillator 10 to the skin 20 so that the first skin portion 21 is part of the feedback branch 13. This step in particular can be performed by bringing the active element 14 into contact with the skin 20, which active element is in turn connected to oscillator 10.

Preferably, the auxiliary element 15 too which may comprise the metallic housing body 40 can be brought into contact with the skin 20.

In the case of a unipolar measurement, the first skin portion 21 is defined by the contact region between the active element 14 and the skin 20; in this case, the auxiliary element 15 can be brought into contact with the skin 20 in two ways:

- if the individual carrying out measurement is the same individual on which measurement is carried out, due to the fact that this person has the housing body 40 in his/her hand, a connection takes place between the housing body 40 (i.e. the auxiliary element 15) and the skin 20; if the individual carrying out measurement (the operator) is a person different from that on which measurement is carried out (the patient) , the operator must hold the housing body 40 in his/her hand and position the active element 14 into contact with the patient's skin; in addition, the operator with his/her other hand for example, must touch the patient at another skin region.

On the contrary, in the case of a bipolar measurement, apparatus 1 will have two "direct" contact points with the patient's skin, and the first skin portion 21 will be defined between the contact region between the active element 14 and skin 20, and the contact region between the auxiliary element 15 and skin 20.

The invention achieves important advantages.

First of all, the apparatus in accordance with the invention can be manufactured in a very simple manner, due to the limited number of circuit components and connections required.

In addition, the measurement carried out is precise and reliable, due to tuning between the oscillator frequency and the characteristic frequency of the nervous rete innervating the skin portion the impedance of which is calculated.

In the light of the above, it is also apparent that the apparatus of the invention has reduced manufacturing costs and minimum overall bulkiness.

It will be also recognised that the apparatus is fully devoid of external wiring, which will make it very practical and of easy use. Since the concerned voltages are very low, and it is possible ^'to operate without the apparatus being connected to a power line (due to the feeding unit positioned within the housing body, for example) , the apparatus is very safe and no risks at all exist during operation.

Another advantage resides in the facility of use of the apparatus in accordance with the invention, since it is sufficient to position the active element into contact with the patient's skin and operate said activation means for obtaining the desired measurement.

Claims

C L A I M S

1. An apparatus for measuring the cutaneous electrical impedance of an individual, comprising: - an oscillator (10) operatively associable with a first skin portion (21) of said individual; tuning means (11) to carry out tuning of an oscillation frequency of said oscillator (10) with a characteristic frequency of the nervous rete innervating said first skin portion (21) , thereby obtaining a corresponding tuned frequency (f) of said oscillator (10);

- an output block (30) connected to said oscillator (10) to generate an output signal (31) representative of the electrical impedance (Zeq) of said first skin portion (21), said output signal (31) being a function of said tuned frequency (f) .

2. An apparatus as claimed in claim 1, characterised in that said oscillator (10) comprises:

- an amplifier (12);

- a feedback branch (13) for feeding back said amplifier (12) .

3. An apparatus as claimed in claim 2, characterised in that said tuning means (11) comprises an" active element

(14) connected to said oscillator (10) and operatively associable with said first skin portion (21) so that said first skin portion (21) is included in said feedback branch (13) .

4. An apparatus as claimed in claim 3, characterised in that said active element (14) is an electrode.

5. An apparatus as claimed in anyone of claims 2 to 4, characterised in that said tuning means (11) further comprises an auxiliary element (15) operatively associable with the skin (20) of said individual to close said feedback branch (13) .

6. An apparatus as claimed in claim 5, characterised in that said auxiliary element (15) is associable with a second skin portion (22) different from said first skin portion (21) , the latter being defined by the contact region between said active element (14) and the individual's skin (20) .

7. An apparatus as claimed in claim 5, characterised in that said first skin portion (21) is included between the contact region between said active element (14) and the skin (20) , and the contact region between said auxiliary element (15) and the skin (20).

8. An apparatus as claimed in anyone of the preceding claims, characterised in that it further comprises a housing body (40), preferably of cylindrical shape, to at least partly house said oscillator (10) and output block (30) .

9. An apparatus as claimed, in claims 7 and 8, characterised in that said auxiliary element (15) comprises said housing body (40)

10. An apparatus as claimed in anyone of claims 3 to 9, characterised in that said active element (14) has a substantially conical or pyramidal shape (14a), the converging end of said structure (14a) being suitable for getting into contact with the skin (20) of said individual .

11. An apparatus as claimed in claim 10, characterised in that said active element (14) is mounted on an axial end (40a) of said housing body (40) .

12. An apparatus as claimed in anyone of the preceding claims, characterised in that the value of the electrical impedance (Zeq) incorporated in said output signal (31) is inversely proportional to said tuned frequency (f) .

13. A method of measuring the cutaneous electrical impedance of an individual, comprising:

- providing an oscillator (10) capable of generating electric signals at different frequencies; - tuning the frequency of said oscillator (10) with the characteristic frequency of the nervous rete innervating a first skin portion (21) of an individual, thereby obtaining a corresponding tuned frequency (f) of said oscillator (10) ; - generating an output signal (31) representative of the electrical impedance (Zeq) of said first skin portion (21) as a function of said tuned frequency (f)..

14. A method as claimed in claim 13, characterised in that said step of tuning the oscillator frequency comprises a step of connecting said oscillator (10) to the skin (20) of said individual in such a manner that said first skin portion (21) is included in a feedback branch (13) of said oscillator (10).

15. A method as claimed in claim 14, characterised in that the step of connecting said oscillator (10) to the skin of said individual comprises a step of bringing at least one active element (14) into contact with the skin (20) of said individual, the active element being connected to said oscillator (10) .

16. A method as claimed in claim 15, characterised in that said first skin portion (21) is defined by the contact region between said active element (14) and the skin (20) .

17. A method as claimed in anyone of claims 14 to 16, characterised in that said step of connecting said oscillator (10) to the skin (20) of said individual further comprises bringing an auxiliary element (15) connected to said oscillator (10) into contact with the skin (20) of said individual.

18. A method as claimed in claim 17, characterised in that said first skin portion (21) is included between the contact region between said active element (14) and the skin (20) , and the contact region between said auxiliary element (15) and the skin (20).