SU1759402A1 - Device for measuring active and reactive components of biological tissue impedance - Google Patents

Abstract

A device for measuring the active and reactive components of the impedance of biological tissues makes it possible to increase the measurement accuracy. The output voltage of the generator 1 symmetric rectangular pulses in the integrator 2 is converted into a triangular voltage and after the converter 3 the voltage-current in the form of triangular current pulses is supplied to the current electrodes 4. The voltage removed from the potential electrodes 5 through the differential amplifier 6, synchronous detector 7, the DC amplifier 10 is fed to the measuring device 11. The control voltage to the synchronous detector 7 is supplied through the dip switch 8 or directly from the gene rator 1, or through phase shifting by 90 ° cascade 9. In one position of the switch 8, the readings of the measuring device 11 are proportional to the active component of the impedance of the bioobject, in the other - its reactive component. 1 il. SP

Description

The invention relates to the field of medicine and medical technology and can be used for the rapid diagnosis of various diseases and the quantitative assessment of the extent of pathological changes in tissues and organs.

Devices are known for separately measuring the components of the complex resistance and, in particular, the active and reactive components of the impedance of biological tissues, for example, rheographs. According to the device and principle of operation, rheographs are divided into bipolar (two-electrode) and tetrapolar (four-electrode).

A bipolar rheograph consists of an AC bridge, into one of the arms of which a biological object is connected with two electrodes. The other arm includes an alternating calibrated resistor and a capacitor, which serve to balance the AC bridge across the active and capacitive components of the impedance of the biological tissue. Based on the readings of the calibrated resistor and capacitor, the active and capacitive resistors are determined.

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biological tissue at the working frequency of the graph.

However, when using bridge circuits, the measured electrical characteristics of biological tissue inevitably include the electrical characteristics of the electrode-biological tissue interface, which also have active and capacitive resistances. Therefore, it is difficult to differentiate the electrical properties of biological tissue from the errors introduced by the electrical properties of the electrodes in two-electrode reographs with the use of bridge circuits.

The closest in technical essence to the proposed is a device for measuring the active and reactive components of the impedance of biological tissues 3, comprising a high frequency generator, a measurement object connected in a four-electrode circuit (tetrapolar method), an isolation transformer whose primary winding with the object of measurement, it can be shunted with a capacitor or resistor depending on the position of the existing switch. The secondary winding of the transformer is connected in series with the potential electrodes of the sample, the total voltage from which depends on the phase relationships.

The known device does not allow measurements of the active and reactive components of the impedance of a biological object, i.e., active resistance R and capacitive resistance Xc with sufficient accuracy for the following reasons. In the general case, in the biological object under study, the values of Xc and R are unknown. Then, when measuring, for example, the active component of impedance R, it is necessary to fully compensate the capacitive component of impedance Xc. In this device, this compensation is carried out by connecting a capacitor to the primary winding of the transformer, the capacitance of which on the measured part must be exactly equal to the capacitance of the biological object. If by chance it turns out that the capacitances are equal, then a full compensation of the capacitive component Xc occurs and the output component R is recorded at the output. If the capacitance resistance of the capacitor is less or more than Xc of the biological object, incomplete compensation or overcompensation will occur and the output of this device as an active component R will register some impedance, which may have a capacitive or even inductive character. Similar

The phenomena will also be observed when measuring the capacitive component of the impedance. Thus, the known device does not accurately compensate for the active and reactive components of the impedance of biological tissue and the capacitive properties of the interface between current electrodes — biological tissue changes its electrical characteristics from frequency over wide limits (by several orders of magnitude). AT

5 therefore, the presence of a measuring circuit sensitive to phase relations, an inductive element (transformer) is a source of additional uncontrollable errors.

The aim of the invention is to improve the measurement accuracy.

The drawing shows the functional diagram of the device for measuring the active and

5 reactive components of impedance biological tissue.

The device contains a generator of symmetric rectangular pulses, an integrator 2, a converter 3 voltage

0-current, two current electrodes 4, two potential electrodes 5 differential amplifier 6. synchronous detector 7, dzhokhzitionny switch 8, phase-shifting 90 ° cascade 9, amplifier 10

5 direct current and measuring device 11.

A device for measuring the active and reactive components of the impedance of biological tissues works as follows

0 way.

The generator 1 of symmetric square-wave pulses produces strictly symmetric square-wave voltage pulses with a duty cycle equal to two,

5 that is necessary to ensure the operation of the synchronous detector with high accuracy. Symmetric rectangular voltage pulses are applied to integrator 2, where the conversion occurs

0 rectangular pulses into a sawtooth voltage, which is then applied to the voltage-current converter 3. From the output of the converter 3, the current is supplied to the current electrodes 4, which are located

5 on the bioobject. The need to introduce stabilization of the probing or measuring current is caused by the fact that the transient resistances of the interface between the current and electrodes — biological tissue are not constant and depend on many factors:

clamping electrodes, contact time, moisture, electrode material and their area. The measurement accuracy depends on the accuracy of maintaining a constant measuring current.

The voltage drop is removed from the surface of the biological tissue using potential electrodes 5 and is fed to the input of differential amplifier 6. The increased voltage is fed to the synchronous detector 7. If the DIP switch 8 is in the Xc position, the current phase will be ahead of the control pulses by 90 °, and the output of the synchronous detector 7 appears a voltage proportional to the capacitance of the tissue. If the dip switch 8 is in the R position, the phase will coincide with the phase of the control pulses, and the output of the synchronous detector 7 is voltage proportional to the active resistance of the biological tissue. The detected signal from the output of the synchronous detector 7 enters the DC amplifier 10, from the output of which the amplified voltage is applied to the measuring device 11, the readings of which are proportional to the active or capacitive resistance of the fabric.

Claims (1)

The invention The device for measuring the active and reactive components of the impedance of biological tissues, containing two current and two potential electrodes and a two-position switch, characterized in that, in order to improve the measurement accuracy, sequentially connected generator of symmetric square impulses, an integrator and a converter are introduced into it voltage - current, the outputs of which are connected to current electrodes, are connected in series by a differential amplifier, whose inputs are connected to potential electrodes, a synchronous detector, the control input of which is connected to the output of a two-position switch, a DC amplifier and measuring device, as well as a phase-shifting 90 ° cascade, the input of which is connected to the integrator's input and the first input of the two-position switch, and the output connected to the second input two-way switch.