SU1287843A1 - Apparatus for measuring electric signal of bioobject - Google Patents

Abstract

The invention is intended to measure the diagnostic parameters of a biological object during physiological and psychological studies and to improve measurement accuracy by compensating for low-frequency interference. The device comprises a current source 1, electrodes 2 and 3, a generator 4, a switch 5, amplifiers 6 and 8, a delay element 7, a memory element 9, interpolators 10 and 14, a correction unit 11, a recorder 12 and a voltage meter 13. When the generator 4 in the single-run mode, the recorder 12 captures the resistance of the bioobject. The device compensates for low-frequency interference arising from the bioobject's own current on electrodes 2 and 3 by measuring this current, for which switch 5 electrodes 2 and 3 are connected to amplifier 6. The signal proportional to its own current is detected by memory element 9 At the same time, it is fed to a correction unit 11, where it is summed up with a measured value proportional to the resistance of the bio-object. Compensation can be made of the constant and slowly varying component of the bioobject's current with the correction generated and stored in the element 9 with a single start of the generator, and the dynamic values of the current corrected for each discrete measurement, which makes it possible to reduce the measurement error below 5% . 1 il. S (L you 00 00 4; with

Description

The invention relates to medical technology, namely to devices for measuring diagnostic parameters of a biological object, and can be used in physiological and psychological studies.

The aim of the invention is to improve the measurement accuracy by compensating for low-frequency interference.

The drawing shows a structural electrical circuit of the device.

A device for measuring the electrical resistance of a bioobject contains a current source 1, a first electrode 2, a second electrode 3, a pulse generator 4 connected in series, a switch 5, a current amplifier 6, a delay element 7, a normalizing amplifier 8, a memory element 9, a second (control) the input of which is connected to the output of the pulse generator 4, the first interpolator 10, the correction block 11 and the recorder 12, the voltage meter 13, the input of which is connected to the output of the first interpolator 10, and the second interpolator 14 whose output is connected to The second input of the correction unit 11, and the input to the second output of the switch 5, the second input of which is connected to the output of the current source 1, and the third and fourth inputs to the first 2 and second 3 electrodes respectively.

In addition, the design of the generator 4 pulses provides a single start mode and a continuous pulse mode. The delay element 7 has an adjustable delay At, and the normalizing amplifier 8 is made on an operational amplifier and has an adjustable gain factor K. Memory element 9 is made in the form of a block of analogue memory of a closed type and has a synchronization input. Correction unit 11 can be performed, for example, in the form of an analog adder, and the first 10 and second 14 interpolators can be made in the form of active low-frequency filters. As the recorder 12, a recording device with a graduated scale can be used.

A device for measuring the electrical resistance of a bioobject works as follows.

The pulse generator 4 is set to the single-shot mode and in the absence of a signal at its output, the switch 5 connects to the first and second electrodes 2 and 3 parallel to the current source 1 and the second interpolator 14. At a constant measuring current I |, coming from the current source 1 through electrodes 2 and 3 to the bioobject, the voltage Yfi (t) supplied from electrodes 2 and 3 to the input of the second interpolator 14, is proportional to the value of the measured resistance Ra (t) of the bioobject, which generally depends on time t. UK (i) 7x-BaCt).

A signal proportional to the resistance of the bioobject is recorded by the recorder 12, calibrated in units of resistance. In the continuous resistance measurement mode, the function of the second interpolator 14 is only to amplify the signal.

At the same time, electrodes 2 and 3 receive their own bioobject current, caused by electrophysiological processes occurring in the structures of the bioobject and the polarization of tissues induced by the measuring current of the device. The current of the bio-object I (t) also depends on time, and distorts the signal UR (t), which can lead to an increase in the measurement error of the resistance of the bio-object.

The device corrects low-frequency interference caused by the bioobject's own current, by measuring the bioobject's current and introducing the correction by the correction unit 11, which is formed on the basis that the dependences Ra (t) and I (t)

5 are similar to each other and there is a certain time shift between them. When a pulse is applied from the pulse generator 4, switch 5 disconnects electrodes 2 and 3 from current source 1 and second interpolator 14 and connects electrodes 2 and 3 to

0 input amplifier 6 current. In this case, the measurement of the bioobject's own current is made. The voltage of the signal Ui (t) at the input of amplifier 6 current is equal to

and, (t) I (t) RBx,

where RBX is the input impedance of amplifier 6

 current.

After amplification, the signal arrives at delay element 7, where its fixed time shift At is carried out in the range from 10 ms to 10 s. The signal is then scaled by the normalizing amplifier 8 and fixed by the memory element 9. This voltage value is fed through the first interpolator 10 to the voltage meter 13 and at the same time, as a correction, is fed to the first input of the correction unit 11,

5 where algebraically summed with the measured value Uj (t) proportional to the resistance of the bio-object.

Amendments are introduced taking into account the individual characteristics of the biological object under study as follows.

Measuring current I | a single 10% increment of the stepped shape is given. At the same time, Ii ± 0, l, where Lop is the value of the absolute threshold of sensitivity of a biological object to a current stimulus.

5 During the jump in the measuring current, the function Ra (t) is recorded and, when it reaches 90% of the steady-state resistance value, the instant ti is recorded. Then

0

the time shift At, which must be set in delay element 7, is equal to

 -to,

where to is the time instant of the current increment.

The gain of the normalizing amplifier 8 is set numerically equal to the ratio

 I

-1ttrAll

where All is the magnitude of the measurement jump

current;

 the measured value of the voltage increment received by the recorder 12 at a current jump of All.

The device works in two modes. When compensating for a constant and slowly varying component of the current of a bioobject, a continuous measurement of the resistance is made, and the correction is formed during a single (or discrete with an interval of 10-15 min) start of the generator of 4 pulses. The correction voltage is memorized by the memory element 9 and is continuously fed to the first input of the correction unit 11, where it is subtracted from the signal U coming from electrodes 2 and 3 when measuring the resistance.

When compensating for the dynamic values of the bioobject current, the correction is made continuously while measuring Ra (t) and 1 (1). The generator 4 operates in a continuous pulsed mode, applying pulses to a first input of the switch 5 with a quench I and a frequency of 10 Hz. In this case, two sequences of amplitude-modulated pulses URi I / are removed from electrodes 2 and 3. The first sequence of pulses Un, - restores the second interpolator 14 from the output of which signal l (t)

five

arrives at the second input of the block 11 correction. A correction voltage is applied to the first input of the correction unit 11, which is formed from the second sequence of pulses If, scaled and received the required time shift. The correction signal is then stored for each discrete measurement by the memory element 9 and further through the first interpolator 10 as an analog signal is fed to the first input of the correction unit 11. The operation of the memory element 9 is synchronized by a control signal with a frequency of 10 Hz, coming from the output of the generator of 4 pulses.

The proposed device makes it possible to measure the resistance of a biological object with an error not exceeding 5% in the resistance range of 20–200 kΩ.

Claims (1)

Invention Formula 0 A device for measuring the electrical resistance of a bioobject, containing a current source, a first electrode, a second electrode and a series-connected correction unit and a recorder, characterized in that, in order to improve the measurement accuracy by compensating for low-frequency noise, a series-connected pulse generator, a switch, current amplifier, delay element, normalizing amplifier, memory element, the second input of which is connected to the output of the pulse generator, the first interpolator and measuring instrument The input of which is also connected to the first input of the correction unit, and the second interpolator, the output of which is connected to the second input of the correction unit, and the input with the second output of the switch, the second input of which is connected to the output of the current source, and the third and fourth inputs, respectively, with the first electrode and the second electrode. five 0