JPH0245036A - Method for measuring organism potential - Google Patents

Abstract

PURPOSE:To accurately detect a contact state with an organism by applying a reference signal to the organism, detecting this reference signal by an electrode, and inspecting the organism signal detecting state of the electrode. CONSTITUTION:A method for measuring a cardiac potential applies the reference signal between a human organism and an earth. The reference signal and the cardiac potential are detected by the electrode. While the reference signal is amplified in a reference signal amplifier 2, the cardiac potential is amplified in a cardiac potential amplifier 3. The reference signal amplifier 2 is equipped with a differential amplifier 26 to measure the potential between the earth and the human organism at its input side. The cardiac potential for the specific point of the human organism is inputted to the cardiac potential amplifier 3. The reference signal detected by an electrode 4 is inputted to the reference signal amplifier 2, this signal is amplified in the reference signal amplifier 2, and the contact state of the electrode 4 is inspected. For the reference signal, for example, an alternating signal such as a sine wave or a rectangular wave is used in order to remove the influence of an error caused by the contact potential between the electrode 4 and a body surface 13.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is mainly used for electrocardiographs or electroencephalograms,
We will discuss methods for measuring cardiac potentials and electroencephalogram potentials that appear on the surface of the human body.

[Prior art and its problems] In electrocardiographs and electroencephalograms, in order to accurately measure the biopotential appearing on the body surface using electrodes that come into contact with the living body, it is necessary to increase the contact resistance between the electrode and the body surface. It is important to keep it sufficiently low. However, the contact resistance with the electrode varies greatly in some parts of the body surface, and also varies greatly due to individual differences. Making the human input impedance of the first-stage amplifier to which the electrodes are connected sufficiently higher than the contact resistance reduces measurement errors due to variations in contact resistance. However, a first-stage amplifier with high human input impedance is easily affected by inductive noise, and it is difficult to maintain a high input impedance for a long period of time, and measurement errors due to aging tend to occur.

In actual biopotential measurement, it is best to make the contact resistance between the electrode and the living body sufficiently lower than the human input impedance of the first stage amplifier, and this is the cause of errors in biopotential measurement. Particularly, in a body surface electrocardiograph that simultaneously measures potentials from a large number of living body surfaces and displays the same potential diagram of the living body surface, measurement errors at each point have a significant effect on the displayed diagram.

Furthermore, when measuring biopotential from many points simultaneously, it is extremely difficult to accurately measure biopotential from all points.

Additionally, non-contact insulator electrodes have been developed that measure biopotential by bringing a planar electrode close to the body surface via a dielectric without directly contacting the body surface. In this electrode, a biopotential is induced to the electrode plate via a capacitor made of the body surface, the electrode plate, and a dielectric.

The lowest frequency that this electrode can detect is determined by the capacitance and the human input impedance of the head amplifier, and the larger the capacitance and input impedance, the lower the frequency of biological signals that can be detected. However, with this structure of electrodes, as with contact type electrodes, the detected biopotential varies depending on the contact state between the electrode and the body surface. If the dielectric does not completely adhere to the body surface, the biopotential detected by the electrodes will decrease.

Therefore, the electrode with this structure cannot always accurately measure the biopotential.

[Object of the invention] The present invention was developed in order to eliminate this drawback.
An important purpose of this invention is to apply a reference signal to a living body and measure this reference signal with an electrode to test whether the electrode accurately detects the biopotential, thereby making it possible to accurately measure the biopotential. To provide a measurement method.

[Means for Solving Conventional Problems] The biological potential measuring method of the present invention is a biological potential measurement method that detects an electrical signal generated in the biological body by the electric potential induced by the electrode by bringing an electrode into contact with or close to the biological body. This is a potential measurement method in which a reference signal is applied to a living body, this reference signal is detected by an electrode, and the biological signal detection state of the electrode is examined.

[Operations and Effects] In the biological potential measurement method of the present invention, a reference signal is applied to a living body, and the electrodes detect both this reference signal and the biological signal. For this reason, if the contact state between the electrode and the living body is poor and the biological potential cannot be measured accurately, the measurement level of the reference signal also decreases. Therefore, depending on the reference signal level detected by the electrode, it can be easily determined whether the electrode can accurately measure the biopotential.

Now, if the electrode does not come into complete contact with the living body and can only detect the biopotential at a level that is half of the correct value, the reference signal level detected by this electrode will also drop to one-half. That is, it can be determined from the reference signal level that the contact between the electrodes is poor and the measured potential of the living body is half.

Therefore, when the -1 electrode detects the reference signal, the state of contact with the living body can be accurately detected.

[Preferred embodiment] Embodiments of the present invention will be described below based on the drawings.

The biopotential measurement method of the present invention is mainly used to measure cardiac potentials and brain waves appearing on the surface of the human body. However, the biopotential measuring method of the present invention can also be used to measure all potentials appearing on the surface of a living body, such as measuring myoelectric potential. In particular, the method of the present invention is most suitable for an apparatus that simultaneously measures biopotential from a plurality of points and displays the relative potential with adjacent electrodes, or displays an equipotential diagram from the overall measured potential signal.

Hereinafter, a specific example of using the method of the present invention for electrocardiogram measurement will be described, but it can also be used in almost the same manner for electroencephalogram and myoelectric potential measurement.

In particular, the biopotential measuring method of the present invention is most suitable for a device that detects signals from multiple points on a living body, such as a body surface electrocardiograph that detects electrocardiographic signals from multiple points on the body surface.

A body surface electrocardiograph measures cardiac potentials from, for example, 40 to 1000 points on the body surface. Cardiac potential is measured with electrodes. Thus, between 40 and 1000 electrodes are brought into contact with the body surface. The electrocardiographic signals measured by each electrode are converted into digital quantities and input into a computer. The computer is
The input signal is operated to calculate, for example, the potential distribution diagram on the body surface shown in FIG. The calculated potential distribution map is displayed on a monitor or printer.

If the contact state of any electrode is insufficient, an error will occur in the cardiac potential induced by the electrode, and a distortion will occur in the body surface distribution map.

By looking at the body surface distribution map, it is not possible to determine whether the cause of the distortion is in the living body or due to measurement error.

A method for inspecting the contact state of the electrodes will be described below.

The electrocardiogram measuring method shown in FIG. 1 applies a reference signal between the human body and the ground. A reference signal and a cardiac potential are detected at the electrodes. The reference signal is amplified by a reference signal amplifier 2, and the cardiac potential is amplified by an electrocardiogram amplifier 3. The reference signal amplifier 2 includes a differential amplifier 26 at its input end that measures the potential between the ground and the human body. The electrocardiogram amplifier 3 receives the electrocardiogram potential at a specific point on the human body.

The reference signal detected by the electrode 4 is input to the reference signal amplifier 2, this signal is amplified by the reference signal amplifier 2, and the contact state of the electrode 4 is inspected.

For example, an alternating current signal such as a sine wave or a rectangular wave is used as the reference signal in order to eliminate the influence of errors caused by the contact potential between the electrode 4 and the body surface 13.

An alternating current with little level fluctuation is used as the reference signal applied to the human body. This is because the reference signal amplifier 2 measures the contact state of the electrode 4 by detecting the detection signal level. However, if all the electrodes 4 detect the reference signal at the same time, it is also possible to apply a reference signal whose level varies somewhat to the human body. This is because the relative values of the contact states of all electrodes can be checked using the reference signal. For example, when the reference signal level is lower than the reference value, if the contact state of all electrodes is perfect, all electrodes can measure the reference signal at the same level but lower than the reference value.

The frequency of this reference signal is determined by the reference signal amplifier 2 for low frequency.
is adjusted to the amplifiable frequency range of . Reference signal amplifier 2
In addition, when using a low frequency operational amplifier, signals with a maximum frequency of several tens of kilohertz to several hundred kilohertz can be amplified. Therefore, the oscillation frequency of the reference signal oscillator l is several k
Hz - adjusted to several 100 kHz or less. However, if an element capable of amplifying high frequencies is used in the reference signal amplifier 2, it is also possible to set the frequency of the reference signal to a higher frequency, for example, 500 KHz-fiMHz. Also, if the frequency of this reference signal is too low,
Since one cycle is too long, it is usually higher than IHz, preferably 1
The frequency is determined to be 0 Hz or higher.

The frequency of the reference signal is preferably equal to the frequency of the power supply driving the device, for example adjusted to 50-60H2. This frequency is effective in reducing the influence of induced noise from the power supply. This is because when the reference signal is equal to the frequency of the power supply, the induced noise and the reference signal become signals with the same period. That is, if the period of the noise induced into the electrode or the head amplifier and the reference signal are equal, the induced noise will be masked in the reference signal measured by the electrode. When the frequency of the reference signal is equal to the power signal frequency, a power transformer can be used for the oscillator.

The reference signal level applied to the human body by the reference signal oscillator l is set such that the S/N ratio of the detected reference signal is sufficiently good.
The peak-to-peak voltage is usually determined to be 2 mV or more, preferably 5 mV or more, and more preferably 10 mV or more.

If the reference signal level is too high, the reference signal amplifier 2 will clip the human input signal. As shown in FIG. 1, when applying a reference signal directly to the human body, the output voltage of the reference signal oscillator 1 is adjusted to 20V or less, preferably IOV or less, from peak to peak.

The human power impedance of the reference signal amplifier 20 is adjusted to be sufficiently high compared to the body surface contact potential of the electrode. For example, it is usually determined to be 500Ω or more, preferably IMΩ or more, and more preferably 5MΩ or more. The human power impedance of the reference signal amplifier 2 depends on the type of electrode used, i.e.
It is determined based on the contact resistance of the surface of the electrode. If the contact resistance of the electrode is low, it can be used even if it is less than 500Ω. A reference signal amplifier with low human impedance can measure the reference signal with less influence of induced noise.

When the human power impedances of the reference signal amplifier 2 and the electrocardiogram amplifier 3 are made equal, the reference signal amplifier 2 and the electrocardiogram amplifier 3 can measure the reference signal detected by the electrode 4 and the cardiac potential under the same conditions.

The output impedance of reference signal amplifier 2 is sufficiently low.
It is preferably designed to be IKΩ or less.

The reference signal amplifier 2 removes the DC component with a coupling capacitor 5 connected to the output side of the differential amplifier 26, rectifies this signal with a diode 6, and adjusts the measurement level of the reference signal detected at the electrode 4. Measure.

This reference signal amplifier 2 rectifies the measured reference signal with a diode 6 and charges a smoothing capacitor 23. The smoothing capacitor 23 provides an output signal proportional to the peak value of the reference signal measured by the electrode 4.

When the reference signal is a sine wave, it is possible to continuously measure the amplitude of the reference signal detected by the electrode 4. FIG. 2 shows a reference signal amplifier 22 that can continuously measure the amplitude of a reference signal. This reference signal amplifier 22 continuously measures the amplitude of a sine wave using the principle of A25ln2θ+A"cos2θ=A2. In other words, the amplitude of the sine wave (Asinθ), which is the reference signal measured by the electrode, is continuously measured.
) is squared by the multiplier 7 to obtain a signal of A25in2θ. In addition, the sine wave is integrated by the integrating circuit 9, and a cosine wave (Acos θ
) and square this cosine wave with multiplier 8 to obtain A2c
I am getting the oS20 signal. The output signals of multiplier 7.8 are added by adder lO to obtain a signal of A''5in2θ+A2cos2θ=A2.This signal does not include an AC component, and an output corresponding to amplitude 1=(A) is obtained. Since this circuit outputs the amplitude level of the reference signal detected by the electrode as a DC component, the contact state of the electrode can be detected continuously at all times.

In the biopotential measuring method of the present invention, a reference signal of a constant level is applied to the human body, and the contact state of the electrode is detected based on the measurement level of this reference signal. If the amplification factor of the electrocardiogram amplifier is controlled based on the level of the reference signal detected by the electrode, or in other words, the state in which the electrode is in contact with the living body, then accurate cardiac Potential can be measured. In order to realize this, the amplification factor of the electrocardiogram amplifier 3 shown in FIG. 1 is controlled by the output voltage of the reference signal amplifier 2.

A state in which the contact state of the electrode 4 is good, in other words, the electrode 4
When the electrocardiogram amplifier 3 is able to measure a reference signal at a predetermined level, the electrocardiogram amplifier 3 increases the predetermined amplification factor, for example, 1.
The detected cardiac potential is amplified 000 times or 2000 times.

When the reference signal level decreases due to poor contact of the electrode 4 with the body surface, the cardiac potential level measured by the 'electrode also decreases. When the contact state of the electrodes 4 deteriorates and the reference signal level detected by the electrodes 4 falls from a specified value, the amplification factor of the electrocardiogram amplifier 3 is controlled to be high. The amplification factor of the electrocardiogram amplifier 3 is controlled by the output of the reference signal amplifier 2 that has decreased from a specified value, and when the reference signal level decreases, the increase rate of the electrocardiogram amplifier 3 is reduced by 1o.
oo times or higher than 2000 times. Therefore, 5. The electrocardiogram amplifier 3 includes a reference power source 12 for measuring whether the reference signal level is within a specified value. Reference power supply 12
The output of is compared to a reference signal level in comparator ll.

The output signal of the comparator 11 adjusts the amplification factor of the electrocardiogram amplifier 3. The reference power source 12 is adjusted to be equal to the output voltage of the reference signal amplifier 2 when the electrode 4 is in normal contact with the body surface. In other words, when the output signal level of the comparator 11 is zero, the electrode 4 measures the correct potential, and as the contact state of the electrode 4 deteriorates and the level of the reference signal decreases, the output level of the comparator 11 increases. It gets expensive. Therefore, the electrocardiogram amplifier 3 increases the amplification factor as the output level of the comparator 11 increases.

This state will be explained with reference to FIG. Figure 3 (A) (B)
In FIG. 3(A), the electrodes measure a correct potential, and FIG. 3(B) shows a state in which the contact state of the electrodes is poor and the measured potential is low. In these figures, (1) is the cardiac potential detected by the electrodes, (2) is the reference signal detected by the electrodes, (3) is the output of the electrocardiogram amplifier 3 corrected by the reference signal level, (4) shows the output of the comparator 11 of the electrocardiogram amplifier 3.

As shown in FIG. 3A(4), when the electrodes detect the correct potential, the output of the comparator becomes zero, and the electrocardiogram amplifier amplifies the electrocardiogram signal at a predetermined amplification factor.

As shown in Figure 3B (2), when the reference signal level decreases, the output level of the electrocardiogram amplifier comparator increases as shown in (4), and this signal increases the amplification factor of the electrocardiogram amplifier. Adjusted high, it greatly amplifies the correct low measured cardiac potential.

The electrocardiogram amplifier 3 is an automatic gain control amplifier, and is controlled so that the amplification factor increases in inverse proportion to the magnitude of the reference signal level detected by the reference signal amplifier 2. In other words, when the output level of the reference signal amplifier 2 is half of the specified value, the amplification factor of the electrocardiogram amplifier 3 is set to twice the specified value, and when the reference signal level is one-third, the amplification factor of the electrocardiogram amplifier 3 is set to twice the specified value. The amplification factor of is increased by 3 times. This is because the electrodes measure the reference signal and the cardiac potential together, so if the reference signal level is halved due to poor electrode contact, the measured cardiac potential will also be halved. That is, when the reference signal level detected by the electrodes is half, the correct cardiac potential can be calculated by amplifying the cardiac potential twice.

The measurement method shown in FIG. 1 can also measure the cardiac potential and the reference signal simultaneously. However, when using this circuit to continuously measure the reference signal together with the cardiac potential, the level of the reference signal applied to the human body must be adjusted to a low level so that the reference signal does not affect the cardiac potential. The reference signal is removed by using an amplifier with high sensitivity and low noise, or by making the frequency of the reference signal sufficiently higher than the electrocardiogram signal, and by providing the electrocardiogram amplifier with a filter that removes the reference signal.

This circuit can continuously or nearly continuously correct the cardiac potential while detecting the reference signal level.

In actual electrocardiogram measurement, the contact state of the electrodes rarely changes significantly in a short period of time. For this reason, it is also possible to detect the contact state of the electrodes at a certain period of time, measure the cardiac potential after that, and correct the cardiac potential using a reference signal that is fixed at 1UII. That is, the reference signal measurement and the electrocardiogram measurement can be time-shifted and measured in a time-division manner.

In the full constant circuit shown in FIG. 1, when the cardiac potential and the reference signal are measured in a time-division manner, there is no need to apply the reference signal to the human body when measuring the cardiac potential. Therefore, in this case, as shown in the figure, a shorting switch 1' is connected to the output side of the reference signal oscillator 1, and when measuring the cardiac potential, the shorting switch is shorted or the oscillation of the reference signal oscillator 1 is stopped. .

The second invention does not specify the method of applying the reference signal to the human body as shown in FIG. FIG. 4 shows another embodiment in which a reference signal is applied to the human body. In the device shown here, a buffer amplifier 17 connected to the electrode 44 amplifies both the reference signal and the electrocardiographic signal. In this device, both the reference signal and the electrocardiographic signal measured by the electrodes 44 are input to the buffer amplifier 17 . Therefore, this method can realize the feature that the electrode 44 can determine the reference signal and the electrocardiographic signal under the same conditions.

The circuit shown in this figure measures the cardiac potential and the reference signal in a time-division manner. This circuit also measures the reference signal by passing a weak current corresponding to the reference signal through the human body.

The method of measuring the reference signal using the circuit shown in this figure is to apply the output of the reference signal oscillator 41 between the right foot and both hands of the human body. That is, a reference signal is applied to the human body by applying electricity between the right foot and both hands. The electrode 44 detects both the cardiac potential and the reference signal, and the combined amplifier 24 amplifies this detection signal.

The combined use amplifier 24 switches between the reference signal and the cardiac potential and amplifies it in a time-division manner. That is, after detecting the reference signal and measuring the contact state of the electrode 44, the cardiac potential is measured, and the measured level of the cardiac potential is corrected using the measured level of the reference signal.

Therefore, the combined amplifier 2-4 has the control circuit 14,
It is possible to switch between the reference signal and the cardiac potential to be amplified. The control circuit 14 applies the reference signal to the human body only when the combined amplifier 24 amplifies the reference signal. Therefore, the switching element 1 is connected between the output of the reference signal oscillator 41 and both hands.
5 is connected. The switching element 15 is controlled to turn on and off by the control circuit 14.
It is switched to the on state only when measuring the reference signal.

A detailed diagram of the combination amplifier 24 shown in FIG. 4 is shown in FIG. This combination amplifier 24 includes an electrocardiogram amplifier 43, a reference signal amplifier 42, and a manual changeover switch I6. The manual changeover switch 16 is switched by the control circuit 14. When the input selector switch 16 is in the position shown by the solid line in the figure, the detection signal of the electrode 44 is input to the electrocardiogram amplifier 43.

When the manual changeover switch 16 is switched to the position shown by the chain line, the detection signal of the electrode 44 is manually input to the reference signal amplifier 42.

The reference signal amplifier 42 amplifies the input reference signal,
A capacitor 45 on the output side removes the DC component. The reference signal of the AC component from which the DC component has been removed is passed through the diode 4.
6, and converted into a direct current proportional to the level of the reference signal. Since the DC voltage on the output side of the diode 46 is proportional to the reference signal level detected by the electrode, the contact state of the electrode can be inspected and confirmed using this output signal level.

The output voltage of the diode 46, which is the output of the reference signal amplifier 42, can be observed on a monitor such as a cathode ray tube oscilloscope or television, or printed on a printer and checked to determine the contact state of the electrodes. can. When observing the output of the reference signal amplifier 42 on a monitor or printing it on a printer for confirmation, it can also be measured at the input end or output side of the capacitor 45.

When checking the contact status of electrodes on a monitor or printer, apply a reference signal to the human body and check the contact status of all electrodes.
After confirming that the electrode is in good condition and comes into contact with the human body,
The application of the reference signal to the human body is stopped and the cardiac potential is measured.

In the circuit shown in Figure 1, the contact status of the electrodes can also be confirmed on a monitor or printer. In this case, the output waveform of the differential amplifier 12G is measured.

Devices that measure cardiac potential by checking the contact status of electrodes with a monitor or printer cannot accurately measure cardiac potential unless all electrodes are in good condition and in contact with the human body. A device that controls the amplification factor of an electrocardiogram amplifier using a reference signal can accurately measure cardiac potential even if the electrodes are in poor contact.

The circuits shown in FIGS. 4 and 5 can also control the amplification factor of the electrocardiogram amplifier 43 by the contact state of the electrodes, similarly to the device shown in FIG. 1. In this case, the electrocardiogram amplifier 3 in Figure 1
Similarly, an automatic gain control circuit is used in the electrocardiogram amplifier 43. The electrocardiogram amplifier 43 has an amplification factor controlled by the output of the reference signal amplifier 42, and corrects the electrocardiogram detection signal of the electrode according to the contact state of the electrode.

That is, the signal from the electrode 44 is amplified by the buffer amplifier 17 at the first stage, passes through the manual changeover switch 16, and is input to the electrocardiogram amplifier 43 or the reference signal amplifier 42.

The amplification factor of the electrocardiogram amplifier 43 is controlled by the output signal of the reference signal amplifier 42, and after correcting the detected electrocardiogram to the correct value,
The final stage differential amplifier 18 compares it with a reference level.

However, since this circuit measures the reference signal and the cardiac potential in a time-division manner, a sample and hold element 47 is connected to the output side of the diode 46. The sample and hold element 47 temporarily stores the output level of the reference signal amplifier, and controls the amplification factor of the electrocardiogram amplifier 43 using the stored voltage value. The sample and hold element 47 is reset the moment the switch 16 controlled by the control circuit 14 is switched to the reference signal amplifier, and stores the voltage value input to the diode thereafter.

The final stage differential amplifier 118 amplifies the difference component between the sum of the detected potentials of one foot and both hands and the electrocardiographic amplifier 43, as in FIG. However, although not shown, it is also possible to use a differential amplifier as the electrocardiogram amplifier 43 and use the electrocardiogram amplifier 43 to amplify the cardiac potential compared to a reference level.

By the way, the time period in which the reference signal is applied to the human body from the reference signal oscillator 41 and the amplifier amplifies the reference signal is preferably set to be longer than one cycle of the reference signal. This is to remove the DC component contained in the cardiac potential induced in the electrode 44.

When the metal electrode 44 comes into contact with the surface of the human body, a local battery is formed between the conductive liquid such as sweat on the surface of the human body and the metal electrode, and a direct current component generated by this local battery is included in the cardiac potential. The electromotive force of this local battery fluctuates significantly depending on the state of contact between the electrode 44 and the body surface. Therefore, the electrode 44
The DC component included in the cardiac potential induced by the current changes, and the zero level of the detected potential changes. Using alternating current as the reference signal,
By measuring the plus-minus peak-to-peak voltage and detecting the level of the reference signal, the influence of the DC component included in the cardiac potential induced in the electrodes can be eliminated. That is,
Even if the zero level changes, the peak-to-peak voltage of the reference signal does not change.

Furthermore, even if a half-cycle sine wave starting from zero and ending at zero volts is used as the reference signal, the influence of the DC component included in the cardiac potential can be removed.

That is, by correcting the reference signal measured by the electrode to zero volts at the start and at the end of a half cycle, the DC component contained in the electrode measurement signal can be removed. For example, if the reference signal level measured by the electrode 44 is 100 mV at the start and 150 mV at the end of the half cycle, as shown in FIG.
0mV to zero volts, 150mV at the end of half cycle
can be corrected to zero volts to remove fluctuations in the DC component.

Also, when measuring the reference signal, since the cardiac potential is induced on the body surface, the cardiac potential is added to the reference signal induced to the electrodes. However, when the frequency of the reference signal is made sufficiently high compared to the frequency of the cardiac potential, and the level of the reference signal detected by the electrode is measured as the level between the plus and minus peaks and peaks of the reference signal. , it is possible to eliminate measurement errors due to fluctuations in the zero level of the reference signal due to cardiac potential.

By the way, the measurement method shown in FIG. 4 cannot measure the reference signal and the cardiac potential at the same time, so the detection time of the reference signal is
Constrain the detection time of cardiac potential. In other words, the cardiac potential cannot be detected while the reference signal is being detected and the contact state of the electrodes is being measured.

Therefore, it is better to shorten the reference signal detection time and lengthen the cardiac potential measurement time. Increasing the oscillation frequency of the reference signal oscillator 41 can shorten the detection time of the reference signal. Therefore, in order to shorten the measurement time of the reference signal, the oscillation frequency of the reference signal oscillator 41 is set to the highest possible frequency that can be amplified by the amplifier.

However, depending on the measurement method, when detecting an electrocardiogram waveform that repeats at a certain period, even if the detection time of the reference signal is long,
There are few restrictions on detecting electrocardiographic signals. That is, after detecting the reference signal and measuring the contact state of the electrodes, it is possible to measure the electrocardiographic signal of l-few beats.

FIG. 7 and FIG. 8 show the time period in which a reference signal is applied to the human body with respect to an electrocardiographic signal. In these drawings, (1) shows the electrocardiographic waveform induced by the electrodes, and (2) shows the reference signal. In these figures, the horizontal axis shows the time axis, and the vertical axis shows the voltage value.

In the method shown in FIG. 7, as shown in (2), a reference signal is applied to the human body during a time period when the electrocardiographic signal is at almost zero level. In this method, the reference signal hardly restricts the measurement time of the electrocardiographic signal. This is because normal electrocardiographs do not measure cardiac potential during times when cardiac potential hardly appears.

In this measurement method, a reference signal is applied to the human body, the contact state of the electrode is measured, and then the cardiac potential is measured for a certain period of time (for example, one beat), and the measured value of the cardiac potential is compared to the previously measured reference signal. Correct at the measurement level. This method is most suitable when measuring cardiac potential continuously over a fixed period of time or at extremely short time intervals (for example, at intervals of several microseconds to several milliseconds).

By the way, in the measurement of cardiac potential, the contact state of the electrodes often does not change so rapidly. In other words, if the contact state of the electrodes is poor, the level of the entire electrocardiogram waveform often decreases at an almost constant rate for a certain period of time. Therefore, when measuring cardiac potential, as shown in Figure 7, when the electrocardiographic signal is at almost zero level, a reference signal is applied to the human body to measure the contact state of the electrodes, and the electrocardiographic signal immediately after that is measured. In most cases, measuring near the peak value and correcting the electrocardiographic signal using the previously measured reference signal does not result in a very large error.

Shortening the time from detecting the contact state of the electrodes to detecting the cardiac potential is effective for more accurate electrocardiographic measurement. This can be achieved by detecting the contact state of the electrodes every time immediately before measuring the cardiac potential.

In the measurement method shown in FIG. 8, a reference signal is applied to the human body for an extremely short period of time, as shown in (2). In this method, after applying a reference signal to the human body and measuring the contact state of the electrodes, the reference signal is stopped and the cardiac potential is measured. With this method, the cardiac potential can be detected and corrected immediately after the contact state of the electrodes is detected. Therefore, even if the contact state of the electrodes changes during one beat, the cardiac potential can be corrected accurately.

For this measurement method, the time to apply the reference signal to the human body is
Shorter than the time required to measure cardiac potential. For example, if the cardiac potential is measured at 1 millisecond intervals and the time required to measure the cardiac potential (the time required to AD transform the cardiac potential or store it in the sample and hold circuit) is 100 microseconds, the reference signal The time of application of the drug to the human body is determined to be less than 900 microseconds.

The frequency of a sine wave with one period of 900 microns is approximately 1-1 kHz. Therefore, in this case, it is preferable to use a reference signal with a frequency higher than 1.5 kHz, considering the margin. A reference signal of this frequency can be sufficiently amplified with an inexpensive operational amplifier.

If the frequency of the reference signal is 15 kHz, 10 or more cycles of the reference signal can be detected within 900 microseconds.

As shown in FIG. 4, in the method of passing a reference signal through the human body, the induced potential of the reference signal appears to vary depending on the position of the electrode. However, in an experiment actually conducted by the present inventors, a reference signal oscillator 41 was connected between one foot and both hands, as shown in FIG. When detected, there was almost no difference in the level of the reference signal in the chest. This is presumed to be because the entire human body becomes one conductor, and this entire conductor is at the same level. That is, the resistance of the human body is considerably smaller than the contact resistance (R) between the human body and the reference signal oscillator l, and it is assumed that the entire human body has the same level of voltage.

Therefore, when the electrodes are in normal contact with the body surface, all electrodes detect the reference signal at the same level.

Therefore, the reference signal detected by the electrode can be used to measure the contact state of the electrode without being corrected depending on the detection position.

As shown in FIG. 4, even when measuring the contact state of electrodes by passing a reference signal through the human body, it is also possible to measure the reference signal and the cardiac potential at the same time. To achieve this, a reference signal is continuously applied to the human body. The electrocardiographic signal to which the reference signal is added is detected by electrodes. The signal detected at the electrode is
As shown in FIG. 9, the electrocardiographic waveform fluctuates with the reference signal. A reference signal is selected from this signal using a bandpass filter through which only the reference signal passes. The output signal of the bandpass filter is proportional to the reference signal level detected at the electrodes. That is, the contact state of the electrodes is measured using the output signal of the bandpass filter. The electrocardiogram signal is
As shown in FIG. 9, it can be detected as the potential at the midpoint C between the positive and negative peaks AB of the reference signal. To measure the potential at the intermediate point C, positive and negative peak voltages of adjacent reference signals are detected and averaged in synchronization with the reference signal, or the voltage at the positive and negative intermediate points is detected.

In place of FIG. 5, FIG. 10 shows a circuit that can detect the reference signal and the electrocardiographic signal together. This circuit includes a reference signal amplifier 92 including a bandpass filter 19 and an electrocardiogram amplifier 93.

This circuit can be used in place of the amplifier of FIG. However, when using this circuit, since the reference signal is continuously applied to the human body, the switching means 15 between the reference signal oscillator and the human body is not necessarily required, and the electrocardiogram amplifier 43 and the reference signal amplifier 42 are connected. The input selector switch 16 and the control circuit 14 are also not required.

This circuit uses a bandpass filter 19 to detect a reference signal from the signal detected by the electrode. The output of the bandpass filter 19 is rectified by a diode 96 to obtain a reference signal output proportional to the reference signal level. at the same time,
The signals detected by the electrodes are amplified by an electrocardiogram amplifier 93.

Although not shown, a synchronization signal is manually input to the electrocardiogram amplifier 93 from a reference signal oscillator. The electrocardiogram amplifier 93 outputs the positive and negative peak values of the reference signal, or a signal at an intermediate point between the positive and negative peaks, depending on the synchronization signal from the reference signal oscillator. When positive and negative peak values of the reference signal are output, this output signal can be A/D converted to obtain an average value.

In addition, as shown by the chain line in FIG.
It is also possible to connect a band eliminate filter 20 to the input end to remove the reference signal, and use the band eliminate filter 20 to remove the reference signal and detect the electrocardiographic signal.

The electrocardiographic signal detected by the electrodes is corrected and amplified by the reference signal amplifier 92, which is an automatic gain control circuit, in the same manner as described above.

The circuits shown in FIGS. 1 and 4 correct and amplify the electrocardiographic signal using the reference signal level detected by the electrodes.

However, in this invention, it is not necessary to correct the electrocardiographic signal using the reference signal measured by the electrodes. The simplest method is to amplify the reference signal measured by the electrodes and display it directly on a monitor, then check the contact status of the electrodes by looking at the monitor to ensure that all electrodes can measure electrical signals from the body surface. After confirmation, the electrocardiogram signal can also be measured.

By the way, the present invention can be most effectively used in a "body surface electrocardiograph" that measures biopotential from a large number of points, processes the measurement results on a computer, and displays them on a monitor or printer. A body surface electrocardiograph measures electrocardiographic signals from the chest of a human body, calculates and displays an equipotential diagram of the body surface from the measured electrocardiographic signals. This electrocardiograph typically measures electrocardiographic signals simultaneously from 50 to several hundred electrodes.

This electrocardiograph temporarily stores electrocardiographic signals measured by electrodes in a computer memory and processes them. In this case, before measuring the electrocardiogram signal, the reference signal of the human body is measured with electrodes, the measurement result is stored in memory, and the electrocardiogram signal measured immediately after the reference signal is calculated using the stored value in the memory. Correction is also possible. For example, a reference signal of IHz or higher is applied to the human body, measured with electrodes, amplified to a certain amplification factor, converted from analog to digital and stored in memory, and immediately after that, the reference signal is applied to the human body. Stop applying the signal, measure the electrocardiographic signal with the electrodes, amplify the electrocardiographic signal to a certain amplification factor, store it in memory, and correct the stored value of the electrocardiographic signal with the stored value of the reference signal. It is also possible. In other words, an electrocardiographic signal measured with an electrode whose reference signal level is one-half of the specified value is corrected by multiplying by 2, and an electrocardiogram signal measured with an electrode whose reference signal level is one-third of the specified value is corrected by multiplying it by 2. The measured electrocardiographic signal is multiplied by 3 and corrected.

The circuits shown in FIGS. 1 and 4 use an automatic gain control circuit in the electrocardiographic signal amplifier to correct the electrocardiographic signal.
When the electrocardiographic signal is processed by a computer, it is also possible to store both the reference signal and the electrocardiographic signal in the computer, and use the computer's reference signal to perform the processing to correct the electrocardiographic signal.

The circuit shown in FIG. 1 can apply a reference signal without passing the reference signal to the living body. In this method, a reference signal oscillator 1 is connected to the ground and the human body, the entire human body is set at the same potential, and a reference signal is applied with the ground as a reference. The reference signal measured by the electrode is detected as a reference signal with respect to ground, and the contact state of the electrode is measured.

Furthermore, as shown in FIG. 11, it is also possible to connect a reference signal oscillator 111 between the foot and the ground, and amplify the reference signal with an electrocardiogram amplifier 113. This circuit is
Since the entire human body has the same potential and can be varied by the reference signal, in other words, the entire human body has the same potential with respect to the reference signal. I thought it couldn't be done. That is, since the electrocardiogram amplifier 113 measures the relative potential of the chest with respect to both hands and one leg, it is considered that the electrocardiogram amplifier 113 cannot measure the reference signal if the entire human body fluctuates at the same potential.

However, strangely, when the present inventors actually conducted an experiment, they were able to measure the reference signal using an electrocardiogram amplifier. The reason why the electrocardiogram amplifier 113 can measure the reference signal is that the human power impedance of the summing amplifier 114, which has a voltage gain of 1 for measuring the potentials of both hands and one foot, is not infinite. That is, when the input terminal flows to the summing amplifier 114, the signal actually input to the summing amplifier 114 becomes somewhat lower than the reference signal applied to the foot. When the input terminal flows to the summing amplifier 114, the summing amplifier 11
A voltage drop is generated by multiplying the resistance value between the input terminal No. 4 and the human body (input terminal resistance value) by the input terminal, and a reference signal that is lower by this voltage drop is manually input to the summing amplifier. In other words, the actual input signal of the summing amplifier 114 does not have the same potential as the human body. The difference between the signal actually input to the summing amplifier 114 and the reference signal of the human body is equal to the value obtained by multiplying the input resistance value by the input terminal. Although the input end resistance value is constant, the input current of the summing amplifier 114 is proportional to the reference signal, so
The difference between the actual input signal of the summing amplifier 114 and the reference signal is
Proportional to the reference signal. The electrocardiogram amplifier 113 compares the output signal of the summing amplifier 114 with the detected voltage of the electrodes, and amplifies the difference component. If the actual input voltage of the summing amplifier 114 is not at the same potential as the human body, a signal at a level different from the reference signal is input to one of the electrocardiographic amplifiers 113.

Therefore, the electrocardiogram amplifier 1113 can measure the reference signal.

This circuit has the advantage that the reference signal can be easily measured because the reference signal can be measured without changing the connection of the electrocardiogram amplifier 113.

A distorted waveform can also be used as the reference signal applied to the human body. The easiest way to apply a reference signal to the human body does not require an oscillator. An electric wire of several tens of centimeters to several meters can be used as a reference signal oscillator. The reference signal can be applied by connecting an electric wire to the point on the human body where the reference signal is applied. Noise is induced from the power source into the wires connected to the human body. This induced noise is a distorted sine wave equal to the frequency of the power supply.

Although the induced noise of the power supply is distorted, it causes the human body to fluctuate to the same potential, so it can be used as a reference signal.

This method is the easiest way to apply a reference signal to the human body.

Furthermore, as shown in FIG. 12, it is also possible to apply a reference signal to the human body without directly connecting the reference signal oscillator 121 to the human body. That is, as shown in the figure, an induction electrode 123 is provided below the human body via an insulating material 122 such as synthetic resin, a reference signal is applied between the induction electrode l23 and the ground, and a reference signal is applied to the human body from the induction electrode 123. It is also possible to detect the contact state of the electrode 124 by inducing a signal and measuring a reference signal induced in the human body with the electrode 124.

In this case, the reference signal is induced into the human body via the capacitance between the induction electrode 123 and the human body.

The apparatus shown in FIG. 12 includes a calculation means 125 for calculating the electrocardiographic signal detected by the electrodes 124, and a monitor 126 for displaying the calculation results of the calculation means 125.

The calculation means 125 performs calculation processing on the electrocardiographic signal to create a potential distribution map on the body surface. The calculation means 125 simultaneously takes in electrocardiographic signals from all electrodes at fixed time intervals, for example, at intervals of 0.1 to 5 msec.

A potential distribution map on the body surface is calculated at regular time intervals from the captured electrocardiographic signals.

The monitor 126 displays the calculated potential distribution diagram, for example, 0
, are displayed in order at intervals of 1 to 10 seconds.

In FIG. 12, three electrodes in contact with the body surface are shown for clarity. However, as mentioned earlier, electrocardiographs that create body surface distribution maps are equipped with a large number of electrodes.

The electrocardiograph shown in FIG. 1 includes a monitor 25 with integrated calculation means. This monitor displays a body surface potential distribution diagram, similar to the calculation means and monitor shown in FIG.

By the way, in the biopotential measuring method of the present invention, the biopotential measuring means is not limited to an electrode that measures the biopotential by contacting the living body, but any member capable of detecting an electrical signal from the living body,
For example, a non-contact type electrode that does not come into direct contact with a living body but measures the biopotential by bringing it close to the living body can also be used. Non-contact electrodes are attached to the body surface and are connected via a certain capacitance. That is, the electrode and the biological surface constitute a capacitor, and the biological potential is measured via this capacitor.

In this case, the electrode cannot measure the DC potential of the living body, but the AC component is detected through the electrode's capacitor. Electrodes with this structure increase the human power impedance of the first-stage amplifier to which the electrodes are connected, and widen the area with the body surface, thereby increasing capacitance and allowing detection of signals with low frequency components. That is, the contact impedance of this electrode with the body surface is reduced in inverse proportion to the area of the electrode that specifies capacitance and the frequency of the biological signal.

Further, as the member for detecting biological signals, a magnetic sensor or the like that detects magnetism emitted by a living body can be used. The magnetic sensor is
The magnetic field appearing on the body surface is measured by bringing it close to the body surface. In this case, the reference signal applied to the living body uses a magnetic signal so that it can be detected by a magnetic sensor.

[Brief explanation of the drawing]

1 and 4 are block diagrams showing specific examples of the device used in the biopotential measuring method of the present invention, FIG. 2 is a block diagram of the amplifier shown in FIG. 1, and FIG. Graph showing the waveform induced by the electrocardiogram, the corrected electrocardiographic signal, and the output waveform of the comparator. Figure 5 is a block diagram showing an example of an amplifier used in conjunction with the device shown in Figure 4. Figure 6 is a graph showing the waveform induced by the electrode. Graphs showing induced reference signal waveforms; FIGS. 7 to 9 are graphs showing electrocardiographic waveforms and reference signals detected by electrodes;
FIG. 10 is a block diagram of an amplifier that can be used in the combined amplifier of FIG. 5, and FIGS. 11 and 12 are block diagrams showing other embodiments in which a reference signal is applied to the human body. 1...Reference signal oscillator, 2...Reference signal amplifier, 3...Electrocardiogram amplifier, 4...Electrode, 5...Cup Ring capacitor 6...
・Diode, 7... Multiplier, 8...
...Multiplier, 9...Integrator circuit, 1
0... Adder, 11... Comparator, 12... Reference power supply, 13...
・Body surface, Todo... Control circuit, 15... Switching element, 16... Input selector switch, 17... Buffer amplifier, 18...・Differential amplifier, 19...Band pass filter 20
...Band Eliminate Filter-22...
... Reference signal amplifier, 23 ... Capacitor 24 ... Combined amplifier 25 ... Monitor, 26 ...
... Differential amplifier, 41 ... Reference signal oscillator, 42 ... Reference signal amplifier, 43 ... Electrocardiogram amplifier, 44 ... Electrode, 45 ... ...Coupling capacitor 46.
...Diode, 47...Sample and hold element, 92...
...Reference signal amplifier, 93... Electrocardiogram amplifier, 96... Diode, 111... Reference signal oscillator, 113... Electrocardiogram amplifier, 114... ...Additional amplifier, 121...Reference signal oscillator 122...Insulating material, 123...
Induction electrode, 124... Electrode, 126... Monitor.

Claims (1)

[Claims] In the biological potential measurement method, a reference signal is applied to the living body and this reference signal is detected by the electrode. A method for measuring biopotential, comprising: inspecting a biosignal detection state of an electrode.