JP2007082938A - Electrocardiographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrocardiographic apparatus which does not need to stick the electrodes directly to skin to allow measurement of an electrocardiographic complex. <P>SOLUTION: The electrocardiographic apparatus comprises a pair of measurement insulating electrodes 1, 1 and a measurement circuit 2 which includes a pair of voltage followers 3, 3 and a differential amplifier 4, wherein a pair of the measurement insulating electrodes 1, 1 are positioned opposite to a human body to insulate electrically each other and connected to the measurement circuit 2; a pair of the voltage followers 3, 3 detect a change in voltage caused by electrostatic binding between each measurement insulating electrode 1 and the human body; and the differential amplifier 4 is connected to both the voltage followers 3, 3 through their respective output ends. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrocardiogram measuring apparatus capable of measuring an electrocardiogram waveform without attaching an electrode to the skin.

Measurement of an electrocardiogram is an important means for maintaining and managing health, and an electrocardiogram is measured in various healthcare fields.
In general, in the measurement of an electrocardiogram, three electrodes are directly attached to a covering, two of these electrodes are used for signal measurement, one electrode is used for grounding, and these three electrodes are connected to a measurement circuit. In-phase noise is removed by differentially amplifying the output signals of the two electrodes. As a result, highly accurate electrocardiogram measurement can be performed.

By the way, in order to measure an electrocardiogram in daily life, it is necessary to measure the electrocardiogram by a simpler method. Therefore, a capacitively coupled electrocardiogram measuring device has been proposed (see Non-Patent Document 1).
As shown in FIG. 8, the electrocardiogram measuring apparatus comprises a measurement insulating electrode (10) to be placed facing the skin of a human body and a ground electrode (11) to be directly attached to the skin. (10) is connected to the input terminal of the measurement circuit (9), and the ground electrode (11) is connected to the ground terminal of the measurement circuit (9).

The measurement circuit (9) includes a voltage follower (12) that is connected to the measurement insulation electrode (10) and detects a voltage change due to capacitive coupling between the measurement insulation electrode (10) and the human body. The output signal of the follower (12) is supplied to the personal computer (15) through the band pass filter (13) and the notch filter (14).
According to the electrocardiogram measurement apparatus, the electrocardiogram can be easily measured as compared with a general electrocardiogram measurement using three electrodes.

In addition, although the sensor which measures a biological signal is provided in the seatbelt in a motor vehicle, or a sheet | seat, the apparatus which measures a driver | operator's heart rate and respiration rate is proposed (refer patent documents 1-4). The sensor of the measuring device is an electromagnetic wave sensor, a pressure sensor, or a piezoelectric sensor, and any of the measuring devices only measures a heartbeat signal synchronized with a heartbeat, and measures an electrocardiogram that is an electrical activity of the heart. Is not intended to do.
Ko Keun Kim, Yong Kyu Lim, KwangSuk Park “The Electrically Non-contacting ECG Measurement on the Toilet SeatUsing the Capacitively-coupled Insulated Electrodes” Proceedings of the 26th Annual International Conference of the IEEE EMBS, San Francisco, CA, 2004, PP.2375 -2378 Japanese Patent Laid-Open No. 5-261107 JP 2001-260698 A JP 2004-345617 A JP 2005-95408 A

However, in the electrocardiogram measuring apparatus shown in FIG. 8, since the ground electrode (11) needs to be directly attached to the skin, the measurement of the electrocardiogram is still troublesome and has a sense of restraint.
Therefore, an object of the present invention is to provide an electrocardiogram measuring apparatus that can measure an electrocardiogram simply by arranging two measurement insulating electrodes on the skin without facing the skin, and arranging them.

Thus, as a result of intensive studies, the inventors have conceived that the ground electrode can be omitted by using the earth as the ground, and the present invention has been completed.
An electrocardiogram measuring apparatus according to the present invention includes a pair of measurement insulating electrodes (1) and (1) that are to be placed opposite to each other in an electrically insulated state, and electrostatic capacitances between each measurement insulating electrode (1) and the human body. A measurement circuit (2) that detects a voltage change due to capacitive coupling, differentially amplifies two voltage changes detected by both measurement insulating electrodes (1) and (1), and outputs it as an electrocardiogram waveform signal. Yes.

  Specifically, the measurement circuit (2) is connected to the pair of measurement insulating electrodes (1) (1), and changes in voltage due to capacitive coupling between the measurement insulation electrodes (1) and the human body. And a differential amplifier (4) to which the output ends of both amplifier circuits are connected.

In the electrocardiogram measuring apparatus of the present invention, only a pair of measurement insulating electrodes (1) and (1) are provided as electrodes, and the ground electrode is omitted.
In the case of capacitively coupled electrocardiogram measurement using the ground as a ground, a single electrode for signal measurement is originally sufficient, but in reality, noise from the environment is large. The two electrodes have a two-pole configuration, a voltage change due to capacitive coupling between each measurement insulating electrode (1) and the human body is detected by a pair of amplifier circuits, and the detection signal of the two poles is a differential amplifier (4). Amplify differentially. As a result, common-mode noise is removed, and a highly accurate electrocardiogram waveform signal is obtained.

In a specific configuration of the present invention, the pair of measurement insulating electrodes (1) (1) is incorporated in a member to be pressed against a human body seated on the seat, for example, a seat belt (8) in an automobile.
In this case, the pair of measurement insulating electrodes (1) and (1) is incorporated into the shoulder belt portion of the seat belt (8), so that the pair of measurement insulation electrodes (1) and (1) can be used by the seat belt wearer. It is arranged on both sides of the heart, and thereby the S / N ratio can be increased.

  According to the electrocardiogram measuring apparatus according to the present invention, the two measurement insulated electrodes may be arranged so as to face the human body without being directly attached to the skin, so that the electrocardiogram can be measured more easily than in the past. .

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
As shown in FIG. 1, an electrocardiogram measuring apparatus according to the present invention includes a pair of measurement insulating electrodes (1) (1) to be disposed opposite to a human body in an electrically insulated state, and each measurement insulating electrode (1). A measurement circuit that detects a voltage change due to capacitive coupling between human bodies, differentially amplifies two voltage changes detected by both measurement insulating electrodes (1) and (1), and outputs it as an electrocardiogram waveform signal ( 2), and the ground terminal of the measurement circuit (2) is grounded.
The ground electrode to be attached to the human body is omitted.

The measurement circuit (2) is connected to a pair of measurement insulation electrodes (1) (1) and detects a voltage change due to capacitive coupling between each measurement insulation electrode (1) and the human body. (3) (3) and a differential amplifier (4) to which the output ends of both voltage followers (3) and (3) are connected. The output signal of the differential amplifier (4) is a bandpass filter (5 ) And the notch filter (6), and then supplied to the personal computer (7).
As the voltage follower (3), a high input impedance operational amplifier ("TL071" manufactured by Texas Instruments) is used.

  The band pass filter (5) has a pass band in the frequency region of the electrocardiogram waveform. The notch filter (6) is a digital filter that removes 60 Hz noise caused by a fluorescent lamp or a commercial power source by FFT (Fast Fourier Transform). The voltage follower (3) is an example of an amplifier circuit that detects a voltage change.

Here, the measurement principle of the electrocardiogram measurement apparatus of the present invention will be described. As shown in FIG. 1, it is considered that the human body is capacitively coupled with the earth (earth) and connected to the ground terminal of the measurement circuit (2) via the earth (earth). Therefore, the capacitance between the human body and the measurement insulating electrode (1) is C _E , the capacitance between the human body and the ground (ground) is C _G , and the capacitance between the measurement circuit (2) and the ground (ground). , C _K , the resistance value of the operational amplifier input stage constituting the voltage follower is R _in , the capacitance value is C _in , the heart potential is V _heart , and the output voltage is V _out , one insulated electrode for measurement The measurement circuit unit composed of (1) and one voltage follower (3) can be represented by the equivalent circuit shown in FIG.
Incidentally, the voltage follower (3) is represented by a parallel circuit of the resistance value R _in the capacitance value C _in FIG. 2.

In the equivalent circuit, when the relationship between the _heart generated potential V _heart and the output voltage V _out is derived, the following equation 1 is obtained.

In Equation 1, the input resistance of the operational amplifier which constitutes a voltage follower (3) R _in sufficiently large, and the input capacitance C _in of the operational amplifier is other capacitance C _E, C _G, sufficiently larger than C _K In this case, V _heart = V _out .
That is, according to the voltage follower (3), the generated potential of the heart can be detected without changing the voltage value.

In this embodiment, the operational amplifier constituting the voltage follower (3) has an input resistance value R _in of 10 ¹² Ω and an input capacitance value C _in of 18 pF. On the other hand, since the capacitor capacitances C _G and C _K to the ground are about 7.12 × 10 ⁻³ F, if an electrode is produced and arranged so as to satisfy C _in << C _E , it is non-existent to the human body. An electrocardiogram can be derived for the contact.

  However, in the electrocardiogram measuring apparatus of the present invention, as shown in FIG. 1, a measurement circuit unit comprising a measurement insulating electrode (1) and a voltage follower (3) is arranged in parallel, and the outputs of both measurement circuit units are differential amplifiers ( 4) Differential amplification is performed. This eliminates common-mode noise and realizes highly accurate electrocardiogram measurement.

3 and 4 show an example in which the electrocardiogram measuring apparatus of the present invention is applied to electrocardiogram measurement in an automobile.
As shown in FIG. 4, the pair of measurement insulating electrodes (1) and (1) are respectively incorporated in the shoulder belt portions of the seat belt (8), whereby the pair of measurement insulation electrodes (1) and (1). Are arranged on both sides of the heart and are pressed and held by the human body.

  Each measurement insulating electrode (1) is configured by wrapping a copper plate with high-quality paper. Here, the copper plate has a size of 50 mm × 20 mm × 5 mm, and the fine paper covering the copper plate has a thickness of 0.1 mm.

  The pair of measurement insulating electrodes (1), (1) is connected to the measurement circuit (2) shown in FIG. The measurement circuit (2) has a pair of voltage followers (3) and (3) connected to a pair of measurement insulating electrodes (1) and (1) and the output terminals of both voltage followers (3) and (3). The output signal of the differential amplifier (4) is supplied to the personal computer (7) through the band-pass filter (5), and the notch filter is omitted. .

The electrocardiogram measuring apparatus shown in FIG. 3 was produced, and using this, an electrocardiogram was measured in a sitting position for five healthy adult men (age: 23 years ± 1). In addition, an electrocardiogram was simultaneously measured using a conventional general three-electrode type electrocardiogram measuring device (Tiac Electronics “AP1524”). In order to avoid electrical interference between the two electrocardiogram measurement devices, the measurement circuits of both devices were driven by batteries.

As a result, the result shown in FIG. 5 was obtained. In FIG. 5, the left vertical axis represents an electrocardiogram waveform output V _out [μV] measured by the two-electrode capacitance type electrocardiogram measuring apparatus of the present invention, and the right vertical axis represents a conventional general three-electrode type. An electrocardiogram waveform output ECG [mV] measured by the electrocardiogram measuring apparatus is shown.
As is apparent from this figure, according to the two-electrode capacitance type electrocardiogram measuring device of the present invention, the conventional three-electrode type electrocardiogram measuring device is not used even though the ground electrode and the notch filter are omitted. The electrocardiogram waveform is measured with the same high accuracy, and not only the R wave but also the T wave can be detected.

On the other hand, FIG. 6 shows an electrocardiogram waveform output V _out [μV] by a conventional two-electrode capacitance type electrocardiogram measuring apparatus (FIG. 8) using a measurement insulating electrode and a ground electrode, and a conventional general electrode. An electrocardiogram waveform output ECG [mV] by a three-electrode type electrocardiogram measuring apparatus is shown.
As is clear from this figure, in the two-electrode capacitance type electrocardiogram measuring device using the measurement insulating electrode and the ground electrode, the noise included in the electrocardiogram waveform is increased as compared with the conventional three-electrode type electrocardiogram measuring device. However, although it is possible to detect the R wave, it is difficult to detect the T wave.

  Also, when the measurement result of the electrocardiogram measurement apparatus of the present invention shown in FIG. 5 is compared with the measurement result of the conventional electrocardiogram measurement apparatus shown in FIG. 6, the former measurement result has higher accuracy, In electrocardiogram measurement using two electrodes, it is more advantageous for improving measurement accuracy to use one electrode as a ground electrode and to eliminate noise by differential amplification than to use it as a ground electrode. I understand.

7 is a one-electrode capacitance type electrocardiogram using a single measurement insulating electrode (1), omitting one of the pair of measurement insulating electrodes (1) and (1) shown in FIG. The result of having performed the electrocardiogram measurement by constituting the measuring device is shown.
As is clear from this figure, although the noise component is large, it has been found that the R-wave can be detected even by the one-electrode capacitance type electrocardiogram measuring apparatus.

As described above, according to the two-electrode capacitance type electrocardiogram measuring apparatus of the present invention, the pair of measurement insulating electrodes (1) and (1) are opposed to the skin from the top of the clothes without being directly attached to the skin. Since it only has to be deployed, the electrocardiogram can be measured more simply than before.
In particular, as shown in FIG. 3, in an electrocardiogram measurement in an automobile, the electrocardiogram can be measured with high accuracy without being equipped with a notch filter because it is not affected by 60 Hz noise caused by a fluorescent lamp or a commercial power source. .

  For measurement in a room that is affected by 60 Hz noise caused by a fluorescent lamp or a commercial power supply, it is effective to equip a notch filter (6) as shown in FIG. Measures such as covering 1) with a shield or shielding the signal line are also effective.

In order to satisfy the relationship of C _in << _CE which is one of the conditions for satisfying the above equation 1, in this embodiment, the measurement insulating electrode (1) is configured by wrapping a copper plate with fine paper. This increases the dielectric constant between the copper plate and the heart, but it is also effective to shorten the distance between the copper plate and the heart and to increase the size of the copper plate.

  If the electrogram measurement device according to the present invention is applied to electrocardiogram measurement in an automobile, the driver's autonomic nerve activity is continuously evaluated, for example, by constantly measuring heartbeat fluctuations. It is possible to take various safety measures such as preventing abnormal driving due to an increase in the number of people, or detecting a sudden abnormality in cardiac activity and stopping the vehicle safely.

  The insulating electrode for measurement (1) is not limited to a metal plate, and can be configured using conductive fibers. For example, it is possible to realize an electrocardiogram measuring apparatus that can measure an electrocardiogram only by wearing it by braiding an insulating electrode made of conductive fibers into the underwear.

In the above embodiment, the voltage follower (3) is used for amplification in the measurement circuit (2). However, the present invention is not limited to this, and various amplification circuits such as an inverting amplifier and a non-inverting amplifier can be used.
Furthermore, the measurement insulating electrode (1) is configured by wrapping a copper plate with high-quality paper. However, the present invention is not limited to this, and the electrode may be configured with other conductors. It may be used.

It is a block diagram which shows the structure of the electrocardiogram measuring apparatus which concerns on this invention. It is an equivalent circuit diagram of the main components of the electrocardiogram measuring apparatus. It is a block diagram which shows the application example of the electrocardiogram measuring device which concerns on this invention. It is a figure which shows the structure which incorporated the measurement insulating electrode in the seatbelt. It is a graph which shows the measurement result by the 2-electrode electrostatic capacitance type electrocardiogram measuring device of the present invention. It is a graph which shows the measurement result by the conventional 2 electrode electrostatic capacitance type electrocardiogram measuring device. It is a graph which shows the measurement result by the 1-electrode electrostatic capacitance type electrocardiogram measuring device. It is a block diagram which shows the structure of the conventional 2 electrode electrostatic capacitance type electrocardiogram measuring device.

Explanation of symbols

(1) Insulation electrode for measurement
(2) Measuring circuit
(3) Voltage follower
(4) Differential amplifier
(5) Bandpass filter
(6) Notch filter
(7) Personal computer
(8) Seat belt

Claims (5)

  A pair of measurement insulating electrodes (1) and (1) to be placed opposite to each other in an electrically insulated state on the human body, and detecting voltage changes due to capacitive coupling between each measurement insulating electrode (1) and the human body An electrocardiogram measuring apparatus comprising a measurement circuit (2) for amplifying a difference between two voltages detected by both measurement insulating electrodes (1) and (1) and outputting the amplified signal as an electrocardiogram waveform signal.   The measurement circuit (2) is connected to the pair of measurement insulating electrodes (1) (1) and detects a voltage change due to capacitive coupling between each measurement insulation electrode (1) and the human body. The electrocardiogram measuring device according to claim 1, comprising an amplifier circuit and a differential amplifier (4) to which the output terminals of both amplifier circuits are connected.   The electrocardiogram measurement device according to claim 1 or 2, wherein the pair of measurement insulating electrodes (1) (1) is incorporated in a member to be pressed against a human body seated on a seat.   The electrocardiogram measuring device according to claim 3, wherein the member is a seat belt (8) in an automobile.   The electrocardiogram measuring device according to claim 4, wherein the pair of measurement insulating electrodes (1), (1) are respectively incorporated in a shoulder belt portion of a seat belt (8).

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