The present invention relates to a living body measuring sensor and a living body measuring method, more particularly to a living body measuring sensor and a living body measuring method for obtaining an electrocardiogram without making a direct contact with a body surface of a measuring subject.
An electrocardiogram obtained by a conventional electrocardiograph records a ventricular function measured at rest, wherein a variation of a voltage generated on a body surface of a measuring subject is recorded. The electrocardiogram is a record of an electric activity generated in a heart pulsation, wherein the voltage generated on the body surface as a result of a cardiac muscle excited by generation and propagation of stimulations prior to a cardiac contraction is recorded using a curved line.
In the conventional measurement, it is necessary for the measuring subject to lie on a medical examination table on his/her back and stay at rest. A fixed electrode 51 is fixed to the measuring subject in each measurement and formed from the conductive paste as described above. Further, the electrode is depressurized/pressurized and thereby fixed to the body surface prior to the commencement of the measurement. Therefore; there is a limit in conducting the measurement in such a manner that the measuring subject can be relaxed during the measurement.
Further, in the case of a patient having a paroxysmal or temporary heart disease, it is necessary to record the electrocardiogram by an electrocardiogram recorder, for example, for as long as 24 hours. The patient is, as in this case, forcibly left in the state where the fixed electrode 51 is attached to the body surface. When the fixed electrode 51 is attached to the body surface for as long as a few hours, the surface in contact with the electrode becomes itchy or an allergic reaction may cause the surface to be sore due to inflammation. If a cloth or the like is interposed between the fixed electrode 51 and a skin 10 so as to prevent the metal from directly contacting the skin 10, a living body electric signal cannot be directly detected from the fixed electrode 51.
A possible method is to detect the living body electric signal by capacitance-coupling the fixed electrode 51 via the cloth and thereby mounting the electrode on the skin 10. However, the method is rather awkward because an output of the fixed voltage 51 shows a high impedance and a noise voltage is thereby increased as shown in
Japanese Unexamined Patent Application No. 2002-159458 recites a living body electric signal induction sensor and a recording system in which a conductive fiber is woven into a predetermined portion of a clothing, the living body electric signal is detected by the conductive fiber constituting an induction-electrode, and the electrocardiogram is recorded on a recorder housed in a pocket of the clothing.
However, in the case of using the conductive fiber as the induction electrode, the conductive fiber may fail to closely contact the skin, which cannot assure an accurate electrocardiogram. Further, the conductive fiber includes the risk of inducing the allergic reaction in the same manner as in the metal electrode.
Therefore, an object of the present invention is to provide a living body measuring sensor and a living body measuring method capable of measuring an electrocardiogram using a capacitance in a less invasive manner.
The present invention relates to the living body measuring sensor for detecting a living body electric signal from a body surface of a measuring subject, which comprises a conductive electrode capacitance-coupled on the body surface of the measuring subject via an insulating member and a living body electric signal extractor circuit for extracting the living body electric signal from the conductive electrode as a low impedance signal.
According to the present invention, the conductive electrode is mounted on the body surface of the measuring subject via the insulating member and the living body electric signal is outputted as the low impedance signal. Thereby, the electrocardiogram can be measured in the less invasive manner without any adverse effect from the noise, and a risk of inducing an allergic reaction can be eliminated.
The conductive electrode is preferably a metal electrode.
The conductive electrode is preferably a conductive fiber.
The insulating member is preferably a thin cloth.
The living body electric signal extractor circuit preferably includes an impedance converter circuit whose input is a high input impedance and output is a low impedance.
The living body electric signal extractor circuit preferably further includes a filter circuit for extracting a frequency component including the living body electric signal from the output of the impedance converter circuit.
The living body electric signal extractor circuit preferably further includes an amplifier circuit for amplifying the living body electric signal outputted from the impedance converter circuit using a high gain.
A barium titanate porcelain may be provided as a high permittivity member to be provided between the conductive electrode and the insulating member.
The living body measuring method according to the present invention extracts the living body electric signal with the low impedance by capacitance-coupling and thereby mounting the living body measuring sensor including the conductive electrode on the body surface of the measuring subject via the insulating member and thereby mounting the sensor on the body surface of the measuring subject.
The living body measuring sensor 1 is brought into close contact with a surface of the skin 7 via a thin cloth 6 formed from silk or the like serving as an insulating member so as to detect a variation of a living body electric signal generated on the body surface of the measuring subject.
As shown in
The living body electric signal of the high impedance detected by the living body measuring sensor 1 is supplied to an instrumentation amplifier 12 via an input terminal 11, and converted into the living body electric signal of the low impedance, and then supplied to an LPF (low-pass filter) 13. In the instrumentation amplifier 12, an input impedance is set to 1000 GΩ, and a gain is set to 62 times as a result of changing a value of an externally added resistance. The LPF 13 extracts a frequency component equal to or below 100 Hz from the living body electric signal and supplies a result of the extraction to a DC servo circuit 14. The DC servo circuit 14 applies the servo so that a variation of a DC component of the living body electric signal is controlled to be zero, which is supplied to a noise eliminating filter 15. The noise eliminating filter 15 is adapted to be switched upon necessity so that the frequency component of 50 Hz or 60 Hz can be extracted from the living body electric signal, and supplies the living body electric signal of the extracted frequency component to an inversion amplifier 16.
The inversion amplifier 16 amplifies the living body electric signal, which is inverted by the instrumentation amplifier 12, by 16 times, and inverts the living body electric signal to an initial polarity of the signal. Accordingly, the living body electric signal is amplified by 62×16≅1000 times. The inverted living body electric signal is supplied to a DC servo circuit 17, which applies the servo in the same manner as the DC servo circuit 14 so that the variation of the DC component of the living body electric signal becomes zero, and supplies it to a noise eliminating filter 18. The noise eliminating filter 18 is adapted to be switched upon necessity so that the frequency component of 50 Hz or 60 Hz can be extracted from the living body electric signal in the same manner as the noise eliminating filter 15 in the previous stage. The living body electric signal extracted by the noise eliminating filter 18 is sampled by an A/D converter 19 and converted into a digital signal, and then supplied to a processing device 20 to be subjected to necessary processes. As a result, the electrocardiographic waveform is outputted.
As another possible constitution, an analog living body electric signal is outputted from the noise eliminating filter 18 and the electrocardiographic waveform is observed by an oscilloscope.
As described above, according to the present embodiment, the silver electrode 2 of the living body measuring sensor 1 is brought into close contact with the skin 7 of the measuring subject via the cloth 6, the device whose input impedance is set to be higher is used as the instrumentation amplifier 1 of the living body measuring device 21, the DC servo circuits 14 and 17 provided in two stages apply the servo so as to lead the variation of the DC component to be zero, and the noise eliminating filters 15 and 18 provided in two stages select and extract one of the frequency bands of 50 Hz and 60 Hz from the living body electric signal. Thereby, the electrocardiographic waveform can be outputted.
Therefore, the electrocardiogram can be measured in a less invasive manner by mounting the living body measuring sensor 1 on an underwear formed from silk, cotton or the like. Further, a risk of inducing an allergic reaction, which was generated by the conventional method of directly mounting the fixed electrode mounted on the body, can be eliminated because the living body measuring sensor 1 is mounted on the skin via the underwear or the like.
The cloth interposed between the living body measuring sensor 1 and the body surface of the measuring subject is not limited to silk or cotton, and may employ a synthetic fiber or Japanese paper having a thickness approximately equal to that of the cloth formed from any of the foregoing materials.
As described above, according to the present embodiment, the living body measuring sensor 1a comprising the silver electrode 2 making a close contact with the one surface of the barium titanate porcelain 4 and retrieving the living body electric signal is disposed on the skin 7 of the measuring subject via the thin cloth 6, the barium titanate porcelain 4 and the thin cloth 6 are capacitance-coupled, the living body electric signal is retrieved from the silver electrode 2, and the output of the living body measuring sensor 1 is supplied to the living body measuring device so as to output the electrocardiogram.
In the foregoing description, the application of the barium titanate porcelain 4 as the high permittivity member was described. However, the present invention is not limited to the material, and may employ a high permittivity member of some other type.
The living body measuring sensors 1 and 1a respectively shown in
A woven body formed from a conductive yarn 33 and a non-conductive yarn 34 constitutes the conductive fabric 31 as shown in
Connecting the conductive fabric 31 to the input terminal 11 of the living body measuring device 21 shown in
In the embodiment shown in
Thus far, the preferred embodiments of the present invention were described referring to the drawings, however, the present invention is not limited to the embodiments shown in the figures. The shown embodiments can be modified and corrected in various manners within the scope identical to the present invention and the scope of its equivalence.
The present invention, wherein the living body measuring sensor 1 is brought into contact with a body surface of a measuring subject by means of the capacitance coupling using the cloth 6 between the metal electrode 2 and the body surface of the measuring subject as the capacitance, the living body electric signal is extracted from the metal electrode 2, and the output of the living body measuring sensor 1 is supplied to the living body measuring device 21 including the impedance converter having the high input impedance and low output impedance so as to read the voltage waveform, can be utilized in measuring the electrocardiogram in the less a invasive manner.
Number | Date | Country | Kind |
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2003-346299 | Oct 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP04/12632 | 9/1/2004 | WO | 4/3/2006 |