GB2070240A - Circuit arrangement for measuring the heart rate - Google Patents
Circuit arrangement for measuring the heart rate Download PDFInfo
- Publication number
- GB2070240A GB2070240A GB8105028A GB8105028A GB2070240A GB 2070240 A GB2070240 A GB 2070240A GB 8105028 A GB8105028 A GB 8105028A GB 8105028 A GB8105028 A GB 8105028A GB 2070240 A GB2070240 A GB 2070240A
- Authority
- GB
- United Kingdom
- Prior art keywords
- signal
- heart
- mean value
- pulse
- circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000008280 blood Substances 0.000 claims abstract description 15
- 210000004369 blood Anatomy 0.000 claims abstract description 15
- 238000011156 evaluation Methods 0.000 claims abstract description 15
- 238000005259 measurement Methods 0.000 claims description 34
- 230000007423 decrease Effects 0.000 claims description 5
- 230000000087 stabilizing effect Effects 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 17
- 230000001457 vasomotor Effects 0.000 abstract description 15
- 230000005540 biological transmission Effects 0.000 abstract description 13
- 230000002792 vascular Effects 0.000 abstract description 4
- 239000003990 capacitor Substances 0.000 description 7
- 230000017531 blood circulation Effects 0.000 description 3
- 230000001419 dependent effect Effects 0.000 description 3
- 210000000624 ear auricle Anatomy 0.000 description 3
- 230000004907 flux Effects 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 230000002238 attenuated effect Effects 0.000 description 1
- 210000004204 blood vessel Anatomy 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 210000000883 ear external Anatomy 0.000 description 1
- 238000009532 heart rate measurement Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/024—Detecting, measuring or recording pulse rate or heart rate
- A61B5/02416—Detecting, measuring or recording pulse rate or heart rate using photoplethysmograph signals, e.g. generated by infrared radiation
Abstract
When the heart rate is measured by means of a light source (23) which irradiates tissue (21) through which blood circulates and a light detector (14), the evaluation is influenced not only by differences in transmission, but also by vaso- motor activity of the vascular system. Therefore a control circuit (2) for the light source (23) ensures that the mean value of the output signal of the detector (14) remains constant, and also a control circuit (9) stabilises the heart-pulse signal which is applied to an evaluation/ display device 13. The heart-pulse amplitude is averaged over several heart-pulse periods (10), the mean value being used as a real value for a control circuit (9) which stabilizes the electrical heart-pulse signal. The light source (23) may be pulsed (1) and the detected signal demodulated (3). The amplified (6) and filtered (5) signal is composed with a reference level (at 7) and the output fed via a band rejection filter (22) to the light source controll amplifier (2) and via a bandpass filter (9a) to pulse amplifier (9). <IMAGE>
Description
SPECIFICATION
Circuit arrangement for measuring the heart rate
The invention relates to a circuit arrangement for measuring the heart rate of a person, comprising a controllable light source, a light receiver which supplies a measurement signal corresponding to the attenuation of light from said source via a measurement path through tissue whose blood content varies in response to the pulse, a filter arranged selectively to extract a heart-pulse signal corresponding to the heart rate from the measurement signal, said extracted heart-pulse signal being applied to an evaluation device, and a controller which controls the light source in accordance with the measurement signal so that the mean value with respect to time of the input signal of the controller remains at least approximately constant. Such a circuit will be referred to herein as a circuit arrangement of the kind specified.
A A circuit arrangement of this kind is known from German Offenlegungsschrift 27 27 138.
During a measurement, light from the light source is transmitted through a fold of the skin of the external ear, the tip of a finger or similar tissue whose blood content varies in response to the pulse, and the light flux occurring on the other side of the measurement location is measured by the light receiver. The amplitude modulation of the light flux represents information relation to the variation of the blood content at the measurement location from which the heart rate is determined by means of the evaluation device.
The controller ensures that the measurement signal remains independent of individual differences in the optical properties of skin and tissue (transmission) to a high degree, thus facilitating the evaluation of the measurement signal.
However, in the known apparatus faults can occur which impede accurate evaluation of the measurement signal. The invention recognizes the fact that these faults are caused by vasomotor activity in the vascular system. The blood vessels are then contracted or dilated, so that the transported volume of blood changes, thus causing a variation in the modulation of the measurement signal. The vasomotor activity causes variations which are much slower than the heart rate of the person under examination.
It is an object of the invention to provide a circuit arrangement of the kind set forth where vasomotor activity during a measurement has substantially no effect on the accuracy of the result of the heart rate measurement.
According to the invention there is provided a circuit arrangement for measuring the heart rate of a person, comprising a controllable light source, a light receiyer which supplies a measurement signal corresponding to the attenuation of light from said source via a measurement path through tissue whose blood content varies in response to the pulse, a filter arranged selectively to extract a heartpulse signal corresponding to the heart rate from the measurement signal, said extracted heart-pulse signal being applied to an evaluation device, and a controller which controls the light source in accordance with the measurement signal so that the mean value with respect to time of the input signal of the controller remains at least approximately constant, characterized in that there is provided a control circuit for stabilizing the amplitude of the heart-pulse signal with respect to slow fluctuations with respect to time of the modulation of the measurement signal, the amplitude-stabilized heart-pulse signal being applied to the evaluation device.
Slow fluctuations with respect to time are to be understood to mean variations whose upper limit frequency is substantially lower than the heart rate. Vasomotor activity becomes apparent as slow fluctuations with respect to time of the amplitude of the heart-pulse signal, and these fluctuations are suppressed to a high degree by the control circuit, so that in practice the evaluation device only receives a periodic signal of substantially constant amplitude which can be readily evaluated.
In an embodiment in accordance with the invention, the control circuit comprises a mean value circuit which is connected after the filter in the signal path and which supplies an output signal which corresponds to the mean value of the amplitude of the heartpulse signal averaged over several periods of the heart-pulse signal. This mean value circuit can be formed by the series connection of a diode and a capacitor in the simplest case, a resistor then being connected parallel to the capacitor (rectifying circuit). The output signal which corresponds to the mean value of the heart-pulse signal amplitude over several heart-pulse signal periods is derived from the capacitor which has a time constant of a few seconds In conjunction with the resistor.In a further embodiment in accordance with the invention, an amplifier whose gain can be controlled by the output signal of the mean value circuit is connected between the filter and the mean value circuit. The gain of the amplifier is controlled in dependence on the output signal of the mean value circuit, so that it decreases as the output signal of the mean value circuit increases and vice versa.
In a further embodiment in accordance with the invention, the output signal of the mean value circuit forms in conjunction with the output of a reference value generator, as a target value for the controller, the target value thus formed increasing as the mean value decreases.
The controller which renders the heart-pulse signal independent of the transmission is thus caused at the same time to compensate for fluctuations of the heart-pulse amplitude which are caused by vasomotor activity. For example, if the amplitude of the heart-pulse signal decreases due to vasomotor activity, the emission of the light source is increased until the heart-pulse signal again equals its reference value.
In a further preferred embodiment in accordance with the invention, a further evaluation device is connected to the output of the mean value circuit. A circuit arrangement of this kind enables not only the heart rate, but also a quantity corresponding to the vasomotor condition of the vascular system, to be monitored.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, of which Figure 1 shows a circuit arrangement in which the measurement location is irradiated with pulsed light, and
Figure 2 shows a circuit arrangement in which the measurement location is irradiated with light of constant intensity.
A pulse generator 1 generates a squarewave signal of constant amplitude, constant frequency and constant duty-cycle. This signal is applied to an amplifier 2, the gain of which can be controlled by the voltage on a control input 24. A light source 23 whose intensity is dependent on the output voltage of the amplifier 2, for example, an infra-red LED, is connected to the output of the amplifier 2. Together with a light receiver 14, for example, a phototransistor, this LED is arranged so that the phototransistor 14 measures the intensity of the light which is emitted by the light source 23 and which is attenuated at the measurement location 21 by tissue, for example, a finger or an ear lobe through which the blood circulates.
For a predetermined intensity of the light source 23, the output signal of the light receiver 14 is a measure of the attenuation of the light via the measurement location. The output signal of the phototransistor is also pulse-shaped: however, the pulse amplitude will not be constant but will fluctuate as the blood circulation at the measuring location changes. However, this fluctuation or modulation is comparatively small. It amounts to only approximately 1%. The receiver circuit 3 which includes the light receiver 14, therefore, should be constructed so that any additional disturbing extraneous light component arriving at the light receiver, is substantially excluded and amplitude modulation due to a shift of the working point by disturbing ambient light is prevented as much as possible.
As in the circuit arrangement described in
German Offenlegungsschrift 27 27 138, the disturbing light component can be compensated for in practice by applying the signal from the output electrode of the phototransistor 14 to the further processing circuit via a capacitor which is charged to a voltage corresponding to the disturbing light component by means of a switch which is switched on and off in time with the light pulses. said voltage being substracted from the output signal (switch open) during the light pulses, so that the disturbing light component is cancelled out. Any amplitude modulation by the disturb- ing light component can be minimized by operating the phototransistor with a constant collector voltage, i.e. by connecting its collector to the emitter of a transistor whose base is connected to a constant voltage.
Thus, the output of the receiver circuit 3 carries a pulse-shaped signal whose frequency corresponds to the frequency of the pulse signal supplied by the pulse generator 1 and whose amplitude is primarily dependent on the constant attenuation via a measurement location and only secondarily on the blood circulation through the tissue. Via an impedance converter 4, this signal is applied to a bandpass filter 5, the central frequency of which corresponds to the frequency (5 kHz) of the pulses supplied by the pulse generator 1 and whose bandwidth is chosen so that the transmission factor for the sidebands generated by the blood impulse modulation is not smaller in practice than the transmission factor for the central frequency. Interference frequencies situated outside the useful signal bandwidth can thus be filtered out.
An amplifier 6 whose gain is step-wise adjustable, is connected to the output of the bandpass filter 5. Very large transmission variations such as occur when a finger tip is irradiated instead of an ear lobe (the transmission may in that case become smaller by a factor of 100) have to be compensated thereby, because the control circuit itself cannot compensate for such wide variations. The output signal of the amplifier 6 is applied to an amplitude demodulator 18 which has a behaviour with respect to time which corresponds to that of a lowpass filter having an upper cut-off frequency of approximately 100
Hz. The demodulator output signal consists of a direct voltage component which is proportional to the mean value of the amplitude of the pulse-shaped output signal of the receiver circuit and of a superposed alternating voltage component which is generated by the blood impulses.
The demodulator output signal is applied to the real value input of a PI-controller 7 (proportional and integral error controller) and is compared with a reference value supplied by a reference value generator 8. The output signal of the PI controller 7 is applied, via a band-rejection filter 22 which filters out the signal components originating from the blood impulses, to the control input 24 of the variable amplifier 2. The gain thereof is thus controlled so that as the output signal of the amplifier circuit 3 increases, the gain of the amplifier 2 is decreased. A constant signal amplitude can thus be ensured at the output of the receiver circuit 3 for a given measurement location (ear lobe or finger tip) for the same person or for different persons, regardless of transmission differences.When a constant signal is present on the reference value input of the PI controller 7, the output signal thereof is only proportional to the transmission of the irradiated tissue (neglecting the slight modulation by the blood impulse signal). The measurement quantity, available, for example, at the terminal 15, can be evaluated and displayed as information concerning the tissue transmission. Between the point 15 and the display instrument a further amplifier stage may be connected whose gain is varied step-wise and in the opposite sense with respect to the gain of the amplifier stage 6, so that the product of the gain of the two amplifier stages is a constant and the signal displayed is independent of the setting of the amplifier stage 6.
The band-rejection filter 22 connected between the output of the PI controller 7 and the control input of the variable amplifier 2, serves to prevent the signal components originating from the blood impulse signal from affecting the light-source control, since otherwise these desired signal components would also be more or less removed.
The output signal of the Pl controller 7 is applied. via a bandpass filter 9a which passes only those frequency components (0.5 to 40
Hz) which are characteristic of the blood impulse signal. to an amplifier stage 9 whose gain can be controlled by the voltage on the control input 91. The output 16 of the amplifier circuit thus carries the pulse signal, i.e a signal whose variation with respect to time corresponds to the blood circulation through the measurement location and hence to the blood pulse or heart beat of the person under examination. This signal can be digitized and synchronized with the pulse frequency by means of a threshold value switch 12 connected to the output 16 of the amplifier 9.
The heart rate can be displayed in beats per minute in a counting, arithmetic and display circuit 13.
As has already been stated, vasomotor activity is liable to affect the amplitude of the heart-pulse signal. thus exerting an unfavourable effect on the accuracy of the evaluation.
The effect of vasomotOr activity on the amplitude of the heart-pulse signal can be compensated to a high degree by means of a control circuit which inter alia comprises a mean value circuit 1 0. This circuit supplies a signal which corresponds to the mean value of the heart-pulse amplitude averaged over several
heart-pulse periods (i.e. qver several seconds).
In the simplest case, this circuit may com
prise a diode which is connected to the output
of the amplifier 9 and whose other connection is connected to ground via a capacitor, a
resistor being connected parallel to the capaci
tor, said resistor being proportioned so that a
time constant of a few seconds is obtained.
The capacitor voltage thus corresponds to the mean value of the amplitude of the heart
pulse signal. This mean value is applied to an
impedance converter 11, the output 17 of
which thus carries a signal which is a measure
for the amount of vasomotor activity of the vascular system. Via the connection 19, this
signal can be applied, additionally to the
signal supplied by the reference value generator
8, to the reference value input of the PI
controller 7 so that the reference value de creases as the amplitude of the heart-pulse
signal increases.
Even though this solution does not require
an additional controller, it has the drawback
that the direct voltage component of the out ) put signal of the PI controller 7 is also depen
dent on the vasomotor activity, so that the
signal at the point 15 is no longer solely a
measure of the transmission. This drawback
can be avoided by supplying the output signal of the impedance converter 11 to the control
input 91 of the variable gain amplifier 9 via
the connection 20 instead of to the PI-control
ler 7 via the connection 19, so that the gain
of the amplifier 9 decreases as the amplitude i of the heart-pulse signal increases and vice
versa. The signal at the output 16 of the
amplifier 9 is in both cases independent of
the vasomotor activity to a high degree.
Therefore, the circuit arrangement enables an accurate determination and evaluation of
the heart-pulse signal to be made indepen
dently of differences in the transmission and
variations in the vasomotor activity. Moreover,
in addition to the heart-pulse signal and its frequency. the transmission of the measure
ment location and the amount of vasomotor
activity present, can also be determined and
displayed (signals on the terminals 15 and
The use of pulse-wise emitted light renders
the circuit highly independent of the light
originating from the environment of the mea
surement location.If the measurement loca
tion can be sufficiently shielded from ambient light, however, the generation of light pulses
can be dispensed with and use can be made
instead of a source of constant illumination
(constant light). The circuit arrangement is
then substantially simplified as can be seen from Fig. 2 in which corresponding parts are
denoted by the same reference numerals as
used in Fig. 1.
It is shown that the pulse generator 1 is
dispensed with and that instead of the vari I able gain amplifier use is made of a simple direct voltage amplifier 2, the light source being connected to the output thereof. A bandpass filter 5 is no longer required, because no sidebands can occur when constant illumination of the measurement location is used. Obviously, a demodulator can also be dispensed with. The heart-pulse signal is filtered only from the output signal of the Plcontroller 7 by the bandpass filter 9a. The output signal of the band-rejection filter 22 serves as the input signal for the direct voltage amplifier 2.
Claims (5)
1. A circuit arrangement for measuring the heart rate of a person, comprising a controllable light source, a light receiver which supplies a measurement signal corresponding to the attenuation of light from said course via a measurement path through tissues whose blood content varies in response to the pulse. a filter arranged selectively to extract a heart-pulse signal corresponding to the heart-rate from the measurement signal, said extracted heart-pulse signal being applied to an evaluation device, and a controller which controls the light source in accordance with the measurement signal so that the mean value with respect to time of the input signal of the controller remains at least approximately constant, characterized in that there is provided a control circuit for stabilizing the amplitude of the heart-pulse signal with respect to slow fluctuations with respect to time of the modulation of the measurement signal, the amplitude-stabilized heart-pulse signal being applied to the evaluation device.
2. A circuit arrangement as claimed in
Claim 1, characterized in that the control circuit includes a mean value circuit which is connected after the filter in the signal path, and which supplies an output signal which corresponds to the mean value of the amplitude of the heart-pulse signal averaged over several periods of the heart-pulse signal.
3. A circuit arrangement as claimed in
Claim 2, characterized in that between the filter and the mean value circuit there is connected an amplifier whose gain can be controlled by the output signal of the mean value circuit.
4. A circuit arrangement as claimed in
Claim 2, characterized in that the output signal of the mean value circuit forms in conjunction with the output of a reference value generator the target control value for said controller, the target value thus formed increasing as the mean value decreases.
5. A circuit arrangement as claimed in
Claim 2, characterized in that a further evaluation device is connected to the output of the mean value circuit.
6 A circuit arrangement of the kind specified for measuring the heart rate of a person, substantially as herein described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19803006477 DE3006477A1 (en) | 1980-02-21 | 1980-02-21 | CIRCUIT FOR MEASURING THE PULSE OF A PERSON WITH A CONTROLLABLE LIGHT SOURCE |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2070240A true GB2070240A (en) | 1981-09-03 |
| GB2070240B GB2070240B (en) | 1983-08-17 |
Family
ID=6095178
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8105028A Expired GB2070240B (en) | 1980-02-21 | 1981-02-18 | Circuit arrangement for measuring the heart rate |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS56132938A (en) |
| DE (1) | DE3006477A1 (en) |
| FR (1) | FR2476472A1 (en) |
| GB (1) | GB2070240B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4510940A (en) * | 1981-11-27 | 1985-04-16 | Nederlandse Centrale Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek | Plethysmograph pressure correcting arrangement |
| GB2150725A (en) * | 1983-11-30 | 1985-07-03 | Aisin Seiki | Safety apparatus for a road vehicle |
| US4539997A (en) * | 1981-10-28 | 1985-09-10 | Nederlandse Centrale Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek | Method and device for controlling the cuff pressure in measuring the blood pressure in a finger by means of photo-electric plethysmograph |
| GB2165352A (en) * | 1984-09-06 | 1986-04-09 | Ablec Ltd | Measuring heart rate |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0073123B1 (en) * | 1981-08-21 | 1987-04-01 | National Research Development Corporation | Blood pressure measurement |
| FR2524792B1 (en) * | 1982-04-13 | 1985-09-27 | Fenestraz Louis | METHOD FOR MEASURING CARDIO-VASCULAR VALUES AND DEVICE FOR IMPLEMENTING SAME |
| JPS61187836A (en) * | 1985-02-15 | 1986-08-21 | 株式会社 津山金属製作所 | Pulse meter |
| GB8628698D0 (en) * | 1986-12-01 | 1987-01-07 | Kon Israel | Pulse rate detector |
| JPH02257929A (en) * | 1989-03-09 | 1990-10-18 | Makutaa Kk | Instrument for measuring transmissivity through living organism |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1962335B2 (en) * | 1969-12-12 | 1976-11-11 | Hellige Gmbh, 7800 Freiburg | METHOD FOR ERROR-FREE DETECTION OF THE PERIPHERAL PULSE AND ARRANGEMENT FOR PERFORMING THE METHOD |
| AR200173A1 (en) * | 1973-02-08 | 1974-10-24 | Detection Sciences | DIAGNOSTIC INSTRUMENT FOR MONITORING THE MICROCIRCULATORY SYSTEM OF A PATIENT |
| US3993047A (en) * | 1974-07-10 | 1976-11-23 | Peek Sanford C | Instrumentation for monitoring blood circulation |
| US4063551A (en) * | 1976-04-06 | 1977-12-20 | Unisen, Inc. | Blood pulse sensor and readout |
| DE2727138A1 (en) * | 1976-06-17 | 1977-12-29 | Bentley Lab | Portable heart beat frequency meter - with emission of radiation pulses according to tissue density |
-
1980
- 1980-02-21 DE DE19803006477 patent/DE3006477A1/en not_active Withdrawn
-
1981
- 1981-02-18 FR FR8103173A patent/FR2476472A1/en not_active Withdrawn
- 1981-02-18 GB GB8105028A patent/GB2070240B/en not_active Expired
- 1981-02-19 JP JP2230181A patent/JPS56132938A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4539997A (en) * | 1981-10-28 | 1985-09-10 | Nederlandse Centrale Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek | Method and device for controlling the cuff pressure in measuring the blood pressure in a finger by means of photo-electric plethysmograph |
| US4510940A (en) * | 1981-11-27 | 1985-04-16 | Nederlandse Centrale Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek | Plethysmograph pressure correcting arrangement |
| GB2150725A (en) * | 1983-11-30 | 1985-07-03 | Aisin Seiki | Safety apparatus for a road vehicle |
| GB2165352A (en) * | 1984-09-06 | 1986-04-09 | Ablec Ltd | Measuring heart rate |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2476472A1 (en) | 1981-08-28 |
| GB2070240B (en) | 1983-08-17 |
| DE3006477A1 (en) | 1981-09-03 |
| JPS56132938A (en) | 1981-10-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |