FR2476472A1 - CIRCUIT FOR MEASURING CARDIAC PULSATION - Google Patents

Abstract

WHEN MEASURING THE HEART RATE WITH A SOURCE OF LIGHT LIGHTING THE BLOOD FLOWING TISSUE, THE DEFINITION OF THIS HEART RATE IS INFLUENCED NOT ONLY BY DIFFERENCES IN TRANSMISSION BUT ALSO BY ACTIVITIES OF THE VASOMOTRIC SYSTEM BLOOD VESSELS. THE CIRCUIT CONFORMING TO THE INVENTION INCLUDES AN ADJUSTMENT CIRCUIT SUCH AS THE OUTPUT SIGNAL OF THE LIGHT RECEIVER 14 MEASURING THE TRANSMITTED RADIATION REMAINS CONSTANT, THE TRANSMISSION DIFFERENCES AND THE TRANSMISSION FLUCTUATIONS BEING WITHOUT INFLUENCE ON THE PULSE DEFINITION. HEART, AND ALSO COMPENSATES VASOMOTOR ACTIVITIES. TO DO THIS, THE AVERAGE VALUE OF THE AMPLITUDE OVER SEVERAL PULSE PERIODS IS DETERMINED BY MEANS OF A CIRCUIT 16 AND THIS AVERAGE VALUE SERVES AS THE ACTUAL VALUE FOR THE CONTROL CIRCUIT GIVING PLACE TO THE STABILIZATION OF THE ELECTRIC SIGNAL IN THE FORM OF D 'IMPULSE. THIS STABILIZED SIGNAL IS PROVIDED TO A VALUE DEFINING DEVICE 12, 13. THE ACTUAL VALUE CHARACTERIZING THE VASOMOTOR ACTIVITIES IS ALSO REPRODUCIBLE. APPLICATION: HOSPITAL EQUIPMENT.

Description

"Circuit for measuring heartbeat."

  The invention relates to a circuit for measuring the pulse

  a person's heart with a light source.

  of a light receiver providing a measurement signal corresponding to the attenuation at which

  the place of measurement, of a filter which, on the basis of that

  measurement signal, isolates a signal in the form of an impulse corresponding to

  heartbeat and supplied to a value-setting device, and a regulator which, depending on the measurement signal, controls the light source

  so that the average value of the input signal of the regula-

  at least approximately constant.

  Such a circuit is known from the German document "Offenlegungsschrift" NI 27 27 138. During the measurement, the

  The light from the light source is controlled by a fold of

  the epidermis of the auricle of the ear, by the top of a finger or something like that, while the receiver of light measures the luminous current which is produced on the other side of the place of measurement. This luminous current comprises, as amplitude modulation, information about the variation of the blood content on the measurement site, and with the aid of this information is defined the pulsation

  heart rate using the value setting device.

  The controller ensures that the measuring signal

  it is largely independent of the individual differences in the optical properties of the epidermis and the tissue (transmission), which significantly facilitates the definition of the value of the

measurement signal.

  However, also when using the device con-

  disturbances are possible and hinder the definition of

  precise measurement value. The inventor realized that these disturbances are caused by

  vaso-motor activities of the blood vessel system.

  As a consequence of these activities, the blood vessels shrink or expand, which changes the volume of

  transported blood and results in a variation of

  the measurement signal. These vasomotor activities are: -

  generally much slower than heartbeat

of the person examined.

  The object of the invention is to provide a circuit which

  belongs to the genus mentioned in the preamble and in whose use vasomotor activities occurring during

  the measure hardly influence the accuracy of the

  Measurement result obtained when measuring the pulse rate. For this purpose, the circuit according to the invention is remarkable in that it comprises a control circuit in front of

  stabilize the amplitude of the pulse-like signal

  in response to slow fluctuations in signal modulation

  the signal thus stabilized with regard to

  its amplitude is provided to the definition device

valuable.

  By the term "slow fluctuations" is meant here

  variations whose upper limit frequency is

  lower than the pulse rate. Activities __

  vasomotrices result as fluctuations in the amplitude of the

  pulse-shaped signal, and said feedback circuit

  This setting substantially eliminates these fluctuations, so that the value-defining device receives only a signal whose amplitude is practically constant and of which it is

easy to set the value.

  Another embodiment of the circuit according to the invention is remarkable in that the control circuit comprises a circuit of average value connected after the filter and providing an output signal corresponding to the average amplitude over several periods of the signal. in shape

  pulse. In the simplest case, this circuit of

  their average can be formed by series

  both a diode and a capacitor, shunted by a resistor

  this (rectifier circuit). The corresponding output signal

  to the average value of the signal amplitude in the form of im-

  several periods of this signal, is taken from

  capacitor frames which, in cooperation with the resistor

  tance, has a time constant equal to a few seconds.

  Yet another embodiment of the circuit according to the invention is remarkable in that between the filter and the average value circuit is connected an amplifier whose amplification can be controlled by the output signal of the average value circuit. Depending on the output signal of the average value circuit, the amplification coefficient of said amplifier is controlled to decrease when the output signal of the average value circuit increases, and

Conversely.

  Yet another embodiment of the circuit according to the invention is remarkable in that the signal of

  output of the average value circuit and the signal of a genera-

  setting value are used together to

  ve for the regulator, and that the guideline value thus

  increases when said average value decreases.

  In this way, the regulator that makes the signal

  of the transmission, thus also serves to eliminate fluctuations in the amplitude of the

  pulse, caused by vasomotor activities.

  When, for example on the basis of vasomotor activities,

  the amplitude of said signal decreases, the emission of the light source

  is increased to the point where the signal

again its original value.

  A last embodiment of the compliant circuit

  the invention is remarkable in that another circuit for de-

  value finish is connected to the output of the circuit of

  their average. With the aid of such a circuit according to the invention

  In addition to the heartbeat, it is therefore possible to

  also a parameter corresponding to the vaso-

  motor of the blood vessel system.

  The following description, next to the drawings

  annexed, all given by way of example, will make it

  how can the invention be realized.

  Figure 1 shows a circuit in which the

  right of measurement undergoes the influence of a pulsating beam of light.

  Figure 2 shows a circuit in which the

  right of measurement is influenced by a light whose

tensity-remains constant.

  A generator 1 provides a crenellated signal whose amplitude, frequency and width are constant.

  This signal is supplied to an amplifier 2 whose amplification

  The output of the amplifier is connected to a light source whose light intensity is a function of the output voltage of the amplifier 2.

  light, for example a diode 23 emitting infrared light,

  red. This diode 23 and a light receiver 14, for example a phototransistor, are placed so that

  during a measurement, said phototransistor 14 measures the intensity

  light emitted by the source 23 and attenuated on the

  right of measurement (21) by a tissue traversed by the blood, by

  example the tip of a finger or an earlobe.

  In the presence of the light intensity given in advance in

  Regarding the light source 23, the output signal.

  The light receiver 14 is a measure of the attenuation of light passing through the measurement location. The output signal of the phototransistor 14 also in the form of a pulse, but the amplitude of this pulse is not constant but fluctuates as a result of the blood situation on the spot

  measurement. However, this fluctuation or modulation is

  weakly weak. It reaches only about 1 X. This is why

  the receiver circuit 3 comprising the light receiver

  re 14 must be designed to eliminate to a large extent the parasitic light arriving near the receiver 14

  and to significantly prevent amplitude modulation by

  work point placement as a result of parasitic light.

  As is also the case in the response circuit

  German document 27 27 138, cited above, the elimination of

  nation of parasitic light is practically possible

  since the signal from the output electrode of the phototran-

  sistor 14 is supplied to the rest of the processing circuit via a capacitor which, under the action of a

  switched on and off in the rhythm of the impulse

  light is loaded up to the value-which corresponds to the parasitic light and which during the pulses of light-

  (open switch) is subtracted from the voltage

  signal at the output signal, so that the light

  razor is eliminated. The amplitude modulation caused by the parasitic light can be kept low

  that the phototransistor operates at a voltage of

  constant because its collector is connected to the emitter of a transistor whose base is connected to a

constant voltage.

  The output of the receiver circuit 3 thus makes available a signal in the form of a pulse whose frequency corresponds to that of the signal which is supplied by the generator 1 and whose amplitude is primarily a function of the constant attenuation on the measuring place and only second

  of the blood state of the tissue. Through a trans-

  impedance former 4, said signal is supplied to a bandpass filter 5 whose central frequency corresponds to the

  frequency (5 kHz) of the pulses provided by the generator 1-

  whose bandwidth is chosen in such a way that the

  transmission of sideband components

  blood pressure modulation is not practiced

  not less than the transmission factor for the center frequency. As a result, the parasitic frequencies outside the useful signal bandwidth

are therefore eliminated.

  At the output of the filter 5 is connected an amplifier

  6 whose amplification coefficient is gradually adjustable

  LEMENT. As a result, the very large variations in

  such as these occur when instead of the earlobe, the top of a finger (the transmission may

  in this case becoming 100 times smaller) is subject to

  influence of radiation, must be compensated for

"- '. -2476472

  6- that the only control circuit is not able to eliminate such variations. The output signal of the amplifier

  6 is supplied to an amplitude demodulator 18 whose behavior

  in time corresponds to that of a pass filter.

  low at upper limit frequency equal to approximately 100 Hz.

  the output signal of the demodulator 18 is formed by a

  constant voltage voltage which is proportional to the voltage

  their average of the output signal amplitude of the circuit

  receiver 3, as well as by an alternating voltage component

  superimposed, generated by the impulses of blood.

  The output signal of the demodulator 18 is supplied to the actual value input of a PI controller 7 and compared to the set value that a generator 8 provides. Through a band-locking element 22 which filters out the signal components from the blood pulses, the output signal of said PI-regulator 7 is supplied to the control input 24 of the adjustable amplifier 2. Therefore, the

  amplification coefficient of this amplifier 2-is com--

  - mandé so that in the case where the output signal of the amplifier 3 increases, said amplification coefficient

  decreases. In this way, it becomes possible, and this inde-

  apart from the transmission differences for a place of

  determined measure (earlobe or fingertip) of

  for the same person or for different persons, a constant signal amplitude on the output of the receiver circuit 3. In the presence of a constant signal on the value input of the regulator-PI 7, -the output signal 7Oreste still only proportional to the transmission of the radiated fabric. (If in the first instance, we neglect the low modulation that gives rise to the blood pulse signal). This measurement parameter which is available for example on terminal 15, can be evaluated as information about the transmission in the tissue, and reproduced. In addition, another amplification stage

  3 can be connected between point 15 and the

  production, another stage whose production amplification coefficient, another stage whose amplification coefficient can be modified gradually and in the opposite direction to that in which the amplification coefficient of the stage 6 varies, so that the product Amplification coefficients of the two amplification stages are constant and the reproduced signal is independent of the stage setting.

comparison 6.

  The band-locking element 22 connected between the output of the PI-regulator 7 and the control input of the adjustable amplifier 2 has the task of preventing the signal components coming from the blood pulse from influencing the setting, as this would also mean that the said signal components would be eliminated to a certain extent.

more or less big.

  Through a band-pass filter 9a which only passes the characteristic frequency components (0.5 Hz to Hz) for the pulse of blood, the signal

  output of the PI-regulator 7 is provided on one floor.

  cation 9 whose amplification coefficient can be

  The output 16 of the amplification circuit is therefore the seat of the signal in the form of a pulse, that is to say a signal whose gait corresponds to the state of the blood on. the place of measurement and hence the pulsations of blood or heartbeats of the person examined. By a threshold value switch connected to the output 16 of the amplifier stage 9, said signal can be digitized and brought in synchronism with the

  pulse frequency. In a counting circuit, cal-

  and reproduction 13, the frequency of the car-

  diaques can be provided in pulsations per minute.

  As already mentioned, vasomotor activities are

  to influence the amplitude of the impulse signal.

  which may have adverse effects on the pre-

  definition of value. The influence that

  Vasomotor tensions exert on the amplitude of the signal

  can be largely eliminated by a com-

  Dortant among others-a circuit of average value 10. This circuit provides a signal corresponding to the average value

  amplitudes over several impulse periods (i.e.

say over several seconds).

  In the simplest case, this circuit 10 may comprise a diode connected to the output of the amplifier stage 9,

  the other terminal of the diode being grounded through a

  denser shunted by a resistor whose ohmic value is such that it results in a time constant equal to a few seconds. The voltage at the plates of the capacitor corresponds to the mean value of the amplitude of the signal

  of pulse shape. This average voltage-value is

  denies an impedance transformer 11 whose output-17 puts

  therefore available a signal constituting a measure of

  vasomotor diseases of the blood vessel system. Through

  the link 19, this signal can be supplied in addition to the

  generated by the control value generator 8 and

  This is done in such a way that the setting value decreases when the signal amplitude in the form of the PI-regulator 7 is adjusted.

of impulse increases.

  Although this solution does not require the use of an additional regulator, it nevertheless has the disadvantage that also the DC voltage component of the signal of

  PI-7 regulator output is a function of the vaso-

  motor, so that the signal on point 15 is not a measure for transmission. It is possible to avoid

  this disadvantage when the output signal of the transforma-

  Impedance transmitter 11 is not supplied to the PI regulator. 7 through the link 19 but is provided, through the link 20, to the control input 91 of the amplifier stage 9 with an adjustable amplification coefficient, and this in particular

  so that the amplification coefficient of the am-

  9 decreases as the amplitude of the pulse-shaped signal increases, and vice versa. In both cases, the

  signal on the output 16 of the amplifier stage 9 is in-

  dependent. to a great extent vasomotor activities.

  This is why the circuit makes it possible to define the signal in

  form of impulse and the precise value of it inde-

  differences in transmission and fluctuations

  in vasomotor activities. Moreover, besides the pulse-shaped signal and its frequency, it is also possible to define, by measurement, the transmission in the measuring place and the vasomotor activities.

(signals on terminals 15 and 17).

  By the use of a light emitted in the form of an impulse,

  the operation of the circuit is very independent of

  from the surroundings of the measurement area.

  In the case where the measuring point can be protected to a sufficient extent in relation to the light of the environment

  however, it is possible to omit the generation of impulse

  and instead of these pulses, use a beam of light of constant intensity. It simplifies

  the circuit as shown in Figure 2 represents

  such a circuit, the corresponding parts of the figures

  1 and 2 being indicated by the same references.

  It is found that in this case, the pulse generator

  1 can be omitted, and instead of the coeffi-

  of adjustable amplification, it is possible to use

  a simple continuous voltage amplifier at the output of-

  which is connected the light source. The use of a

  bandpass 5 is no longer necessary, since

  when a light beam of constant amplitude is used

  te on the place of measurement, the formation of band signals

  lateral is impossible. It goes without saying that

  use of a demodulator may be omitted. The filter passes

  band 9a filters out the pulse-shaped signal

  only on the basis of the output signal of the regulator-

  PI 7. The output signal of the band-locking element 22 then serves as the input signal of the amplifier

DC voltage 2.

Claims (5)

RESELLS: ications   1.- Circuit for measuring the heartbeat of a person using a controlled light source, a   light receiver providing a measurement signal cor-   responding to the mitigation of the location   of a filter which, on the basis of said signal of measurement,   sure, isolates a pulse-shaped signal corresponding to   the heartbeat and provided to a device for defining   value, as well as a regulator which, depending on the measurement signal, controls the light source so that the average value of the input signal of the regulator remains constant at least approximately, characterized in that   this circuit comprises an adjustment circuit (9, 10, 11, 20) -   to stabilize the amplitude of the pulse signal compared to the slow fluctuations of the modulation of the measurement signal, and that the signal and stability in this   amplitude is provided to the definition device. nition of value (12, 13).   2. Circuit according to claim 1, characterized in that the control circuit comprises a circuit of value   medium (10) connected after the filter (9a) and supplied   an output signal corresponding to the average amplitude   over several periods of the signal in the form of a pulse.   3. Circuit according to claim 2, characterized in that between the filter (9a) and the average value circuit (10) is connected an amplifier (9) whose amplification   can be controlled by the output signal from the circui-t. average value.   4. Circuit according to Claim 2, characterized in that the output signal of the average value circuit (10)   and the signal of a setting value generator (8) serves   wind direction value set for the regulator (7), and that the guideline value thus formed increases when said average value decreases.   5. Circuit according to claim 2, characterized in that another value definition circuit is connected.   at the output of the average value circuit (10).