JPS6122564Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a method for obtaining data regarding heartbeats and pulses from electrical signal waveforms corresponding to heartbeats and pulses.
This invention relates to a pulse detection circuit.

A method of detecting a heartbeat or pulse and using it as a signal when measuring the heartbeat or pulse rate per unit time or measuring blood pressure, etc. is already well known. In the field of medical electronics, it is customary to detect a heartbeat as an electrical signal called an electrocardiographic signal, and to detect a pulse as an electrical signal, blood flow in a peripheral blood vessel is detected as an electrical signal using a photoelectric converter. The magnitude of these electrical signals varies greatly from person to person, and even for the same person, it changes significantly depending on the environment at the time of measurement, physical condition, and the like. Therefore, in order to reliably detect a signal, the detection level, that is, the threshold value of the comparator, must be extremely low, which tends to cause erroneous observations due to noise. This problem will be explained using a heartbeat wave as an example.

FIG. 1 is a diagram showing one of the heartbeat waves. A heartbeat wave generally consists of an R wave having the largest amplitude, and P waves, T waves, etc. before and after the R wave. Normally, processing such as detecting R waves and counting the number per unit time is performed. However, this R
Since the T wave that follows the wave often has an amplitude close to that of the R wave, even if the detection level described above is substantially automatically adjusted using an automatic gain control circuit, for example, the level may not match the level of the T wave. As the area approaches, it becomes extremely difficult to reliably prevent detection of T-waves.
In order to solve this problem, the present applicant proposed an invention entitled "Heartbeat, Pulse Detector" (Japanese Patent Application No. 55-47992).
have already applied. This detector circuit will hereinafter be referred to as a conventional circuit. This conventional circuit is R
After detecting the wave, the detection level is maintained at a sufficiently high value corresponding to the peak value of the R wave for an appropriate time to prevent detection of the T wave, and when detecting the R wave, the detection level is set appropriately. By lowering the value to a certain value, this can be detected reliably and furthermore, erroneous observation due to external noise can be prevented.

Moreover, if a noise signal that is extremely larger than the normal input signal is input due to artifacts (noise prevention due to body movement, etc.), the voltage stored in the time constant circuit for determining the threshold value will be extremely high in the above configuration. and the detection level becomes extremely high. Therefore, the following R wave may not be detected for several beats.

An object of the present invention is to provide an improved heartbeat/pulse detection circuit that can prevent malfunctions as much as possible when an extremely large noise signal is input as described above.

In order to achieve the above object, the heartbeat/pulse detection circuit according to the present invention maintains the maximum value of an input wave through a diode with a time constant circuit consisting of a capacitor and a resistor connected in parallel, and then maintains the maximum value of the input wave at the above-mentioned time. In a heartbeat/pulse detection circuit that detects a heartbeat or pulse using a threshold value based on the voltage of a constant circuit, an abnormal input signal detection circuit is provided to detect an input signal exceeding the maximum level of a predicted normal input wave. The detection circuit is configured to attenuate the voltage of the time constant circuit with a smaller time constant when the detection circuit detects an abnormal input signal.

According to the above configuration, the above-mentioned problems are solved,
The purpose of the invention is fully achieved.

Hereinafter, the detection circuit according to the present invention will be explained in more detail with reference to the drawings and the like.

FIG. 2 is a circuit diagram showing an embodiment of the detection circuit according to the present invention. An electrocardiographic signal consisting of a train of pulses as described above with reference to FIG. 1 is input to input terminal 1, and an operational amplifier A ₁ (hereinafter referred to as (simply referred to as _A1 ). A ₁
forms a voltage comparator which produces an output when an input signal exceeding a threshold connected to its inverting input terminal is applied to its non-inverting input terminal.
Further, the electrocardiogram signal is connected to a non-inverting input terminal of an operational amplifier A ₂ (hereinafter simply referred to as A ₅ ) forming a peak hold circuit. A diode _D1 is connected between the output terminal and the inverting input terminal of _A2 .

A parallel circuit of capacitor C ₁ and resistor R ₁ forms a threshold voltage generation circuit.

The voltage of capacitor C ₁ is connected as a threshold value to the inverting input terminals of A ₁ and A ₂ .
The output of _A2 matches the input signal and charges the capacitor _C1 when the signal connected to the non-inverting input terminal is in the process of rising above the level of the inverting input terminal. When the input signal starts falling, the capacitor
The charge on C ₁ is slowly discharged through resistor R ₁ . That is, the threshold voltage gradually drops from the peak voltage to prepare for the next detection. The above configuration is common to the configuration of the conventional circuit described above.

Input terminal 1 is an operational amplifier for detecting abnormal input signals.
Connected to the non-inverting input terminal of A ₃ (hereinafter referred to as A ₃ ). The inverting input terminal of _A3 is connected to the reference voltage source N.
is connected to form a voltage comparator that produces an output when the voltage applied to the non-inverting input terminal is greater than the reference voltage. This voltage is set to a voltage that exceeds the maximum value of an electrocardiographic signal that is normally expected, that is, a voltage that can be considered to be noise without such an electrocardiographic signal. The time constant circuit has a resistor R ₂ as a collector load and a transistor T ₁ connected in parallel. The resistor R ₂ is selected to have a value sufficiently smaller than the resistor R ₁ of the time constant circuit. The output of A ₃ is connected via a diode D ₂ to a capacitor C ₂ , to which a series circuit _of resistors R ₄ and R ₃ is connected in parallel. The base of the transistor T ₁ is connected to the resistor R ₄
and connected to the R ₃ connection point. When current is supplied to capacitor _C2 through _D2 , the transistor
T ₁ is turned on for a certain period of time determined by the time constant C ₂ ·(R ₃ +R ₄ ) and the voltage division ratio of R ₃ and R ₄ to discharge the charge of C ₁ .

Next, the operation of the circuit according to the above configuration will be explained with reference to the waveform diagram shown in FIG. 3, while comparing it with a conventional circuit.

Figure 3 shows an example in which the electrocardiogram signal previously explained in detail in Figure 1 appears at time points t1, _{t2 ... t7} , and noise occurs between time points _t2 and _t3 . ing. In the figure, the broken line indicated by a indicates the voltage at point a in FIG. 2, that is, the threshold voltage. b indicates the level of the reference voltage N for detecting abnormal input. Figure B shows the response output waveform of the conventional circuit described above, and Figure C shows the response output waveform of the circuit according to the present invention.

The R wave of the heartbeat pulse generated at time t ₁ shown in A is detected by A ₁ based on the threshold determined by the R wave of the previous heartbeat pulse, and a detection output O shown in C is sent out. The same applies to time t ₂ . Subsequently, when there is a noise input that exceeds the level indicated by the broken line b, an output appears at _A3 as shown in D until the noise input falls to the level b.
This causes the voltage on capacitor C ₂ to change as shown at E, and transistor T ₁ is turned on for a period shown at F, rapidly discharging the charge on capacitor C ₁ through R ₂ . As shown in the waveform a from the peak of the noise to t ₃ in A of the same figure, the threshold value decreases, so that the electrocardiographic signal generated at the time t ₃ can be detected. In the conventional circuit, as shown in Figure 3 a', the threshold value attenuates with a large time constant (C ₁ R ₁ ), so it is difficult to detect electrocardiographic signals occurring at times t ₃ , t ₄ , and t ₅ . I can't.

As is clear from the above comparison, according to the present invention, even if noise occurs, malfunctions can be kept to a minimum. Also, take measures such as detecting the occurrence of output at _A3 and activating a circuit that indicates the occurrence of noise input to display an alarm, or stopping the operation of the entire circuit for a certain period of time. You can also do it. Furthermore, when the number of output pulses per unit time is displayed using a counter or the like, it is also possible to correct it using the number of outputs generated in _A3 .

The above was explained in detail using heartbeat detection as an example.
This circuit is equally applicable to pulse detection.

[Brief explanation of the drawing]

FIG. 1 is a graph for explaining electrocardiographic signals, FIG. 2 is a circuit diagram showing an embodiment of the detection circuit according to the present invention, and FIG. 3 is a waveform diagram for explaining the operation. A ₁ , A ₂ , A ₃ ... operational amplifier, D ₁ , D ₂ ... diode, R ₁ , R ₂ , R ₃ , R ₄ ... resistor, T ₁ ... transistor, C ₁ , C ₂ ... Capacitor, N...Reference voltage source.

Claims (1)

[Scope of utility model registration request] The maximum value of the input wave is held by a time constant circuit consisting of a capacitor and a resistor connected in parallel through a diode.
The heartbeat/pulse detection circuit detects subsequent input waves using a threshold based on the voltage of the time constant circuit, and includes an abnormal input signal detection circuit that detects an input signal that exceeds the maximum level of a predicted normal input wave. A heartbeat/pulse detection circuit, characterized in that the voltage of the time constant circuit is attenuated with a smaller time constant when the abnormal input signal detection circuit detects an abnormal input signal.