JPH07110274B2 - Ultrasonic heart rate measuring device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic heart rate measuring apparatus used when measuring a cycle of a biological signal, particularly a fetal heartbeat signal by an ultrasonic Doppler method. More specifically, it relates to a detection method for ultrasonic Doppler signals.

(Prior Art) As a detection method of an ultrasonic Doppler signal in this type of ultrasonic heart rate measuring apparatus, conventionally, a structure as shown in FIG. 6 has been generally used. In the figure, 1
Is an original oscillator, and 2 is a wave transmitter drive circuit for driving a wave transmitter 3 by a signal oscillated by the original oscillator 1. From the wave transmitter 3 driven by this drive circuit 2, a fetal heart The ultrasonic signal us is transmitted to the measured object A.

Reference numeral 4 denotes a wave receiver, which is a reflected wave signal from the object A to be measured.
receive rs. Reference numeral 5 is a preamplifier, and 6 is a multiplier, which multiplies the original oscillation signal from the original oscillator 1 by the signal received by the wave receiver 4 and amplified by the preamplifier 5. Reference numeral 7 is a low-pass filter (hereinafter referred to as LPF), which removes high frequency components of the output signal from the multiplier 6. A compressor 8 limits the signal amplitude to a predetermined value. An envelope detector 9 detects the envelope of the output signal from the compressor 8 and outputs it.

In the case of the ultrasonic Doppler signal detection method having the above-mentioned configuration, as shown in FIG. 7A, the ultrasonic signal from the transmitter 3 is transmitted from the transmitter 3 to the measured object A that moves back and forth along the x-axis. sent us, and the reflected wave signal rs from the measured object A
When the wave is received by the wave receiver 4, the output signal from the above-mentioned compressor 8 corresponds to the waveform of the reciprocating motion of the object A to be measured as shown in FIG. 7B (a). Such a waveform is input, and a signal having such a waveform is input to the envelope detector 9 and the envelope is detected, whereby the reciprocating motion of the object A to be measured as shown in FIG. 7B (c). A detection output with the same sign is obtained for both positive and negative waveforms, and two pulses are output for one heartbeat.

Further, in addition to the above-mentioned configuration, as disclosed in, for example, Japanese Patent Laid-Open No. 54-105875, among reflected wave signals obtained by a probe, the systole of cardiac activity There has been known a device in which a pulse is generated by detecting a transition point between the pulse and the diastole and the heart rate is measured by counting the pulse.

(Problems to be Solved by the Invention) However, among the above-mentioned conventional techniques, in the general one shown in FIG. 6, two pulses are output for each reciprocating movement of the measured object, Alternatively, there may be one output pulse depending on the reciprocating movement, so when measuring the heart rate by counting pulses, it is easy to reach a double count value or a half count value.
There has been a problem that a predetermined heart rate cannot be measured accurately.

In the latter disclosed in Japanese Patent Laid-Open No. 54-105875, although the reciprocating direction of the measured object can be detected, the upper sideband output and the lower sideband output are baseband Since it is a plastic signal, it is indispensable to install envelope detection means at the latter stage of them and perform subtraction processing on the output thereof, which complicates the circuit configuration. In addition, there is a problem that the result of the subtraction process may not be accurate when the moving speed of the measured object is slow, which has a drawback that the measurement accuracy of the heart rate is adversely affected.

The present invention has been made in view of the above circumstances, and can output one pulse for one heartbeat, can measure the heart rate with extremely high accuracy, and has an overall circuit configuration. It is an object of the present invention to provide an ultrasonic heart rate measuring device that can be made simple.

(Means for Solving the Problem) In order to achieve the above object, an ultrasonic heart rate measuring apparatus according to the present invention is an ultrasonic signal that creates two signals having a constant angular frequency and different phases by 90 °. Creating means, a wave transmitter that drives an ultrasonic signal to an object to be measured by being driven by one of the two signals, and receives a reflected wave signal from the object to be measured. The wave receiver, the multiplying means for multiplying the two signals output from the ultrasonic signal generating means by the signal received by the wave receiver, and the phases of the output signals of these multiplying means are each 90 °. Phase shifting means for shifting the phase, a signal obtained from one output signal of these phase shifting means and the other output signal of each of the multiplying means, and the other output signal of the phase shifting means and one output signal of the multiplying means Multiply by multiplying with the signal obtained from And the stage,
And a subtracting means for subtracting the output signals of these multiplying means.

(Operation) According to the present invention, the ultrasonic wave signal is transmitted to the object to be measured by driving the wave transmitter by the signal of either one of the two signals having the constant angular frequency and the phases different from each other by 90 °. Is
And the reflected wave signal from the measured object is received by the wave receiver. The received signal undergoes a Doppler shift proportional to the movement of the measured object, and the angular frequency of this Doppler shift includes positive and negative values according to the movement of the measured object. By detecting such positive and negative signs through each operation of multiplication, 90 ° phase shift, multiplication and subtraction, one pulse is output for one reciprocation of the measured object, The desired heart rate can be accurately measured.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an ultrasonic Doppler signal detection system in an ultrasonic heart rate measuring apparatus according to the present invention. In the figure, 1 to 5 and A are the same as the conventional example shown in FIG.
The detailed description thereof is omitted.

In FIG. 1, reference numeral 10 denotes a frequency divider (or a phase shifter), which are signals sin ω ₀ t and cos ω ₀ t whose angular frequency ω ₀ is constant by the original oscillator 1 and whose phases are different from each other by 90 °. To create. Here, t represents time, and in the following description, to avoid complexity, t is omitted in the unmistakable part in the description.

The angular frequencies ω ₀ of these two signals are set so as to match the resonance frequencies of the wave transmitter 3 and the wave receiver 4, and one of them, the signal sin ω ₀ , drives the wave transmitter 3 The ultrasonic signal us is transmitted to the object A to be measured.

11A and 11B are multipliers, and these multipliers 11A and 11B are two signals sin output from the frequency divider (or phase shifter) 10.
ω ₀ and cos ω ₀ are multiplied by the received signal S {= sin (ω ₀ + ωd)} output from the preamplifier 5, respectively. However, ωd is the angular frequency of the Doppler shift. 12A, 12
B is an LPF, which removes the component of the angular frequencies 2ω ₀ + ωd of the two signals S ₀ and C ₀ output from the multipliers 11A and 11B. 13
A and 13B are compressors that limit the amplitude of each input signal to a predetermined value.

14A and 14B are 90 ° phase shifters, and the above compressors are 13A and 13B.
The phases of the output signals S ₁ and C ₁ from each are shifted by 90 °.

15A and 15B are multipliers, and these multipliers 15A and 15B are signals S ₁ and C ₁ output from the above-mentioned compressors 13A and 13B and having a phase difference of 90 ° and outputs from the above 90 ° phase shifters 14A and 14B. signal
Multiply S ₂ and C ₂ . 16 is a subtractor, which is the multiplier 15A, 15B
The output signals S ₃ and C ₃ are subtracted and detected and output.

Next, the detection operation of the ultrasonic Doppler signal in the ultrasonic heart rate measuring apparatus having the above configuration will be described.

The original oscillator 1 and the frequency divider (or phase shifter) 10 allow the two angular frequency ω _{0 to} be constant and to coincide with the resonance frequencies of the transmitter 3 and the receiver 4 and to be different in phase from each other by 90 °. Signal sin
Create ω ₀ t and cos ω ₀ t. One of these signals si
By driving the wave transmitter 3 via the wave transmitter driving circuit 2 by n ω ₀ t, the ultrasonic signal us is sent to the object A to be measured and the object to be measured as shown in FIG. 2A. Object A
The reflected wave signal rs from is received by the wave receiver 4.

The signal rs thus received is x of the object A to be measured.
It is subjected to Doppler shift proportional to the reciprocating motion along the axis, and its angular frequency ωd shows positive and negative signs due to the action of the measured object A as shown in Fig. 2B (a), and this is detected. By doing so, a detection output as shown in FIG. 2B (b) can be obtained. The details of the operation described above will be described below.

The signal S received by the wave receiver 4 is S = Asin (ω ₀ t + ωdt + α) (1) Here, A is the amplitude and α is the angular velocity (constant). Since A and α are not essential, A
= 1 and α = 0, S = sin (ω ₀ + ωd) t (2), which is output from the preamplifier 5.

Next, the output signal S from the preamplifier 5 and the output signal from the frequency divider (or phase shifter) 10 are 90 ° relative to each other.
The signals sin ω ₀ and cos ω ₀ having different phases are respectively multiplied by the multipliers 11A and 11B, and the following two signals S ₀ and C ₀ are output.

2 · S ₀ = 2 · S · sin ω ₀ t = 2 · sin (ω ₀ + ωd) t · sin ω ₀ t = cos ωdt−cos (2ω ₀ + ωd) t (3) 2 · C ₀ = 2 · S · _{cosω 0 t = 2 · sin (} ω 0 + ωd) t · cosω 0 t = sin (2ω 0 + ωd) t + sinωdt ...... (4) Next, the above-mentioned (3), is the angular frequency in the equation (4) 2
The component of ω ₀ + ωd is removed by LPF12A, 12B, and then
Input to the compressors 13A, 13B, where (1) above
Approximately a predetermined value regardless of the magnitude of the amplitude A shown in the formula
Limited to S ₁ and C ₁ .

When the measured object approaches, ωd ≧ 0,
Since ωd <0 when moving away, the physical observation waveform is S1 = cosωdt (5) when ωd ≧ 0 (5) C1 = sinωdt (6) When ωd <0, S1 = cosωdt = cos (- ωd) t = cos | ωd | t (9) C1 = sin ωdt = −sin (−ωd) t = −sin | ωd | t (10)

The outputs S ₁₁ and C ₁₁ from these compressors 13A and 13B are input to the 90 ° phase shifters 14A and 14B, respectively, and are phase-shifted by 90 ° to become signals S ₂ and C ₂ . These S ₂ and C ₂ are, when ωd ≧ 0, S2 = cos (ωdt−π / 2) = cos (π / 2−ωdt) = sin ωdt (7) C2 = sin (ωdt−π / 2) = -Sin (π / 2-ωdt) = -cosωdt (8) When ωd <0, the phase is shifted by 90 °, and S2 = cos (| ωd | t−π / 2) = cos (π / 2− | ωd | t) = sin | ωd | t (11 ) C2 = −sin (| ωd | t−π / 2) = sin (π / 2− | ωd | t) = cos | ωd | t (12)

Next, by inputting S ₁ , C ₁ and S ₂ , C ₂ into multipliers 15A, 15B, respectively, creating S ₃ , C ₃ , and subtracting this by subtracter 16, the following detection Output is obtained.

That is, when the .omega.d ≧ 0, the (5) ~ (8) C3 -S3 = S2 · C1-S1 · C2 = sinωdt · sinωdt-cosωdt · from equation ^{(-cosωdt) = sin 2 (ωdt} ) + cos 2 ( ωdt) = 1 (13), and when ωd <0, C3−S3 = S2 · C1−S1 · C2 = sin | ωd | t ・ (−sin | ωd | t) −cos | ωd | t ・ −cos |
ωd | t = sin ² | ωd | t−cos ² | ωd | t = −1 (14).

As is clear from the above equations (13) and (14), the detection output becomes a positive or negative constant output that matches the sign of the angular frequency ωd, and the measured object as shown in FIG. A rectangular wave detection output corresponding to the reciprocating motion of the object A can be obtained.

In the above embodiment, a frequency divider (or phase shifter) sin .omega ₀ the output of the 10 showed a cos .omega _0, which need not necessarily be sinusoidal, for example, using a Ic logic circuit, the As shown in FIGS. 3 (a), (b), and (c), two signals having different 90 ° phases may be created.

In addition, the multipliers 11A and 11 arranged in the latter stage of the preamplifier 5
Instead of B, as shown in FIG. 4, a switching circuit composed of open drain logic circuits 11A1 and 11B1 and a transistor Tr may be used.

As shown in FIG. 5A, the 90 ° phase shifters 14A and 14B branch the output signals S ₁ and C ₁ from the compressors 13A and 13B into two, respectively, and output the branched signals. Two circuits 13A1, 13A2, 13B1, 13B2 so that the phase difference is 90 °.
It may be configured by using each of the circuits 13A1 and 13A in this case.
As shown in FIG. 5B, 2, 13B1 and 13B2 are composed of resistors R and R1, a capacitor C, and an operational amplifier OP, so that
As shown in the phase shift characteristics in the figure, it is possible to widen the frequency range in which the 90 ° phase can be shifted. In order to expand the frequency range in which the 90 ° phase shifter can perform the 90 ° phase shift, each of the circuits 13A1, 13A2, 13B1 and 13B2 may be connected in series in plural stages.

Further, a differentiating circuit may be used as the 90 ° phase shifting means.

(Effect of the invention) As described above, according to the present invention, with respect to the reciprocating movement of the object to be measured, a rectangular wave detection output having positive and negative signs corresponding to the movement is obtained, and Since the direction can be detected directly, one pulse is output for each heartbeat of the measured object, and by counting the pulses, the desired heart rate can be measured very accurately and highly accurately. It's big.

Moreover, the reciprocating motion of the object to be measured can be directly output as a pulse, and no envelope detection means or subtraction processing means for the output thereof is required. Therefore, the circuit configuration of the entire device is simplified and the cost is low. A highly accurate ultrasonic heart rate measuring device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an ultrasonic Doppler signal detection system in an ultrasonic heart rate measuring apparatus according to an embodiment of the present invention, FIG. 2A is an explanatory view of a main part at the time of measurement, and FIG. 2B is FIG. 3 is a waveform diagram for explaining the detection operation, FIG. 3 is a signal waveform diagram showing another method of creating two signals, FIG. 4 is a circuit configuration diagram of a main part showing another embodiment of the present invention, and FIG. FIG. 5B is a block diagram of an essential part showing another embodiment of the present invention, and FIG.
FIG. 5C is a circuit configuration diagram of a main part of the figure, FIG. 5C is a phase shift characteristic diagram of FIG. 5B,
FIG. 6 is a block diagram showing a configuration of an ultrasonic Doppler signal detection method in a conventional general ultrasonic heart rate measuring device,
FIG. 7A is an explanatory view of the main part at the time of measurement by the one shown in FIG.
FIG. 7B is a waveform diagram for explaining the detection operation according to the conventional example. (Explanation of symbols) 1 ... Original oscillator, 3 ... Transmitter, 4 ... Receiver, 10 ...
Frequency divider (or phase shifter), 11A, 11B, 15A, 15B ... Multiplier, 14A, 14B ... 90 ° phase shifter, 16 ... Subtractor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-51-126171 (JP, A) JP-A-54-105875 (JP, A) JP-A-51-145375 (JP, A) JP-A-52- 123582 (JP, A) JP 60-85372 (JP, A) JP 53-46188 (JP, A) Actual development 53-148586 (JP, U)

Claims (1)

[Claims] 1. An ultrasonic signal producing means for producing two signals having a constant angular frequency and a phase difference of 90 °, and an ultrasonic signal to be measured driven by any one of the two signals. A wave transmitter for sending to the object, a wave receiver for receiving a reflected wave signal from the object to be measured, two signals output from the ultrasonic signal creating means, and a wave received by the wave receiver. Means for multiplying the respective output signals, phase shifting means for shifting the phases of the output signals of the multiplying means by 90 °, output signals (S2) of one of these phase shifting means, and the other of the multiplying means. Signal (C1) obtained from the output signal of
And multiplying means for multiplying the other output signal (C2) of the phase shifting means and the signal (S1) obtained from one output signal of the multiplying means, and output signals (S2.C1, S2) of these multiplying means.
1 · C2) An ultrasonic heart rate measuring device, characterized by comprising subtraction means for subtracting each other.