JPH0216137B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a fetal heart rate meter that counts the heart rate of a fetus using the ultrasonic Doppler method. Conventional Doppler fetal heart rate monitors based on the Doppler method detect periodicity and derive heart rate by extracting pulsatile components derived from the movement of the cardiac muscle or valves of the fetal heart. . However, although this method is well-developed, it still has some drawbacks. for example,
There are two points below. (1) If the fetal heart deviates from the directivity of the probe, there will be no signal and work will no longer be possible. This point cannot be completely resolved even if a wide-angle directional probe is used. (2) When observations are made during light work while walking, periodic movements of the mother's body produce periodic artifacts that are confused with heartbeats. From this point of view, even when attempting to observe the dynamics of fetal physiology, accurate observation has been difficult when the mother's body is under stress. In view of these points, an object of the present invention is to solve the above-mentioned problems.
The object of the present invention is to provide a fetal heart rate monitor for dynamic observation that solves the problems (1) and (2). In order to achieve such an objective, the present invention uses a carrier frequency (frequency of the sound wave transmitted by the probe) that is higher than the Doppler shift value of the artifact caused by the sudden movement of the mother's body in the ultrasonic Doppler method. ), only the pulsatile Doppler signal from the fetal artery blood flow exhibiting a Doppler shift of 0.3 per mil (0/00) or more is extracted using a filter, and the fetal heart rate is measured. . The present invention will be explained in detail below using the drawings. In the first place, the proper way to evaluate the blood flow velocity of a Doppler blood flow signal is to focus on the Doppler shift frequency or its distribution rather than its amplitude. However, if the Doppler blood signal is extracted through a bandpass filter whose center frequency is near the highest possible Doppler shift frequency and whose passband has a moderate cut at the bottom, it is possible to focus on the amplitude rather than the frequency. However, it is possible to obtain almost the same results as by focusing on the flow velocity. In addition, in the case where only the rising edge of blood pulsation is to be detected, the lower cut of the band pass filter may be made sharp. Such a filter corresponds to a Doppler filter in a broad sense, and the myocardium, valves, and body movement artifacts are all considered to be unnecessary components with low Doppler shifts. The present invention includes a bandpass filter that is compatible with a Doppler shift of about 0.3 to 1 bar mil relative to a carrier frequency, which is much higher than that of the conventional filter, and means for performing amplitude detection thereafter. FIG. 1 shows a block diagram of one embodiment. In the figure,
1 is a probe that transmits and receives ultrasonic waves to and from the subject (mother body); 2 is an oscillator that generates high-frequency energy to drive the probe; 3 is a Doppler receiver that obtains a Doppler shift signal from a reflected wave signal; 4 indicates a Doppler shift ratio of a Doppler filter (for example, a low-cut filter) that has a cut-off characteristic of at least 24 dB/octave or higher, which allows components of 0.3 to 1 per mil to pass through, but sharply cuts off components of less than that. , 5 is a detection circuit,
6 is a low-pass filter, and 7 is a binarization circuit. In such a configuration, the probe that is energized by the high frequency energy from the oscillator 2 and generates an ultrasonic wave then receives the reflected wave, converts it into an electrical signal, and outputs it. The Doppler receiver 3 obtains a Doppler shift signal from the frequency of the oscillator 2 (corresponding to the frequency of the sound wave transmitted by the probe) and this electrical signal. The next-stage Doppler filter 4 extracts only pulsatile Doppler blood flow signals in a useful range, that is, a Doppler shift ratio of about 0.3 to 1 per mil with respect to the carrier frequency. This filtering effect can suppress interference with blood flow signals due to maternal movement or fetal movement. After detecting this pulsating Doppler signal, a low-pass filter 6 removes its high-frequency components to obtain a pulsating waveform as shown in FIG. 2A. Next, this signal is applied to a binarization circuit 7 and binarized at a certain threshold level, thereby obtaining a pulse train signal as shown in FIG. 2B. The pulse signal obtained in this way is connected to a heart rate meter (not shown).
The fetal heart rate can be easily determined by inputting and measuring the fetal heart rate. That is, the present invention cuts periodic signals with large amplitudes from heart valves, etc., which are signal components with a Doppler shift of 0.30/00 or less relative to the carrier frequency, and
The heart rate is measured by capturing a periodic signal with a small amplitude from the arterial blood flow, which is a high component of ~10/00. By doing so, signal components with a low Doppler shift ratio caused by the movement of the mother's body or the like can be sufficiently removed. Further, since signals from heart valves and the like are not required, heart rate measurement can be continued even if the directivity of the probe deviates from the fetal center as long as a signal from any fetal arterial blood flow can be captured. Note that if a signal of 0.30/00 or less is captured, the signal from the heart valve can be captured, but the signal due to rapid body movement will be mixed in. Also, 0.15
If a signal of 0/00 or less is captured, it is almost impossible to remove the signal due to body movement. Further, signals of 10/00 or higher are due to noise inherent to the device, and signals in this region are unnecessary. FIG. 3 is a diagram showing another embodiment of the present invention. In the same figure, the waveform of the Doppler shift signal obtained through the filter 4 in the same manner as above is obtained by specifically determining its rising point with the zero-cross detector 21, and by activating the monostable vibrator 22 with the output of the detector. A pulse train signal consisting of pulses with a certain time width is obtained. When this pulse train signal is applied to a low-pass filter 6, a pulsating waveform is obtained in the same manner as in the case of FIG. 1, which is similarly determined and output by the binarization circuit 7 as a signal with a period corresponding to the fetal heartbeat. Note that the method for determining the period of the fetal heartbeat based on the output signal from the Doppler filter 4 is not limited to this embodiment, and a method using the Fourier transform method or autocorrelation method may be adopted. . Furthermore, with respect to fetal blood flow signals, it is necessary to distinguish between Doppler signals of fetal arterial blood flow and those of maternal artery blood flow, and to extract only the Doppler signals of fetal arterial blood flow. Physiological standard parameters are used to differentiate between the two types of arterial blood flow. In other words, as shown in Figure 4, from the envelope of a certain frequency band of the blood flow signal or the envelope of the spectrum viewed from a broadband perspective, we can calculate the length of the period t _d (shorter in the fetus), the stroke output If we focus on one or both of the rise times t _r (shorter in the fetus) of the flow pattern in the fetus, we can see that there are statistical differences as roughly shown in Table 1, so the Doppler signal of the fetal arterial blood flow It is possible to distinguish and extract only

[Table] That is, FIG. 5 shows an example of the configuration of a means for distinguishing blood flow signals between mother and child arteries, and in this figure, the maximum point and minimum point are Detection is performed by charge/discharge type peak followers 52, 53. Fig. 6 is a waveform diagram showing the working process, and Fig. 7 is a waveform diagram showing the working process.
An example of the circuit of the important part of the figure is shown. In FIG. 7, an amplifier A ₁ , a capacitor C ₁ ,
The part consisting of diode D ₁ , resistor R ₁ and current source CS ₁ forms a positive peak follower, and likewise A ₂ ,
The portion consisting of C ₂ , D ₂ , R ₂ and CS ₂ forms a negative peak follower. C ₁ and ₂ are charged only in the direction allowed by D ₁ and ₂ so as to follow the signal waveform (input pulse wave 51), but in the opposite direction they are charged only at a rate controlled by each CS ₁ and ₂ . cannot discharge, so
The terminal waveforms of C ₁ and C ₂ can only follow an uphill or downhill slope (in the same order) toward the top or bottom point of the corresponding side, as shown in FIG. 6, 61 and 62. While tracking, the output of A ₁ or A ₂ follows the input voltage, but when it cannot follow, a negative saturation value is output. The large amplitude rise and fall during this period are
It is differentiated by C ₃ to C ₆ and R ₃ to _{R 6} and applied to G ₁ to _{G 4} . When the exclusive OR gates G ₁ to _{G 4} are connected as shown, they each respond to a narrow pulse of a desired polarity. The results are summarized by G ₅ , and when any one of them arrives (in principle, they cannot come at the same time), an interrupt request is sent to the CPU (not shown), and the CPU immediately thereafter determines which one occurs on port U ₁ . Observe whether any interrupts occur. CPU
The work to be done includes measuring the time width between b and d as shown in Figure 6, and determining whether the signal source is the mother or child by taking into account that value and the data in Table 1 above. do. Note that measuring the time interval for each type of interrupt based on the interrupt using software is a well-known technique, and its explanation will be omitted here. In addition, when the above-mentioned heart rate value is measured based on the cardiac period τ, each period between d and d in Fig. 6 corresponds to τ,
Furthermore, since there is little variation in the timing of each d point due to the nature of the signal, it is most preferable to utilize this timing. Furthermore, mother and child can be distinguished based on T _r in FIG. 4 as described above, and, although palliative, it can also be done based on the time between c and d in FIG. 6. As explained above, the fetal heart rate monitor for dynamic observation of the present invention extracts a signal consisting of a component with a Doppler shift ratio of about 0.3 to 1 per mil to the carrier frequency. That is, the heartbeat cycle is obtained not from a signal from the fetal heart valve, etc., which has a low Doppler shift ratio, but from a signal from the fetal arterial blood flow, which has a high Doppler shift ratio. Therefore, it is possible to sufficiently remove signal components with low Doppler shift ratios caused by maternal movement, fetal movement, etc., and obtain a pulse train signal related only to the fetal heartbeat without these influences, making it possible to accurately measure the fetal heart rate. can. Additionally, if it is possible to capture signals from the blood flow in any of the fetal arteries, it is possible to obtain pulse train signals related to fetal heartbeat even if the directivity of the probe deviates from the fetal heart, making heart rate measurement easier. It can be carried out.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a fetal heart rate meter for measuring dynamics according to the present invention, FIG. 2 is an operational waveform diagram of each part in FIG. 1, and FIG. 3 is a diagram of another embodiment of the present invention. , Fig. 4 is a diagram for explaining the physiological standard parameters of arterial blood flow, Fig. 5 is a diagram showing the configuration of manual cutting for distinguishing between mother and child arterial blood flow signals, and Fig. 6 is a diagram for explaining the physiological standard parameters of arterial blood flow. A waveform diagram for explaining the operation, and FIG. 7 is a more detailed configuration diagram of a part of FIG. 5. 1... Subject, 2... Oscillator, 3... Doppler receiver,
4... Doppler filter, 5... detection circuit, 6... low pass filter, 7... binarization circuit, 21... zero cross detector, 22... monostable vibrator.

Claims (1)

[Scope of Claims] 1. Fetal heart rate obtained by applying a probe from above the maternal abdominal wall to obtain a Doppler shift signal based on the fetal arterial blood flow using the ultrasound Doppler method, and determining the fetal heart beat cycle from this signal. The meter is equipped with a Doppler filter that blocks components with a ratio of Doppler shift to the carrier frequency of about 0.3 permil or less, and by passing the Doppler shift signal through the Doppler filter, mainly components with a ratio of Doppler shift to the carrier frequency of about 0.3 to 1 permil are included. 1. A fetal heart rate monitor for dynamic observation, characterized in that it is capable of extracting a signal consisting of the following, and obtaining a signal related to the beating cycle of the fetal heart without being affected by maternal agitation or fetal movement. 2. The first aspect of the present invention is characterized in that the fetal heart rate value is obtained by detecting the periodicity of changes in the short-term average frequency of the fetal blood flow signal obtained through the Doppler filter.
Fetal heart rate monitor for dynamic observation as described in section. 3. With respect to the fetal blood flow signal obtained through the Doppler filter, the Doppler signal of the fetal arterial blood flow and that of the maternal artery blood flow are distinguished based on the length of the ejection period of the heartbeat stroke. A fetal heart rate monitor for dynamic observation according to claim 1.