JPH0321174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic blood pressure monitor that detects Korotkoff sounds (K sounds) using a microphone (K sound sensor) and digitally displays systolic and diastolic blood pressure.

In general, the loudness of the K sound varies from person to person, and even within the same person, it varies depending on the time of day or physical condition. However, in conventional electronic blood pressure monitors, the K sound detection sensitivity, that is, the K sound detection threshold for distinguishing between K sounds and noise, is constant, so for people with loud K sounds, the systolic blood pressure may be lower than the actual level. It also had the disadvantage that it was measured too high, and for people with a low K sound, it was measured lower than it actually was. Furthermore, in the blood pressure monitor itself, most of the K sound sensors have characteristics that change with temperature, and furthermore, there are variations in temperature characteristics, so there is a drawback that complete compensation cannot be achieved under fixed temperature compensation conditions.

Blood pressure measurement is not based on the volume of the K sound itself;
The cuff pressure is measured when the sound begins to be heard and the cuff pressure when the K sound is no longer heard.
When the K sound becomes inaudible, it is when the K sound is completely buried in the noise, and since the strength of the K sound and the strength of the noise are in a proportional relationship as mentioned above, it is difficult to identify the K sound. Level (level at which the K sound can be heard if the output of the K sound sensor is higher than this)
If it is set in proportion to the noise level, it becomes possible to measure blood pressure based on a fixed standard regardless of individual differences in the magnitude of the K-sound and noise, variations in temperature characteristics of the sensitivity of the K-sound sensor, etc. From this perspective, when determining the threshold for K sound detection, the noise level is detected to suppress the influence of noise, the threshold is determined based on this output, and the blood pressure is set to detect the K sound. The time was right.

However, in the above-mentioned blood pressure monitor, the output signal of the K sound sensor is continuously detected and taken in as a noise signal, so when the K sound occurs, this K sound signal is also reflected in the threshold value, and the threshold value The level always tended to be high, making it impossible to accurately determine the timing at which the K sound began to be heard and when it disappeared, making it impossible to accurately measure blood pressure.

The present invention has been made to solve the above problems, and by capturing only the noise signal in the section where no K sound occurs and controlling the threshold for K sound detection, it is possible to detect the K sound with extremely high accuracy. The purpose is to detect and improve blood pressure measurement performance. Since the K sound is synchronized with the pulse sound, the present invention achieves the above object by detecting the pulse sound and detecting noise between the pulse sound and the pulse sound.

An embodiment of the present invention will be described in detail below based on the drawings. FIG. 1 shows a block diagram of the electronic blood pressure monitor of the present invention. Reference numeral 1 denotes a pressure sensor, the output voltage of which is amplified by a differential amplifier 2, and a pulse sound is detected by a transducer 3. That is, when the signal voltage obtained by amplifying the output of the transducer 3 with the amplifier 4 exceeds the reference voltage _V1 , the output of the voltage comparator 5 is inverted, and a pulse representing the pulse sound detection section is obtained. The inverter 6 outputs pulses only in the section where no pulse sound is detected.
It is input to AND gate 9. Reference numeral 7 denotes a circuit for detecting that the cuff pressure is being reduced. When decompression is started and preparations for inputting the K sound are completed, the output of this decompression detection circuit 7 is inverted and the AND gate 9 is opened. In this state, the pulse of the above-mentioned pulse sound pause period is
When input to the counter decoder circuit 10 of the analog multiplexer through the AND gate 9, 1
Analog gates 16a, 16b...
... are opened, and the output voltage of the integrator 15 is sequentially taken into the memories 17a, 17b, etc. On the other hand, the K sound component extracted from the output of the K sound sensor 11 by the transducer 12 is amplified by the amplifier 13 and then rectified by the full wave rectifier 14, and this output signal is sent to the voltage comparator 19. and is smoothed by an integrator 15. The capacitor of this integrator 15 is discharged by the switch 20 during the pulse sound detection period, so that only the noise voltage during the pulse-free period is integrated. The output voltage of the integrator 15 represents the noise level in each section, and the noise level in each section is sequentially changed to the analog gates 16a, 16b, . . .
are latched to the memories 17a, 17b, . . . through the memory devices 17a, 17b, . Of course this memory device 17a
Although the object of the present invention can be achieved with only one circuit, in this embodiment, the average value of multiple circuits is taken by the average value circuit 18 to prevent the influence of sudden fluctuations in the noise level. be. FIG. 2 shows the simplest example of a specific circuit, in which capacitors C ₁ to _{C 4} are used as the memory devices 17 a to 17 d, and the average value circuit 18 is closed immediately after the analog gates 16 b to 16 d are closed. It consists of switches Sb to Sd. The output voltage of the average value circuit is used as the reference voltage _V2 of the voltage comparator 19, and the other input of the voltage comparator 19, that is, the output voltage of the full-wave rectifier 14, is used as the threshold voltage _V2.
When the voltage exceeds 1, the output of the voltage comparator 19 is inverted, and the first K sound detection circuit 8 detects the first K sound. The average value circuit 1 is determined by this 1st K sound detection output.
8 is held, and the average value of the noise level at this time is used as the threshold value _V2 until the end of the measurement. According to this configuration, the noise levels for the four most recent sections up to the detection of the 1st K tone are stored, so the noise level at the time of measurement can be compensated with extremely high accuracy.

In the above embodiment, the K sound detection threshold set in the comparator is changed depending on the noise level, but the reference signal set in the comparator 19 is kept constant.
The gain of the amplifier 13 at the front stage may be changed depending on the noise level. When we say that the threshold value is relatively changed in the claims, we mean to include this point.

As mentioned above, in setting the K sound discrimination threshold, the blood pressure monitor of the present invention measures the noise level only by the K sound sensor output between K sounds, and uses this noise level to determine the K sound discrimination threshold. Because the threshold is set, the detection output of the K sound itself is not mixed into the noise level data as in the past, and this data is accurate.
The threshold value is not set excessively, and therefore the accuracy of blood pressure measurement can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of the electronic blood pressure monitor of the present invention, and FIG. 2 is a specific circuit diagram of the main parts of the same. 1 is a pressure sensor, 2 is a differential amplifier, 3 is a transducer, 4 is an amplifier, 5 is a voltage comparator, 6 is an inverter, 7 is a cuff pressure reduction detection circuit, 8 is a 1st K sound detection circuit , 9 is
AND gate, 10 is a counter decoder circuit, 1
1 is the K-sound sensor, 12 is the waveform, 13 is the amplifier,
14 is a full-wave rectifier, 15 is an integrator, 16 is an analog multiplexer, 16a to 16d are analog gates, 17a to 17d are memories, 18 is an average value circuit, 19 is a voltage comparator, and 20 is a switch.

Claims (1)

[Claims] 1. In an electronic blood pressure monitor that has a pressure sensor that detects cuff pressure and a K-sound sensor that detects Korotkoff sounds (hereinafter referred to as K-sounds), pulse sounds are detected from the output of the pressure sensor using a wave detector. The noise level in the blood vessel is detected by averaging the output of the K sound sensor in the section where the signal is below a preset reference value VI, and the threshold for K sound detection is linked to the above noise level. A blood pressure monitor characterized by relative changes.