JPS633613B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blood pressure monitor that measures blood pressure using Korotkoff sounds, and its purpose is to display the condition when blood pressure measurement is performed under good conditions. , other objectives are to reliably detect second-phase dullness in Korotkoff sounds and display blood pressure measurements in good conditions, to enable blood pressure measurements to be performed in correct conditions, and to provide guidance on measurement techniques. , the purpose is to improve.

Currently, the standard clinical method for indirect blood pressure measurement is
It is based on the auscultation method by Korotkov.
This method involves wrapping a cuff band around the subject's upper arm, injecting air into the cuff band, and applying pressure 20 to 30 mmHg higher than the expected systolic blood pressure, compressing the brachial artery and stopping blood flow. Next, the air pressure inside the cuff band,
That is, the cuff pressure is gradually exhausted at a rate of 2 to 3 mmHg/sec. Eventually, when the cuff pressure reaches the systolic blood pressure, the brachial artery opens slightly and blood begins to flow. At this time, damped vibrations called Korotkoff sounds (hereinafter abbreviated as K sounds) are generated in the lateral direction of the blood vessel wall. As the cuff pressure is further lowered, the K sound continues to occur in synchronization with the pulse, but eventually disappears when the artery opens sufficiently and the blood flow becomes constant. The cuff pressure when the K sound first occurs is the systolic blood pressure, and the cuff pressure before it disappears, that is, when the K sound last occurs, is the diastolic blood pressure.

Mr. Swan showed that the characteristics of the K sound can be distinguished into five points and four phases, as shown in Figure 1. At first, a weak crisp sound was heard (first
phase), then a dull tone occurs (phase 2), the tone becomes crisp and clear again (phase 3), and then it suddenly becomes a weak dull tone (phase 4). The beginning of hearing the first K sound is the first
point, and the transition points of each phase are the second to fourth points,
The fifth point is the point where the K sound disappears (actually, the last point heard). Generally, the first point is the systolic blood pressure and the fifth point is the diastolic blood pressure.

In conventional blood pressure measurements, the phase of this K sound is generally not controlled. or,
As a result of actual measurements, it was found that in many cases, the voiced sound of the second phase did not occur and the sound transitioned from the first phase to the third phase. Therefore, if you raise your arm before applying pressure and then lower your arm to take measurements, or if you take measurements by clenching and opening your hands several times before applying pressure,
It was found that the second phase of voiced sounds occurred in most cases, and that the K sound changed correctly from the first phase to the fourth phase. In addition, when second-phase dullness occurs, the amplitude of the K sound becomes larger than when it does not occur, making it easier to hear, increasing the S/N ratio, making blood pressure measurement easier, and reducing measurement errors. It was found that reliable measurements could be made.

The present invention has been made in view of this point, and by detecting and displaying whether or not second-phase dullness has occurred, it is possible to know whether blood pressure measurement was being performed under good conditions, and to ensure reliable blood pressure measurement. This allows measurements to be made. On the other hand, the clear sound waveform of the K sound is as shown in Figure 2 a, and the turbid sound waveform is as shown in Figure 2 b.
become that way. In Figures 2a and b, A is the output of the K sensor, and B is the output passed through a filter in the K sound range (approximately 20 to 200 Hz). The voiced sound is considered to be a small signal portion in the latter half of the K sound signal. Therefore, by paying attention to this time lag, voiced sounds can be detected. The present invention will be explained in detail below with reference to Examples.

In Fig. 3, 1 is a Korotkoff sound sensor (K
The K-sound sensor 1 consists of a microphone, etc., and the signal detected by the K-sound sensor 1 as shown in Figure 4a is passed through a Korotkoff sound filter (K-sound filter) 2 to extract only the K-sound signal as shown in Figure 4b. Detect.
This K sound signal is passed through the first comparator 3 to obtain an output as shown in FIG. 4c, and passed through the expansion circuit 4 to obtain a signal as shown in FIG. 4d. This signal is input to the control circuit 5. The process up to this point is the same as the conventional K sound detection method.

Next, a circuit for detecting voiced sounds will be explained. A certain period of time (approx.
10 to 100 msec), the gate signal generating circuit 7 generates a delayed signal as shown in FIG. Generates a gate signal of ~200msec). On the other hand, a signal as shown in FIG. 4g is obtained through a second comparator 8 which adjusts the output of the K sound filter 2 to a level suitable for detecting voiced sounds. This signal and the gate signal are passed through an AND gate 9 to detect the dullness of the K sound as shown in FIG. Further, the pressure within the cuff band 10 is detected by a pressure transducer 11 and input to the control circuit 5. In the control circuit 5, the pressure transducer 1 when the output of the expansion circuit 4 first occurs
The cuff pressure obtained from step 1 is displayed as the systolic blood pressure value, and the cuff pressure that occurs last is displayed on the display 12 as the diastolic blood pressure value. Furthermore, when a voiced sound is detected during the continuous generation of the K sound and the output of the AND gate 9 is obtained, the second phase of the voiced sound is detected by a part of the display 12 or another display immediately or after the blood pressure measurement is completed. , informs you that blood pressure measurement was possible under good conditions.

As described above, the present invention includes a gate means that is turned on for a predetermined time after a predetermined time from the time of detection of Korotkoff sounds, and a second Korotkoff sound detection means whose detection level is set to a level corresponding to the detection of voiced sounds,
The detection output of the second Korotkoff sound detection means that passes while the gate means is on is used as the second-phase voiced sound detection output, and the presence of the detection output is displayed by the voiced sound detection display means. Because of this, when measuring blood pressure, the subject can evaluate for himself whether or not he was able to measure blood pressure in the correct condition, which has the effect that anyone can measure blood pressure in the correct condition.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram of Korotkoff sound, Figure 2 a, b
3 is a block circuit diagram of an embodiment of the present invention, and FIGS. 4a to 4h are waveform diagrams of main parts of the same Korotkoff sounds. 1...Korotkoff sound sensor, 2...Korotkoff sound filter, 5...control circuit, 6...delay circuit,
7...Gate signal generation circuit, 12...Display device.

Claims (1)

[Claims] 1. Detection of Korotkoff sounds in a blood pressure monitor equipped with a first Korotkoff detection means for detecting Korotkoff sounds of a certain level or higher, and means for displaying the maximum and minimum values of cuff cuff pressure at the time of detection of each Korotkoff sound. The second Korotkoff sound detection means is provided with a gate means that is turned on for a certain time after a certain time from the point in time, and a second Korotkoff sound detection means whose detection level is set to a level corresponding to the detection of voiced sounds. A blood pressure monitor characterized in that the detection output of the detection means is a second-phase voiced sound detection output, and the presence of the detection output is displayed by a voiced sound detection display means.