JPH0344766B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a Korotkoff sound collection device for a blood pressure monitor.

[Background technology]

Currently, the standard clinical method for non-invasive blood pressure measurement is based on auscultation using Korotkoff sounds. In this method, a cuff is wrapped around the upper arm of the human body, and air is injected into the ischemic cuff (rubber air bag) inside the cuff, pressurizing the blood pressure to a level 20 to 30 mmHg higher than the expected systolic blood pressure, thereby opening the artery. Apply pressure to stop blood flow. Next, the air pressure inside the ischemic cuff is gradually exhausted at a rate of 2 to 3 mmHg/sec. Eventually, the artery opens slightly and blood begins to flow, producing a damped vibration sound called Korotkoff's sound in the lateral direction of the blood vessel wall. This Korotkoff sound continues to occur in synchronization with the pulse, but eventually disappears when the artery is sufficiently opened and blood flow becomes constant. The cuff pressure of the arm cuff when the Korotkoff sounds occur is the systolic blood pressure value, and the cuff pressure before the Korotkoff sounds disappear, that is, the last time the Korotkoff sounds occur, is the diastolic blood pressure value.

FIG. 1 shows a configuration diagram when a doctor measures blood pressure by auscultation, in which a cuff 2 wrapped around an upper arm 1 of the body is pressurized by a pressure ball 7 via a conduit 5. 8 is the exhaust adjustment valve, 3 is the stethoscope,
4 is a doctor and 6 is a column of mercury. As mentioned above, the arm cuff 2 is pressurized by the pressure ball 7, and the exhaust adjustment valve 8 is
Adjust the cuff pressure using the stethoscope 3.
is placed near the finger side of the arm cuff 2, the doctor 4 distinguishes the Korotkoff sounds by ear, and the cuff pressure at the onset and disappearance of the Korotkoff sounds can be determined by reading the mercury column 6. Measuring blood pressure using such auscultation method requires considerable skill and skill, and often involves subjective judgment, resulting in variations in measurement accuracy. Therefore, electronic blood pressure monitors that can be easily and stably measured even by laymen have been developed. However, in conventional electronic blood pressure monitors, the characteristics of a stethoscope and the characteristics of human hearing have not been sufficiently taken into account, and therefore, the difference between blood pressure measurements taken by a doctor has become a problem. In other words, in the conventional electronic blood pressure monitor,
The Korotkoff sound is detected by a sensor such as a microphone built into the arm cuff, and the appropriate frequency band is determined based on the judgment of the doctor through auscultation and statistically (by taking a large amount of clinical data so that it is relatively optimal). It was distinguished by Therefore, the Korotkoff sounds heard by the doctor and the Korotkoff sounds detected by the sensor and filter have essentially different characteristics and cannot be said to match. In addition, in order to determine the optimal sensor, filter frequency band, and comparator level, statistical matching is required, which requires analysis of a large amount of clinical data, resulting in the problem of requiring a huge amount of time and effort for development. It was hot.

[Purpose of the invention]

The present invention has been provided in view of the above-mentioned points, and an object of the present invention is to distinguish Korotkoff sounds under the same conditions as those used by doctors by auscultation, and to perform accurate blood pressure measurement consistent with auscultation. The present invention provides a Korotkoff sound collection device for a blood pressure monitor.

[Disclosure of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 2 shows a configuration diagram of an embodiment of the present invention. Reference numeral 2 denotes a cuff that is wrapped around the upper arm 1 of the body, and 6 is a conduit through which air is introduced into the cuff 2 by means of a pressurizing ball 7. 3 is a stethoscope, which is composed of a conduit 3a, a stethoscope head 3b, and the like. Further, the earmuff portion of the stethoscope 3 is configured as follows. That is, a microphone holder 10 is attached to one earmuff, and a microphone 11 for detecting Korotkoff sounds is attached to the end of the microphone holder 10. A microphone holder 10 and a pseudo microphone 12 are also attached to the other earmuff. Here, the distance from the end of the earmuff of the stethoscope 3 to the detection surface of the microphone 11 is set equal to the length of the external auditory canal (approximately 30 mm). The frequency and gain characteristics of the stethoscope 3 in this state are as shown in curve A shown in Fig. 4, and the stethoscope characteristics when a human actually wears the stethoscope in the ear are as shown in curve A shown in Fig. 4. become that way. Therefore, the ear-worn corrector 9 is used to make the characteristics of the stethoscope 3 as shown in FIG. 4B. This ear-worn corrector 9
In this example, an injection needle 9a (length 50 mm, diameter 1.2 mm) is inserted into two microphone holders 10, and the other ends are communicated with each other through a conduit 9a (length 135 mm, diameter 4 mm). This results in the same stethoscope characteristics as those heard by humans.

The microphone 11 itself has frequency characteristics, and the electret type microphone 11 used in this embodiment has microphone sensitivity characteristics as shown in FIG. 5a. Therefore, in order to flatten the microphone sensitivity characteristics, it is necessary to perform correction using a microphone sensitivity correction filter 13 having characteristics opposite to the microphone sensitivity characteristics as shown in FIG. 5b.

Next, human hearing has frequency characteristics, and low-frequency sensitivity is generally poor. As for the characteristics of human hearing,
Equal loudness curves for pure tones are used. Figure 6a is a 60dB equal loudness curve (ISO/R226)
It is. This was obtained by combining the sound pressure levels measured for each frequency of 60 1000Hz phones. Then, find the inverse characteristic of this characteristic.
The characteristics of the audibility correction filter shown in FIG. 6 are those in which 1000 Hz is 0 dB, which is configured as the audibility correction filter 14 so as to be equivalent to the state of hearing with the human ear. In this way, the outputs of the stethoscope 3, the ear-worn corrector 9, and the microphone 11 attached to the microphone holder 10 are filtered by the microphone sensitivity correction filter 13 having the characteristics shown in FIG. 5b, and the microphone sensitivity correction filter 13 having the characteristics shown in FIG. 6b. By passing the signal through the audibility correction filter 14, the same Korotkoff sound signal as felt by the doctor's ears can be obtained.

Further, 15 is a comparator which, if the output level from the audibility correction filter 14 is above a predetermined value, recognizes it as a Korotkoff sound signal and sends it to the control circuit 18 at the next stage. Reference numeral 16 denotes a pressure sensor that detects the cuff pressure of the cuff 2. The output of the pressure sensor 16 is input to the A/D converter 17, and the output of the A/D converter 17, which is converted into a digital signal, is sent to the control circuit 18. It will be done. The control circuit 18 measures the systolic diastolic blood pressure value based on the output of the comparator 15 and the output of the A/D converter 17, and displays the value on the display 1.
9 displays the measured value digitally.

Therefore, in blood pressure measurement, the cuff 2 is wrapped around the upper arm 1, and the membrane surface of the stethoscope 3 is placed on the artery near the finger side of the cuff 2. After that, the arm cuff 2 is pressed by the pressure ball 7.
Air is pumped into the ischemic cuff inside the patient and pressurized to 20 to 30 mmHg higher than the expected systolic blood pressure. Next, the exhaust control valve 8 is adjusted to exhaust the air at a rate of 2 to 3 mmHg/sec. At the same time, the stethoscope 3, the ear-worn corrector 9, and the microphone 11 detect the Korotkoff sound, and the microphone sensitivity correction filter 1
3 and an auditory correction filter 14, a comparator 15 recognizes a signal of a certain level or higher as a Korotkoff sound, and inputs it to a control circuit 18 as a Korotkoff sound pulse. On the other hand, the cuff pressure is detected by a pressure sensor 16 connected through a conduit 6, and inputted to a control circuit 18 after passing through an A/D converter 17. In the control circuit 18, the cuff pressure obtained by the pressure sensor 16 and the A/D converter 17 when the Korotkoff sound pulse is first inputted is displayed on the display 19 as the systolic blood pressure value, and the cuff pressure obtained when the Korotkoff sound pulse is inputted last is displayed on the display 19. The cuff pressure at that time is displayed on the display 19 as the diastolic blood pressure value. Thereafter, the exhaust control valve 8 is fully opened to rapidly exhaust the air in the ischemic cuff in the arm cuff 2, and the measurement is completed.

By the way, when actually measuring blood pressure using the method of this embodiment, the conduit 3a portion of the stethoscope 3 is approximately 70 cm long, which is inconvenient for measurement and also tends to pick up noise.
Also, since the frequency characteristic of only the stethoscope head 3b excluding the conduit 3a is almost flat, the microphone 1 is connected to the straight stethoscope head 3b excluding the conduit 3a.
An easy-to-use blood pressure monitor can be obtained by attaching the blood pressure monitor 1 and configuring the conduit 3a shown in FIG. Its configuration is shown in FIG. In other words, as shown in FIG. 3, a microphone 11 is built into the arm cuff 2 instead of a stethoscope, and the difference between the frequency characteristics of this microphone 11 and the stethoscope characteristics shown in FIG. This is realized by a stethoscope characteristic correction filter 20. The components after the auditory sensation correction filter 14 are the same as in the basic example described above. In this way, instead of a stethoscope, a microphone 11 is built into the arm cuff 2, and the difference between the frequency characteristics of this microphone 11 and the stethoscope characteristics when actually worn on the ear is detected by the stethoscope characteristics correction filter 20. As a result, malfunctions due to noise are eliminated, and it is easy to use and perform measurements. This eliminates the need to use a stethoscope, making it easy to use and allowing each filter to
0 and 14, it is possible to measure blood pressure in the same condition as it is felt with the doctor's ears, so it is possible to perform a measurement that closely matches blood pressure measurement using the auscultation method performed by a doctor.

〔Effect of the invention〕

As described above, the present invention provides a stethoscope that collects Korotkoff sounds, a microphone holder attached to both ear flaps of the stethoscope, and a distance from the end of the ear flap of the stethoscope to the detection surface. Insert the injection needle into the Korotkoff sound detection microphone attached to one microphone holder so that the length is approximately equal to the length of the external auditory canal of the ear, and into the pseudo microphone attached to this microphone and the other microphone holder. An ear-worn corrector connects the bases of the injection needles with a conduit to make the stethoscope characteristic when the stethoscope is actually worn in the ear, and a microphone sensitivity correction device that flattens the frequency characteristics of the microphone itself. Since it is equipped with a filter and an audibility correction filter that adjusts the output of the microphone sensitivity correction filter to the audibility characteristics of the body's own ear, it is possible to take stethoscope characteristics and audibility characteristics into consideration. It is possible to obtain the same Korotkoff sound signal as the Korotkoff sound, thereby performing Korotkoff sound recognition, which has the effect of making it possible to perform a measurement that closely matches blood pressure measurement performed by a doctor's auscultation method.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing blood pressure measurement by a doctor's auscultation method, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a block diagram showing an example improved from Fig. 2 above, and Fig. 4
The figure shows the stethoscope characteristic diagram as above, the figure 5a shows the microphone sensitivity characteristic diagram as above, the figure b shows the microphone sensitivity correction filter characteristic diagram as above, the figure 6a shows the auditory sensitivity characteristic diagram as above, and the figure b shows as above. FIG. 3 is a stethoscope, 9 is an ear-worn corrector, 9a is a syringe needle, 9b is a conduit, 10 is a microphone holder, 11 is a microphone, 12 is a pseudo microphone, 13 is a microphone sensitivity correction filter, and 14 is an auditory sensation correction filter. It is.

Claims (1)

[Scope of Claims] 1. A stethoscope that collects Korotkoff sounds, a microphone holder attached to each earmuff of the stethoscope, and a distance from the end of the earmuff of the stethoscope to the detection surface. Insert the injection needle into the Korotkoff sound detection microphone attached to one microphone holder so that the length is approximately equal to the length of the external auditory canal of the ear, and into the pseudo microphone attached to this microphone and the other microphone holder. An ear-worn corrector that connects the bases of the injection needles with a conduit to give stethoscope characteristics when the stethoscope is actually worn in the ear, and a microphone sensitivity correction filter that flattens the frequency characteristics of the microphone itself. A Korotkoff sound collection device for a blood pressure monitor, comprising: and an auditory sensation correction filter that matches the output of the microphone sensitivity correction filter to the auditory characteristics of the body's own ears. 2. The Korotkoff sound collection device for a blood pressure monitor according to claim 1, characterized in that an inverse characteristic of a 60 dB equal loudness curve is used as the audibility correction filter.