Sphygmomanometer, blood pressure measuring method, and korotkoff sound detection device

Abstract

To extract a Korotkoff sound from a sound generated from a body part to be measured with a good S / N ratio.SOLUTION: A sphygmomanometer includes a diaphragm 62 arranged to receive pressure of air in an air pipe 37d on one surface 62a as part of a pipe wall of the air pipe 37d connected to a cuff in a fluid-circulation manner, or continued to the pipe wall. The diaphragm 62 blocks the pressure of the air in the air pipe 37d in a compression process or a decompression process, of the cuff and causes a sound of a frequency band of a Korotkoff sound of a sound transmitted through the air in the air pipe 37d from a body part to be measured to be transmitted through the diaphragms 62. A chamber Cm arranged including the diaphragm 62 as part of a peripheral wall is provided on the other surface 62b side opposite to one surface 62a with respect to the diaphragm 62. A sound detection device provided facing the air in the chamber Cm is disposed on a part other than the diaphragm 62 of the peripheral wall of the chamber Cm.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a sphygmomanometer and a blood pressure measurement method, more particularly to a sphygmomanometer and a blood pressure measurement method for measuring blood pressure based on Korotkoff sounds generated at a measurement site, and also to a Korotkoff sound detection device included in such a sphygmomanometer and for extracting Korotkoff sounds from sounds generated at the measurement site. [Background technology]

[0002] Conventionally, as a Korotkoff sound detection device (and blood pressure monitor), for example, as disclosed in FIG. 2 of Patent Document 1 (JP Patent Publication 58-180132 A), there is known a device that includes a diaphragm (metallic membrane) that vibrates in response to sound collected from a cuff band that is wrapped around the upper arm of the human body and pressurized, and has a mechanical resonance point within the frequency band in which Korotkoff sounds exist, and a means for converting the mechanical vibration of the diaphragm into an electric signal. This configuration is understood as a condenser microphone. The document states that the mechanical resonance characteristics of the diaphragm make it possible to remove noise components other than the Korotkoff sounds and extract only the Korotkoff sounds. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 58-180132 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the sound generated by the measured part (broadly defined as a wave propagating through an elastic medium such as air) includes not only Korotkoff sounds (frequency band; about 20 Hz to 500 Hz) but also pressure pulse waves (frequency band; about several tens of Hz), which are pulse wave vibrations of the artery passing through the measured part. The two frequency bands overlap, and the amplitude of the pressure pulse wave is larger than that of the Korotkoff sounds. For this reason, in practice, the configuration described in Patent Document 1 has a problem in that it is difficult to extract only the Korotkoff sounds from the sounds generated by the measured part.

[0005] Therefore, an object of the present invention is to provide a blood pressure monitor and blood pressure measurement method that measures blood pressure based on Korotkoff sounds generated by a measurement site, which can extract Korotkoff sounds from sounds generated by the measurement site with a good S / N ratio (signal-to-noise ratio), thereby improving the accuracy of blood pressure measurement.Another object of the present invention is to provide a Korotkoff sound detection device that is included in such a blood pressure monitor and can extract Korotkoff sounds from sounds generated by the measurement site with a good S / N ratio. [Means for solving the problem]

[0006] In order to solve the above problems, the blood pressure monitor disclosed herein comprises: A sphygmomanometer for measuring blood pressure based on Korotkoff sounds generated at a measurement site, A pressure cuff configured to be attached to the measurement site; A pump, an air pipe fluidly connecting the cuff and the pump; a pressure control unit that supplies air to the cuff through the air piping by the pump to pressurize the measurement site, or that exhausts the air from the cuff through the air piping to reduce pressure; a diaphragm is provided as a part of a tube wall of the air piping or connected to the tube wall, and is arranged so as to receive the air pressure in the air piping on one side, the diaphragm being configured to block the air pressure in the air piping during the pressurization or depressurization process of the cuff by the pressure control unit, while allowing sounds in the frequency band of the Korotkoff sounds, among sounds transmitted from the measurement site through the air in the air piping, to pass through the diaphragm; a chamber is provided on the other surface side of the diaphragm opposite to the one surface, the chamber including the diaphragm as a part of a peripheral wall, and sound transmitted through the diaphragm is transmitted to air occupying the chamber; a sound detection device is provided on a portion of the peripheral wall of the chamber other than the diaphragm so as to face the air in the chamber, and the sound detection device receives the sound transmitted through the diaphragm via the air occupying the chamber and converts it into an electric signal; A blood pressure calculation unit is provided to calculate the blood pressure at the measurement site based on the electrical signal. It is characterized by:

[0007] Here, the "one side" and "other side" of the diaphragm refer to both expanding sides of the diaphragm.

[0008] The phrase "the diaphragm is arranged so as to be connected to the pipe wall" of the air pipe includes, for example, a mode in which the diaphragm is arranged so as to be connected to the pipe wall of another pipe branching off from the air pipe.

[0009] In the blood pressure monitor disclosed herein, in a state where a pressing cuff is attached to a measurement site, a pressure control unit uses the pump to supply air to the cuff through the air piping to pressurize the measurement site, or discharges the air from the cuff through the air piping to depressurize the measurement site. The diaphragm receives the air pressure in the air piping on one side and blocks the air pressure in the air piping during the pressurization or depressurization process of the cuff by the pressure control unit. On the other hand, the diaphragm transmits through the diaphragm sounds in the frequency band of the Korotkoff sounds among the sounds transmitted from the measurement site through the air in the air piping. As a result, the sounds transmitted through the diaphragm are transmitted to the air occupying the chamber. The sound detection device receives the sounds transmitted through the diaphragm through the air occupying the chamber and converts them into an electrical signal. The blood pressure calculation unit calculates the blood pressure of the measurement site based on the electrical signal.

[0010] Here, in this blood pressure monitor, the diaphragm blocks the air pressure in the air piping, so that the influence of the pressure pulse wave, which is the arterial pulse wave vibration (frequency band; about several tens of Hz), on the sound generated by the measured part can be reduced. Moreover, the sound detection device receives the sound that has passed through the diaphragm via the air occupying the chamber, in other words, receives it at a position separated from the diaphragm (which directly receives the pressure pulse wave). Therefore, the influence of the pressure pulse wave can be further reduced. As a result, this blood pressure monitor can extract Korotkoff sounds with a good S / N ratio from the sound generated by the measured part. Therefore, the accuracy of blood pressure measurement can be improved.

[0011] If the chamber is sealed, the diaphragm will bend as the air pressure in the air pipe gradually changes during the pressurization or depressurization process of the cuff, and the air pressure in the chamber will change. If there is such a change in the air pressure in the chamber, for example, if the sound detection device is a condenser microphone, the sensitivity of the microphone will change, which is not preferable. In addition, the dynamic range of the condenser microphone needs to be a width equivalent to the change in cuff pressure (approximately 0 to 300 mmHg), so the resolution of the Korotkoff sound will decrease. In addition, the durability and reliability of the sound detection device will be adversely affected.

[0012] Therefore, in one embodiment of the blood pressure monitor, A pressure relief hole that fluidly communicates the inside and outside of the chamber is provided in the peripheral wall of the chamber other than the diaphragm, and the pressure relief hole acts to suppress the pressure of the air in the chamber from changing from atmospheric pressure. It is characterized by:

[0013] In the blood pressure monitor of this embodiment, a pressure relief hole that allows fluid to flow between the inside and outside of the chamber is provided in the peripheral wall of the chamber other than the diaphragm. Therefore, when the diaphragm bends as the air pressure in the air pipe gradually changes during the pressurization or depressurization process of the cuff, causing the air pressure in the chamber to change, the pressure relief hole acts to suppress the air pressure in the chamber from changing from atmospheric pressure. Therefore, even if the air pressure in the air pipe changes, it is possible to prevent the pressure change (load) from adversely affecting the sensitivity, resolution, durability, and reliability of the sound detection device.

[0014] Furthermore, as the sound detection device, not only a condenser microphone but also various types of microphones such as a dynamic microphone and a MEMS (Micro Electronics Mechanical System) microphone can be used, increasing the freedom of microphone selection.

[0015] If the pressure relief hole is a wide opening, noise can easily enter the chamber from outside through the wide opening, which can reduce the signal-to-noise ratio of the Korotkoff sound.

[0016] Therefore, in one embodiment of the blood pressure monitor, The pressure relief holes have the form of elongated channels or elongated grooves. It is characterized by:

[0017] In the blood pressure monitor of this embodiment, the pressure relief hole has the form of an elongated conduit or an elongated groove. Therefore, compared with a case where the pressure relief hole is, for example, a wide opening, noise is less likely to enter the chamber from outside the chamber. Therefore, it is possible to prevent the S / N ratio of the Korotkoff sound from decreasing due to the pressure relief hole.

[0018] In one embodiment, the blood pressure monitor comprises: A sound-insulating material having breathability and sound-insulating properties is accommodated inside the elongated duct or the elongated groove. It is characterized by:

[0019] Here, the "soundproofing material having breathability and soundproofing properties" typically includes porous materials such as polyurethane foam.

[0020] In the blood pressure monitor of this embodiment, the sound-proofing material accommodated inside the elongated duct or the elongated groove has air permeability. Therefore, the function of the pressure relief hole to suppress the change in the air pressure in the chamber from the atmospheric pressure is not lost due to the presence of the sound-proofing material. In addition, since the sound-proofing material has sound insulation properties, noise is less likely to enter the chamber from outside the chamber through the elongated duct or the elongated groove, compared to when only air is present inside the elongated duct or the elongated groove. Therefore, it is possible to prevent the S / N ratio of the Korotkoff sound from decreasing due to the pressure relief hole.

[0021] In one embodiment, the blood pressure monitor comprises: The diaphragm is set to have a natural frequency that matches the frequency band of the Korotkoff sound. It is characterized by:

[0022] In the blood pressure monitor of this embodiment, the diaphragm is set to have a natural frequency that matches the frequency band of the Korotkoff sound. Therefore, the diaphragm can selectively transmit sounds that have the frequency band of the Korotkoff sound among the sounds transmitted from the measurement site through the air in the air piping. Therefore, the S / N ratio of the Korotkoff sound can be further improved, and the accuracy of blood pressure measurement can be further increased.

[0023] In one embodiment, the blood pressure monitor comprises: The chamber is configured to have a resonant frequency that matches the frequency range of the Korotkoff sounds. It is characterized by:

[0024] In the blood pressure monitor of this embodiment, the chamber is set to have a resonant frequency that matches the frequency band of the Korotkoff sound. Therefore, the chamber can selectively amplify sounds that have the frequency band of the Korotkoff sound among the sounds that have passed through the diaphragm. Therefore, the S / N ratio of the Korotkoff sound can be further improved, and the accuracy of blood pressure measurement can be further increased.

[0025] In one embodiment, the blood pressure monitor comprises: The diaphragm is made of synthetic resin. It is characterized by:

[0026] In the blood pressure monitor of this embodiment, the diaphragm is made of synthetic resin, which is lighter than a diaphragm made of metal and easier to process during the manufacturing process.

[0027] In one embodiment, the blood pressure monitor comprises: a threshold setting unit that sets a threshold for extracting the Korotkoff sound in the electrical signal output by the sound detection device, The blood pressure calculation unit calculates the blood pressure at the measurement site based on only the signal exceeding the threshold value among the electrical signals. It is characterized by:

[0028] In the blood pressure monitor of this embodiment, the threshold setting unit sets a threshold for extracting the Korotkoff sound in the electrical signal output by the sound detection device. The blood pressure calculation unit calculates the blood pressure at the measurement site based on only the electrical signals that exceed the threshold. Therefore, for example, background noise can be removed from the electrical signal output by the sound detection device. Therefore, the S / N ratio of the Korotkoff sound can be further improved, and the accuracy of blood pressure measurement can be further increased.

[0029] In another aspect, the blood pressure measuring method of the present disclosure includes: A blood pressure measurement method for measuring blood pressure based on Korotkoff sounds generated at a measurement site by the above blood pressure meter, comprising: With the pressing cuff attached to the measurement site, the pressure control unit supplies air to the cuff through the air piping by the pump to pressurize the measurement site, or exhausts the air from the cuff through the air piping to reduce pressure, During the process of pressurizing or depressurizing the cuff by the pressure control section, the diaphragm receives the air pressure in the air piping on one side, blocking the air pressure in the air piping and allowing sounds in the frequency band of the Korotkoff sounds, which are transmitted from the measurement site through the air in the air piping, to pass through the diaphragm, and as a result, the sounds that have passed through the diaphragm are transmitted to the air occupying the chamber, The sound detection device receives the sound transmitted through the diaphragm via the air occupying the chamber and converts it into an electrical signal; The blood pressure calculation unit calculates the blood pressure at the measurement site based on the electrical signal. It is characterized by:

[0030] According to the disclosed blood pressure measurement method, Korotkoff sounds can be extracted with a good S / N ratio from sounds generated at the measurement site, thereby improving the accuracy of blood pressure measurement.

[0031] In yet another aspect, the Korotkoff sound detection device of the present disclosure comprises: A Korotkoff sound detection device included in the blood pressure monitor and configured to extract Korotkoff sounds from sounds generated at the measurement site, a diaphragm is provided as a part of a tube wall of the air piping or connected to the tube wall, and is arranged so as to receive the air pressure in the air piping on one side, the diaphragm being configured to block the air pressure in the air piping during the pressurization or depressurization process of the cuff by the pressure control unit, while allowing sounds in the frequency band of the Korotkoff sounds, among sounds transmitted from the measurement site through the air in the air piping, to pass through the diaphragm; a chamber is provided on the other surface side of the diaphragm opposite to the one surface, the chamber including the diaphragm as a part of a peripheral wall, and sound transmitted through the diaphragm is transmitted to air occupying the chamber; A sound detection device is provided on the peripheral wall of the chamber other than the diaphragm and facing the air in the chamber, and the sound detection device receives the sound transmitted through the diaphragm via the air occupying the chamber and converts it into an electric signal. It is characterized by:

[0032] According to the Korotkoff sound detection device disclosed herein, Korotkoff sounds can be extracted with a good S / N ratio from sounds generated at the measurement site. Effect of the Invention

[0033] As is clear from the above, the blood pressure monitor and blood pressure measurement method disclosed herein can extract Korotkoff sounds from sounds generated by the measurement site with a good S / N ratio, thereby improving the accuracy of blood pressure measurement. Also, the Korotkoff sound detection device disclosed herein can extract Korotkoff sounds from sounds generated by the measurement site with a good S / N ratio. [Brief description of the drawings]

[0034] [Figure 1] 1 is a diagram showing a block configuration of a sphygmomanometer according to an embodiment of the present invention; [Diagram 2] Fig. 2(A) is a perspective view showing a cross-sectional structure of a Korotkoff sound detection device included in the sphygmomanometer, and Fig. 2(B) is a diagram showing a model for setting the resonance frequency of a chamber included in the Korotkoff sound detection device. [Diagram 3] Figures 3(A), 3(B), and 3(C) are diagrams showing various aspects of a thin tube forming a pressure relief hole that allows fluid to flow between the inside and outside of the chamber. Figure 3(D) is a diagram showing the verification result of noise reduction by accommodating a sound-proofing material inside the thin tube shown in Figure 3(C). [Figure 4] 2 is a diagram showing a state in which a pressure cuff of the blood pressure monitor is attached to an upper arm as a measurement site. FIG. [Diagram 5] FIG. 4 is a diagram showing a flow of blood pressure measurement using the sphygmomanometer. [Figure 6] 6(A) and 6(B) are diagrams for explaining the operation of the Korotkoff sound detection device during blood pressure measurement. [Figure 7] 3 is a diagram illustrating an example of a sound signal output by the Korotkoff sound detection device in the blood pressure monitor (embodiment). FIG. [Figure 8] 10A and 10B are diagrams illustrating sound signals output by a Korotkoff sound detection device of a comparative example. [Figure 9] 9(A) and 9(B) are diagrams showing modified examples of the pressure relieving holes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0036] (Outline of blood pressure monitor configuration) 1 shows a block diagram of a blood pressure monitor 1 according to an embodiment of the present invention. This blood pressure monitor 1 is roughly divided into a pressure cuff (hereinafter simply referred to as "cuff") 20 that is attached around a measurement site (in this example, the upper arm), and a main body 10 that is connected to this cuff 20 via an air pipe 37 so as to be capable of fluid communication.

[0037] The cuff 20 includes a bag 21, which is formed by opposing an elongated strip-shaped outer cloth and an inner cloth and sewing (or welding) their peripheral edges together. A fluid bag 22 for compressing the measurement site is contained inside the bag 21.

[0038] The main body 10 is equipped with a control unit 110, a display 50, an operation unit 52, a memory 51, a power supply unit 53, a pressure sensor 31, a pump 32, a valve 33, and a Korotkoff sound detection device 60 for extracting Korotkoff sounds from sounds generated by the measurement site. The main body 10 is further equipped with an A / D conversion circuit 310 for converting an analog output from the pressure sensor 31 into a digital signal, a pump drive circuit 320 for driving the pump 32, a valve drive circuit 330 for driving the valve 33, and an A / D conversion circuit 410 for converting an analog output from the Korotkoff sound detection device 60 into a digital signal. Air pipes 37a, 37b, 37c, and 37d are connected to the pressure sensor 31, the pump 32, the valve 33, and the Korotkoff sound detection device 60, respectively, so as to be capable of fluid communication. These air pipes 37a, 37b, 37c, and 37d merge into one air pipe 37 inside the main body 10, and this air pipe 37 is connected to the fluid bag 22 inside the cuff 20 so as to be able to fluidly communicate with each other. Hereinafter, the air pipes 37a, 37b, 37c, and 37d will be collectively referred to as air pipe 37 as appropriate. In addition, the output of the Korotkoff sound detection device 60 is transmitted to the A / D conversion circuit 410 as a sound signal Ks, which is an electrical signal, by a wiring 71.

[0039] In this example, the display device 50 includes a display, an indicator, and the like, and displays predetermined information (eg, blood pressure measurement results) according to a control signal from the control unit 110.

[0040] The operation unit 52 inputs an operation signal corresponding to an instruction from a user to the control unit 110. In this example, the operation unit 52 includes a measurement switch 52A for receiving an instruction to start / stop blood pressure measurement, and a memory switch 52B for receiving an instruction to call up blood pressure measurement result data stored in the memory 51.

[0041] The memory 51 serves as a storage unit and stores data of a program for controlling the sphygmomanometer 1, setting data for setting various functions of the sphygmomanometer 1, and data of blood pressure measurement results. The memory 51 is also used as a work memory when the program is executed.

[0042] The control unit 110 includes a CPU (Central Processing Unit) and controls the overall operation of the sphygmomanometer 1. Specifically, the control unit 110 acts as a pressure control unit in accordance with a program for controlling the sphygmomanometer 1 stored in the memory 51, and controls the driving of the pump 32 and the valve 33 in response to an operation signal from the operation unit 52. The control unit 110 also acts as a threshold setting unit and a blood pressure calculation unit, calculates the blood pressure value of the measurement site based on the sound signal Ks output by the Korotkoff sound detection device 60, and controls the display 50 and the memory 51. A specific method of measuring blood pressure will be described later.

[0043] Power supply unit 53 supplies power to control unit 110, pressure sensor 31, pump 32, valve 33, display 50, memory 51, A / D conversion circuits 310, 410, pump drive circuit 320, valve drive circuit 330, and microphone 40, which will be described later. Power is supplied to microphone 40 through wiring 71.

[0044] The pressure sensor 31 is a piezo-resistance pressure sensor in this example, which receives the pressure (called "cuff pressure Pc") of the cuff 20 (in this example, the fluid bag 22) through the air piping 37, and outputs an electrical signal value based on a change in electrical resistance due to the piezo-resistance effect to the control unit 110 through the A / D conversion circuit 310. The control unit 110 detects the cuff pressure Pc according to the electrical signal value from the pressure sensor 31.

[0045] The pump 32 supplies air to the fluid bag 22 through the air piping 37 in order to increase the cuff pressure Pc. The valve 33 is opened and closed to control the cuff pressure Pc by discharging or sealing air in the fluid bag 22 through the air piping 37. The pump drive circuit 320 drives the pump 32 based on a control signal provided by the control unit 110. The valve drive circuit 330 opens and closes the valve 33 based on a control signal provided by the control unit 110.

[0046] In this example, the Korotkoff sound detection device 60 generally includes a roughly short cylindrical case 61, a diaphragm 62 arranged across the case 61, a microphone 40 as a sound detection device, and a thin tube 63 forming a hole for relieving pressure.

[0047] Fig. 2(A) illustrates a cross-sectional structure of a Korotkoff sound detection device 60. This Korotkoff sound detection device 60 includes a case 61 including a lower case 61A and an upper case 61B. For ease of understanding, Fig. 2(A) illustrates a longitudinal section of the case 61 cut in half along a vertical plane. Note that the terms "lower", "upper", "vertical", and "horizontal" (described below) are used for convenience of explanation, and the case 61 can be disposed as a unit in any orientation within the main body 10 of the sphygmomanometer 1.

[0048] The lower case 61A includes a cylindrical portion 61A1 that fits around the air pipe 37d, a plate portion 61A2 that has a substantially rectangular plate-like outer shape that spreads horizontally from the upper end of the cylindrical portion 61A1, a recess 61A3 that is provided on the upper surface of the plate portion 61A2 as a circular depression with a flat bottom, and an edge portion 61A4 that bends and extends upward from the end side (the right side in FIG. 2(A)) of the plate portion 61A2. The cylindrical portion 61A1 fits around the air pipe 37d airtight. The space Cd that the recess 61A3 creates on the plate portion 61A2 is fluidically connected to the air pipe 37d (and therefore the air pipe 37) via the cylindrical portion 61A1. In this example, the horizontal dimension of the plate portion 61A2 is set to about 50 mm.

[0049] The upper case 61B includes a substantially rectangular plate portion 61B1 extending substantially parallel to the plate portion 61A2 of the lower case 61A, a dome portion 61B2 protruding upward from the plate portion 61B1 in a circular dome shape, a cylindrical portion 61B3 extending upward from the substantially center of the dome portion 61B2, and an edge portion 61B4 bending downward from an end side (the left side in FIG. 2(A)) of the plate portion 61B1. In this example, the horizontal dimension of the plate portion 61B1 is set to about 50 mm, similar to that of the plate portion 61A2 of the lower case 61A. The horizontal position and dimensions of the dome portion 61B2 are substantially the same as those of the recessed portion 61A3 of the lower case 61A. In this example, the air pipe 38 is airtightly fitted and inserted into the cylindrical portion 61B3. The microphone 40 is airtightly attached to the upper end of the air pipe 38. In this example, a thin tube 63 is attached midway through the air pipe 38. A space Cm (forming a chamber described later) formed by the inner peripheral edge 61B1i of the plate portion 61B1 and the inner edge 61B1i of the dome portion 61B2 is in fluid communication with the microphone 40 via the cylindrical portion 61B3 and the air pipe 38.

[0050] Between the plate portion 61A2 of the lower case 61A and the plate portion 61B1 of the upper case 61B, a substantially circular film-like diaphragm 62 is provided so as to cross and separate the space Cd from the space Cm. In this example, the peripheral portion 62e of the diaphragm 62 is sandwiched between the plate portion 61A2 of the lower case 61A and the plate portion 61B1 of the upper case 61B. This allows the portion of the diaphragm 62 other than the peripheral portion 62e to vibrate up and down as shown by the arrow Bs in FIG. 2(A). The peripheral portion 62e of the diaphragm 62 may be bonded to the plate portion 61A2 of the lower case 61A and / or the plate portion 61B1 of the upper case 61B by an adhesive. In this example, the diaphragm 62 is made of a polyurethane sheet (thickness 0.3 mm) as a synthetic resin. In this example, the effective radius R of the diaphragm 62 (substantially equal to the horizontal radius of the spaces Cd, Cm) is set to R = 16.5 mm. Therefore, this diaphragm 62 is lighter than a diaphragm made of metal, and is easier to process during the manufacturing stage. Also, in this example, the natural frequency of the diaphragm 62 is set to match the frequency band of Korotkoff sounds (approximately 20 Hz to 500 Hz). Therefore, the diaphragm 62 can selectively transmit sounds in the frequency band of Korotkoff sounds.

[0051] The edge 61A4 of the lower case 61A and the edge 61B4 of the upper case 61B are provided for the convenience of aligning the lower case 61A and the upper case 61B with each other in a horizontal plane when assembling the lower case 61A and the upper case 61B. Thanks to these edges 61A4, 61B4, the recess 61A3 of the lower case 61A and the dome portion 61B2 of the upper case 61B can be easily aligned concentrically.

[0052] In this example, a chamber (for simplicity, indicated by the same reference symbol as the space Cm) is formed by the upper surface 62b of the diaphragm 62, the inner peripheral edge 61B1i of the plate portion 61B1, the inner surface 61B2i of the dome portion 61B2, the cylindrical portion 61B3, and the air pipe 38. In this example, the chamber Cm is set to have a resonant frequency that matches the frequency band of the Korotkoff sound (approximately 20 Hz to 500 Hz).

[0053] Specifically, FIG. 2B shows a model of Helmholtz Resonance in a configuration in which the cylindrical portion 61B3 of the upper case 61B and the air pipe 38 are omitted and the chamber Cm is directly connected to the microphone 40 so as to be capable of fluid communication (in this case, the thin tube 63 may be directly attached to the dome portion 61B2 of the upper case 61B as shown in FIG. 1, or may be formed integrally with the dome portion 61B2). In FIG. 2B, S denotes the effective area of ​​the diaphragm 62 (the area of ​​the part that actually vibrates, in m 2 ), V is the internal volume of the chamber Cm (unit: m 3 ), and L is the equivalent neck length (unit: m). In this case, the resonant frequency f of the chamber Cm is given by the theory of Helmholtz resonance as follows: f=(c / 2π)(S / VL) 1 / 2 …(Eq.1) Here, c represents the speed of sound, and c ≈ 340 m / sec. In this example, based on equation (Eq. 1), the resonant frequency f of the chamber Cm is set to match the frequency band of Korotkoff sounds (approximately 20 Hz to 500 Hz).

[0054] Therefore, the chamber Cm can selectively amplify, from among the sounds transmitted through the diaphragm 62, sounds having the frequency band of the Korotkoff sounds.

[0055] The microphone 40 receives the sound transmitted through the diaphragm 62 via the air occupying the chamber Cm and converts it into an electric sound signal Ks. The sound signal Ks mainly contains components that represent Korotkoff sounds. The sound signal Ks is transmitted to the control unit 110 as the output of the Korotkoff sound detection device 60 via the wiring 71 and the A / D conversion circuit 410.

[0056] In this example, the thin tube 63 forming the pressure relief hole has a cylindrical outer shape. As shown in Fig. 3(A), a pressure relief hole 63o that communicates the inside and outside of the chamber Cm so that a fluid can flow therethrough is provided inside the thin tube 63. In this example, the hole 63o is in the form of a long and thin pipe that extends straight. In this example, the axial dimension L of the thin tube 63 is set to about several mm to several cm. The inner diameter Di of the hole 63o is set to about 0.1 mm to several mm.

[0057] When the diaphragm 62 bends as the air pressure in the air pipe 37 (and space Cd) gradually changes during the pressurization or depressurization process of the cuff 20, causing the air pressure in the chamber Cm to change, the hole 63o allows air to flow between the inside and outside of the chamber Cm as shown by the arrow Ai in Fig. 3(A), and acts to suppress the air pressure in the chamber Cm from changing from the atmospheric pressure (ambient pressure) Am. Therefore, even if the air pressure in the air pipe 37 (and space Cd) changes, it is possible to prevent the pressure change (load) from adversely affecting the sensitivity, resolution, durability, and reliability of the microphone 40.

[0058] Here, the pressure relief hole 63o is in the form of a long and thin duct. Therefore, compared with the case where the hole 63o is, for example, a wide opening (not shown), noise is less likely to enter the chamber Cm from outside the chamber Cm through the hole 63o. Therefore, it is possible to prevent the S / N ratio of the Korotkoff sound from decreasing due to the pressure relief hole. In the example of FIG. 3(A), the hole 63o is straight, but this is not limited to this. For example, in the thin tube 63B shown in FIG. 3(B), the pressure relief hole 63oB provided therein is in the form of a long and thin duct that goes back and forth in a zigzag manner. Even in this case, the hole 63oB works to circulate air between the inside and outside of the chamber Cm as shown by the arrow AiB, and to suppress the change in the air pressure in the chamber Cm from the atmospheric pressure Am. Therefore, even if the air pressure in the air pipe 37 (and the space Cd) changes, it is possible to prevent the pressure change (load) from adversely affecting the sensitivity, resolution, durability, reliability, etc. of the microphone 40. Moreover, compared to the example of Fig. 3(A), it is less likely that noise will enter the chamber Cm from outside through the hole 63oB. Therefore, it is possible to further prevent the S / N ratio of the Korotkoff sound from decreasing due to the pressure relief hole.

[0059] In addition, in the thin tube 63C shown in FIG. 3(C), the pressure relief hole 63oC provided therein is in the form of a long and thin pipe extending straight. However, the hole 63oC is filled with polyurethane foam 64, which is a porous material in this example, as a sound insulation material having breathability and sound insulation properties. This polyurethane foam 64 has breathability as shown by the arrow AiC. Therefore, the presence of the polyurethane foam 64 does not impair the function of the hole 63oC to suppress the change in the pressure of the air in the chamber Cm from the atmospheric pressure Am. In addition, since the polyurethane foam 64 has sound insulation properties, noise is less likely to enter the chamber Cm from outside the chamber Cm through the hole 63oC compared to when only air is present inside the hole 63oC. Therefore, it is possible to further prevent the hole 63oC from decreasing the S / N ratio of the Korotkoff sound. For example, FIG. 3(D) shows the results of verifying the extent to which noise sound in the chamber Cm is reduced by placing polyurethane foam 64 inside the hole 63oC when the axial dimension L of the capillary tube 63C is 2 mm and the inner diameter Di of the hole 63oC is approximately 0.2 mm. In this example, before placing polyurethane foam 64 inside the hole 63oC (before time tx), the background noise level (peak-to-peak) Ap-p in the chamber Cm was approximately 0.11 V. In contrast, after placing polyurethane foam 64 inside the hole 63oC (after time tx), the background noise level Ap-p in the chamber Cm was reduced to approximately 0.02 V. In this way, it was verified that the presence of polyurethane foam 64 can effectively reduce noise sound in the chamber Cm.

[0060] (Blood pressure measurement method) When measuring blood pressure, as shown in FIG. 4, the cuff 20 is attached around the measurement site (upper arm in this example) 90 of the user (note that in FIG. 4, for simplicity, the illustration of the inner cloth is omitted). It is assumed that an artery 91 passes through the measurement site 90. The sound generated by the measurement site 90 includes not only Korotkoff sounds (frequency band: about 20 Hz to 500 Hz) but also pressure pulse waves (frequency band: about several tens of Hz) dV, which are pulse wave vibrations of the artery 91 passing through the measurement site 90. The sound generated by the measurement site 90 is transmitted from the space Cc formed by the fluid bag 22 through the air piping 37 to the Korotkoff sound detection device 60 (space Cd) in the main body 10.

[0061] FIG. 5 shows an operational flow when a user measures blood pressure using the sphygmomanometer 1.

[0062] When the user issues a command to start measurement using measurement switch 52A of operation unit 52 provided on main body 10 while cuff 20 is attached to the body part to be measured, control unit 110 performs initialization (step S1 in FIG. 5). Specifically, control unit 110 initializes the processing memory area, turns off (stops) pump 32, and adjusts pressure sensor 31 to 0 mmHg (sets atmospheric pressure to 0 mmHg) with valve 33 open. In this initial state, diaphragm 62 of Korotkoff sound detection device 60 is in a flat state, as shown in FIG. 6(A).

[0063] Next, the control unit 110 functions as a pressure control unit and closes the valve 33 via the valve drive circuit 330 (step S2 in FIG. 5), and then turns on (drives) the pump 32 via the pump drive circuit 320 to start pressurizing the cuff 20 (fluid bag 22) (step S3). That is, the control unit 110 supplies air as a fluid from the pump 32 through the air piping 37 to the fluid bag 22 in the cuff 20. At the same time, the pressure sensor 31 receives the cuff pressure Pc through the air piping 37. The control unit 110 controls the pressurization speed by the pump 32 based on the output of the pressure sensor 31.

[0064] 6(B), in this pressurization process, diaphragm 62 of Korotkoff sound detection device 60 receives the air pressure in air pipe 37 (particularly air pipe 37d) on one surface 62a (the surface on the space Cd side) and bends convexly toward the other surface 62b. This blocks the air pressure in air pipe 37. Furthermore, when the air pressure in chamber Cm is about to change due to the bending of diaphragm 62, pressure relief hole 63o of thin tube 63 allows air to circulate between the inside and outside of chamber Cm as shown by arrow Ai, and acts to suppress the air pressure in chamber Cm from changing from atmospheric pressure Am.

[0065] Next, in step S4 of FIG. 5, the control unit 110 judges whether the cuff pressure Pc has reached a predetermined value (predetermined pressure) based on the output of the pressure sensor 31. Here, the predetermined pressure may be set to, for example, 180 mmHg so as to sufficiently exceed the expected blood pressure value of the user, or may be set to the user's blood pressure value measured previously plus 40 mmHg. The control unit 110 continues to inflate the cuff pressure Pc until it reaches the predetermined pressure, and when the cuff pressure Pc reaches the predetermined pressure (YES in step S4), the control unit 110 stops the pump 32 (step S5). Next, the control unit 110 gradually opens the valve 33 via the valve drive circuit 330 (step S6). This reduces the cuff pressure Pc at a substantially constant speed.

[0066] 6(B), the diaphragm 62 receives the air pressure in the air pipe 37 on one surface 62a, blocking the air pressure in the air pipe 37 and vibrating as shown by the arrow Bs, allowing sounds in the frequency band of the Korotkoff sound to pass through the diaphragm 62. As a result, the sound that has passed through the diaphragm 62 is transmitted to the air occupying the chamber Cm. The microphone 40 receives the sound that has passed through the diaphragm 62 via the air occupying the chamber Cm, converts it into an electric sound signal Ks, and outputs it via the wiring 71.

[0067] Here, the diaphragm 62 blocks the air pressure in the air piping 37, so that the influence of the pressure pulse wave dV, which is the pulse wave vibration of the artery 91, on the sound generated by the measurement site 90 can be reduced. Moreover, the microphone 40 receives the sound transmitted through the diaphragm 62 via the air occupying the chamber Cm, in other words, receives it at a position separated from the diaphragm 62 (which directly receives the pressure pulse wave). Therefore, the influence of the pressure pulse wave dV can be further reduced. This makes it possible to remove noise due to the pressure pulse wave dV from the sound generated by the measurement site 90.

[0068] In addition, the diaphragm 62 is set to have a natural frequency that matches the frequency band of the Korotkoff sound, so it can selectively transmit sounds that have the frequency band of the Korotkoff sound among the sounds that have been transmitted from the measurement site 90 through the air in the air piping 37 (and space Cd). Furthermore, the chamber Cm is set to have a resonant frequency that matches the frequency band of the Korotkoff sound, so it can selectively amplify sounds that have the frequency band of the Korotkoff sound among the sounds that have been transmitted through the diaphragm 62. Therefore, the Korotkoff sound can be extracted with a good S / N ratio.

[0069] During this decompression process, as shown in step S7 (Korotkoff sound extraction processing) of Figure 5, the control unit 110 acquires the sound signal Ks output by the Korotkoff sound detection device 60 (microphone 40) via the A / D conversion circuit 410, and extracts a signal representing the Korotkoff sound (called the "Korotkoff sound signal Kc") from the sound signal Ks.

[0070] Specifically, FIG. 7 illustrates the sound signal Ks output by the Korotkoff sound detection device 60. The mountain-shaped curve in FIG. 7 represents the cuff pressure Pc. In this example, the cuff pressure Pc reaches a predetermined pressure of 180 mmHg about 17 seconds after the start of pressurization, and the depressurization process starts from that point. In this example, the sound signal Ks includes a plurality of pulse-shaped Korotkoff sound signals Kc that exceed the background noise level Ap-p (about 0.02 V in this example). In this example, the control unit 110 works as a threshold setting unit and sets a threshold TH (about 0.06 V in this example) that exceeds the background noise level Ap-p for the sound signal Ks. Then, the control unit 110 extracts only the signal that exceeds the threshold TH from the sound signal Ks as the Korotkoff sound signal Kc. This makes it possible to remove background noise from the sound signal Ks. Therefore, the S / N ratio of the Korotkoff sound can be further improved. At the same time, under the control of control unit 110, memory 51 stores the amplitude of the extracted Korotkoff sound signal Kc in association with the time at which the Korotkoff sound signal Kc was generated.

[0071] 5, the control unit 110 functions as a blood pressure calculation unit to calculate the blood pressure at the measurement site based on the Korotkoff sound signal Kc stored in the memory 51. Specifically, in the above-mentioned decompression process, the cuff pressure Pc at the time when the Korotkoff sound signal Kc first appears is determined as the systolic blood pressure SYS (Systolic Blood Pressure), and the cuff pressure Pc at the time when the Korotkoff sound signal Kc last appears is determined as the diastolic blood pressure DIA (Diastolic Blood Pressure).

[0072] Once the blood pressure values ​​(systolic blood pressure SYS and diastolic blood pressure DIA) have been calculated in this manner (YES in step S9), the control unit 110 functions as a pressure control unit and performs control to turn off the pump 32, open the valve 33, and rapidly exhaust the air in the cuff 20 (fluid bag 22) (step S10). After this, the control unit 110 performs control to display the calculated blood pressure values ​​on the display 50 and store them in the memory 51.

[0073] Thus, according to this blood pressure measurement method, Korotkoff sounds can be extracted with a good S / N ratio from sounds generated by measurement site 90, and therefore the accuracy of blood pressure measurement can be improved.

[0074] The present inventors have produced a blood pressure monitor including a Korotkoff sound detector according to FIG. 2 of Patent Document 1 (JP Patent Publication 58-180132 A) as a comparative example. The parts of the blood pressure monitor other than the Korotkoff sound detector are configured in the same manner as in the blood pressure monitor 1 described above. FIG. 8 illustrates a sound signal Ks' output by the Korotkoff sound detector. In the example of FIG. 8, the cuff pressure Pc reaches a predetermined pressure of 180 mmHg about 17 seconds after the start of pressurization, and the depressurization process starts from that point. In the sound signal Ks' of this comparative example, as can be seen by comparing it with the verification result of FIG. 7, the signal corresponding to the Korotkoff sound signal Kc is buried in noise. For this reason, it can be said that it is difficult to extract only the Korotkoff sound from the sound generated by the measurement site in this comparative example.

[0075] In the above-mentioned decompression process (steps S6 to S9 in FIG. 5), diaphragm 62 of Korotkoff sound detection device 60 gradually attempts to return from the state in which it is bent convexly toward the other surface 62b as shown in FIG. 6(B) to the flat state shown in FIG. 6(A). When this causes the air pressure in chamber Cm to change, pressure relief hole 63o of thin tube 63 allows air to circulate between the inside and outside of chamber Cm as shown by arrow Ai, and acts to suppress the air pressure in chamber Cm from changing from atmospheric pressure Am.

[0076] Therefore, the air pressure in chamber Cm is prevented from changing from atmospheric pressure Am not only during the pressurization process (steps S3 to S4 in FIG. 5) but also during the depressurization process (steps S6 to S9 in FIG. 5). As a result, it is possible to prevent adverse effects on the sensitivity, resolution, durability, and reliability of microphone 40 due to changes in air pressure (load) in air piping 37. Furthermore, various types of microphones, such as not only condenser microphones but also dynamic microphones and MEMS (Micro Electronics Mechanical System) microphones, can be used as microphone 40, increasing the freedom of microphone selection.

[0077] (Modification) In the above example, the pressure relief holes 63o, 63oB, 63oC for the chamber Cm are in the form of elongated conduits provided inside the capillaries 63, 63B, 63C, but are not limited thereto. The pressure relief holes may be in the form of elongated grooves 41d, 61B2d shown in Fig. 9(A) or elongated grooves 61B1d shown in Fig. 9(B). In Fig. 9(A) and Fig. 9(B), the same reference numerals are used to designate components corresponding to those already described, and duplicated explanations will be omitted.

[0078] In the examples of Korotkoff sound detection devices 60′ and 60″ shown in FIGS. 9(A) and 9(B), the cylindrical portion 61B3 of the upper case 61B and the air piping 38 are omitted from the example of FIG. 2(A). Instead, a through hole 61B2o is provided at the top of the dome portion 61B2 of the upper case 61B, and further, a commercially available MEMS microphone 40A having a flat, approximately rectangular parallelepiped outer shape is closely attached to the top surface of the dome portion 61B2 via a substrate 41 having a through hole 41o. The chamber Cm is fluidically connected to the microphone 40A via the through-hole 61B2o of the dome portion 61B2 and the through-hole 41o of the substrate 41. Therefore, the microphone 40A can receive the sound transmitted through the diaphragm 62 via the air occupying the chamber Cm, convert it into an electric sound signal Ks, and output it. The dimension of the microphone 40A in the planar direction (the direction in which it spreads out flat) is several mm square.

[0079] In the example of the Korotkoff sound detection device 60' shown in Fig. 9(A), the pressure relief holes for the chamber Cm consist of an elongated groove 61B2d formed in the top surface of the dome portion 61B2 of the upper case 61B, and an elongated groove 41d formed in a position that overlaps with and corresponds to the elongated groove 61B2d on the underside (the surface in contact with the dome portion 61B2) of the substrate 41. When the diaphragm 62 bends as the air pressure in the air piping 37 (and space Cd) gradually changes during the pressurization or depressurization process of the cuff 20, causing the air pressure in the chamber Cm to change, these elongated grooves 41d, 61B2d allow air to circulate between the inside and outside of the chamber Cm via the through-hole 61B2o of the dome portion 61B2, as shown by arrows AiD in Fig. 9(A), and act to suppress the air pressure in the chamber Cm from changing from the atmospheric pressure Am. Therefore, even if the air pressure in the air pipe 37 (and the space Cd) changes, it is possible to prevent the pressure change (load) from adversely affecting the sensitivity, resolution, durability, and reliability of the microphone 40A. Note that one of the elongated grooves 41d and 61B2d may be omitted.

[0080] In the example of Korotkoff sound detection device 60" shown in FIG. 9(B), the pressure relief hole for chamber Cm consists of a long, thin groove 61B1d formed in the underside (the surface in contact with diaphragm 62) of plate portion 61B1 of upper case 61B. When diaphragm 62 bends as the air pressure in air piping 37 (and space Cd) gradually changes during the pressurization or depressurization process of cuff 20, causing the air pressure in chamber Cm to change, this long, thin groove 61B1d allows air to circulate between the inside and outside of chamber Cm, as shown by arrows AiE in FIG. 9(B), and acts to suppress the air pressure in chamber Cm from changing from atmospheric pressure Am. Therefore, even if the air pressure in air piping 37 (and space Cd) changes, it is possible to prevent the pressure change (load) from adversely affecting the sensitivity, resolution, durability, and reliability of microphone 40A.

[0081] Note that a sound-insulating material having breathability and sound-insulating properties (e.g., polyurethane foam) may be accommodated in the elongated grooves 41d, 61B2d shown in Fig. 9(A) and the elongated grooves 61B1d shown in Fig. 9(B). This makes it possible to prevent the elongated grooves 41d, 61B2d, or 61B1d from lowering the S / N ratio of the Korotkoff sound.

[0082] It should be noted that blood pressure measurement by the sphygmomanometer 1 may be performed during the pressurization process, not during the depressurization process.

[0083] Furthermore, the part to be measured is not limited to the upper arm, but may be an upper limb other than the upper arm, such as the wrist, or a lower limb, such as the ankle.

[0084] The above-mentioned embodiments are merely examples, and various modifications are possible without departing from the scope of the present invention. The above-mentioned embodiments can be realized independently, but the embodiments can also be combined with each other. In addition, the various features of the different embodiments can be realized independently, but the features of the different embodiments can also be combined with each other. [Explanation of symbols]

[0085] 1. Blood pressure monitor 10. Main Unit 20 Cuff 22 Fluid bag 31 Pressure Sensor 32 Pump 33 Valve 40,40A Microphone 41 Substrate 41d, 61B1d, 61B2d Long and narrow groove 60,60′,60″ Korotkoff sound detector 62 Diaphragm 63,63A,63B,63C Tube 63o, 63oB, 63oC Pressure relief holes 64 Polyurethane foam

Claims

1. A sphygmomanometer for measuring blood pressure based on Korotkoff sounds generated at a measurement site, A pressure cuff configured to be attached to the measurement site; A pump, an air pipe fluidly connecting the cuff and the pump; a pressure control unit that supplies air to the cuff through the air piping by the pump to pressurize the measurement site, or that exhausts the air from the cuff through the air piping to reduce pressure; a diaphragm is provided as a part of a tube wall of the air piping or connected to the tube wall, and is arranged so as to receive the air pressure in the air piping on one side, the diaphragm being configured to block the air pressure in the air piping during the pressurization or depressurization process of the cuff by the pressure control unit, while allowing sounds in the frequency band of the Korotkoff sounds, among sounds transmitted from the measurement site through the air in the air piping, to pass through the diaphragm; a chamber is provided on the other surface side of the diaphragm opposite to the one surface, the chamber including the diaphragm as a part of a peripheral wall, and sound transmitted through the diaphragm is transmitted to air occupying the chamber; a sound detection device is provided on a portion of the peripheral wall of the chamber other than the diaphragm so as to face the air in the chamber, and the sound detection device receives the sound transmitted through the diaphragm via the air occupying the chamber and converts it into an electric signal; A blood pressure calculation unit is provided to calculate the blood pressure at the measurement site based on the electrical signal. A blood pressure monitor characterized by the above.

2. 2. The blood pressure monitor according to claim 1, A pressure relief hole that fluidly communicates the inside and outside of the chamber is provided in the peripheral wall of the chamber other than the diaphragm, and the pressure relief hole acts to suppress the pressure of the air in the chamber from changing from atmospheric pressure. A blood pressure monitor characterized by the above.

3. 3. The blood pressure monitor according to claim 2, The pressure relief holes have the form of elongated channels or elongated grooves. A blood pressure monitor characterized by the above.

4. 4. The blood pressure monitor according to claim 3, A sound-insulating material having breathability and sound-insulating properties is accommodated inside the elongated duct or the elongated groove. A blood pressure monitor characterized by the above.

5. The blood pressure monitor according to any one of claims 1 to 4, The diaphragm is set to have a natural frequency that matches the frequency band of the Korotkoff sound. A blood pressure monitor characterized by the above.

6. The blood pressure monitor according to any one of claims 1 to 4, The chamber is configured to have a resonant frequency that matches the frequency range of the Korotkoff sounds. A blood pressure monitor characterized by the above.

7. The blood pressure monitor according to any one of claims 1 to 4, The diaphragm is made of synthetic resin. A blood pressure monitor characterized by the above.

8. The blood pressure monitor according to any one of claims 1 to 4, a threshold setting unit that sets a threshold for extracting the Korotkoff sound in the electrical signal output by the sound detection device, The blood pressure calculation unit calculates the blood pressure at the measurement site based on only the signal exceeding the threshold value among the electrical signals. A blood pressure monitor characterized by the above.

9. A blood pressure measurement method for measuring blood pressure based on Korotkoff sounds generated at a measurement site by the sphygmomanometer according to claim 1, comprising: With the pressing cuff attached to the measurement site, the pressure control unit supplies air to the cuff through the air piping by the pump to pressurize the measurement site, or exhausts the air from the cuff through the air piping to reduce pressure, During the process of pressurizing or depressurizing the cuff by the pressure control section, the diaphragm receives the air pressure in the air piping on one side, blocking the air pressure in the air piping and allowing sounds in the frequency band of the Korotkoff sounds, which are transmitted from the measurement site through the air in the air piping, to pass through the diaphragm, and as a result, the sounds that have passed through the diaphragm are transmitted to the air occupying the chamber, The sound detection device receives the sound transmitted through the diaphragm via the air occupying the chamber and converts it into an electrical signal; The blood pressure calculation unit calculates the blood pressure at the measurement site based on the electrical signal. A blood pressure measuring method comprising:

10. A Korotkoff sound detection device included in the blood pressure monitor according to claim 1, which extracts Korotkoff sounds from sounds generated at the measurement site, a diaphragm is provided as a part of a tube wall of the air piping or connected to the tube wall, and is arranged so as to receive the air pressure in the air piping on one side, the diaphragm being configured to block the air pressure in the air piping during the pressurization or depressurization process of the cuff by the pressure control unit, while allowing sounds in the frequency band of the Korotkoff sounds, among sounds transmitted from the measurement site through the air in the air piping, to pass through the diaphragm; a chamber is provided on the other surface side of the diaphragm opposite to the one surface, the chamber including the diaphragm as a part of a peripheral wall, and sound transmitted through the diaphragm is transmitted to air occupying the chamber; A sound detection device is provided on the peripheral wall of the chamber other than the diaphragm and facing the air in the chamber, and the sound detection device receives the sound transmitted through the diaphragm via the air occupying the chamber and converts it into an electric signal. A Korotkoff sound detection device.

Images