Pressure sensor pad and pressure measuring device

Abstract

To accurately measure a change over time in pressure on an object with a pressure sensor without using a cuff.SOLUTION: This pressure sensor pad is for pressing, against an object, a pressure sensor for measuring a change over time in the pressure on the object, and is formed from a porous body having an elastic coefficient of 0.1 MPa or less. The thickness of the pressure sensor pad is 3 mm to 10 mm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a pressure sensor pad for pressing a pressure sensor against an object to measure changes in pressure of the object over time. [Background technology]

[0002] A wristwatch-type blood pressure measurement device that is worn on a person's wrist to measure blood pressure values ​​has been proposed (see, for example, Patent Document 1). This blood pressure measurement device includes a pressure sensor that uses, for example, a piezoelectric element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-002183 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional blood pressure measurement devices include a cuff (arm cuff) for compressing the artery. Therefore, the presence of the cuff tends to make the device relatively large. Furthermore, the pressure on the artery caused by the cuff tends to make the user feel a sense of pressure and strain on the heart. Thus, conventional blood pressure measurement devices have the problem of needing a cuff to measure blood pressure accurately.

[0005] Note that this problem is not limited to blood pressure measurement devices, but is a common problem among pressure measurement devices equipped with a pressure sensor for measuring changes in the pressure of an object over time.

[0006] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

[0007] The technology disclosed in this specification can be realized, for example, in the following forms.

[0008] (1) The pressure sensor pad disclosed in this specification is for pressing a pressure sensor against an object to measure changes in pressure of the object over time. The pressure sensor pad is formed of a porous material with an elastic modulus of 0.1 MPa or less. The thickness of the pressure sensor pad is 3 mm or more and 10 mm or less. This pressure sensor pad allows the pressure sensor to accurately measure changes in pressure of the object over time without using a cuff.

[0009] (2) In the pressure sensor pad, the thickness of the pressure sensor pad may be 5 mm or more and 10 mm or less. With this configuration, the pressure sensor can measure changes in the pressure of the object over time with even greater accuracy.

[0010] (3) In the pressure sensor pad, the compressive stress-compressive strain curve of the porous body may be divided by two inflection points of the curve and may include a first region, a second region, and a third region arranged in order of increasing compressive strain, and the porous body may be in the first region or the second region when a preload of 0.5 N or more and 1.5 N or less is applied. This configuration enables the pressure sensor to measure changes in the pressure of the object over time with even greater accuracy.

[0011] (4) In the pressure sensor pad, the pressure of the object may be blood pressure. With this configuration, the pressure sensor can accurately measure changes in blood pressure over time.

[0012] (5) The pressure measuring device disclosed in this specification includes the pressure sensor pad and the pressure sensor pressed against the object by the pressure sensor pad. With this configuration, it is possible to accurately measure changes in the pressure of the object over time using the pressure sensor pressed against the object by the pressure sensor pad without using a cuff.

[0013] (6) In the pressure measuring device, the pressure sensor may include a piezoelectric element. With this configuration, it is possible to measure changes in the pressure of an object over time with the same accuracy as when a capacitance-type pressure sensor is used.

[0014] The technology disclosed in this specification can be realized in various forms, such as a pressure sensor pad, a pressure measuring device including a pressure sensor and a pressure sensor pad, a method of manufacturing or using a pressure measuring device, etc. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a blood pressure measurement device 100 according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing a state in which the blood pressure measurement device 100 of the present embodiment is worn. [Figure 3] FIG. 1 is an illustration showing a typical compressive stress-compressive strain curve for the foamed hyperelastic material used to form the pad 10. [Figure 4] FIG. 1 is an explanatory diagram showing an example of changes over time in blood pressure values ​​BP measured by a blood pressure measurement device 100. [Figure 5] An explanatory diagram showing the configuration of the experimental device 200 used for performance evaluation. [Figure 6] Graph showing pressure pulse waves measured by the experimental device 200 [Figure 7] Graph showing the measurement results of the compressive stress-compressive strain curves for samples SA1 to SA4 [Figure 8] Graph showing the measurement results of the compressive stress-compressive strain curve when the thickness t of the pad 10 is changed for sample SA1. [Figure 9] Graph showing the measurement results of the compressive stress-compressive strain curve when the thickness t of the pad 10 is changed for sample SA2. [Figure 10] Graph showing pressure pulse waves when the thickness t of the pad 10 and the preload PP applied to the pad 10 are varied for sample SA1. [Figure 11]FIG. 10 is an explanatory diagram showing the evaluation results of the measurement accuracy of the pressure pulse wave when the thickness t of the pad 10 and the preload PP applied to the pad 10 are varied for sample SA1. [Figure 12] Graph showing pressure pulse waves when the thickness t of the pad 10 and the preload PP applied to the pad 10 are varied for sample SA2. [Figure 13] FIG. 10 is an explanatory diagram showing the evaluation results of the measurement accuracy of the pressure pulse wave when the thickness t of the pad 10 and the preload PP applied to the pad 10 are varied for sample SA2. [Figure 14] Graph showing the measurement accuracy of pressure pulse waves using a pressure sensor DETAILED DESCRIPTION OF THE INVENTION

[0016] (Configuration of blood pressure measurement device 100) Fig. 1 is an explanatory diagram showing the configuration of a blood pressure measurement device 100 according to this embodiment. Fig. 2 is an explanatory diagram showing the wearing state of the blood pressure measurement device 100 according to this embodiment.

[0017] The blood pressure measurement device 100 of this embodiment is a device for measuring a person's blood pressure. As shown in Fig. 2, the blood pressure measurement device 100 is worn on the person's wrist WP and measures the blood pressure for each beat according to the tonometry method using a pressure sensor 20 pressed against the radial artery BV running on the radius RA near the body surface SU. The blood pressure measurement device 100 is an example of a pressure measurement device.

[0018] The blood pressure measurement device 100 includes a band 40, a main body 30, a pressure sensor 20, and a pressure sensor pad (hereinafter also simply referred to as a "pad") 10.

[0019] The band 40 is a belt-like member for fixing the blood pressure measurement device 100 to a person's wrist WP. The main body 30 and the pad 10 are attached to the band 40.

[0020] The main unit 30 is a part that controls the entire blood pressure measurement device 100. The main unit 30 includes, for example, an integrated circuit, a display, a communication interface, and a battery that supplies power to each component. The main unit 30 communicates with the pressure sensor 20 and other devices via the communication interface in accordance with a communication standard such as Bluetooth (registered trademark). The main unit 30 also displays various images on the display. In the example of FIG. 1, the display of the main unit 30 displays images indicating the time (4:08 p.m.), blood pressure values ​​(systolic blood pressure 117, diastolic blood pressure 71), blood glucose level (81), pulse rate (76), health status (good), and remaining battery power.

[0021] The pressure sensor 20 is a sensor for measuring changes in pressure over time. The pressure sensor 20 includes a piezoelectric element that outputs a voltage signal corresponding to the force (pressure). In this embodiment, the pressure sensor 20 uses a PZT (lead zirconate titanate) film formed as a piezoelectric element on a flexible substrate. The PZT film thickness is, for example, 2 μm.

[0022] The pad 10 is interposed between the band 40 or the main body 30 and the pressure sensor 20, and serves to press the pressure sensor 20 against a person's wrist WP. The pad 10 allows the blood pressure measurement device 100 to measure blood pressure and other biological information with high accuracy without using a cuff. In this embodiment, the pad 10 is a porous body, formed, for example, from a foamed superelastic material. Examples of materials for forming the pad 10 include polyurethane sponge, melamine sponge, and ethylene propylene diene rubber sponge. In this embodiment, the pad 10 is substantially flat and rectangular in plan view. The width and height of the pad 10 may be, for example, 10 mm or more and 30 mm or less, or 15 mm or more and 25 mm or less.

[0023] FIG. 3 is an explanatory diagram showing a typical compressive stress-compressive strain curve of the foamed hyperelastic material used to form the pad 10. This compressive stress-compressive strain curve includes a first region R1, in which the compressive strain ε increases approximately linearly with increasing compressive stress σ; a second region R2, continuous with the first region R1, in which the compressive strain ε increases at a substantially constant compressive stress σ; and a third region R3, continuous with the second region R2, in which the compressive stress σ increases more rapidly than in the first region R1. In the first region R1, the material deforms linearly due to bending of the porous walls. In the second region R2, the porous walls deform significantly. The second region R2 is also called the plateau region. In the third region R3, the porous walls compress against each other, causing a sudden increase in the compressive stress σ. Each region in the compressive stress-compressive strain curve is defined by an inflection point POI, where the second derivative of the curve becomes zero.

[0024] As shown in FIG. 2 , the attachment positions of the pressure sensor 20 and the pad 10 on the band 40 are set so that the pressure sensor 20 and the pad 10 are positioned above the radial artery BV when the blood pressure measurement device 100 is attached to a person's wrist WP. When the blood pressure measurement device 100 is attached to a person's wrist WP, the pressure sensor 20 outputs a voltage signal indicating changes over time (pressure pulse waves) in the internal pressure of the radial artery BV (i.e., blood pressure) to the main body 30. The main body 30 converts the voltage signal output from the pressure sensor 20 into a blood pressure value. This allows the blood pressure measurement device 100 to measure the blood pressure value. The radial artery BV is an example of an object whose pressure is measured by the pressure sensor 20.

[0025] FIG. 4 is an explanatory diagram showing an example of changes over time in blood pressure BP measured by the blood pressure measurement device 100. FIG. 4 shows changes over time in blood pressure BP over a period T0 equivalent to one cardiac beat. Generally, a curve showing changes over time in blood pressure BP has a shape in which an ejection wave Ws, a reflected wave (tidal wave) Wt, and a dicrotic wave Wd are arranged in this order. The ejection wave Ws and the reflected wave Wt are observed during the systolic phase T1 of the heart, which corresponds to the first half of the pulse, and the dicrotic wave Wd is observed during the diastolic phase T2 of the heart, which corresponds to the second half of the pulse. In the curve shown in FIG. 4, the blood pressure P0 at the start of the pulse is the minimum blood pressure, and the blood pressure P1 at the peak of the ejection wave Ws is the maximum blood pressure. The shape of the curve showing changes over time in blood pressure BP is determined by factors such as cardiac pulsation, valve opening and closing, blood vessel stiffness, and blood viscosity. Therefore, by using a known method, it is possible to predict blood glucose levels, the state of arteriosclerosis, and cardiovascular events (heart failure, myocardial or cerebral infarction, cardiovascular death, etc.) from, for example, the blood pressure P2 at the peak of the reflected wave Wt or the AI ​​(Augmentation Index) value, which is the ratio of blood pressure P2 to blood pressure P1 (=P2 / P1).The blood pressure measurement device 100 of this embodiment displays blood pressure values, blood glucose levels, pulse rate, and health status on the display of the main body 30 based on the measurement results from the pressure sensor 20.

[0026] (Detailed configuration of Pad 10) The pad 10 of this embodiment is formed from a porous material with an elastic modulus of 0.1 MPa or less. The elastic modulus of the material forming the pad 10 may be 0.08 MPa or less, 0.05 MPa or less, or 0.01 MPa or less. The elastic modulus of the material forming the pad 10 is the slope of the linear portion in the first region R1 of the compressive stress-compressive strain curve shown in Figure 3. When a preload of 0.5 N or more and 1.5 N or less is applied, the pad 10 is in the state of the first region R1 or the second region R2 of the compressive stress-compressive strain curve.

[0027] In this embodiment, the thickness t of the pad 10 is 0.5 mm or more and 20 mm or less. The thickness t of the pad 10 may be 1 mm or more and 15 mm or less, 3 mm or more and 10 mm or less, 5 mm or more and 9 mm or less, or 6 mm or more and 8 mm or less.

[0028] (Example) A number of samples of the pad 10 used in the blood pressure measurement device 100 with different characteristics were prepared and their performance was evaluated. FIG. 5 is an explanatory diagram showing the configuration of an experimental device 200 used in the performance evaluation. The experimental device 200 includes a test stand 210, a force gauge 220, a charge amplifier 230, and an oscilloscope 240. A person's hand HH was placed on the test stand 210, with the pressure sensor 20 placed on the wrist. A sample of the pad 10 was then placed on top of the test stand 210, and a preload was applied to the pad 10 so as to press the pressure sensor 20 against the person's wrist. In this state, the waveform showing the time-dependent change in blood pressure (pressure pulse wave) measured by the pressure sensor 20 was read by the oscilloscope 240.

[0029] Fig. 6 is a graph showing pressure pulse waves measured by the experimental device 200. Fig. 6 shows pressure pulse waves measured when a preload of 0.5 N was applied to the pad 10 for multiple samples SA1 to SA8 made of different materials. The materials used to make each sample are as follows: Sample SA1: Ethylene propylene diene rubber foam Sample SA2: Ethylene propylene diene rubber sponge (closed cell) Sample SA3: Polyurethane sponge (open cell) Sample SA4: Melamine sponge (net type) Sample SA5: Polyurethane sponge Sample SA6: Ultra-low hardness urethane sheet Sample SA7: Special pore polyurethane sponge Sample SA8: Chloroprene rubber sponge

[0030] As shown in Figure 6, of the eight samples, samples SA1 to SA5 clearly show the waveform of a pressure pulse wave having an ejection wave Ws, a reflected wave Wt, and a dicrotic wave Wd, so it can be said that if the materials for these samples are used to fabricate pad 10, the accuracy of pressure measurement by pressure sensor 20 will be improved. In particular, samples SA1, SA3, and SA5 show the waveform of a pressure pulse wave very clearly, so it can be said that if the materials for these samples are used to fabricate pad 10, the accuracy of pressure measurement by pressure sensor 20 will be further improved.

[0031] Fig. 7 is a graph showing the measurement results of the compressive stress-compressive strain curves for samples SA1 to SA4. As shown in Fig. 7, all of samples SA1 to SA4 have an elastic modulus E of 0.1 MPa or less. Furthermore, all of samples SA1 to SA4 are in the first region R1 or the second region R2 on the compressive stress-compressive strain curve when a preload of 0.5 N or more and 1.5 N or less is applied.

[0032] Fig. 8 is a graph showing the measurement results of the compressive stress-compressive strain curve for sample SA1 when the thickness t of pad 10 is varied. As shown in Fig. 8, when a preload of 0.5 N or more and 1.5 N or less is applied to sample SA1, regardless of whether the thickness t is 1 mm, 5 mm, or 10 mm, the compressive stress-compressive strain curve is in the first region R1 or the second region R2.

[0033] Fig. 9 is a graph showing the measurement results of the compressive stress-compressive strain curve for sample SA2 when the thickness t of pad 10 is varied. As shown in Fig. 9, when a preload of 0.5 N or more and 1.5 N or less is applied to sample SA2, regardless of whether the thickness t is 1 mm, 5 mm, or 10 mm, the compressive stress-compressive strain curve is in the first region R1 or the second region R2.

[0034] FIG. 10 is a graph showing the pressure pulse wave for sample SA1 when the thickness t of pad 10 and the preload PP applied to pad 10 are varied. FIG. 11 is an explanatory diagram showing the evaluation results of the pressure pulse wave measurement accuracy for sample SA1 when the thickness t of pad 10 and the preload PP applied to pad 10 are varied. As shown in FIGS. 10 and 11 , when the thickness t is 3 mm and the preload PP is 1.0 N, when the thickness t is 5 mm and the preload PP is 0.5 N or 1.0 N, and when the thickness t is 10 mm and the preload PP is 0.5 N, 1.0 N, or 1.5 N, a pressure pulse wave waveform including an ejection wave Ws, a reflected wave Wt, and a dicrotic wave Wd was clearly displayed, as indicated by "◯" in FIG. 11 . In other cases, the pressure pulse wave waveform was not clearly displayed, as indicated by "X" in FIG. 11 .

[0035] FIG. 12 is a graph showing the pressure pulse wave for sample SA2 when the thickness t of pad 10 and the preload PP applied to pad 10 are varied. FIG. 13 is an explanatory diagram showing the evaluation results of the pressure pulse wave measurement accuracy for sample SA2 when the thickness t of pad 10 and the preload PP applied to pad 10 are varied. As shown in FIGS. 12 and 13 , when the thickness t was 5 mm and the preload PP was 0.3 N, 0.5 N, 1.0 N, or 1.5 N, and when the thickness t was 10 mm and the preload PP was 0.5 N, 1.0 N, or 1.5 N, a pressure pulse wave waveform including an ejection wave Ws, a reflected wave Wt, and a dicrotic wave Wd was clearly displayed, as indicated by "◯" in FIG. 13 . In other cases, the pressure pulse wave waveform was not clearly displayed, as indicated by "X" in FIG. 13 .

[0036] FIG. 14 is a graph showing the measurement accuracy of pressure pulse waves by a pressure sensor. FIG. 14 shows the pressure pulse waves measured by the pressure sensor 20 of this embodiment and the pressure pulse waves measured by the pressure sensor 20X of the comparative example. The pressure sensor 20 of this embodiment has a PZT film formed as a piezoelectric element on a flexible substrate. The pressure sensor 20X of the comparative example is a capacitance-type pressure sensor (FS1M-5NP manufactured by THK PRECISION). As shown in FIG. 14, the pressure pulse waves measured by the two pressure sensors 20 and 20X are almost identical (correlation coefficient: 0.99), confirming that the pressure sensor 20 of this embodiment has measurement accuracy comparable to that of the capacitance-type pressure sensor 20X.

[0037] (Effects of this embodiment) As described above, the pad 10 of this embodiment is used to press the pressure sensor 20 against the human body to measure changes in blood pressure over time, and is made of a porous material with an elastic modulus of 0.1 MPa or less, and has a thickness t of 3 mm or more and 10 mm or less. The pad 10 of this embodiment allows the pressure sensor 20 to accurately measure changes in blood pressure over time without using a cuff.

[0038] The thickness t of the pad 10 of this embodiment is not less than 5 mm and not more than 10 mm. According to the pad 10 of this embodiment, the pressure sensor 20 can measure changes in blood pressure over time with even greater accuracy.

[0039] The compressive stress-compressive strain curve of the porous body used to form the pad 10 of this embodiment is divided by two inflection points POI of the curve and includes a first region R1, a second region R2, and a third region R3 arranged in order of increasing compressive strain, and is in the state of the first region R1 or the second region R2 when a preload of 0.5 N or more and 1.5 N or less is applied to the pad 10. According to the pad 10 of this embodiment, the pressure sensor 20 can measure changes in blood pressure over time with even greater accuracy.

[0040] The blood pressure measuring device 100 of this embodiment includes a pad 10 and a pressure sensor 20 pressed against the human body by the pad 10. According to the blood pressure measuring device 100 of this embodiment, it is possible to accurately measure changes in blood pressure over time by the pressure sensor 20 pressed against the human body by the pad 10, without using a cuff.

[0041] In the blood pressure measurement device 100 of this embodiment, the pressure sensor 20 includes a piezoelectric element. The blood pressure measurement device 100 of this embodiment can measure changes in blood pressure over time with the same accuracy as when a capacitance-type pressure sensor is used.

[0042] (Variation) The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible.

[0043] The configuration of the blood pressure measurement device 100 in the above embodiment is merely an example and can be modified in various ways. For example, the shape and material of the pad 10 are merely an example and can be modified in various ways.

[0044] In the blood pressure measurement device 100 of the above embodiment, the pressure sensor 20 is pressed against the wrist using the pad 10 to measure pressure, but the location where blood pressure is measured using the pressure sensor 20 is not limited to the wrist and may be other parts of the human body such as the neck, feet, or ears.

[0045] In the above embodiment, an example in which the pad 10 is applied to the blood pressure measuring device 100 has been described. However, the pad 10 disclosed in this specification is not limited to blood pressure measuring devices and may be used in general applications in which a pressure sensor for measuring changes in pressure over time of an object is pressed against the object. [Explanation of symbols]

[0046] 10: Pressure sensor pad 20: Pressure sensor 30: Main body 40: Band 100: Blood pressure measuring device 200: Experimental equipment 210: Test stand 220: Force gauge 230: Charge amplifier 240: Oscilloscope BV: Radial artery R1: First region R2: Second region R3: Third region RA: Radius WP: Wrist Wd: Dicrotic wave Ws: Ejection wave Wt: Reflected wave

Claims

1. A pressure sensor pad for pressing a pressure sensor for measuring a change in pressure of an object over time against the object, It is formed of a porous body having an elastic modulus of 0.1 MPa or less, The thickness of the pressure sensor pad is 3 mm or more and 10 mm or less. Pressure sensor pad.

2. 2. The pressure sensor pad according to claim 1, The thickness of the pressure sensor pad is 5 mm or more and 10 mm or less. Pressure sensor pad.

3. 3. The pressure sensor pad according to claim 1, The compressive stress-compressive strain curve of the porous body includes a first region, a second region, and a third region, which are separated from each other by two inflection points of the curve and arranged in order of increasing compressive strain, A pressure sensor pad that is in the first region or the second region when a preload of 0.5 N or more and 1.5 N or less is applied.

4. 3. The pressure sensor pad according to claim 1, A pressure sensor pad, wherein the pressure of the object is blood pressure.

5. The pressure sensor pad according to claim 1 or 2; the pressure sensor being pressed against the object by the pressure sensor pad; A pressure measuring device comprising:

6. 6. The pressure measuring device according to claim 5, The pressure sensor comprises a piezoelectric element.

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