Blood flow sensor, blood flow measurement device, blood flow measurement method, device provided with blood flow sensor, and composite sensor

Abstract

Provided are a blood flow sensor, a blood flow measurement device, a blood flow measurement method, a device provided with a blood flow sensor, and a composite sensor, which are capable of measuring blood flow with high precision, high accuracy, and high-speed responsiveness. A blood flow sensor (1) that estimates the skin blood flow velocity of a living body on the basis of the skin thermal conductivity of the living body and the skin surface temperature difference of the living body, the blood flow sensor (1) being provided with: an insulating flexible substrate (5) that can be attached to the skin surface of the living body; a conductive wiring pattern (51) formed on the flexible substrate (5); a substantially annular thermal stimulation generation unit (2) that heats or cools the skin surface of the living body; a central thin film thermistor (3) disposed in the center of the thermal stimulus generating unit (2); and at least two peripheral thin-film thermistors (4) disposed at positions at a predetermined distance from the peripheral edge of the thermal stimulus generating unit (2), the at least two peripheral thin-film thermistors (4) being disposed on a straight line passing through the center of the central thin-film thermistor (3).

Description

TECHNICAL FIELD

[0001] The present application relates to a blood flow sensor, a blood flow measuring apparatus, a blood flow measuring method, an apparatus provided with a blood flow sensor, and a composite sensor. BACKGROUND

[0002] Blood flow measurement is utilized in fields of health condition and presence or absence of disease, medical, sports, and beauty industries, and the like. For example, in the medical field, blood flow measurement is performed using a blood flow sensor in diagnosis of poor blood circulation such as pressure sores, critical lower limb ischemia, or blood flow monitoring during dialysis, surgery.

[0003] In the past, a device that is mounted on a tissue and a method for monitoring heat transport characteristics (for example, thermal conductivity, thermal diffusivity, heat capacity) of a tissue such as skin have been proposed. The device is conformally mounted on the tissue and is provided with one or more thermal actuators (heat stimulus generation portions) and a plurality of temperature sensors (for example, refer to Patent Literature 1 and Patent Literature 2).

[0004] In addition, a device that measures a temperature conduction coefficient of a living body and evaluates blood flow of the living body based on the temperature conduction coefficient, and a device that determines a pressure sore risk degree have been proposed (refer to Patent Literature 3).

[0005] However, the shape of the thermal actuator shown in Patent Literature 1 and Patent Literature 2 is circular, and data obtained by temperature measurement by temperature sensors arranged around the circular heat source is used when calculating the blood vessel depth and the blood flow velocity. Since temperature conduction is dispersed from the center of measurement in the circular heat source, there is a problem that the measurement sensitivity and reproducibility are poor. Furthermore, the temperature sensor is formed of a resistance body of a 10 μm width filament of chromium / gold, and the resistance value is converted into temperature, but a deviation in the thickness and line width of the sensor easily occurs due to the shape, and as a result, a deviation in the resistance value caused by a deviation in the heat capacity of each resistance body is large. Although the difference between the temperatures measured by two of the resistance bodies is used in the calculation of the blood vessel depth, the temperature measurement accuracy is low due to the above two reasons.

[0006] Figure 10 is a graph of calculating the blood vessel depth. The horizontal axis indicates time (s), and the vertical axis ΔT' indicates the temperature difference of the two temperature sensors, and ΔT's indicates the final steady state value of the ΔT'. That is, the vertical axis indicates the time-dependent temperature change. In addition, h indicates the blood vessel depth (mm), and the broken line (h = 1 mm to 2 mm) indicates the simulation data based on the finite element model for each blood vessel depth, and the solid line (measured value) indicates the measured data. The graph indicates the comparison of the finite element model of the skin and the measured data for determining the approximate depth of the blood vessel, and it is known that the stability of the signal is low, and the calculation of the blood vessel depth takes more than 120 seconds, and the accuracy is also low.

[0007] In addition,Figure 11 is a graph showing the relationship between the blood flow velocity and the temperature difference, and each symbol of the horizontal axis indicates the following. v: blood flow velocity (m / s), L: distance between the thermal actuator and the temperature sensor (m), c f : specific heat of blood (J·kg -1 ·K -1 ), p f : density of blood (kg·m -2 ), l f : thermal conductivity of blood (W·m -1 ·K -1 ), R: vessel thickness (m). Each symbol described above is a known coefficient except for v. That is, the horizontal axis is a dimensionless number proportional to the blood flow velocity v. In the range of about 0.001 m / s to 1 m / s of the blood flow velocity of a living body, the determination coefficient R 2 < 0.3, and it can be said that there is almost no correlation.

[0008] Further, the temperature measuring portion of the device shown in Patent Literature 3 is a thermocouple, and there is a problem of poor sensitivity and precision. A Peltier element is used as the thermal stimulation generating portion, and a method of cooling the corresponding portion is adopted. Therefore, the cooling of the skin temperature takes time, and it takes a long time to obtain the skin thermal conductivity. The blood flow sensor needs to detect a small skin temperature difference of a living body, and thus high sensitivity and precision are required for the temperature detection, but in the device shown in Patent Literature 3, it is difficult to achieve high sensitivity and precision in the temperature detection.

[0009] Prior Art Documents

[0010] Patent Literature

[0011] Patent Literature 1: Japanese Patent Application Laid-Open No. 2017-532079

[0012] Patent Literature 2: Japanese Patent Application Laid-Open No. 2021-519641

[0013] Patent Literature 3: Japanese Patent No. 5327840 SUMMARY

[0014] An object of an embodiment of the present application is to provide a blood flow sensor, a blood flow measuring device, a blood flow measuring method, a device provided with a blood flow sensor, and a composite sensor, which can measure blood flow with high precision, high accuracy, and high speed responsiveness.

[0015] An embodiment of the present application relates to a blood flow sensor that estimates a skin blood flow rate of a living body based on a skin thermal conductivity of the living body and a skin surface temperature difference of the living body, characterized by including: a flexible substrate that is insulative and can be attached to a skin surface of the living body; a conductive wiring pattern formed on the flexible substrate; a substantially circular ring-shaped heat stimulus generating portion that heats or cools the skin surface of the living body; one central portion thin film thermistor disposed at a central portion of the heat stimulus generating portion; and at least two peripheral portion thin film thermistors disposed at positions apart from a peripheral portion of the heat stimulus generating portion by a certain distance, the at least two peripheral portion thin film thermistors being disposed on a straight line passing through a center of the central portion thin film thermistor.

[0016] The blood flow sensor according to the embodiment can measure blood flow with high precision, high accuracy, and high speed responsiveness.

[0017] An embodiment of the present application relates to a blood flow measuring apparatus characterized by including a control processing portion that controls each component of a blood flow sensor. The components are a heat stimulus generating portion, a central portion thin film thermistor, and peripheral portion thin film thermistors. The control processing portion is, for example, built into a controller connected to the blood flow sensor.

[0018] In addition, an embodiment of the present application relates to a blood flow measuring method using a blood flow sensor that includes: a flexible substrate that is insulative and can be attached to a skin surface of a living body; a conductive wiring pattern formed on the flexible substrate; a substantially circular ring-shaped heat stimulus generating portion that heats or cools the skin surface of the living body; one central portion thin film thermistor disposed at a central portion of the heat stimulus generating portion; and at least two peripheral portion thin film thermistors disposed at positions apart from a peripheral portion of the heat stimulus generating portion by a certain distance, the at least two peripheral portion thin film thermistors being disposed on a straight line passing through a center of the central portion thin film thermistor, the blood flow measuring method being characterized by including: a first process of calculating a skin thermal conductivity; a second process of calculating a blood vessel depth near a body surface; and a third process of calculating a blood flow rate near the body surface.

[0019] An embodiment of the present application relates to an apparatus including a blood flow sensor, and is characterized by including the blood flow sensor. The blood flow sensor is suitably mounted on various apparatuses, such as a medical device for diagnosing poor blood circulation such as bedsores and critical lower limb ischemia, blood flow monitoring during dialysis and surgery, a cosmetic device for skin diagnosis based on blood flow measurement, an apparatus for training evaluation for exercise, and a health examination device for blood flow monitoring based on daily life. The apparatus to which the blood flow sensor is mounted is not particularly limited.

[0020] In addition, the composite sensor according to the embodiment of the present application is a composite sensor in which a deep temperature sensor is assembled on a blood flow sensor.

[0021] (EFFECT OF INVENTION)

[0022] According to the embodiment of the present application, it is possible to provide a blood flow sensor, a blood flow measuring device, a blood flow measuring method, a device provided with a blood flow sensor, and a composite sensor, which can measure blood flow with high precision, high accuracy, and high speed responsiveness. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a plan view showing a blood flow sensor according to the first embodiment of the present application.

[0024] Figure 2 is a plan view showing a state in which a heat shield is provided on the blood flow sensor.

[0025] Figure 3 shows the heat shield in the blood flow sensor, (a) is a perspective view, (b) is a bottom view, and (c) is a plan view.

[0026] Figure 4 is a structural view for explaining a thin film thermistor in the blood flow sensor.

[0027] Figure 5 is a graph showing measured data of time-dependent temperature change of the thin film thermistor in the central portion of the blood flow sensor.

[0028] Figure 6 is a graph showing comparison of time-dependent temperature change of the thin film thermistor in the central portion of the blood flow sensor with a simulation result.

[0029] Figure 7 is a graph showing a relationship between blood flow velocity and temperature change.

[0030] Figure 8 is a table showing comparison of temperature coefficients of resistance of various resistance bodies.

[0031] Figure 9 is a flowchart showing an outline of blood flow velocity measurement.

[0032] Figure 10 is a graph showing a conventional calculation of vessel depth.

[0033] Figure 11 is a graph showing a relationship between a dimensionless number proportional to blood flow velocity and a temperature difference in the conventional technology.

[0034] (EXPLANATION OF SYMBOLS)

[0035] 1: Blood flow sensor

[0036] 2: Heat stimulation generating part (heater)

[0037] 3: Thin-film thermistor in the central part

[0038] 4: Thin-film thermistors in the surrounding area

[0039] 5: Flexible substrate

[0040] 10: Heat insulation cover

[0041] 10a: concave part

[0042] 21: Central Region

[0043] 31: Insulating substrate

[0044] 32: Thermal film

[0045] 33a, 33b: Electrode layers

[0046] 34: Protective film

[0047] 51: Wiring Pattern

[0048] 52: Connector connection part Detailed Implementation

[0049] The following is for reference Figures 1 to 9 The blood flow measuring device according to the first embodiment of the present invention will be described. Figure 1 This is a top view showing the blood flow sensor. Figure 2 This is a top view showing the blood flow sensor with a heat shield installed. Figure 3 (a) is a three-dimensional view of the heat shield, (b) is a bottom view of the heat shield, and (c) is a top view of the heat shield. Figure 4 This is a structural diagram used to illustrate thin-film thermistors. Figure 5 This is a graph showing the measured data of the time-varying temperature change of the thin-film thermistor in the central part. Figure 6 This is a graph comparing the time-varying temperature of the thin-film thermistor in the central part with simulation results. Figure 7 It is a graph showing the relationship between blood flow velocity and temperature changes. Figure 8 This is a table comparing the temperature coefficients of resistance of various resistive elements. Additionally, Figure 9 This is a flowchart illustrating a summary of blood flow velocity measurement.

[0050] It should be noted that, for ease of explanation, the scale of each component in the drawings has been appropriately altered to ensure that each component is of a recognizable size. Furthermore, identical or comparable parts are labeled with the same symbols, and redundant explanations are omitted.

[0051] The blood flow measuring device of this embodiment infers the blood flow velocity of the organism's skin based on the thermal conductivity of the organism's skin and the temperature difference of the organism's skin surface, making the heat stimulation generating part approximately circular, and the temperature sensor uses a thin-film thermistor.

[0052] like Figure 1 As shown, the blood flow measuring device includes a blood flow sensor 1 and a controller (not shown). The blood flow sensor 1 includes a heater 2 as a heat stimulation generating part, a thin-film thermistor 3 in the center, and a thin-film thermistor 4 in the surrounding part. These components are mounted on an insulating flexible substrate 5.

[0053] The flexible substrate 5 is formed of polyimide resin and has a circular portion 5a and a wiring portion 5b extending from a portion of the circular portion 5a. The back side of the circular portion 5a serves as a temperature sensing portion, forming a contact surface that contacts the object being measured (body surface). A double-sided adhesive sheet is provided on this contact surface, allowing it to be attached to the object being measured. The double-sided adhesive sheet is biocompatible.

[0054] The heater 2 is a bendable wiring structure made of fine copper wire, disposed on the circular portion 5a of the flexible substrate 5. By forming the wiring structure into a bendable structure, heat dissipation can be suppressed and sensitivity can be improved. The heater 2 is generally formed into a ring shape, with a central circular region 21 in the center where the wiring of the heater 2 is not present.

[0055] A thin-film thermistor 3 is disposed in the central part of the heater 2, i.e., the central region 21. For example... Figure 4 As shown, the thin-film thermistor 3 has an insulating substrate 31, on which a thermistor 32, a pair of electrode layers 33a and 33b, and a protective film 34 are formed. Furthermore, the structure of the thin-film thermistors 4 in the peripheral portion is basically the same as that in the central portion; therefore, the description will focus on the thin-film thermistor 3 in the central portion.

[0056] The insulating substrate 31 is generally rectangular in shape, with dimensions of 1 mm in length (width) × 0.5 mm in width (height), and a thickness of 200 µm or less, preferably 150 µm or less, and is formed of glass or ceramic material.

[0057] The thermistor film 32 is a thermistor film that functions as a temperature sensor, and it is an NTC thermistor film made of oxide semiconductor with a negative temperature coefficient. The thermistor film is formed on the insulating substrate 31 and on the electrode layers 33a and 33b by sputtering in a manner that spans the electrode layers 33a and 33b, and is electrically connected to the electrode layers 33a and 33b.

[0058] The thermistor film is composed of a thermistor material, which is composed of two or more elements selected from transition metals such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe), serving as the main component and containing a composite metal oxide with a spinel structure. Additionally, secondary components may be included to improve properties. The composition and content of the main and secondary components can be appropriately determined according to the desired characteristics.

[0059] A pair of electrode layers 33a and 33b are formed on the insulating substrate 31 and are electrically connected to the thin-film thermistor 3, and are arranged opposite each other with a predetermined interval. Specifically, the pair of electrode layers 33a and 33b are formed by sputtering a metal thin film, and the metal material can be a noble metal such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), ruthenium (Ru), or their alloys, such as Ag-Pd alloys. Furthermore, in this embodiment, the electrode layers 33a and 33b are formed under the film of the thin-film thermistor 3, but they can also be formed on or within the film of the thermistor thin film 32.

[0060] The protective film 34 covers the area where the thermistor film 32 is formed, and covers the electrode layers 33a and 33b in such a way that at least a portion of the electrode layers 33a and 33b are exposed to form exposed portions. The protective film 34 can be formed by sputtering silicon dioxide (SiO2), silicon nitride (Si3N4), etc., or by printing lead glass, borosilicate glass, lead borosilicate glass, etc.

[0061] Two thin-film thermistors 4 are arranged around the central thin-film thermistor 3 and the heater 2, and are positioned opposite each other. That is, they are arranged in a point-symmetrical manner with the central thin-film thermistor 3 as the center. More specifically, the peripheral thin-film thermistors 4 are arranged on a straight line passing through the center of the central thin-film thermistor 3, near the edge of the circular portion 5a in the flexible substrate 5. Therefore, the three thin-film thermistors—the central thin-film thermistor 3 and the peripheral thin-film thermistors 4—are arranged in a straight line at equal intervals.

[0062] Furthermore, in this case, the thin-film thermistors 4 in the peripheral portion are positioned at a certain distance from the periphery of the heater 2, which serves as the heat stimulation generating part, and are arranged such that the distances to the opposing thin-film thermistors 4 in the peripheral portion are approximately equal. In addition, there can be multiple thin-film thermistors 4 in the peripheral portion, for example, four or more, and they can be configured in multiple pairs, but it is sufficient that there are at least two thin-film thermistors 4 in the peripheral portion.

[0063] The aforementioned central thin-film thermistor 3 and the surrounding thin-film thermistors 4 are arranged with the thermistor film 32 and a pair of electrode layers 33a and 33b formed on the surface of the insulating substrate 31 facing the object being measured, i.e., the body surface side that becomes the contact surface, and are mounted on the flexible substrate 5. Therefore, the central thin-film thermistor 3 and the surrounding thin-film thermistors 4 are arranged face-down on the flexible substrate 5. Alternatively, they can be arranged face-up.

[0064] Additionally, a conductive wiring pattern 51 is formed on the flexible substrate 5. The wiring pattern 51 is a pattern that connects the heater 2, the central thin-film thermistor 3, and the peripheral thin-film thermistors 4 and guides them towards the wiring portion 5b. The ends of the wiring pattern 51 function as connector connection portions 52.

[0065] The blood flow measuring device includes a controller, which has a control processing unit that controls each component. The blood flow sensor 1 is connected to the controller via a connector connection part 52.

[0066] In addition, such as Figure 2 and Figure 3 As shown, a heat shield 10 can also be installed on the blood flow sensor 1 to cover it. The heat shield 10 is made of a heat-insulating material such as polyurethane foam. By covering the blood flow sensor 1 with the heat shield 10, heat loss during heating by the heater 2 and heat dissipation from the skin temperature of the blood flow sensor 1 can be prevented, thereby improving the temperature detection accuracy and blood flow measurement accuracy of the thin-film thermistors 3 and 4.

[0067] The heat shield 10 has a roughly fan-shaped shape, with a portion of a circular arc cut off. It is approximately 1 mm thick, and a roughly fan-shaped recess 10a, smaller than the overall shape, is formed on its bottom surface. Therefore, by covering the heater 2 of the blood flow sensor 1, the central thin-film thermistor 3, and the surrounding thin-film thermistor 4 with the recess 10a, heat dissipation can be suppressed. Furthermore, the side surface of the portion where the circular arc was cut off can also be covered.

[0068] Next, refer to Figures 5 to 8 The blood flow measurement method in the blood flow measurement device will be described. In this embodiment, the blood flow velocity of the living organism is calculated. Generally speaking, it is calculated by performing three steps in stages: calculating the thermal conductivity of the skin, calculating the depth of blood vessels, and calculating the blood flow velocity.

[0069] In blood flow measurement, a release liner pre-attached to a double-sided adhesive sheet on the back side of the flexible substrate 5 of the blood flow sensor 1 is peeled off. Next, the temperature-sensing part is attached to the surface of the object being measured, bringing it into contact with the surface, and the power supply to the blood flow measurement device is turned on to activate it. In this case, the blood flow sensor 1 is attached such that the central thin-film thermistor 3 and any two opposing peripheral thin-film thermistors 4 overlap on the blood vessels near the surface of the organism. That is, the peripheral thin-film thermistors 4 are attached in a manner that follows the flow of blood in the blood vessels, and the central thin-film thermistor 3 and at least two peripheral thin-film thermistors 4 are positioned on the same blood vessel near the surface of the organism.

[0070] <First Process>

[0071] The first step is to calculate the thermal conductivity of the skin. In the calculation of thermal conductivity, heater 2 is used as a temperature sensor. After heating the heater 2, which is roughly circular and serves as the heat stimulation generating part, the time-varying temperature change of the skin surface is measured approximately two seconds after the heater 2 is heated.

[0072] Furthermore, the time-dependent temperature change of the skin surface is obtained by treating heater 2 as a resistive element of copper and converting the temperature from its resistance value. Similarly, the time-dependent temperature change is also measured for materials with known thermal conductivity, and a database is pre-created based on these measurements. Then, the database is compared with the time-dependent temperature change of the skin surface, and the thermal conductivity of the material with the closest temperature change data is assigned as the thermal conductivity of the skin.

[0073] <Second Process>

[0074] The second step is to calculate the depth of blood vessels near the body surface. The calculation of blood vessel depth uses a thin-film thermistor 3 located in the center. While the generally annular heater 2 is heated, the time-varying temperature change of the thin-film thermistor 3 in the center is measured.

[0075] Figure 5 This is a graph representing the measured temperature change over time for the thin-film thermistor 3 in the central part. The horizontal axis represents time (s), the vertical axis ΔTt represents the temperature difference between heater 2 before heating and after heating for t seconds, and ΔTs represents the final steady-state value of ΔTt. Figure 5 As shown, when measuring time-varying temperature changes using the thin-film thermistor 3 in the central part, very good signal stability is exhibited. Therefore, even data from a short period (approximately 4 to 10 seconds) after heating begins from the heater 2 are highly reliable and can be used.

[0076] Figure 6This is a graph representing simulation data from a finite element model based on skin and measured data from the time-varying temperature changes of a thin-film thermistor 3 in the central part of a simulated organism with known blood vessel depth. Measured and simulated values ​​for blood vessel depths h of 1.3 mm and 1.7 mm are shown. Both show good agreement between the measured and simulated data, and the blood vessel depth can be calculated from short-term temperature change measurements (approximately 4–10 seconds).

[0077] <Third Process>

[0078] The third step is to calculate the blood flow velocity near the body surface. The blood flow velocity is calculated using a thin-film thermistor 4 in the surrounding area. With the approximately annular heater 2 fully heated, the temperature difference on the skin surface of the organism is measured based on the temperature difference generated in the thin-film thermistor 4 in the surrounding area. This temperature difference is affected by the blood flow velocity, the thermal conductivity of the skin, and the depth of blood vessels near the body surface. Therefore, the thermal conductivity of the skin obtained in the first step and the value of the blood vessel depth obtained in the second step are used in the calculation of the blood flow velocity. The relationship between the blood flow velocity and the temperature difference generated in the thin-film thermistor 4 in the surrounding area is expressed by (Equation 1). Here, v represents the blood flow velocity, α and β represent arbitrary coefficients defined by the thermal conductivity of the skin obtained in the first step, the blood vessel depth obtained in the second step, and the known thermal properties of the organism's blood, with SI units representing the dimension of temperature, and ΔT representing the temperature difference (°C) of the thin-film thermistor 4 in the surrounding area. The known thermal properties of the organism's blood are its specific heat, density, and thermal conductivity.

[0079]

[0080] The results of measuring the blood flow velocity of simulated blood in a simulated organism using the above methods are as follows: Figure 7 As shown, good linearity was observed when the horizontal axis (blood flow velocity) was displayed logarithmically. Furthermore, by calculating α = 0.205, β = -0.27 [°C], and R² = 0.97 from the graph (Equation 1), it can be confirmed that v and ΔT have a very good correlation. Therefore, it can be concluded that the blood flow velocity can be calculated with high accuracy by measuring the temperature difference of the surrounding thin-film thermistor 4. The temperature difference of the surrounding thin-film thermistor 4 varies depending on the blood flow velocity because: if the flow rate decreases, it receives more heat from the heater 2, causing the temperature of the surrounding thin-film thermistor 4, located downstream of the blood flow, to rise, thus increasing the temperature difference.

[0081] in addition, Figure 8This table compares the temperature coefficient of resistance (% / K) of various resistive elements at 20°C. It shows that in the NTC thin-film thermistor of this embodiment, the temperature coefficient of resistance (% / K) is -3.9. The absolute value of the temperature coefficient of resistance of the thin-film thermistor is approximately 10 times that of the metal wire thermistor, indicating high sensitivity to temperature. That is, it can be said to be advantageous for capturing changes in skin temperature caused by minute changes in blood flow velocity.

[0082] Based on this result, it can be confirmed that the blood flow sensor 1 of this embodiment can calculate the blood flow rate with high accuracy.

[0083] Regarding the blood flow measurement methods described above, for calculating the blood flow velocity in an organism, refer to... Figure 9 The operation of the blood flow measuring device is explained. Figure 9 This is a flowchart outlining the blood flow velocity measurement process. These actions are primarily performed by a program built into the control processing unit of the controller.

[0084] First, the release liner is peeled off from the double-sided adhesive sheet attached to the temperature-sensing part of the blood flow sensor 1. Then, the temperature-sensing part is attached to the surface of the object being measured, making it contact the surface, and the power supply to the blood flow measuring device is turned on to start it (step S1). In this case, the blood flow sensor 1 is attached such that the central thin-film thermistor 3 and any two opposing peripheral thin-film thermistors 4 overlap on the blood vessels near the surface of the organism. That is, the peripheral thin-film thermistors 4 are attached in a manner that follows the flow of blood in the blood vessels. The thermal conductivity of the skin is calculated (first step S2). Next, the depth of the blood vessels near the body surface is calculated (second step S3). Next, the blood flow velocity near the body surface is calculated (third step S4). The measurement result of the blood flow velocity of the organism is displayed on the controller or recorded and output (step S5).

[0085] As described above, according to this embodiment, blood flow can be measured with high precision, high accuracy, and high-speed response. Specifically, in this embodiment, the heater 2 has a generally annular shape with tortuous wiring. Therefore, the heat from the inner edge of the generally annular heater 2 after heating diffuses along the radial direction, and the center of the generally annular heater 2 becomes a region where the heat is isotropically concentrated, resulting in a region where various thermal effects cancel each other out. Therefore, by placing the thin-film thermistor 3 in the central region 21, the influence of external interference can be reduced. In other words, the shape of the heater 2 and the placement of the thin-film thermistor 3 in the central region are means to help solve the problems of the prior art.

[0086] Furthermore, due to the use of thin-film thermistors 3 and 4 in the central and surrounding areas, the temperature sensitivity is high. The heat capacity was calculated based on measured data, and the average result is 0.26 × 10⁻⁶. -3 The resistance value was measured in J / K, with a deviation of ±3%. Additionally, the resistance of a resistive element formed from fine copper wire was measured, with an average value of 0.16 kΩ and a deviation of ±20%. This resistance deviation is synonymous with the deviation in heat capacity. That is, if a resistive element formed from the same fine metal wire is used as a temperature sensor, the resistance deviation will be large, making accurate temperature measurement difficult. Therefore, because the heat capacity deviation of a thin-film thermistor is small, the resistance deviation can be suppressed, thereby improving temperature measurement accuracy.

[0087] Next, the composite sensor according to the second embodiment of the present invention will be described. This embodiment is a composite sensor formed by combining a deep temperature sensor with the blood flow sensor 1 in the first embodiment. The deep temperature sensor has a structure as disclosed, for example, in Japanese Patent No. 5779806. In addition, the structure of Japanese Patent Application No. 2022-087131 filed by the applicant is referenced.

[0088] The general structure involves superimposing a deep temperature sensor onto a blood flow sensor 1. A heat insulation element is mounted on the blood flow sensor 1, and a heating element layer and a control thin-film thermistor are disposed on the heat insulation element. Furthermore, the thin-film thermistor 3 in the central part of the blood flow sensor 1 also functions as the measurement thin-film thermistor for the deep temperature sensor. It should be noted that the deep temperature sensor can employ either the heat flow compensation method or the dual heat flow method.

[0089] According to the above embodiments, by applying processing methods such as adjusting the deviation of the thin-film thermistor 3 in the central part and the thin-film thermistor 4 in the surrounding part, a blood flow sensor 1 with high accuracy and high reliability can be provided.

[0090] It should be noted that the aforementioned heat-generating part can also be cooled using a cooling device such as a Peltier element.

[0091] The blood flow sensor 1 of the present invention is applicable to blood flow measurement in biological devices used in medical equipment for diagnosing poor blood circulation, such as pressure ulcers and severe lower limb ischemia, or for monitoring blood flow during dialysis and surgery, but is not limited thereto. It can be suitably installed in various devices such as cosmetic devices for skin diagnosis based on blood flow measurement, devices for sports training assessment, and health check devices for blood flow monitoring in daily life. Furthermore, it is anticipated that a composite sensor formed by combining a deep temperature sensor with the blood flow sensor 1 can be suitably installed in devices for heatstroke detection. There are no particular limitations on the application device. For example, the velocity of the fluid inside a pipe can be determined using the same principle for pipes in mechanical devices and industrial piping.

[0092] This invention is not limited to the structure of the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, the above embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included within the scope of the invention as described in the claims and its equivalents.

Claims

1. A blood flow sensor that infers the skin blood flow velocity of an organism based on the skin thermal conductivity and the temperature difference between the skin surface and the organism, the blood flow sensor being characterized by comprising: An insulating, flexible substrate that can be attached to the skin surface of the organism; A conductive wiring pattern is formed on the flexible substrate; A roughly circular heat stimulation generating part heats or cools the skin surface of the organism; A thin-film thermistor is disposed in the center of the heat stimulation generating portion; and At least two thin-film thermistors with peripheral portions are disposed at a certain distance from the periphery of the heat-generating portion. The at least two peripheral thin-film thermistors are arranged on a straight line passing through the center of the central thin-film thermistor.

2. A blood flow sensor, characterized in that, A heat shield is provided to cover the blood flow sensor as described in claim 1.

3. The blood flow sensor according to claim 1 or 2, characterized in that, The thin-film thermistor in the central part and the thin-film thermistor in the surrounding part are adjusted.

4. The blood flow sensor according to claim 1 or 2, characterized in that, The roughly annular heat-generating part is a heater.

5. The blood flow sensor according to claim 4, characterized in that, The heater has a tortuous structure.

6. The blood flow sensor according to claim 1 or 2, characterized in that, Two to six thin-film thermistors are disposed in the surrounding area at a certain distance from the periphery of the heat stimulation generating part.

7. The blood flow sensor according to claim 1 or 2, characterized in that, The thin-film thermistor in the central part and the thin-film thermistor in the surrounding part have a substrate and a thermistor film and electrode layer formed on the substrate, and are arranged such that the thermistor film and electrode layer are facing the contact surface of the object being measured.

8. The blood flow measuring device according to claim 1 or 2, characterized in that, The blood flow measuring device has a control processing unit that controls the various components of the blood flow sensor.

9. A device equipped with a blood flow sensor, characterized in that, It possesses the blood flow sensor as described in claim 1.

10. A method for measuring blood flow, using a blood flow sensor, said blood flow sensor comprising: An insulating, flexible substrate that can be attached to the skin surface of a living organism; A conductive wiring pattern is formed on the flexible substrate; A roughly circular heat stimulation generating part heats or cools the skin surface of the organism; A thin-film thermistor is disposed in the center of the heat stimulation generating portion; and At least two thin-film thermistors with peripheral portions are disposed at a certain distance from the periphery of the heat-generating portion. The at least two peripheral thin-film thermistors are arranged on a straight line passing through the center of the central thin-film thermistor. The blood flow measurement method is characterized by including: The first step is to calculate the thermal conductivity of the skin; The second step is to calculate the depth of blood vessels near the body surface; as well as The third step is to calculate the blood flow velocity near the body surface.

11. The blood flow measurement method according to claim 10, characterized in that, In the third step of calculating the blood flow velocity near the surface of the body, known thermal properties of biological blood are used, namely, the specific heat, density, and thermal conductivity of blood.

12. A composite sensor, characterized in that, It is formed by combining a deep temperature sensor with the blood flow sensor described in claim 1.

13. The composite sensor according to claim 12, characterized in that, The deep temperature sensor includes a thin-film thermistor.

14. The composite sensor according to claim 12 or 13, characterized in that, The deep temperature sensor uses the principle of heat flow compensation.

15. The composite sensor according to claim 12 or 13, characterized in that, The deep temperature sensor uses the principle of dual heat flow.

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