Blood flow sensor, blood flow measurement device, blood flow measurement method, device comprising 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 comprising the 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, which estimates skin blood flow velocity of a living body from a skin thermal conductivity of the living body and a skin surface temperature difference of the living body, is provided with: an insulating flexible substrate 5 which is attachable to a skin surface of the living body; a conductive wiring pattern 51 which is formed on the flexible substrate 5; a substantially annular heat stimulation generating unit 2 which heats or cools the skin surface of the living body; one central thin film thermistor 3 disposed at a central part of the heat stimulation generating unit 2; and at least two peripheral thin film thermistors 4 arranged at a predetermined distance from peripheral edges of the heat stimulation generating unit 2. Said at least two peripheral thin film thermistors 4 are arranged on a straight line passing through the center of the central thin film thermistor 3.

Description

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

[0001] The present invention relates to a blood flow sensor, a blood flow measurement device, a blood flow measurement method, an apparatus equipped with a blood flow sensor, and a composite sensor.

[0002] Blood flow measurement is used to understand health conditions and the presence or absence of disease, and in fields such as medicine, sports, and beauty. For example, in the medical field, blood flow sensors are used to measure blood flow in the diagnosis of poor circulation such as bedsores and severe lower limb ischemia, and for monitoring blood flow during dialysis and surgery.

[0003] Conventionally, devices and methods for monitoring the thermal transport properties (e.g., thermal conductivity, thermal diffusivity, and heat capacity) of tissues such as skin have been proposed. The devices are conformally attached to the tissue and include one or more thermal actuators (thermal stimulus generators) and multiple temperature sensors (see, for example, Patent Documents 1 and 2). Also proposed are devices for measuring the thermal diffusivity of a living body and evaluating the blood flow rate of the living body from the thermal diffusivity, as well as devices for determining the risk of bedsores (see Patent Document 3).

[0004] However, the thermal actuators shown in Patent Documents 1 and 2 have a circular shape, and when calculating blood vessel depth and blood flow velocity, they use temperature data measured by temperature sensors placed around the circular heat source. With a circular heat source, temperature conduction diverges from the measurement center, resulting in poor measurement sensitivity and reproducibility. Furthermore, the temperature sensor is formed from a 10 μm-wide chromium / gold filament resistor, and its resistance value is converted to temperature. However, due to its shape, the sensor thickness and wire width tend to vary, resulting in large variations in resistance value due to variations in heat capacity between resistors. Although the difference in temperature measured by the two resistors is used to calculate blood vessel depth, the temperature measurement accuracy is low for the above two reasons.

[0005] FIG. 10 is a graph showing the calculation of blood vessel depth. The horizontal axis represents time (s), the vertical axis represents ΔT', the temperature difference between the two temperature sensors, and ΔT's, the final steady-state value of ΔT'. In other words, the vertical axis represents the temperature change over time. Furthermore, h represents blood vessel depth (mm), with the dashed line (h = 1 mm to 2 mm) representing simulation data using a finite element model for each blood vessel depth, and the solid line (measured value) representing actual measurement data. The graph shows a comparison between the finite element model of skin and the actual measurement data to determine the approximate blood vessel depth. It can be seen that the signal stability is low, and calculation of blood vessel depth takes more than 120 seconds, and the accuracy is also low.

[0006] FIG. 11 is a graph showing the relationship between blood flow velocity and temperature difference, and the symbols on the horizontal axis represent 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 ), ρ ｆ : Blood density (kg m －２ ), λ ｆ : Thermal conductivity of blood (W m －１ ・K －１ ), R: blood vessel diameter (m). Each of the above symbols is expressed as a known coefficient except for v. In other words, the horizontal axis is a dimensionless number proportional to the blood flow velocity v. In the range of approximately 0.001 to 1 m / s, which is the blood flow velocity in a living body, the coefficient of determination R ２ is <0.3, which means that there is almost no correlation.

[0007] Furthermore, the device disclosed in Patent Document 3 uses a thermocouple as the temperature measurement unit, which has problems with poor sensitivity and accuracy. It uses a Peltier element as the thermal stimulus generation unit and employs a method of cooling the relevant unit. This means that it takes time to cool the skin temperature, and it takes a long time to determine the skin thermal conductivity. Because blood flow sensors must detect slight differences in skin temperature in living organisms, high sensitivity and accuracy are required for temperature detection, but the device disclosed in Patent Document 3 makes it difficult to achieve high sensitivity and accuracy in temperature detection.

[0008] Special Table of Contents No. 2017-532079 Publication of Special Publication No. 2021-519641 Publication of Patent No. 5327840

[0009] An embodiment of the present invention aims to provide a blood flow sensor, a blood flow measurement device, a blood flow measurement method, an apparatus equipped with a blood flow sensor, and a composite sensor that can measure blood flow with high precision, high accuracy, and high-speed response.

[0010] A blood flow sensor according to an embodiment of the present invention is a blood flow sensor that estimates the skin blood flow velocity of a living body from the skin thermal conductivity of the living body and the skin surface temperature difference of the living body, and is characterized by comprising: an insulating flexible substrate that can be attached to the skin surface of the living body, a conductive wiring pattern formed on the flexible substrate, a substantially annular thermal stimulus generator that heats or cools the skin surface of the living body, a central thin-film thermistor disposed in the center of the thermal stimulus generator, and at least two peripheral thin-film thermistors disposed at a certain distance from the periphery of the thermal stimulus generator, the at least two peripheral thin-film thermistors being arranged on a straight line passing through the center of the central thin-film thermistor. The blood flow sensor of this embodiment can measure blood flow with high precision, high accuracy, and high response.

[0011] The blood flow measuring device according to the embodiment of the present invention is characterized by having a control processing unit that controls each component of the blood flow sensor. The components refer to a thermal stimulus generator, a central thin-film thermistor, and a peripheral thin-film thermistor. The control processing unit is built into, for example, a controller connected to the blood flow sensor.

[0012] Furthermore, a blood flow measurement method according to an embodiment of the present invention is a blood flow measurement method using a blood flow sensor comprising an insulating flexible substrate that can be attached to the skin surface of a living body, a conductive wiring pattern formed on the flexible substrate, an approximately circular thermal stimulus generating unit that heats or cools the skin surface of the living body, one central thin-film thermistor arranged in the center of the thermal stimulus generating unit, and at least two peripheral thin-film thermistors arranged at a certain distance from the periphery of the thermal stimulus generating unit, wherein the at least two peripheral thin-film thermistors are arranged on a straight line passing through the center of the central thin-film thermistor, and is characterized by including a first step of calculating the thermal conductivity of the skin, a second step of calculating the blood vessel depth near the body surface, and a third step of calculating the blood flow velocity near the body surface.

[0013] A device equipped with a blood flow sensor according to an embodiment of the present invention is characterized by being equipped with a blood flow sensor. The blood flow sensor can be suitably equipped and applied to various devices, such as medical devices for diagnosing poor circulation such as bedsores and critical limb ischemia, and for monitoring blood flow during dialysis and surgery, beauty devices for skin diagnosis using blood flow measurement, devices for evaluating sports training, and health check devices for monitoring blood flow in daily life. The devices to which the blood flow sensor can be applied are not particularly limited. Furthermore, a composite sensor according to an embodiment of the present invention combines a blood flow sensor with a deep temperature sensor.

[0014] According to embodiments of the present invention, it is possible to provide a blood flow sensor, a blood flow measurement device, a blood flow measurement method, an apparatus equipped with a blood flow sensor, and a composite sensor that can measure blood flow with high precision, high accuracy, and high-speed response.

[0015] 1 is a plan view showing a blood flow sensor according to a first embodiment of the present invention; FIG. 2 is a plan view showing the state in which the blood flow sensor is provided with an insulating cover; FIG. 3 shows the insulating cover in the blood flow sensor, with (a) being a perspective view, (b) being a bottom view, and (c) being a plan view; FIG. 4 is a configuration diagram for explaining a thin film thermistor in the blood flow sensor; FIG. 5 is a graph showing actual measurement data of the temperature change over time of the thin film thermistor in the center of the blood flow sensor; FIG. 6 is a graph showing a comparison between the temperature change over time of the thin film thermistor in the center of the blood flow sensor and simulation results; FIG. 7 is a graph showing the relationship between blood flow velocity and temperature change; FIG. 8 is a table comparing the temperature coefficients of resistance of various resistors; FIG. 9 is a flowchart showing an overview of blood flow velocity measurement; FIG. 10 is a graph showing a conventional method for calculating blood vessel depth; FIG. 11 is a graph showing a conventional method for calculating a dimensionless number proportional to blood flow velocity and a temperature difference.

[0016] A blood flow measuring device according to a first embodiment of the present invention will now be described with reference to FIGS. 1 to 9. FIG. 1 is a plan view showing a blood flow sensor, FIG. 2 is a plan view showing the blood flow sensor with an insulating cover attached, FIG. 3(a) is a perspective view showing the insulating cover, FIG. 3(b) is a bottom view showing the insulating cover, and FIG. 3(c) is a plan view showing the insulating cover. FIG. 4 is a diagram illustrating the configuration of a thin-film thermistor. FIG. 5 is a graph showing actual measurement data of the temperature change over time of the thin-film thermistor in the central portion, FIG. 6 is a graph comparing the temperature change over time of the thin-film thermistor in the central portion with simulation results, and FIG. 7 is a graph showing the relationship between blood flow velocity and temperature change. FIG. 8 is a table comparing the temperature coefficients of resistance of various resistors. FIG. 9 is a flowchart outlining blood flow velocity measurement.

[0017] In each drawing, the scale of each component has been appropriately changed for the purpose of explanation so that each component can be recognized. Furthermore, the same or corresponding parts are given the same reference numerals, and duplicate explanations will be omitted.

[0018] The blood flow measuring device of this embodiment estimates the skin blood flow velocity of a living body from the skin thermal conductivity of the living body and the skin surface temperature difference of the living body, and has a thermal stimulus generating unit that is approximately circular and uses a thin-film thermistor as the temperature sensor.

[0019] As shown in Figure 1, 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 thermal stimulus generator, a central thin-film thermistor 3, and peripheral thin-film thermistors 4. These components are mounted on an insulating flexible substrate 5.

[0020] The flexible substrate 5 is made of polyimide resin and has a circular portion 5a and a wiring portion 5b extending from a part of the circular portion 5a. The back side of the circular portion 5a is the temperature-sensing portion and forms the contact surface that comes into contact with the measurement object (body surface). A double-sided adhesive sheet is provided on this contact surface so that it can be attached to the measurement object. The double-sided adhesive sheet is biocompatible.

[0021] The heater 2 has a meandering wiring structure made of thin copper wires and is arranged in the circular portion 5a of the flexible substrate 5. The meandering wiring structure can suppress heat dissipation and improve sensitivity. The heater 2 is formed in a roughly annular shape as a whole, with a circular central region 21 in the center where the heater 2 wiring is not present.

[0022] One central thin-film thermistor 3 is disposed in the central portion of the heater 2, i.e., in the central region 21. As shown in Figure 4, the thin-film thermistor 3 has an insulating substrate 31, on which a heat-sensitive thin film 32, a pair of electrode layers 33a, 33b, and a protective film 34 are formed. The peripheral thin-film thermistors 4 have basically the same configuration as the central thin-film thermistor 3, so the central thin-film thermistor 3 will be described as a representative.

[0023] The insulating substrate 31 is substantially rectangular, measuring 1 mm wide x 0.5 mm long, and has a thickness of 200 μm or less, preferably 150 μm or less, and is made of glass or ceramic material.

[0024] The thermosensitive thin film 32 is a thermosensitive resistive thin film that functions as a temperature sensor, and is an NTC thermistor thin film made of an oxide semiconductor having a negative temperature coefficient. The thermistor thin film is formed by sputtering on the insulating substrate 31 and on the electrode layers 33 a and 33 b, so as to straddle the electrode layers 33 a and 33 b, and is electrically connected to the electrode layers 33 a and 33 b.

[0025] The thermistor thin film is made of a thermistor material containing, as its main component, a composite metal oxide having a spinel structure, which is composed of two or more elements selected from transition metal elements such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe). Subcomponents may also be included to improve characteristics. The composition and content of the main component and subcomponents can be determined appropriately depending on the desired characteristics.

[0026] The pair of electrode layers 33a, 33b are formed on the insulating substrate 31 and are electrically connected to the thin-film thermistor 3. The electrode layers 33a, 33b are disposed facing each other with a predetermined gap between them. Specifically, the pair of electrode layers 33a, 33b are formed by depositing a thin metal film by sputtering. Examples of suitable metal materials include precious metals such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), and ruthenium (Ru), as well as alloys thereof, such as Ag-Pd alloys. In this embodiment, the electrode layers 33a, 33b are formed below the thin-film thermistor 3, but they may also be formed on or within the heat-sensitive thin film 32.

[0027] The protective film 34 covers the region where the heat-sensitive thin film 32 is formed, and also covers the electrode layers 33a and 33b by forming exposed portions so that at least a part of the electrode layers 33a and 33b is exposed. The protective film 34 is made of silicon dioxide (SiO ２ ), silicon nitride (Si ３ N ４ Alternatively, lead glass, borosilicate glass, lead borosilicate glass, or the like can be formed by a printing method.

[0028] Two peripheral thin-film thermistors 4 are disposed around the central thin-film thermistor 3 and heater 2, facing each other. That is, they are disposed in point symmetry with respect to the central thin-film thermistor 3. More specifically, the peripheral thin-film thermistors 4 are disposed on a straight line passing through the center of the central thin-film thermistor 3, near the edge of the circular portion 5a of the flexible substrate 5. Therefore, the three thin-film thermistors, the central thin-film thermistor 3 and the peripheral thin-film thermistors 4, are disposed in a straight line at equal intervals.

[0029] In this case, the peripheral thin-film thermistors 4 are disposed as thermal stimulus generating parts at a fixed distance from the periphery of the heater 2, and are disposed so that the distances to the opposing peripheral thin-film thermistors 4 are approximately equal. The peripheral thin-film thermistors 4 may be plural, for example, four or more, and may form plural pairs, as long as there are at least two or more peripheral thin-film thermistors 4.

[0030] The central thin-film thermistor 3 and peripheral thin-film thermistors 4 are mounted on the flexible substrate 5 with the heat-sensitive thin film 32 and the pair of electrode layers 33a, 33b formed on the surface of the insulating substrate 31 facing the object to be measured, i.e., the body surface side that serves as the contact surface. Therefore, the central thin-film thermistor 3 and peripheral thin-film thermistors 4 are mounted face-down on the flexible substrate 5. However, they may also be mounted face-up.

[0031] In addition, 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 leads them to the wiring portion 5b. The end of the wiring pattern 51 functions as a connector connection portion 52.

[0032] The blood flow measuring device is provided with a controller having a control processing unit that controls each component, and the blood flow sensor 1 is connected to the controller via a connector connecting portion 52.

[0033] 2 and 3, a heat insulating cover 10 may be attached to cover the blood flow sensor 1. The heat insulating cover 10 is made of a heat insulating material such as urethane foam, and by covering the blood flow sensor 1 with the heat insulating cover 10, heat loss during heating by the heater 2 and heat radiation of the skin temperature of the blood flow sensor 1 can be prevented, thereby improving the temperature detection accuracy of the thin film thermistors 3 and 4 and the blood flow measurement accuracy.

[0034] The insulating cover 10 has an outer shape that is roughly fan-shaped, with a portion of the circular arc missing. It has a thickness of about 1 mm, and a roughly fan-shaped recess 10a that is smaller than the outer shape is formed on the bottom side. Therefore, by having the recess 10a cover the heater 2, central thin-film thermistor 3, and peripheral thin-film thermistor 4 of the blood flow sensor 1, heat dissipation can be suppressed. Note that the side surface at the portion missing the circular arc may also be covered.

[0035] Next, a blood flow measurement method in the blood flow measurement device will be described with reference to Figures 5 to 8. In this embodiment, the blood flow velocity of a living body is calculated. In summary, the calculation is performed in three steps: calculating the thermal conductivity of the skin, calculating the blood vessel depth, and calculating the blood flow velocity.

[0036] To measure blood flow, the release sheet previously attached to the double-sided adhesive sheet provided on the back side of the flexible substrate 5 of the blood flow sensor 1 is peeled off. Next, the temperature-sensing unit is attached to the body surface of the measurement target so that it comes into contact with the surface, and the blood flow measuring device is powered on to start up. In this case, the blood flow sensor 1 is attached so that the central thin-film thermistor 3 and any two opposing peripheral thin-film thermistors 4 overlap on a blood vessel near the body surface of the living body. In other words, the peripheral thin-film thermistors 4 are attached so that they follow the blood flow in the blood vessel, 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 body surface of the living body.

[0037] <First Step> The first step is to calculate the thermal conductivity of the skin. To calculate the thermal conductivity, the heater 2 is used as a temperature sensor. After the heater 2 is heated as the approximately annular thermal stimulus generating unit, the change in temperature over time on the skin surface is measured for approximately 2 seconds after the heater 2 has heated.

[0038] The temperature change over time on the skin surface is calculated by treating the heater 2 as a copper resistor and converting its resistance value into temperature. Similarly, the temperature change over time is measured for materials with known thermal conductivities, and a database is created in advance based on the measurement results. The temperature change over time on the skin surface is then compared with the database, and the thermal conductivity of the material with the closest temperature change data is assigned as the thermal conductivity of the skin.

[0039] <Second Step> The second step is a step of calculating the depth of blood vessels near the body surface. The calculation of the blood vessel depth uses the central thin-film thermistor 3. With the substantially annular heater 2 heated, the time-varying temperature change of the central thin-film thermistor 3 is measured.

[0040] Figure 5 is a graph showing actual measured data of the temperature change over time of the thin-film thermistor 3 in the center. The horizontal axis represents time (s), and the vertical axis represents ΔTt, the temperature difference between before and after t seconds of heating by the heater 2, and ΔTs, the final steady-state value of ΔTt. As shown in Figure 5, when measuring the temperature change over time using the thin-film thermistor 3 in the center, very good signal stability is observed. Therefore, even data from a short period of time (approximately 4 to 10 seconds) after the heater 2 starts heating is highly reliable and can be used.

[0041] Figure 6 is a graph showing simulation data from a finite element model of skin and actual measurement data of the temperature change over time of the thin-film thermistor 3 in the center of a simulated living body with known blood vessel depths. The graph shows actual measurement values ​​and simulation values ​​for blood vessel depths h of 1.3 mm and 1.7 mm. In both cases, the actual measurement data and simulation data show good agreement, and blood vessel depth can be calculated by measuring temperature changes in a short period of time (approximately 4 to 10 seconds).

[0042] <Third Step> The third step is a step of calculating the blood flow velocity near the body surface. The peripheral thin-film thermistor 4 is used to calculate the blood flow velocity. With the annular heater 2 sufficiently heated, the temperature difference at the skin surface of the living body is measured based on the temperature difference generated by the peripheral thin-film thermistor 4. Because 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, the thermal conductivity of the skin calculated in the first step and the blood vessel depth calculated in the second step are used to calculate the blood flow velocity. The relationship between the blood flow velocity and the temperature difference generated by the peripheral thin-film thermistor 4 is expressed by Equation 1. Here, v is the blood flow velocity, α and β are arbitrary coefficients determined by the thermal conductivity of the skin calculated in the first step, the blood vessel depth calculated in the second step, and known thermal properties of the living body's blood. The SI units are in the dimension of temperature, and ΔT represents the temperature difference (°C) of the peripheral thin-film thermistor 4. The known thermal properties of the living body's blood are the specific heat, density, and thermal conductivity of blood. ΔT=-αln(v)+β...(Formula 1)

[0043] Using the above method, the blood flow velocity of simulated blood in a simulated living body was measured. As shown in Figure 7, good linearity was observed when the horizontal axis (blood flow velocity) was plotted logarithmically. Furthermore, from the graph, α in Equation 1 was found to be 0.205, β was -0.27°C, and R2 = 0.97, confirming a very good correlation between v and ΔT. This suggests that blood flow velocity can be calculated with high accuracy by measuring the temperature difference of the peripheral thin-film thermistor 4. The temperature difference of the peripheral thin-film thermistor 4 changes with blood flow velocity because, when the flow rate is reduced, the peripheral thin-film thermistor 4, located downstream of the blood flow, receives more heat from the heater 2, increasing its temperature and increasing the temperature difference.

[0044] FIG. 8 is a table comparing the temperature coefficient of resistance (% / K) of various resistors at 20°C. The NTC thin-film thermistor of this embodiment has a temperature coefficient of resistance (% / K) of -3.9, and the absolute value of the temperature coefficient of resistance of the thin-film thermistor is approximately 10 times larger than that of a thin metal wire resistor, indicating high sensitivity to temperature. In other words, it can be said to be advantageous for detecting changes in skin temperature due to slight changes in blood flow velocity. These results confirm that the blood flow velocity can be calculated with high accuracy using the blood flow sensor 1 of this embodiment.

[0045] The operation of the blood flow measuring device in the blood flow measurement method described above will be described with reference to Fig. 9 when calculating the blood flow velocity in a living body. Fig. 9 is a flowchart showing an outline of blood flow velocity measurement. These operations are mainly executed by a program in the control processing unit built into the controller.

[0046] First, the release sheet attached to the double-sided adhesive sheet of the temperature-sensing portion of the blood flow sensor 1 is peeled off. Then, the temperature-sensing portion is attached to the body surface of the subject, and the blood flow measurement device is powered on and activated (Step S1). In this case, the blood flow sensor 1 is attached so that the central thin-film thermistor 3 and any two opposing peripheral thin-film thermistors 4 overlap the blood vessels near the body surface of the subject. In other words, the peripheral thin-film thermistors 4 are attached so that they are aligned with the blood flow in the blood vessels. The thermal conductivity of the skin is calculated (First Step, Step S2). Next, the blood vessel depth near the body surface is calculated (Second Step, Step S3). Next, the blood flow velocity near the body surface is calculated (Third Step, Step S4). The measurement results of the blood flow velocity of the subject are output by displaying or recording them on the controller (Step S5).

[0047] As described above, according to this embodiment, blood flow can be measured with high accuracy, high precision, and high response. Specifically, in this embodiment, the heater 2 is roughly annular in shape and has meander wiring. Therefore, after heating, the heat from the heater 2 from the inner edge of the roughly annular shape diffuses in the radial direction, and the center of the roughly annular heater 2 is a place where the heat from the heater 2 is isotropically concentrated, creating a region where various thermal effects are offset. Therefore, by arranging the central thin-film thermistor 3 in the central region 21, the effects of external disturbances can be reduced. In other words, the shape of the heater 2 and the arrangement of the central thin-film thermistor 3 described above are means that contribute to solving the problems of the past.

[0048] Furthermore, since thin film thermistors 3 and 4 are used in the central and peripheral portions, the sensitivity to temperature is high. The heat capacity was calculated from the actual measurement data and was found to be 0.26×10 on average. -３ The resistance of a resistor made of thin copper wire was measured to be 0.16 kΩ on average, with a variation of ±20%. This variation in resistance is synonymous with variation in heat capacity. In other words, if a resistor made of similar thin metal wire is used as a temperature sensor, the variation in resistance is large, making it difficult to measure temperature accurately. Therefore, because the variation in heat capacity of a thin film thermistor is small, variation in resistance can be suppressed, thereby improving temperature measurement accuracy.

[0049] Next, a composite sensor according to a second embodiment of the present invention will be described. This embodiment is a composite sensor that combines the blood flow sensor 1 of the first embodiment with a deep temperature sensor. The deep temperature sensor has a configuration as disclosed in, for example, Japanese Patent No. 5779806. The configuration of Japanese Patent Application No. 2022-087131, filed by the applicant of the present invention, is also of reference.

[0050] The general configuration is that a deep temperature sensor is superimposed on the blood flow sensor 1, with a heat insulating material placed on top of the blood flow sensor 1, and a heating element layer and a controlling thin film thermistor placed on top of that. The thin film thermistor 3 in the center of the blood flow sensor 1 also functions as a measuring thin film thermistor for the deep temperature sensor. The deep temperature sensor can use the principle of the heat flow compensation method or the principle of the dual heat flow method.

[0051] According to each of the above embodiments, it is possible to provide a highly accurate and reliable blood flow sensor 1 by applying processing means such as trimming to suppress variations in the central thin-film thermistor 3 and the peripheral thin-film thermistors 4. Note that the thermal stimulus generator can also be cooled using a cooling device such as a Peltier element.

[0052] The blood flow sensor 1 of the present invention described above is suitable for measuring blood flow in living organisms in medical devices, such as for diagnosing poor circulation in conditions such as bedsores and severe lower limb ischemia, and for monitoring blood flow during dialysis and surgery, but is not limited to these. It can also be suitable for use in various devices, such as beauty devices that perform skin diagnosis using blood flow measurement, devices for evaluating sports training, and health check devices that monitor blood flow in daily life. Furthermore, a composite sensor that combines the blood flow sensor 1 with a deep temperature sensor is expected to be suitable for use in heatstroke detection devices, etc. The devices to which it can be applied are not particularly limited. For example, the same principle can be used to determine the velocity of fluid inside pipes in machinery and industrial piping.

[0053] The present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible within the scope of the invention. Furthermore, the above-described embodiment is presented as an example and is not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

[0054] DESCRIPTION OF SYMBOLS 1 Blood flow sensor 2 Thermal stimulus generating section (heater) 3 Central thin film thermistor 4 Peripheral thin film thermistor 5 Flexible substrate 10 Heat insulating cover 10a Recess 21 Central region 31 Insulating substrate 32 Heat sensitive thin film 33a, 33b Electrode layer 34 Protective film 51 Wiring pattern 52 Connector connection section

Claims

1. A blood flow sensor that estimates the skin blood flow velocity of a living organism from the skin thermal conductivity of the organism and the skin surface temperature difference of the organism, comprising: an insulating flexible substrate that can be attached to the skin surface of the organism; a conductive wiring pattern formed on the flexible substrate; a roughly annular thermal stimulus generating unit that heats or cools the skin surface of the organism; one central thin-film thermistor disposed in the center of the thermal stimulus generating unit; and at least two peripheral thin-film thermistors disposed a certain distance from the periphery of the thermal stimulus generating unit, wherein 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 comprising the blood flow sensor according to claim 1 and a heat insulating cover disposed thereon.

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

4. A blood flow sensor according to claim 1 or 2, characterized in that the substantially annular thermal stimulus generating portion is a heater.

5. The blood flow sensor according to claim 4, wherein the heater has a meandering structure.

6. A blood flow sensor as claimed in claim 1 or 2, characterized in that the number of thin film thermistors arranged in the peripheral area at a fixed distance from the periphery of the thermal stimulus generating part is 2 to 6.

7. A blood flow sensor as described in claim 1 or 2, characterized in that the central thin-film thermistor and the peripheral thin-film thermistors have a substrate and a heat-sensitive thin film and an electrode layer formed on the substrate, and the heat-sensitive thin film and electrode layer are arranged so as to face the contact surface which is the object to be measured.

8. A blood flow measuring device according to claim 1 or 2, further comprising a control processing unit for controlling each component of the blood flow sensor.

9. A device equipped with a blood flow sensor, characterized in that it is equipped with the blood flow sensor according to claim 1.

10. A blood flow measurement method using a blood flow sensor comprising: an insulating flexible substrate that can be attached to the skin surface of a living body; a conductive wiring pattern formed on the flexible substrate; a substantially annular thermal stimulus generating unit that heats or cools the skin surface of the living body; one central thin film thermistor disposed in the center of the thermal stimulus generating unit; and at least two peripheral thin film thermistors disposed a certain distance from the periphery of the thermal stimulus generating unit, the at least two peripheral thin film thermistors being arranged on a straight line passing through the center of the central thin film thermistor, the blood flow measurement method comprising: a first step of calculating the thermal conductivity of the skin; a second step of calculating the blood vessel depth near the body surface; and a third step of calculating the blood flow velocity near the body surface.

11. The blood flow measuring method described in claim 10, characterized in that in the third step of calculating the blood flow velocity near the body surface, known thermal characteristic values ​​of the blood of a living body are used, and the known thermal characteristic values ​​of the blood of a living body are the specific heat, density and thermal conductivity of the blood.

12. A composite sensor comprising the blood flow sensor according to claim 1 combined with a deep temperature sensor.

13. The composite sensor of claim 12, wherein the deep temperature sensor comprises a thin film thermistor.

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

15. The composite sensor according to claim 12 or 13, wherein the deep temperature sensor uses the principle of a dual heat flow method.

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