Patent Publication Number: US-2021177272-A1

Title: Living Body Internal Temperature Measuring Device and Living Body Internal Temperature Measuring Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry of PCT Application No. PCT/JP2019/019253, filed on May 15, 2019, which claims priority to Japanese Application No. 2018-105894, filed on Jun. 1, 2018, which applications are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an internal body temperature measurement device and an internal body temperature measurement method for measuring a temperature of a core part of a living body. 
     BACKGROUND 
     A living body has a temperature region which is not affected by a change in an outside air temperature or the like beyond a certain depth from an epidermis toward a core part (see  FIG. 11 ) (hereinafter, the temperature of the region is referred to as a “core temperature” or a “deep body temperature”). It is known that measuring a fluctuation of the core temperature is useful for grasping an internal body rhythm. 
     In order to measure the core temperature, a percutaneous temperature measurement method rather than an invasive measurement such as indwelling is easy and useful for routine body temperature management. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         Non-Patent Literature 1: Akio Nakayama, “Handbook of physiological sciences: Volume 22”, Igaku-Shoin (1987); 
         Non-Patent Literature 2: Shinya Nakagawa et al., “Wearable Core Temperature Thermometer Implemented by the MEMS Heat Flux Sensor”, IEEJ Transactions on Electronics, Vol. 135 (2015) No. 8, p. 343-348. 
       
    
     SUMMARY 
     Technical Problem 
     However, in a conventional percutaneous body temperature measurement device, it is difficult to accurately measure the core temperature. One of the reasons for that is that the apparent depth from the epidermis to the temperature region of the core temperature is changed due to a blood flow, and the measurement value is changed. 
     Generally, it is known that the depth from the epidermis to the temperature region of the core temperature Tc (hereinafter, referred to as a “core temperature depth” in some cases) depends on a blood flow rate as illustrated in  FIG. 12  (Non-Patent Literature 1, FIG. 59). The blood flow of a body surface increases when a blood vessel presents in a dermis layer and called arteriovenous anastomoses (AVA) is dilated by a neural activity of the body. When the blood flow rate of the body surface increases, the heat energy of the core part moves together with the blood flow to a surface layer, and thus the apparent depth from the epidermis to the temperature region of the core temperature Tc becomes shallow. 
     On the other hand, in order to measure the core temperature Tc of a living body  90  in a percutaneous manner, for example, a heat flux sensor  20  illustrated in  FIG. 13  is used to measure a temperature Tu of an upper surface of a heat resistor  20   r  configuring the heat flux sensor  20  and a temperature of a lower surface, that is, an epidermis temperature Ts, and the core temperature Tc is calculated from a value Rx of the heat resistance of the subcutaneous tissue of the living body  90  and a vertical heat resistance value Rr of the heat resistor  20   r  on the basis of following Formula (1) (Non-Patent Literature 2). 
     
       
         
           
             
               
                 
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     In order to measure the core temperature Tc of the living body  90  in the percutaneous manner, the value Rx of the heat resistance of the subcutaneous tissue of the living body  90  is required. However, when the core temperature depth is changed along with the change in the blood flow rate of the body surface, the value Rx of the heat resistance of the subcutaneous tissue of the living body  90  is also changed, and thus, it is difficult to accurately measure the core temperature Tc. 
     In this regard, an object of embodiments of the present invention is to provide an internal body temperature measurement device capable of more accurately measuring a core temperature with a percutaneous temperature measurement method. 
     Means for Solving the Problem 
     In order to achieve the above-described object, an internal body temperature measurement device according to embodiments of the present invention includes: a temperature sensor ( 20 S) which measures an epidermis temperature of a living body; a heat flux sensor ( 20 ) which measures a magnitude of a heat flux discharged from a body surface of the living body; a blood flow sensor ( 30 ) which measures a blood flow rate in a vicinity of the heat flux sensor; a storage unit ( 50 ) which stores a relation between the blood flow rate in the vicinity of the heat flux sensor and a parameter regarding a core temperature of the living body; and an arithmetic circuit ( 40 ) configured to obtain a correction amount of a value of the parameter corresponding to the blood flow rate in the vicinity of the heat flux sensor on a basis of the relation stored in the storage unit and calculate the core temperature of the living body from the epidermis temperature measured by the temperature sensor, the magnitude of the heat flux measured by the heat flux sensor, and the correction amount of the value of the parameter. 
     In the internal body temperature measurement device according to embodiments of the present invention, the arithmetic circuit ( 40 ) may include a first calculation unit ( 41 ) which calculates the correction amount of the value of the parameter corresponding to the blood flow rate in the vicinity of the heat flux sensor on the basis of the relation stored in the storage unit, and a second calculation unit ( 42 ) which calculates the core temperature of the living body on a basis of the epidermis temperature measured by the temperature sensor, the magnitude of the heat flux measured by the heat flux sensor, and the correction amount of the value of the parameter calculated by the first calculation unit. 
     As one configuration example of the internal body temperature measurement device according to embodiments of the present invention, the second calculation unit ( 42 ) may include an estimation unit ( 421 ) which estimates a heat resistance between an epidermis and a core part of the living body from the magnitude of the heat flux measured by the heat flux sensor, a correction unit ( 422 ) which corrects the heat resistance estimated by the estimation unit on a basis of the correction amount of the value of the parameter, and a core temperature calculation unit ( 423 ) which calculates the core temperature of the living body from the epidermis temperature measured by the temperature sensor, the magnitude of the heat flux measured by the heat flux sensor, and the heat resistance obtained by the correction of the correction unit. 
     As one configuration example of the internal body temperature measurement device according to embodiments of the present invention, the second calculation unit may include an estimation unit which estimates a depth (core temperature depth) from an epidermis to a core part of the living body from the magnitude of the heat flux measured by the heat flux sensor, a correction unit which corrects the depth from the epidermis to the core part of the living body estimated by the estimation unit on a basis of the correction amount of the value of the parameter, and a core temperature calculation unit which calculates the core temperature of the living body from the epidermis temperature measured by the temperature sensor, the magnitude of the heat flux measured by the heat flux sensor, and the depth from the epidermis to the core part of the living body obtained by the correction of the correction unit. 
     As one configuration example of the internal body temperature measurement device according to embodiments of the present invention, the second calculation unit ( 42   a ) may include an estimation unit ( 421   a ) which estimates the core temperature of the living body from the epidermis temperature measured by the temperature sensor and the magnitude of the heat flux measured by the heat flux sensor, and a core temperature calculation unit ( 423   a ) which calculates the core temperature of the living body by correcting the core temperature of the living body estimated by the estimation unit on a basis of the correction amount of the value of the parameter calculated by the first calculation unit. 
     In the internal body temperature measurement device according to embodiments of the present invention, the parameter may be the depth from the epidermis to the core part of the living body, the heat resistance, or the core temperature. 
     The internal body temperature measurement device according to embodiments of the present invention further may include at least two of the blood flow sensors. The arithmetic circuit may obtain a representative value of respective blood flow rates measured by the at least two blood flow sensors and obtain the correction amount of the value of the parameter corresponding to the blood flow rate in the vicinity of the heat flux sensor on a basis of the representative value of the blood flow rates and the relation stored in the storage unit. 
     An internal body temperature measurement method according to embodiments of the present invention includes: a step of measuring an epidermis temperature of a living body and a magnitude of a heat flux discharged from a body surface of the living body; a step of measuring a blood flow rate of the body surface; and a step of obtaining, on a basis of a previously prepared relation between a blood flow rate in a vicinity of a heat flux sensor and a parameter regarding a core temperature of the living body, a correction amount of a value of the parameter corresponding to the blood flow rate in the vicinity of the heat flux sensor, and calculating the core temperature of the living body from the epidermis temperature measured by the temperature sensor, the magnitude of the heat flux measured by the heat flux sensor, and the correction amount of the value of the parameter. 
     Effects of Embodiments of the Invention 
     According to embodiments of the present invention, the value of the parameter regarding the core temperature of the living body is corrected according to the blood flow rate of the body surface, and thus the core temperature can be measured more accurately with the percutaneous temperature measurement method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of an internal body temperature measurement device according to a first embodiment of the present invention. 
         FIG. 2  is a diagram illustrating the configuration of the internal body temperature measurement device according to the first embodiment of the present invention. 
         FIG. 3  is a diagram for explaining a positional relation between a heat flux sensor and a blood flow sensor in the internal body temperature measurement device according to the first embodiment. 
         FIG. 4  is a diagram illustrating a relation between a blood flow rate and a depth from an epidermis to a temperature region of a core temperature. 
         FIG. 5  is a flowchart for explaining an operation of the internal body temperature measurement device according to the first embodiment. 
         FIG. 6  is a diagram illustrating one example of a measurement result by the internal body temperature measurement device according to the first embodiment. 
         FIG. 7  is a diagram illustrating a configuration of an internal body temperature measurement device according to a second embodiment of the present invention. 
         FIG. 8  is a diagram for explaining a positional relation between the heat flux sensor and the blood flow sensor. 
         FIG. 9  is a diagram for explaining a positional relation between the heat flux sensor and the blood flow sensor. 
         FIG. 10  is a flowchart for explaining an operation of the internal body temperature measurement device according to the second embodiment. 
         FIG. 11  is a diagram for schematically explaining a temperature distribution of a subcutaneous tissue of a living body. 
         FIG. 12  is a diagram illustrating a relation between the depth from the epidermis to the temperature region of the core temperature and the blood flow rate. 
         FIG. 13  is a schematic diagram for explaining the measurement of the core temperature by the heat flux sensor including a temperature sensor 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
     As illustrated in  FIG. 1 , an internal body temperature measurement device  1  according to a first embodiment of the present invention includes, on a sheet-shaped base material  80 , a heat flux sensor  20 , a blood flow sensor  30 , an arithmetic circuit  40 , a memory  50  which functions as a storage unit, a communication circuit  6   o  which functions as an I/F circuit with an outside, and a battery  70  which supplies power to the arithmetic circuit  40 , the communication circuit  60 , or the like. 
     Herein, the heat flux sensor  20  is a device which measures the movement of heat per unit time/unit area. As illustrated in  FIG. 13 , in this embodiment, the heat flux sensor  20  having a temperature sensor  20 U and a temperature sensor  20 S is used for the upper surface and the lower surface of the heat resistor tor, respectively. The magnitude of heat flux discharged from the body surface of the living body  90  is measured, and at the same time, an epidermis temperature Ts is measured by the temperature sensor  20 S. As the temperature sensors  20 U and  20 S, a well-known thermistor, a thermopile using a thermocouple, an ultrasonic thermometer utilizing the change in sound velocity according to the temperature, an infrared temperature sensor or another optical thermometer utilizing the change in a light absorption rate according to the temperature, or the like is used, for example. 
     The blood flow sensor  30  is a device which is arranged near the heat flux sensor  20  and measures the blood flow rate of the body surface of the living body  90 . As such a blood flow sensor  30 , a laser Doppler blood flowmeter or another optical blood flow sensor which measures a blood flow rate in a subcutaneous tissue by irradiating a skin with a laser or an ultrasonic blood flowmeter is used, for example. 
     The memory  50  stores a relation between the blood flow rate in the vicinity of the heat flux sensor  20 , that is, the body surface and parameters regarding the core temperature Tc of the living body. Herein, the parameters regarding the core temperature Tc of the living body are, for example, a depth (core temperature depth) L from the epidermis to the core part in the living body, a heat resistance Rx of the subcutaneous tissue between the epidermis and the core part in the living body, or the core temperature Tc. The relation between the blood flow rate of the body surface and the parameters regarding the core temperature Tc of the living body may be stored in the memory  50  in the form of a table. However, the relation also may be stored as a function. 
     Further, the memory  50  stores the time-series data of the core temperature which is estimated and calculated from the result obtained by the measurement of the heat flux sensor  20 , that is, the time-series data in which the core temperature and the time when the core temperature is measured are associated with each other. 
     The arithmetic circuit  40  obtains the correction amount of the value of the parameter corresponding to the blood flow rate in the vicinity of the heat flux sensor  20  on the basis of the relation between the blood flow rate of the body surface stored in the memory  50  and the parameter regarding the core temperature Tc of the living body. Further, the arithmetic circuit  40  calculates the core temperature Tc of the living body from the epidermis temperature Ts measured by the temperature sensor  20 S, the magnitude of the heat flux measured by the heat flux sensor  20 , and the correction amount of the value of the parameter. 
     Such an arithmetic circuit  40  can be formed from an arithmetic device and a computer program. For example, the arithmetic circuit  40  can be formed from a first calculation unit  41  which calculates the correction amount of the value of the parameter corresponding to the blood flow rate in the vicinity of the heat flux sensor  20  on the basis of the relation between the blood flow rate and the parameter stored in the memory  50  and a second calculation unit  42  which calculates the core temperature of the living body on the basis of the epidermis temperature Ts measured by the temperature sensor  20 S, the magnitude of the heat flux measured by the heat flux sensor  20 , and the correction amount of the value of the parameter calculated by the first calculation unit  41 . 
     In the internal body temperature measurement device  1  according to this embodiment, for example, in a case where the heat resistance Rx between the epidermis and the core part in the living body is adopted as the parameter, the first calculation unit  41  is configured to calculate the correction amount ΔR of the heat resistance Rx between the epidermis and the core part of the living body corresponding to the blood flow rate in the vicinity of the heat flux sensor  20 . Further, the second calculation unit  42  is formed from an estimation unit  421  which estimates the heat resistance Rx between the epidermis and the core part of the living body from the magnitude of the heat flux measured by the heat flux sensor  20 , a correction unit  422  which corrects the heat resistance Rx estimated by the estimation unit  421  on the basis of the correction amount ΔR of the heat resistance calculated by the first calculation unit  41 , and a core temperature calculation unit  423  which calculates the core temperature Tc of the living body from the epidermis temperature Ts measured by the temperature sensor  20 S, the magnitude of the heat flux measured by the heat flux sensor  20 , and the heat resistance Rx+ΔR obtained by the correction of the correction unit  422 . 
     In a case where the core temperature depth L is adopted as the parameter, the first calculation unit  41  is configured to calculate the correction amount ΔL of the core temperature depth L corresponding to the blood flow rate in the vicinity of the heat flux sensor  20 . Further, the estimation unit  421  may be configured to estimate the depth (core temperature depth) L from the epidermis to the core part of the living body from the magnitude of the heat flux measured by the heat flux sensor  20 . The correction unit  422  may be configured to correct the core temperature depth L of the living body estimated by the estimation unit  421  on the basis of the correction amount ΔL of the core temperature depth L calculated by the first calculation unit  41 . The core temperature calculation unit  423  may be configured to calculate the core temperature Tc of the living body from the epidermis temperature Ts measured by the temperature sensor  20 S, the magnitude of the heat flux measured by the heat flux sensor  20 , and the depth L+ΔL from the epidermis to the core part of the living body obtained by the correction by the correction unit  422 . 
     The communication circuit  6   o  is an I/F circuit which outputs the time-series data of the temperature obtained by the correction of the arithmetic circuit  40  to the outside or outputs an alarm when an error occurs. As such a communication circuit  60 , an output circuit to which a USB or other cable can be connected is used in a case where data or the like is output by wire. For example, a wireless communication circuit based on Bluetooth (registered trademark) or the like may be used. 
     The sheet-shaped base material  8   o  does not only function as a base for placing the heat flux sensor  20 , the blood flow sensor  30 , the arithmetic circuit  40 , the memory  50 , the communication circuit  60 , and the battery  70  but also includes wiring (not illustrated) which connects those elements electrically. Considering that the internal body temperature measurement device  1  is placed on the epidermis of the living body, a deformable flexible substrate is desirably used as the sheet-shaped base material  80 . 
     Further, as illustrated in  FIG. 2 , openings  82  and  83  are provided in a part of the sheet-shaped base material  80 , and the heat flux sensor  20  and the blood flow sensor  30  are placed on the base material  80  so as to be in contact with the epidermis of the living body through the openings  82  and  83 . 
     If the heat resistor  20   r  of the heat flux sensor  20  is formed, for example, in a disc shape, a region of about twice a diameter R of the heat resistor  20   r  affects the measurement of the core temperature Tc. Therefore, in order to measure the blood flow rate of the body surface in the vicinity of the heat flux sensor  20  with the blood flow sensor  30 , as illustrated in  FIG. 3 , the blood flow sensor  30  is installed within the region of twice the diameter R of the heat resistor  20   r  of the heat flux sensor  20 , that is, about a diameter  2 R around the heat resistor  20   r  in plan view. One or multiple blood flow sensors  30  can be also provided in one heat flux sensor  20 , but in this embodiment, one blood flow sensor  30  is provided in one heat flux sensor  20 . 
     [Measurement Principle of Internal Body Temperature Measurement Device] 
     Next, the measurement principle of the internal body temperature measurement device according to this embodiment will be described. 
     As illustrated in  FIG. 13 , the living body  90  has the region of the temperature which is not affected by a change in an outside air temperature or the like beyond a certain depth from the epidermis in a depth direction of the subcutaneous tissue, that is, the core temperature. Typically, the epidermis temperature Ts is lower than the core temperature Tc, and a temperature gradient is generated from the core part toward the epidermis. 
     As described above with Formula (1), in order to measure the core temperature Tc of the living body  90  in a percutaneous manner, the value Rx of the heat resistance of the subcutaneous tissue is required. 
     On the other hand, the heat resistance Rx of the subcutaneous tissue is proportional to the depth (core temperature depth) L from the epidermis to the temperature region of the core temperature Tc of the core part and is inversely proportional to a thermal conductivity k of the subcutaneous tissue. 
         Rx=L/k ( Tc−Ts )  (2)
 
     The thermal conductivity k is determined by a subcutaneous composition. However, the subcutaneous composition does not change in the short term, and thus the heat resistance Rx of the subcutaneous tissue depends on a distance L from the epidermis to the temperature region of the core temperature Tc. As described above, the apparent core temperature depth changes along with the blood flow rate of the body surface ( FIG. 12 ), but in the related art, the change in the depth to the temperature region of the core temperature Tc is not taken into consideration. 
     In this regard, in this embodiment, the depth (core temperature depth) L from the epidermis to the core part of the living body is adopted as the parameter, and the relation L=f(vblood) between the blood flow rate vblood and the apparent core temperature depth L is stored in advance in the memory  50  as illustrated in  FIG. 4 . At this time, the change amount ΔR of the heat resistance of the subcutaneous tissue generated by a change amount Δvblood of the blood flow rate can be calculated from the change amount ΔL of the depth obtained from the relation L=f(vblood) and the change amount Δvblood of the blood flow rate, and the thermal conductivity k of the subcutaneous tissue on the basis of the following formula. 
       Δ L=Δv blood× f ( v blood)  (3)
 
       Δ R=ΔL/k   (4)
 
     The correction amount ΔTc of the core temperature Tc can be calculated from the change amount ΔR of the heat resistance of the subcutaneous tissue on the basis of the following Formula (5), and the core temperature Tc can be corrected on the basis of Formula (6). 
       Δ Tc=ΔR/Rr ×( Ts−Tu )  (5)
 
         Tc=Tc+ΔTc   (6)
 
     Incidentally,  FIG. 4  illustrates one example of the relation between the blood flow rate vblood and the core temperature depth L. The core temperature depth L is expressed by a function f using the blood flow rate vlood as a variable. 
     In summary, in the related art, when the blood flow rate vblood increases, the heat resistance Rx is calculated to be larger than the actual one, so the core temperature is overestimated. However, in this embodiment, the value close to the actual core temperature can be obtained by correcting the heat resistance Rx with the blood flow rate. 
     [Measurement Method of Internal Body Temperature Measurement Device] 
     Next, the operation of the internal body temperature measurement device according to this embodiment will be described with reference to  FIG. 5 . 
     Incidentally, in the memory  50 , the relation L=f(vblood) (see  FIG. 4 ) between the blood flow rate vblood and the apparent core temperature depth L obtained from an experiment or the like is stored in a form of a relational expression f(vblood) or a table. 
     First, the temperature Tu of the upper surface of the heat resistor  20   r  and the temperature of the lower surface, that is, the epidermis temperature Ts are measured by using two temperature sensors  20 U and  20 S of the heat flux sensor  20  (step S 10 ). Further, the blood flow rate of the body surface is measured by using the blood flow sensor  30  (step S 20 ). The operations are repeated a plurality of times to determine whether or not the fluctuation of the upper surface temperature Tu of the heat resistor  20   r  and the epidermis temperature Ts falls within a predetermined range (step S 30 ). When the fluctuation does not fall within the predetermined range (step S 30 : No), it is determined that the heat flux is not in a steady state, the procedure returns to step S 10 , and steps S 10  to S 30  are repeated. 
     On the other hand, when the fluctuation of the upper surface temperature Tu of the heat resistor  20   r  and the epidermis temperature Ts falls within the predetermined range (step S 30 : Yes), it is determined that the heat flux is in the steady state, and an initial value Tco of the core temperature of the living body  90  is estimated from the magnitude of the heat flux measured by the heat flux sensor  20  (step S 40 ). Specifically, the initial value Tco of the core temperature is calculated from the upper surface temperature Tu of the heat resistor  20   r , the epidermis temperature Ts, the heat resistance Rr of the heat resistor  20   r , and the heat resistance Rxo of the subcutaneous tissue as a predetermined reference on the basis of Formula (1), for example. 
     After the initial value Tco of the core temperature Tc is calculated, the upper surface temperature Tu of the heat resistor  20   r  and the epidermis temperature Ts are measured at a predetermined time interval (step S 50 ), and each time the upper surface temperature Tu and the epidermis temperature Ts are measured, the blood flow rate vblood of the body surface in the vicinity of the heat flux sensor  20  is measured by the blood flow sensor  30  (step S 60 ). Further, the change amount Δvblood of the blood flow rate vblood is calculated, and the change amount ΔR of the heat resistance between the epidermis of the subcutaneous tissue and the temperature region of the core temperature Tc is obtained from the change amount Δvblood of the blood flow rate by using the relation L=f(vblood) (see  FIG. 4 ) between the blood flow rate vblood and the apparent core temperature depth L stored in the memory  50 . By using the change amount ΔR of the heat resistance, the correction amount ΔTc of the core temperature Tc is calculated on the basis of Formula (5) (step S 70 ), and the core temperature Tc is corrected on the basis of Formula (6) (step S 80 ). 
     Further, until an indication of completion is given (step S 90 : No), the above steps S 50  to S 80  are repeated, and when the indication of completion is given (step S 90 : Yes), a series of processing is ended. 
     One example of the time-series data of the core temperature Tc obtained by the above correction is illustrated in  FIG. 6 . 
     In a case where the change amount ΔR of the heat resistance of the subcutaneous tissue by the change in the blood flow rate is not taken into consideration similarly to the related art, when the blood flow changes, there occurs a measurement error as indicated by a circle. On the other hand, according to the internal body temperature measurement device according to this embodiment, by calculating the change amount ΔTc of the core temperature Tc associated with the change in the blood flow rate and performing correction, the accurate core temperature Tc can be obtained even when the blood flow change occurs. Accordingly, the fluctuation of the core temperature Tc as an internal body rhythm can be grasped more accurately. 
     Second Embodiment 
     Next, a second embodiment of the present invention and a modification thereof will be described with reference to  FIGS. 7 to 9 . Incidentally, the same reference symbols are used for the components common to the above-described internal body temperature measurement device  1  according to the first embodiment, and the detailed description thereof will be omitted. 
     As illustrated in  FIG. 7 , an internal body temperature measurement device  1   a  according to the second embodiment of the present invention includes, on the base material  80 , the heat flux sensor  20  which includes two temperature sensors  20   u  and  20   s , two blood flow sensors  30 - 1  and  30 - 2 , an arithmetic circuit  40   a , the memory  50 , the communication circuit  60  which functions as the I/F circuit with the outside, and the battery  70  which supplies power to the arithmetic circuit  40   a , the communication circuit  60 , or the like. 
     In this embodiment, two blood flow sensors  30 - 1  and  30 - 2  are arranged in the vicinity of the heat resistor  20   r  of the heat flux sensor  20 . At this time, when the effect of the region of about twice the diameter R of the heat resistor  20   r  on the measurement of the core temperature Tc is taken into consideration, as illustrated in  FIG. 8 , two blood flow sensors  30 - 1  and  30 - 2  are installed within the region of twice the diameter R of the heat resistor  20   r  of the heat flux sensor  20 , that is, about the diameter  2 R around the heat resistor  20   r  in plan view. 
     More specifically, as illustrated in  FIG. 8 , two blood flow sensors  30 - 1  and  30 - 2  are arranged at positions of a line object across the heat resistor  20   r  of the heat flux sensor  20  in plan view. However, the present invention is not limited thereto. For example, as illustrated in  FIG. 9 , in plan view, two blood flow sensors  30 - 1  and  30 - 2  may be arranged to be positioned at two lines passing through the center of the heat resistor  20   r  of the heat flux sensor  20  and crossing each other at right angles. 
     On the other hand, in this embodiment, the core temperature Tc is used as the parameter regarding the core temperature of the living body, and the previously prepared relation Tc=g(vblood) between the blood flow rate vblood and the core temperature Tc is stored in the memory  50 . 
     Similarly to the arithmetic circuit  40  of the internal body temperature measurement device  1  according to the first embodiment, the arithmetic circuit  40   a  includes a first calculation unit  41   a  which calculates the parameter corresponding to the blood flow rate in the vicinity of the heat flux sensor  20 , that is, the correction amount of the value of the core temperature Tc on the basis of the relation stored in the memory  50 , and a second calculation unit  42   a  which calculates the core temperature (Tc+ΔTc) of the living body on the basis of the epidermis temperature Ts measured by the temperature sensor  20 S, the magnitude of the heat flux measured by the heat flux sensor  20 , and the correction amount ΔTc of the core temperature Tc calculated by the first calculation unit  41   a.    
     Among them, the second calculation unit  42   a  is configured to include an estimation unit  421   a  which estimates the core temperature Tc of the living body  90  from the epidermis temperature measured by the temperature sensor  20 S and the magnitude of the heat flux measured by the heat flux sensor  20 , and a core temperature calculation unit  423   a  which corrects the core temperature Tc of the living body  90  estimated by the estimation unit  421   a  on the basis of the correction amount of the value of the parameter calculated by the first calculation unit  41   a  and calculates the core temperature (Tc+ΔTc) of the living body  90 . The above-described arithmetic circuit  40   a  can be formed from an arithmetic device and a computer program. 
     Herein, the internal body temperature measurement device is according to this embodiment includes two blood flow sensors  30 - 1  and  30 - 2  with respect to one heat flux sensor  20 . Thus, the first calculation unit  41   a  of the arithmetic circuit  40   a  is configured to obtain the average value of respective blood flow rates measured by the two blood flow sensors  30 - 1  and  30 - 2  as a representative value of the blood flow rate and obtain the correction amount ΔTc of the core temperature Tc corresponding to the average value of the blood flow rates by using the relation stored in the memory  50 . 
     Next, the operation of the internal body temperature measurement device is according to this embodiment will be described with reference to  FIG. 10 . 
     First, the temperature Tu of the upper surface of the heat resistor  20   r  and the temperature of the lower surface, that is, the epidermis temperature Ts are measured by using two temperature sensors  20 U and  20 S of the heat flux sensor  20  (step S 10 ). Further, the blood flow rate of the body surface is measured by using the blood flow sensor  30  (step S 20 ). The operations are repeated a plurality of times to determine whether or not the fluctuation of the upper surface temperature Tu of the heat resistor  20   r  and the epidermis temperature Ts falls within the predetermined range (step S 30 ). When the fluctuation does not fall within the predetermined range (step S 30 : No), it is determined that the heat flux is not in the steady state, the procedure returns to step S 10 , and steps S 10  to S 30  are repeated. 
     On the other hand, when the fluctuation of the upper surface temperature Tu of the heat resistor  20   r  and the epidermis temperature Ts falls within the predetermined range (step S 30 : Yes), it is determined that the heat flux is in the steady state, and the initial value Tco of the core temperature of the living body  90  is estimated from the magnitude of the heat flux measured by the heat flux sensor  20  (step S 40   a ). Specifically, the initial value Tco of the core temperature Tc is calculated from the upper surface temperature Tu of the heat resistor  20   r , the epidermis temperature Ts, the heat resistance Rr of the heat resistor  20   r , and the heat resistance Rxo of the subcutaneous tissue as the predetermined reference on the basis of Formula (1), for example. 
     After the initial value Tco of the core temperature Tc is calculated, the upper surface temperature Tu of the heat resistor  20   r  and the epidermis temperature Ts are measured at the predetermined time interval (step S 50 ), and each time the upper surface temperature Tu and the epidermis temperature Ts are measured, the blood flow rate vblood of the body surface in the vicinity of the heat flux sensor  20  is measured by the blood flow sensor  30  (step S 60 ). Further, the change amount Δvblood of the blood flow rate vblood is calculated, the correction amount ΔTc of the core temperature Tc is calculated from the change amount Δvblood of the blood flow rate by using the relation Tc=g(vblood) between the blood flow rate vblood and the core temperature Tc stored in the memory  50  (step S 70   a ), and the core temperature Tc is corrected on the basis of Formula (6) (step S 80   a ). 
     Further, until the indication of completion is given (step S 90 : No), the above steps S 50  to S 80   a  are repeated, and when the indication of completion is given (step S 90 : Yes), a series of processing is completed. 
     According to this embodiment, the correction amount ΔTc of the core temperature Tc associated with the change in the blood flow rate is calculated, and the core temperature Tc calculated on the basis of the epidermis temperature Ts and the magnitude of the heat flux is corrected by the correction amount ΔTc, whereby the accurate core temperature Tc can be obtained even when the blood flow change occurs. 
     According to this embodiment, the blood flow rate in the vicinity of the heat flux sensor can be measured accurately by using a plurality of blood flow sensors. Thus, the calculation accuracy of the correction amount according to the blood flow rate is improved, and the core temperature can be grasped more accurately. 
     Incidentally, in this embodiment, two blood flow sensors  30 - 1  and  30 - 2  are used. However, of course, three or more blood flow sensors may be used. 
     Further, as the representative value of respective blood flow rates measured by the plurality of blood flow sensors, the average value of the blood flow rates can be used. However, instead of the average value, a maximum value or a minimum value may be used, and in addition, in the case of using three or more blood flow sensors, a median value or the like may be used. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  1   a  Internal body temperature measurement device 
               20  Heat flux sensor 
               20   u ,  20   s  Temperature sensor 
               20   r  Heat resistor 
               30  Blood flow sensor 
               40  Arithmetic circuit 
               50  Memory 
               60  Communication circuit 
               70  Battery 
               80  Base material 
               90  Living body.