Patent Publication Number: US-2023144382-A1

Title: Temperature Measurement Device and Temperature Measurement Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry of PCT Application No. PCT/JP2020/018096, filed on Apr. 28, 2020, which application is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a temperature measuring device and a temperature measuring method that measure the internal temperature of a subject such as a living body. 
     BACKGROUND 
     In a substance, for example, a living body, when a certain depth is exceeded from the epidermis toward a deep body, there is a temperature area that is not affected by changes in outside air temperature, or the like, and the temperature of this area is called a deep body temperature or a core body temperature. On the other hand, the temperature of a surface layer of a living body that is susceptible to changes in outside air temperature is called a body surface temperature. The body surface temperature may be measured by a percutaneous thermometer in the related art. The body temperature measured by such a percutaneous thermometer in the related art may not reflect the deep body temperature. Therefore, it is difficult to directly measure the deep body temperature, which is the temperature in the deep area of the living body, like the body surface temperature. 
     Therefore, the inventor proposed a noninvasive deep body temperature measurement technology for measuring a skin surface heat flux H Skin  and a skin surface temperature T Skin  by a sensor installed on a skin surface and estimating a deep body temperature T Core  by using these measured values and biothermal resistance R Body  given by initial calibration (see NPL 1 and NPL 2). An Equation for estimating the deep body temperature T Core  is as follows. 
         T   Core   =T   Skin   +R   Body   H   Skin   (1)
 
     The biothermal resistance R Body  is modeled as a constant because it is determined by the thickness from the skin surface to a deep body temperature area at a sensor installation site. However, when the blood flow in capillaries or arteriovenous anastomosis changes due to a warm bath, exercise, or the like, the actual thermal resistance of a living body may change from a value given by initial calibration, resulting in a problem in that an error occurs in an estimated value of the deep body temperature T Core . 
     CITATION LIST 
     Non Patent Literature 
     
         
         NPL 1: Daichi Matsunaga, Yujiro Tanaka, Tomoko Seyama, “Study for miniaturization of a noninvasive deep body temperature sensor considering convection change”, 2020 Institute of Electronics, Information and Communication Engineers (IEICE) General Conference, Communication lecture Proceedings 1, B-19-9, 2020 
         NPL 2: Daichi Matsunaga, Yujiro Tanaka, Tomoko Seyama, “Study of a noninvasive deep body temperature estimation method for convection change in outside air”, 2019 Institute of Electronics, Information and Communication Engineers (IEICE) Communication Society Conference, Communication lecture Proceedings 1, B-19-15, 2019 
       
    
     SUMMARY 
     Technical Problem 
     The present invention has been made to solve the above problems, and an object of the present invention is to provide a temperature measuring device and a temperature measuring method, capable of reducing an error in an estimated value of the internal temperature of a subject caused by a change in blood flow. 
     Means for Solving the Problem 
     A temperature measuring device according to embodiments of the present invention includes: a blood flow meter configured to measure a blood flow near a skin surface of a subject; a sensor configured to measure a temperature and a heat flux of the skin surface of the subject; a storage unit configured to store an initial value of the blood flow in advance; a thermal resistance derivation unit configured to derive thermal resistance of the subject on the basis of an amount of change with respect to the initial value of the blood flow measured by the blood flow meter; and a temperature calculation unit configured to calculate an internal temperature of the subject on the basis of the temperature, the heat flux, and the thermal resistance. 
     Furthermore, a temperature measuring method according to embodiments of the present invention includes: a first step of measuring a blood flow near a skin surface of a subject; a second step of deriving thermal resistance of the subject on the basis of an amount of change with respect to an initial value of the blood flow stored in advance; a third step of measuring a temperature and a heat flux of the skin surface of the subject; and a fourth step of calculating an internal temperature of the subject on the basis of a measurement result in the third step and the thermal resistance derived in the second step. 
     Effects of the Invention 
     According to embodiments of the present invention, deriving the thermal resistance of a subject on the basis of the amount of change in blood flow measured by a blood flow meter enables to reduce an error in an estimated value of the internal temperature of a subject caused by a change in blood flow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram illustrating the configuration of a temperature measuring device according to an embodiment of the present invention. 
         FIG.  2    is a diagram illustrating a thermal equivalent circuit model of a sensor and a living body according to the embodiment of the present invention. 
         FIG.  3    is a flowchart for explaining operations of the temperature measuring device according to the embodiment of the present invention. 
         FIG.  4    is a diagram for explaining operations of the temperature measuring device according to the embodiment of the present invention. 
         FIG.  5    is a block diagram illustrating an example of the configuration of a computer that implements the temperature measuring device according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings.  FIG.  1    is a block diagram illustrating the configuration of a temperature measuring device according to an embodiment of the present invention. The temperature measuring device includes a sensor  1  that measures a temperature T Skin  of a skin surface of a living body  10  (subject) and a heat flux H Skin  on the skin surface, a laser Doppler blood flow meter  2  that measures a blood flow v Blood  near the skin surface of the living body  10 , a storage unit  3  that stores an initial value v Blood  (o) of the blood flow v Blood  in advance, a thermal resistance derivation unit  4  that derives thermal resistance R Combined  of the living body  10  on the basis of the amount Δv Blood  of change with respect to the initial value v Blood  (o) of the blood flow v Blood , a temperature calculation unit  5  that calculates a deep body temperature T (internal temperature) of the living body  10  on the basis of the temperature T Skin , the heat flux H Skin , and the thermal resistance R Combined , and a calculation result output unit  6  that outputs the calculation result of the deep body temperature T Core . 
     The sensor  1  includes a thermal insulation member wo, a temperature sensor  101  disposed on a surface of the thermal insulation member wo in contact with the skin of the living body  10 , and a temperature sensor  102  disposed on a surface of the thermal insulation member wo on a side opposite to the surface in contact with the skin. By the temperature sensor  101 , it is possible to measure the temperature T Skin  of the skin surface of the living body  10 . Furthermore, it is possible to derive the heat flux H Skin  of the skin surface on the basis of a difference between the temperature T Skin  of the skin surface and a temperature T Upper  measured by the temperature sensor  102 . The sensor  1  is attached to the skin surface of the living body  10  by, for example, a thermally conductive double-sided tape. The configuration illustrated in  FIG.  1    is an example, and the sensor  1  may have a configuration different from that illustrated in  FIG.  1   . 
     The laser Doppler blood flow meter  2  includes a sensor probe  200  and a blood flow calculation unit  203 . The sensor probe  200  is provided with a semiconductor laser  201  that irradiates the living body  10  with a laser beam and a photodiode  202  that receives reflected light from the living body  10 . The blood flow calculation unit  203  calculates the blood flow v Blood  of the living body  10  on the basis of an electric signal output from the photodiode  202 . Since the laser Doppler blood flow meter  2  is a well-known technology, detailed description thereof will be omitted. 
       FIG.  2    is a diagram illustrating a thermal equivalent circuit model of the sensor  1  and the living body  10 . In the present invention, not only the thermal resistance R Body  of the living body  10  is modeled, but also thermal energy transferred by blood flow is modeled. In  FIG.  2 ,  11    denotes a blood vessel, T Upper  denotes the temperature of an upper surface of the sensor  1  on a side opposite to the surface in contact with the skin of the living body  10 , R Sensor  denotes the thermal resistance of the sensor  1 , R Blood  denotes heat resistance due to the blood flow, and H Blood  denotes a heat flux due to the blood flow. 
     Thermal resistance given by initial calibration is the combined resistance R Combined  of the thermal resistance R Body  of tissues (skin, fat, muscle, nerve, internal organs, bone, etc.), other than the blood of the living body  10 , and the thermal resistance R Blood  due to the blood flow of the living body  10 . 
         T   Core   =T   Skin   +R   Combined   H   Skin   (2)
 
     In the initial calibration, when the initial value of the deep body temperature T core  of the living body  10 , whose deep body temperature T Core  is to be measured, at a part around the sensor  1  is measured by, for example, a heat flow compensation method or an eardrum thermometer and at the same time, the skin surface temperature T Skin  and the skin surface heat flux H Skin  are measured by the sensor  1 , the initial value R Combined  (o) of the combined resistance R Combined  can be obtained by Equation 2 above. 
     The thermal resistance R Body  is a constant, and the thermal resistance R Blood  is expressed as a function of the blood flow v Blood . Consequently, the combined resistance R Combined  is a function of blood flow v Blood  as expressed by the equation below. 
     
       
         
           
             
               
                 
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     Therefore, a conversion table for the amount of change in the combined resistance R Combined  and the blood flow v Blood  is prepared in advance, and the initial value R Combined  (o) of the combined resistance R Combined  is updated from the amount of change in the blood flow v Blood  measured by a laser Doppler blood flow meter or the like, as expressed by the equation below. 
     
       
         
           
             
               
                 
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     In this way, in the present embodiment, it is possible to reduce an error in the estimated value of the deep body temperature T Core  that occurs when the blood flow changes.  FIG.  3    is a flowchart for explaining operations of the temperature measuring device of the present embodiment. The storage unit  3  of the temperature measuring device stores in advance a conversion table, in which the combined resistance R Combined  of the living body  10  is registered for each amount Δv Blood  of change in the blood flow v Blood , and the initial value v Blood  (o) of the blood flow v Blood  measured by the laser Doppler blood flow meter  2  at the time of the initial calibration. 
     In order to generate the conversion table, the deep body temperature T Core  of the living body  10 , whose deep body temperature T Core , is to be measured, at the part around the sensor  1  is measured by, for example, a heat flow compensation method or an eardrum thermometer while monitoring the blood flow v Blood  at the part around the sensor  1  by the laser Doppler blood flow meter  2 , and the skin surface temperature T Skin  and the skin surface heat flux H Skin  are measured by the sensor  1 . Then, in a case where there is a change in the blood flow v Blood , when the combined resistance R Combined  is calculated by Equation 2 above from the deep body temperature T Core , the skin surface temperature T Skin , and the skin surface heat flux H Skin  when the blood flow v Blood  changes from a non-steady state to a steady state, it is possible to obtain the value of the combined resistance R Combined  corresponding to the amount Δv Blood  of change in the blood flow v Blood . Such measurement is performed for each amount Δv Blood  of change. The above R Combined  (o) is registered in the conversion table as the combined resistance R Combined  when the amount Δv Blood  of change in the blood flow v Blood  is o. 
     The laser Doppler blood flow meter  2  of the temperature measuring device constantly measures the blood flow v Blood  of the living body  10  at the part around the sensor  1  (step S 100  in  FIG.  3   ). 
     The thermal resistance derivation unit  4  of the temperature measuring device derives the combined resistance R Combined  by acquiring, from the conversion table of the storage unit  3 , the value of combined resistance R Combined  corresponding to the amount Δv Blood  of change (=v Blood −v Blood  (o)) of the blood flow v Blood  measured by the laser Doppler blood flow meter  2  (step S 101  in  FIG.  3   ). 
     When the blood flow v Blood  is within a predetermined threshold range centered on the initial value v Blood  (o), the thermal resistance derivation unit  4  determines that there is no change in the blood flow v Blood  (the amount Δv Blood  of change is o), and when the blood flow v Blood  is out of the threshold range, the thermal resistance derivation unit  4  determines that there is a change in the blood flow v Blood  (absolute value of the amount Δv Blood  of change is larger than o). 
     The temperature calculation unit  5  of the temperature measuring device calculates the deep body temperature T Core  of the living body  10  by Equation 2 above on the basis of the of result of the measurement (step S 102  in  FIG.  3   ) of the skin surface temperature Tam and the skin surface heat flux Hain by the sensor  1  and the combined resistance R Combined  derived by the thermal resistance deriving part  4  (step S 103  in  FIG.  3   ). 
     The calculation result output unit  6  of the temperature measuring device outputs the calculation result of the temperature calculation unit  5  (step S 104  in  FIG.  3   ). Examples of the output method include the display of the calculation result, the transmission of the calculation result to the outside, or the like. 
       FIG.  4    is a flowchart for explaining operations of the temperature measuring device of the present embodiment.  FIG.  4    illustrates an example in which the initial calibration is performed at time t=o and a person (the living body  10 ) wearing the sensor  1  and the sensor probe  200  starts taking a warm bath at time t=t1. In  FIG.  4 ,  400    denotes the true value of a deep body temperature T Core ,  401  denotes a deep body temperature T Core  calculated by the method of the related art, and  402  denotes the deep body temperature T Core  calculated by the temperature measuring device of the present embodiment. 
     According to  FIG.  4   , it can be seen that when there is a change in the blood flow v Blood , the combined resistance R Combined  is updated by the thermal resistance derivation unit  4  of the present embodiment from the initial value R Combined  (o) to a value corresponding to the amount Δv Blood  of change in the blood flow v Blood . On the other hand, the thermal resistance R Body  used in the related art remains constant. Consequently, it can be seen that in the related art, an error occurs in the estimated value of the deep body temperature but in the present embodiment, the deep body temperature T Core  approximately equal to the true value can be estimated. 
     As described above, in the present embodiment, the combined resistance R Combined  of the living body  10  is derived on the basis of the amount Δv Blood  of change in the blood flow v Blood , so that it is possible to reduce an error in the estimated value of the deep body temperature T Core  caused by a change in the blood flow v Blood . In the present embodiment, the laser Doppler blood flow meter  2  is used as a blood flow meter, but other blood flow meters may be used. 
     The storage unit  3 , the thermal resistance derivation unit  4 , the temperature calculation unit  5 , and the calculation result output unit  6  described in the present embodiment can be implemented by a computer including a central processing unit (CPU), a storage apparatus, and an interface, and a program that controls these hardware resources. An example of the configuration of the computer is illustrated in  FIG.  5   . 
     The computer includes a CPU  500 , a storage device  501 , and an interface device (hereinafter simply referred to as I/F)  502 . The sensor  1 , the laser Doppler blood flow meter  2 , a display device, a communication device, or the like are connected to the I/F  502 . In such a computer, a program for implementing the temperature measuring method of the present invention is stored in the storage apparatus  501 . The CPU  500  executes the processing described in the present embodiment in accordance with the program stored in the storage device  501 . 
     INDUSTRIAL APPLICABILITY 
     The embodiments of the present invention can be applied to a technology for measuring the internal temperature of a subject such as a living body. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Sensor 
               2  Laser Doppler blood flow meter 
               3  Storage unit 
               4  Thermal resistance derivation unit 
               5  Temperature calculation unit 
               6  Calculation result output unit 
               10  Living body 
               100  Thermal insulation member 
               101 ,  102  Temperature sensor 
               200  Sensor probe 
               201  Semiconductor laser 
               202  Photodiode 
               203  Blood flow calculation unit