Patent Publication Number: US-2022218216-A1

Title: Sphygmomanometer, blood pressure measurement method, and computer-readable recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on an application No. 2018-245724 filed in Japan on Dec. 27, 2018, the entire content of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a sphygmomanometer, a blood pressure measurement method, and a program, and more particularly, to a sphygmomanometer to be worn around a measurement target site in its circumferential direction, a blood pressure measurement method using the sphygmomanometer, and a computer-readable recording medium storing a program for causing a computer to execute such a blood pressure measurement. 
     BACKGROUND ART 
     Conventionally, as a sphygmomanometer of this type, for example, there is one disclosed in Patent Literature 1 (JP 2018-102867 A). The sphygmomanometer has a cuff that is wrapped around a wrist and a main body that is integrally provided with the cuff. The sphygmomanometer is provided with, on an inner side of a band-shaped belt, a bag-shaped sensing cuff that presses an artery, an intervening member provided on an outer side of the sensing cuff, and a bag-shaped pressing cuff provided on an outer side of the intervening member. The main body of the sphygmomanometer includes a pump, an exhaust valve mounted on the pump and configured to be closed or opened according to on/off of the pump, a pressure sensor, a first flow path that fluid-flowably connects the pump with the pressing cuff, and a second flow path that fluid-flowably connects the pump or the first flow path with the sensing cuff and has an on-off valve inserted therein. When the blood pressure is measured using the sphygmomanometer, first, the exhaust valve and the on-off valve are opened, and both the pressing cuff and the sensing cuff are opened to the atmospheric pressure. Next, with the exhaust valve closed and the on-off valve opened, air supply from the pump to the pressing cuff and the sensing cuff is started. When a predetermined amount of air is supplied to the sensing cuff, the on-off valve is closed to seal the sensing cuff. After that, the air supply from the pump to the pressing cuff is continued, and the wrist is compressed by the pressing cuff through the sensing cuff. Then, the blood pressure is calculated by the oscillometric method based on pressure of the air (measured by the pressure sensor) stored in the sensing cuff. 
     SUMMARY OF INVENTION 
     Incidentally, after the blood pressure measurement by the sphygmomanometer and before the next blood pressure measurement, when both the pressing cuff and the sensing cuff are opened to the atmospheric pressure, the air remains in the sensing cuff. Moreover, a remaining amount of the air in the sensing cuff may differ each time depending on a wrapping state (loose or tight) of the belt. The inventors have found that this difference in the remaining amount of the air adversely affects accuracy of blood pressure measurement. 
     Therefore, an object of the present invention is to provide a sphygmomanometer, and a blood pressure measurement method, which can create, before measuring a blood pressure, a state for making a blood pressure measurement accurate. In addition, an object of the present invention is to provide a computer-readable recording medium storing a program for causing a computer to execute such a blood pressure measurement. 
     In order to achieve the above object, a sphygmomanometer according to the present disclosure is a sphygmomanometer comprising: 
     a main body mounted with a pump; a belt extending from the main body and worn around a measurement target site; 
     a sensing cuff arranged, in a worn state of the belt being worn around the measurement target site, at a portion of an inner circumferential side of the belt that crosses an artery passing portion of the measurement target site, and configured in a bag shape so as to allow storage of a pressure transmitting fluid; 
     a pressing member that presses the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site; 
     a fluid circuit that can be configured by switching among a supply mode of suppling the pressure transmitting fluid from the pump to the sensing cuff, a discharge mode of discharging the fluid from the sensing cuff to atmosphere, and a shut-off mode of shutting off fluid supply to the sensing cuff and fluid discharge from the sensing cuff; and 
     a control unit, wherein, 
     the control unit includes, in the worn state: 
     a first preparation processing unit that, with the fluid circuit switched to the discharge mode, operates the pressing member to press the sensing cuff toward the measurement target site and discharges a fluid remaining in the sensing cuff to the atmosphere through the fluid circuit; 
     a second preparation processing unit that, with the fluid circuit switched to the supply mode after operation of the first preparation processing unit, causes the sensing cuff to store a predetermined amount of the pressure transmitting fluid received from the pump through the fluid circuit; and 
     a measurement processing unit that, with the fluid circuit switched to the shut-off mode after operation of the second preparation processing unit, operates the pressing member to press the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site, and meanwhile, calculates a blood pressure of the measurement target site based on a pressure of the pressure transmitting fluid stored in the sensing cuff by an oscillometric method. 
     The “fluid” is typically air, but may be other gas or liquid. 
     The “inner circumferential side” of the belt refers to a side facing the measurement target site in the worn state wrapped around the measurement target site. 
     In another aspect, a blood pressure measurement method according to the present disclosure is a blood pressure measurement method that uses a sphygmomanometer comprising: a main body mounted with a pump; a belt extending from the main body and worn around a measurement target site; a sensing cuff arranged, in a worn state of the belt being worn around the measurement target site, at a portion of an inner circumferential side of the belt that crosses an artery passing portion of the measurement target site, and configured in a bag shape so as to allow storage of a pressure transmitting fluid; a pressing member that presses the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site; and a fluid circuit that can be configured by switching among a supply mode of suppling the pressure transmitting fluid from the pump to the sensing cuff, a discharge mode of discharging the fluid from the sensing cuff to atmosphere, and a shut-off mode of shutting off fluid supply to the sensing cuff and fluid discharge from the sensing cuff, wherein, 
     the method comprising, in the worn state: 
     executing first preparation processing that, with the fluid circuit switched to the discharge mode, operates the pressing member to press the sensing cuff toward the measurement target site and discharges a fluid remaining in the sensing cuff to the atmosphere through the fluid circuit; 
     executing second preparation processing that, with the fluid circuit switched to the supply mode after the first preparation processing, causes the sensing cuff to store a predetermined amount of the pressure transmitting fluid received from the pump through the fluid circuit; and 
     executing measurement processing that, with the fluid circuit switched to the shut-off mode after the second preparation processing, operates the pressing member to press the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site, and meanwhile, calculates a blood pressure of the measurement target site based on a pressure of the pressure transmitting fluid stored in the sensing cuff by an oscillometric method. 
     In yet another aspect, a computer-readable recording medium storing a program according to the present disclosure is a computer-readable recording medium non-transitorily storing a program for causing a computer to execute the above blood pressure measurement method. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a front view showing a schematic external configuration of a sphygmomanometer according to first and second embodiments. 
         FIG. 2  is a side view showing a schematic external configuration of the sphygmomanometer according to the first and second embodiments. 
         FIG. 3  is a perspective view showing a schematic external configuration of the sphygmomanometer according to the first embodiment. 
         FIG. 4  is a cross-sectional view showing a state in which the sphygmomanometer according to the first embodiment is worn around the wrist. 
         FIG. 5  is a diagram showing a schematic configuration of a control system of the sphygmomanometer according to the first embodiment. 
         FIG. 6  is a diagram showing a schematic configuration of a flow path system of the sphygmomanometer according to the first embodiment. 
         FIG. 7  is a schematic flowchart showing a flow of operation of the sphygmomanometer according to the first and second embodiments. 
         FIG. 8  is a flowchart showing an operation of blood pressure measurement preparation processing in the sphygmomanometer according to the first embodiment. 
         FIG. 9  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the first embodiment. 
         FIG. 10  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the first embodiment. 
         FIG. 11  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the first embodiment. 
         FIG. 12  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the first embodiment. 
         FIG. 13  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the first embodiment. 
         FIG. 14  is a diagram illustrating an operation of blood pressure measurement processing in the sphygmomanometer according to the first embodiment. 
         FIG. 15  is a diagram illustrating an operation of the blood pressure measurement processing in the sphygmomanometer according to the first embodiment. 
         FIG. 16  is a diagram exemplifying, in chronological order, an operation timing of a pump and operation timings of on-off valves, at which a series of processing shown in  FIGS. 8 to 15  can be executed. 
         FIG. 17  is a cross-sectional view showing a state in which the sphygmomanometer according to the second embodiment is worn around the wrist. 
         FIG. 18  is a diagram showing a schematic configuration of a control system of the sphygmomanometer according to the second embodiment. 
         FIG. 19  is a diagram showing a schematic configuration of a flow path system of the sphygmomanometer according to the second embodiment. 
         FIG. 20  is a flowchart showing an operation of blood pressure measurement preparation processing in the sphygmomanometer according to the second embodiment. 
         FIG. 21  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the second embodiment. 
         FIG. 22  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the second embodiment. 
         FIG. 23  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the second embodiment. 
         FIG. 24  is a diagram illustrating an operation of the blood pressure measurement preparation processing in the sphygmomanometer according to the second embodiment. 
         FIG. 25  is a flowchart showing an operation of blood pressure measurement processing in the sphygmomanometer according to the second embodiment. 
         FIG. 26  is a diagram illustrating an operation of the blood pressure measurement processing in the sphygmomanometer according to the second embodiment. 
         FIG. 27  is a diagram illustrating an operation of the blood pressure measurement processing in the sphygmomanometer according to the second embodiment. 
         FIG. 28  is a diagram illustrating an operation of the blood pressure measurement processing in the sphygmomanometer according to the second embodiment. 
         FIG. 29  is a diagram illustrating an operation of the blood pressure measurement processing in the sphygmomanometer according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention is described in detail with reference to the drawings. 
     First Embodiment 
     (Configuration of sphygmomanometer according to First Embodiment) 
       FIG. 1  shows a configuration in which a sphygmomanometer  100  according to the present embodiment is viewed from the front.  FIG. 2  shows the configuration of the sphygmomanometer  100  as viewed from the side. Further,  FIG. 3  shows the configuration of the sphygmomanometer  100  viewed from an oblique direction with the belt described later opened. The schematic external configuration of the sphygmomanometer  100  is described with reference to  FIGS. 1 to 3 . 
     The sphygmomanometer  100  mainly includes a main body  10 , two belts  20   a  and  20   b , a pressing cuff  30  constituting a pressing member shown in  FIG. 3 , and a sensing cuff  40 . 
     As shown in  FIGS. 1 to 3 , the main body  10  includes a display device  68  and an operation device  69  constituted of a plurality of buttons. Further, the main body  10  is mounted with a pump described later. Further, the one belt  20   a  and the other belt  20   b  are attached to the main body  10 . The two belts  20   a  and  20   b  extend from the main body  10  and are worn around the measurement target site. By fastening the one belt  20   a  and the other belt  20   b , a state in which the sphygmomanometer  100  is worn on the measurement target site (see  FIG. 4 , which is referred to as a “worn state”) is created. 
     Further, in the present embodiment, the cuffs  30  and  40  constitute a cuff structure having a stacked structure. In the above worn state of the sphygmomanometer  100 , the pressing cuff  30  and the sensing cuff  40  are arranged in this order when viewed from the side of a fastening part  20 T of the belts  20   a  and  20   b . The pressing cuff  30  generates a pressing force on the measurement target site. Then, the pressing force is applied to the measurement target site through the sensing cuff  40 . As shown in JP 2018-102867 A, the cuff structure may include a curler, a back plate, and others (not shown) in addition to the pressing cuff  30  and the sensing cuff  40  described above. A member including such as the belts  20   a  and  20   b , the curler, the pressing cuff  30 , and the back plate functions as a pressing member that generates the pressing force on the measurement target site. The pressing member including the pressing cuff  30  presses the sensing cuff  40  toward the measurement target site, and causes the sensing cuff  40  to compress (press) the measurement target site. 
       FIG. 4  shows a cross-sectional view of the sphygmomanometer  100  being worn around a wrist BW being the measurement target site. As shown in  FIG. 4 , the pressing cuff  30  constituting the pressing member has a bag shape and is arranged between the belts  20   a  and  20   b  and the sensing cuff  40 . As described above, the belts  20   a  and  20   b  are wrapped around the wrist BW in the circumferential direction so that the sphygmomanometer  100  is worn around the wrist BW. In the worn state of the present embodiment, as shown in  FIG. 4 , the wrist BW, the sensing cuff  40 , and the pressing cuff  30  are arranged in this order from the main body  10  toward the fastening part  20 T of the belts  20   a  and  20   b . In the configuration example of  FIG. 4 , the main body  10  is arranged at a portion opposite to the sensing cuff  40  in the circumferential direction of the belts  20   a  and  20   b.    
     In the above worn state, the bag-shaped pressing cuff  30  extends, for example, along the circumferential direction of the wrist BW. Further, the bag-shaped sensing cuff  40  is arranged on the inner circumferential side of the belts  20   a  and  20   b  with respect to the pressing cuff  30  and is in contact with the wrist BW (indirectly or directly), and extends in the circumferential direction so as to cross an artery passing portion  90   a  of the wrist BW. The “inner circumference side” of the belts  20   a  and  20   b  refers to the side facing the wrist BW in the worn state of wrapping around the wrist BW. 
     In  FIG. 4 , a radial artery A 1  and an ulnar artery A 2  of the wrist BW are shown. In the present embodiment, the pressing cuff  30  constituting the pressing member is arranged between the belts  20   a ,  20   b  and the sensing cuff  40 . The pressing cuff  30  presses the sensing cuff  40  toward the wrist BW, causing the sensing cuff  40  to press the wrist BW. Details of a specific example of the sphygmomanometer  100  and an example of wearing the sphygmomanometer  100  are described in JP 2018-102867 A. 
       FIG. 5  shows a schematic configuration of a control system of the sphygmomanometer  100 . As shown in  FIG. 5 , the main body  10  of the sphygmomanometer  100  includes a control unit  65  that is responsible for control, and a plurality of control target constituents  66  to  76  that are controlled by the control unit  65 . Here, the plurality of control target constituents include a power supply  66 , a memory  67 , a display device  68 , an operation device  69 , a communication device  70 , a pump  71 , an exhaust valve  72 , a first pressure sensor (pressing cuff pressure sensor)  73 , and a second pressure sensor (sensing cuff pressure sensor)  74 , and two on-off valves  75  and  76 . 
     The power supply  66  is composed of a rechargeable secondary battery in this example. The power supply  66  supplies driving power to the elements mounted on the main body  10 , for example, the processor  65 , the memory  67 , the display device  68 , the communication device  70 , the pump  71 , the exhaust valve  72 , each of the pressure sensors  73  and  74 , and each of the on-off valves  75  and  76 . 
     The memory  67  stores various types of data. For example, the memory  67  can store the measurement values measured by the sphygmomanometer  100 , the measurement results of the pressure sensors  73  and  74 , and others. Further, the memory  67  can also store various types of data generated by the control unit  65 . The memory  67  includes a random access memory (RAM), a read only memory (ROM), and others. For example, various programs are stored in the memory  67  in a modifiable manner. 
     The display device  68  is composed of a liquid crystal display (LCD) as an example. The display device  68  displays information related to blood pressure measurement such as a blood pressure measurement result and other information according to a control signal from the control unit  65 . The display device  68  may have a function as a touch panel. 
     The operation device  69  is composed of a plurality of buttons that receive instructions from a user. When the operation device  69  receives an instruction from the user, the operation/motion according to the instruction is performed under the control of the control unit  65 . The operation device  69  may be, for example, a pressure-sensitive type (resistive type) or proximity type (capacitance type) touch panel switch. Further, a microphone (not shown) may be provided to receive a voice instruction from the user. 
     The communication device  70  transmits various types of data and various signals to an external device via a communication network, and receives information from the external device via the communication network. The network may be wireless communication or wired communication. 
     The pump  71 , in this example, is composed of a piezoelectric pump and is driven based on a control signal given by the control unit  65 . The pump  71  can supply a pressurizing fluid to the cuffs  30  and  40  through respective flow paths described later. Note that any type of liquid or any type of gas can be adopted as the fluid. In the present embodiment, the fluid is air (hereinafter, the description is made assuming that the fluid is air). The configuration of a flow path system including the pump  71  and other air components  72  to  76  are described later. 
     The exhaust valve  72  is controlled according to the operation of the pump  71 . That is, the opening and closing of the exhaust valve  72  is controlled according to the on/off (supplying air/stop supplying air) of the pump  71 . For example, the exhaust valve  72  closes when the pump  71  is turned on. On the other hand, the exhaust valve  72  opens when the pump  71  is turned off. In the open state of the exhaust valve  72 , for example, the air in the sensing cuff  40  can be discharged to the atmosphere through a flow path described later. The exhaust valve  72  has a function of a check valve, and the discharged air does not flow back. 
     The first pressure sensor  73  and the second pressure sensor  74  include, for example, a piezoresistive pressure sensor. The first pressure sensor  73  detects the pressure in the pressing cuff  30  through a flow path described later. The second pressure sensor  74  detects the pressure in the sensing cuff  40  through a flow path described later. 
     The on-off valves  75  and  76  are respectively inserted into the flow paths described later. The opening and closing (opening degree) of the on-off valves  75  and  76  is controlled based on the control signal given from the control unit  65 . In the open state of the on-off valves  75  and  76 , the air flows through the on-off valves  75  and  76 . On the other hand, in the close state of the on-off valves  75  and  76 , the air does not flow through the on-off valves  75  and  76 . 
     The control unit  65  includes a central processing unit (CPU) in this example. For example, the control unit  65  reads each program and each piece of data stored in the memory  67 . Further, the control unit  65  controls each of the constituents  67  to  76  according to the read program to execute a predetermined operation (function). Further, the control unit  65  performs a predetermined calculation, analysis, processing, and so on, in the control unit  65  according to the read program. It should be noted that a part or all of each function executed by the control unit  65  may be configured in hardware by one or a plurality of integrated circuits or the like. 
     As shown in  FIG. 5 , the control unit  65  according to the present embodiment includes a first preparation processing unit  65 A, a second preparation processing unit  65 B, a third preparation processing unit  65 C, and a measurement processing unit  65 D as functional blocks. The operations of the blocks  65 A to  65 D are described in detail in the description of the operations described later. 
       FIG. 6  shows a schematic configuration of the flow path system of the sphygmomanometer  100 . The sphygmomanometer  100  shown in  FIG. 6  includes the pump  71 , a fluid circuit LC 1 , the pressing cuff  30 , and the sensing cuff  40 . Actually, the pump  71  and the fluid circuit LC 1  are mounted on the main body  10  (see  FIG. 4 ). However, in  FIG. 6 , the flow path system is developed and shown for easy understanding. 
     The fluid circuit LC 1  can be configured by switching between a supply mode PM, a discharge mode DM, and a shut-off mode SM. Note that the supply mode PM is a mode for supplying pressure transmitting air from the pump  71  to the sensing cuff  40 . The discharge mode DM is a mode for discharging the air from the sensing cuff  40  to the atmosphere. The shut-off mode SM is a mode for blocking the air supply to the sensing cuff  40  and the air discharge from the sensing cuff  40 . Further, the fluid circuit LC 1  is configured to operate (expand) the pressing cuff  30  forming the pressing member, or deactivate the same (exhaust air from the pressing cuff  30 ). 
     Specifically, the fluid circuit LC 1  according to the present embodiment includes the exhaust valve  72 , each of the on-off valves  75  and  76 , each of the pressure sensors  73  and  74 , and each of flow paths L 1  to L 4 . Here, the air flows in each of the flow paths L 1  to L 4 . 
     As shown in  FIG. 6 , the flow path L 1  connects the pump  71  and the on-off valve  75 . The flow path L 2  connects the flow path L 1  and the pressing cuff  30 . The flow path L 3  connects the on-off valve  75  and the sensing cuff  40 . Further, the flow path L 4  connects the exhaust valve  72  and the flow path Ll. The on-off valve  75  is inserted between the flow path Ll and the flow path L 3 . The first pressure sensor  73  is connected to the flow path L 2 . The second pressure sensor  74  is connected to the flow path L 3 . Further, the on-off valve  76  is inserted between the flow path L 3  and the atmosphere. 
     (Operation of Sphygmomanometer according to the First Embodiment) 
       FIG. 7  shows a flow of the blood pressure measurement method using the sphygmomanometer  100  according to the present embodiment. After the sphygmomanometer  100  is worn around the wrist BW, as shown in  FIG. 7 , blood pressure measurement preparation processing is performed in step S 1 , and blood pressure measurement processing (step S 2 ) is performed after step S 1 . 
     (Operation of Blood Pressure Measurement Preparation Processing) 
     First, the details of the blood pressure measurement preparation processing in step S 1  is described.  FIG. 8  shows a specific flow of the blood pressure measurement preparation processing according to the present embodiment. 
     (1) First, in the state of the sphygmomanometer  100  being worn around the wrist BW, and with the fluid circuit LC 1  switched to the discharge mode DM, the first preparation processing unit  65 A of the control unit  65  operates (expands) the pressing cuff  30  to press the sensing cuff  40  toward the wrist BW. Then, by the pressing, the air remaining in the sensing cuff  40  is discharged to the atmosphere through the fluid circuit LC 1 . More specific description is as follows. 
     First, in step S 11  of  FIG. 8 , the first preparation processing unit  65 A closes the on-off valve  75  (see the “x” mark of the on-off valve  75  in  FIG. 9 ). Further, in step S 12 , the first preparation processing unit  65 A opens the on-off valve  76 . By the first preparation processing unit  65 A turning the on-off valve  76  to the open state, the first preparation processing unit  65 A switches the fluid circuit LC 1  to the discharge mode DM. 
     Next, in step S 13 , the first preparation processing unit  65 A turns the pump  71  to the ON state. As a result, as shown by arrows W 1  in  FIG. 10 , the pump  71  can supply the air to the pressing cuff  30  through the flow paths L 1  and L 2 . By the supply of air in step S 13 , the pressing cuff  30  is filled with air, and the pressing cuff  30  expands (which can be grasped as the operation of the pressing cuff  30 ). Then, the expansion of the pressing cuff  30  presses the sensing cuff  40  toward the wrist BW. Then, by the pressing, the air remaining in the sensing cuff  40  is discharged to the atmosphere through the flow path L 3  and the on-off valve  76  as shown by arrows W 2  in  FIG. 10 . As described above, in step S 13 , the expansion of the pressing cuff  30  (the pressing force from the pressing cuff  30 ) is used to forcibly discharge an amount of air in the sensing cuff  40  from the sensing cuff  40  to the atmosphere, and thereby, an amount of remaining air in the sensing cuff  40  is brought close to zero. 
     Next, in step S 14 , the first preparation processing unit  65 A determines whether or not the measurement result (pressure in the pressing cuff  30 ) of the first pressure sensor  73  has reached a first pressure threshold value Pth 1 . Note that any value can be adopted for the first pressure threshold value Pth 1 . However, it is desirable that the first pressure threshold value Pth 1  is selected from the viewpoint that the remaining air in the sensing cuff  40  can be substantially pushed out by the expansion of the pressing cuff  30 . For example, as an example, 30 mmHg is adopted as the first pressure threshold value Pth 1 . 
     If the measurement result of the first pressure sensor  73  is less than the first pressure threshold value Pth 1  (NO in step S 14 ), the air supply from the pump  71  to the pressing cuff  30  is continued, while the determination processing in step S 14  is also continued. On the other hand, if the measurement result of the first pressure sensor  73  has reached the first pressure threshold value Pth 1  (YES in step S 14 ), the first preparation processing unit  65 A turns the pump  71  to the OFF state (Step S 15 ). As a result, the supply of air from the pump  71  to the pressing cuff  30  is stopped. 
     Additionally, as described above, the opening and closing of the exhaust valve  72  is controlled in conjunction with the ON/OFF of the pump  71 . Specifically, when the pump  71  is in the ON state, the exhaust valve  72  is in the close state, and when the pump  71  is in the OFF state, the exhaust valve  72  is in the open state. Therefore, in step S 15 , as the pump  71  is turned to the OFF state, the exhaust valve  72  is turned to the open state. Therefore, as shown by arrows W 3  in  FIG. 11 , the air in the pressing cuff  30  is discharged to the atmosphere through the flow paths L 2 , L 1 , L 4  and the exhaust valve  72 . 
     (2) After the operation of the first preparation processing unit  65 A of the control unit  65 , and with the fluid circuit LC 1  switched to the supply mode PM, the second preparation processing unit  65 B of the control unit  65  causes the sensing cuff  40  to store a predetermined amount (appropriate amount) of the pressure transmitting air received from the pump  71  through the fluid circuit LC 1 . More specific description is as follows. 
     First, in step S 16  of  FIG. 8 , the second preparation processing unit  65 B turns the on-off valve  75  to the open state. Next, in step S 17 , the second preparation processing unit  65 B closes the on-off valve  76  (see the “x” mark of the on-off valve  76  in  FIG. 12 ). By the second preparation processing unit  65 B opening the on-off valve  75  and closing the on-off valve  76 , the second preparation processing unit  65 B switches the fluid circuit LC 1  to the supply mode PM. 
     Next, in step S 18 , the second preparation processing unit  65 B turns the pump  71  to the ON state. As a result, as shown by arrows W 4  in  FIG. 12 , the pump  71  can supply air to the pressing cuff  30  through the flow paths L 1  and L 2 , and further, as shown by arrows W 5 , can supply air (which can be grasped as the appropriate amount of pressure transmitting fluid) to the sensing cuff  40  through the flow path L 1 , the on-off valve  75 , and the flow path L 3 . By the supply of air in step S 18 , the pressing cuff  30  is filled with air, and the pressing cuff  30  expands (see  FIG. 12 ). Further, by supplying the air in step S 18 , the sensing cuff  40  is caused to store an appropriate amount of pressure transmitting fluid (see  FIG. 12 ). Note that an amount of the “appropriate amount” is described in, for example, JP  2018 - 102867  A. 
     Next, in step S 19 , the second preparation processing unit  65 B determines whether or not the measurement result (pressure in the sensing cuff  40 ) of the second pressure sensor  74  has reached a second pressure threshold value Pth 2 . Note that any value can be adopted for the second pressure threshold value Pth 2 . For example, as the second pressure threshold value Pth 2 , less than 40 mmHg (preferably 30 mmHg) is adopted. 
     If the measurement result of the second pressure sensor  74  is less than the second pressure threshold value Pth 2  (NO in step S 19 ), the air supply from the pump  71  to the pressing cuff  30  and to the sensing cuff  40  is continued, while the determination processing in step S 19  is also continued. 
     (3) On the other hand, if the measurement result of the second pressure sensor  74  has reached the second pressure threshold value Pth 2  (YES in step S 19 ), after the operation of the second preparation processing unit  65 B, the third preparation processing unit  65 C of the control unit  65  performs the following control before the blood pressure measurement. 
     Specifically, in step S 20  of  FIG. 8 , the third preparation processing unit  65 C closes the on-off valve  75  (see the “x” mark of the on-off valve  75  in  FIG. 13 ). As shown in  FIG. 13 , after step S 13 , the on-off valves  75  and  76  are in the close state (which can be grasped as the switching to the shut-off mode SM of the fluid circuit LC 1 ). 
     Next, in step S 21 , the third preparation processing unit  65 C turns the pump  71  to the OFF state. As a result, the supply of air from the pump  71  to the pressing cuff  30  is stopped (which can be grasped as the non-operation of the pressing cuff  30 ). According to the step S 21 , as shown by arrows W 6  in  FIG. 13 , the air in the pressing cuff  30  which is not operating, is discharged to the atmosphere through the fluid circuit LC 1  (flow paths L 2 , L 1 , and L 4  and exhaust valve  72 ) which is in the shut-off mode SM. The above is the blood pressure measurement preparation processing (steps S 1  in  FIG. 7 , and  FIG. 8 ) executed by each of the preparation processing units  65 A to  65 C of the control unit  65 . 
     As can be seen from the above, by the control of the control unit  65 , the fluid circuit LC 1  according to the present embodiment supplies the pressurizing air from the pump  71  to the pressing cuff  30  when the pressing cuff  30  is operating, and causes the pressing cuff  30  to expand ( FIG. 10 ). This enables the pressing cuff  30  to press the sensing cuff  40  toward the wrist BW. Further, by the control of the control unit  65 , the fluid circuit LC 1  discharges the pressurizing air from the pressing cuff  30  to the atmosphere when the pressing cuff  30  is not operating ( FIG. 11 ). 
     (Operation of Blood Pressure Measurement Processing) 
     After step S 1 . of  FIG. 7  (after the end of the flow of  FIG. 8 ), the measurement processing unit  65 D of the control unit  65  executes the blood pressure measurement processing (step S 2  of  FIG. 7 ). Specifically, the measurement processing unit  65 D turns ON the pump  71  while maintaining the close state of the on-off valves  75  and  76  (the shut-off mode SM of the fluid circuit LC 1 ). As shown by arrows W 7  in  FIG. 14 , this enables the air to be sent into the pressing cuff  30  through the flow paths L 1  and L 2 . Therefore, the pressing cuff  30  can be operated (expanded). The expanded pressing cuff  30  presses the sensing cuff  40  toward the wrist BW. The measurement processing unit  65 D calculates the blood pressure of the wrist BW by the oscillometric method based on the pressure of the pressure transmitting air stored in the sensing cuff  40  while causing the sensing cuff  40  to compress the wrist BW. Details of the specific operation of the blood pressure measurement (blood pressure calculation) processing is described in, for example, JP 2018-102867 A. 
     After the calculation of blood pressure by the measurement processing unit  65 D is completed, the measurement processing unit  65 D turns the on-off valves  75  and  76  to the open state. This allows the air in the sensing cuff  40  to be discharged to the atmosphere through the flow path L 3  and the on-off valve  76  as shown by arrows W 8  in  FIG. 15 , and as shown in arrows W 9  in  FIG. 15 , the air in the pressing cuff  30  is discharged to the atmosphere through the flow paths L 2 , L 1 , and L 4  and the exhaust valve  72 . Therefore, the pressure in the pressing cuff  30  and the pressure in the sensing cuff  40  become atmospheric pressure, and the blood pressure measurement processing ends. 
       FIG. 16  exemplifies, in chronological order, an operation timing of the pump  71  and operation timings of the on-off valves  75  and  76 , at which the above series of processing can be executed. Note that ON of the pump  71  means the supply of air from the pump  71 , and OFF of the pump  71  means the stop of the supply of air by the pump  71 . Further, ON of the on-off valves  75  and  76  means the close state of the on-off valves  75  and  76 , and OFF of the on-off valves  75  and  76  means the open state of the on-off valves  75  and  76 . 
     (Effects) 
     In the sphygmomanometer  100  according to the present embodiment, the control unit  65  performs the predetermined control in the worn state of the belts  20   a  and  20   b  being worn around the wrist BW. That is, with the fluid circuit LC 1  switched to the discharge mode DM, the first preparation processing unit  65 A included in the control unit  65  operates the pressing cuff  30  to press the sensing cuff  40 . This allows the air remaining in the sensing cuff  40  to be discharged to the atmosphere through the fluid circuit LC 1 . As a result, even if the air remains in the sensing cuff  40  after the blood pressure measurement using the sphygmomanometer  100  and before the next blood pressure measurement, the air is forcibly discharged from the sensing cuff  40 . 
     Further, after the operation of the first preparation processing unit  65 A, with the fluid circuit LC 1  switched to the supply mode PM, the second preparation processing unit  65 B causes the sensing cuff  40  to store the predetermined amount of pressure transmitting air received from the pump  71  through the fluid circuit LC 1 . As a result, the pressure transmitting air is stored in the sensing cuff  40 . At this time, because the remaining air has been discharged from the sensing cuff  40  by the operation of the first preparation processing unit  65 A, the amount of pressure transmitting air stored in the sensing cuff  40  becomes constant. 
     Further, after the operation of the second preparation processing unit  65 B, with the fluid circuit LC 1  switched to the shut-off mode SM, the measurement processing unit  65 D operates the pressing cuff  30  to press the sensing cuff  40 . Then, while causing the sensing cuff  40  to compress the wrist BW, the blood pressure of the wrist BW is calculated by the oscillometric method based on the pressure of the pressure transmitting air stored in the sensing cuff  40 . Thereby, for example, as disclosed in JP 2018-102868 A and JP 2018-102867 A, as a result of setting the width dimensions of the belts  20   a  and  20   b , the pressing cuff  30 , and the sensing cuff  40  to be small (for example, about 25 mm), the blood pressure of the wrist BW is calculated accurately even when the compression loss of the pressing cuff  30  occurs during pressurization. In particular, as described above, because the amount of the pressure transmitting air stored in the sensing cuff  40  becomes constant after the operation of the second preparation processing unit  65 B, the blood pressure can be calculated accurately. 
     Further, in the sphygmomanometer  100  according to the present embodiment, by the control of the control unit  65 , the fluid circuit LC 1  supplies the pressurizing air from the pump  71  to the pressing cuff  30  when the pressing cuff  30  is operating, and causes the pressing cuff  30  to expand and to press the sensing cuff  40  toward the wrist BW. On the other hand, by the control of the control unit  65 , the fluid circuit LC 1  discharges the pressurizing air from the pressing cuff  30  to the atmosphere when the pressing cuff  30  is not operating. 
     As described above, in the sphygmomanometer  100  according to the present embodiment, the pressing cuff  30  can be driven (expanded or contracted) by the pump  71 , that is, by means common to the means for supplying the pressure transmitting air to the sensing cuff  40 . Therefore, the configuration of the sphygmomanometer  100  can be simplified as compared with the case in which, for example, the pressing member is constituted of a mechanical actuator. 
     Further, in the sphygmomanometer  100  of the present embodiment, after the operation of the second preparation processing unit  65 B and before the operation of the measurement processing unit  65 D, with the fluid circuit LC 1  switched to the shut-off mode SM, the third preparation processing unit  65 C deactivates the pressing cuff  30  and causes the pressurizing air to be discharged to the atmosphere from the pressing cuff  30 . As a result, the pressing applied to the sensing cuff  40  by the pressing cuff  30  is removed. Therefore, the pressure transmitting air stored in the sensing cuff  40  by the second preparation processing unit  65 B can be distributed inside the sensing cuff  40 . Therefore, when the blood pressure is measured by the measurement processing unit  65 D, the sensing cuff  40  can correctly detect the pressure (pulse wave signal) generated by the arteries Al and A 2  in the wrist BW, making the accuracy of the blood pressure measurement improved. 
     Further, the sphygmomanometer  100  according to the present embodiment further includes the first pressure sensor (pressing cuff pressure sensor)  73  that measures the pressure in the pressing cuff  30 . Therefore, the pressure in the pressing cuff  30  can be measured by the first pressure sensor  73 . Therefore, the pressure in the pressing cuff  30  can be controlled by using the output of the first pressure sensor  73 . This is particularly useful when the air remaining in the sensing cuff  40  is discharged to the atmosphere by the first preparation processing unit  65 A and when the blood pressure is measured by the measurement processing unit  65 D. 
     The sphygmomanometer  100  according to the present embodiment further includes the second pressure sensor (sensing cuff pressure sensor)  74  that measures the pressure in the sensing cuff  40 . Therefore, the pressure in the sensing cuff  40  can be measured by using the second pressure sensor  74 . Therefore, the pressure in the sensing cuff  40  can be controlled by using the output of the second pressure sensor  74 . This is particularly useful when the second preparation processing unit  65 B causes the sensing cuff  40  to store the predetermined amount of pressure transmitting air. 
     Further, in the sphygmomanometer  100  according to the present embodiment, the main body  10  is arranged at the portion opposite to the sensing cuff  40  in the circumferential direction of the belts  20   a  and  20   b . Therefore, for example, when the sphygmomanometer  100  is worn around the wrist BW, the main body  10  is arranged on the back side surface of the wrist (the surface corresponding to the back side of the hand). As a result, the main body  10  is less likely to interfere with the daily life of the user. 
     Second Embodiment 
     (Configuration of sphygmomanometer according to Second Embodiment) 
       FIG. 17  shows a schematic configuration of a sphygmomanometer  100  according to the present embodiment. As can be seen from the comparison between  FIGS. 4 and 17 , positions of the bag-shaped pressing cuffs  30  in the first embodiment and the second embodiment constituting the pressing members are different from each other. That is, in the present embodiment, the pressing cuff  30  is arranged at a portion of the inner circumferential side of the belts  20   a  and  20   b  that becomes opposite to the sensing cuff  40  in the worn state. In other words, in the present embodiment, the pressing cuff  30  is arranged on the side of the main body  10  and not on the side of the fastening part  20 T of the belts  20   a  and  20   b  (see  FIG. 17 ). 
     Further, in the present embodiment, as shown in  FIG. 17 , an auxiliary cuff  50  is added. In the configuration of  FIG. 17 , the auxiliary cuff  50  can be omitted. The auxiliary cuff  50  has a bag shape and is arranged between the belts  20   a  and  20   b  and the sensing cuff  40 . In the worn state of the present embodiment, as shown in  FIG. 17 , the pressing cuff  30 , the wrist BW, the sensing cuff  40 , and the auxiliary cuff  50  are provided in this order from the main body  10  toward the fastening part  20 T of the belts  20   a  and  20   b . In the configuration example of  FIG. 17 , the main body  10  is arranged at a portion opposite to the sensing cuff  40  in the circumferential direction of the belts  20   a  and  20   b.    
     The configuration other than the above is the same between the first embodiment and the second embodiment. Therefore, the description of the same configuration is omitted. 
       FIG. 18  shows a schematic configuration of a control system of the sphygmomanometer  100  according to the present embodiment. As can be seen from the comparison between  FIGS. 5 and 18 , the sphygmomanometer  100  according to the first embodiment includes the two on-off valves  75  and  76 , but the sphygmomanometer  100  according to the present embodiment has four on-off valves  80  to  83 . Note that the control unit  65  controls the opening and closing of each of the on-off valves  80  to  83 . Regarding the configuration of the control system, the configurations other than the above are the same between the first embodiment and the second embodiment. Therefore, the description of the same configuration is omitted. 
       FIG. 19  shows a schematic configuration of a flow path system of the sphygmomanometer  100  according to the present embodiment. The sphygmomanometer  100  shown in  FIG. 19  includes the pump  71 , a fluid circuit LC 2 , the pressing cuff  30 , the sensing cuff  40 , and the auxiliary cuff  50 . Actually, the pump  71  and the fluid circuit LC 2  are mounted on the main body  10  (see  FIG. 17 ). However, in  FIG. 19 , the flow path system is developed in the same manner as shown in  FIG. 6 . 
     As in the first embodiment, the fluid circuit LC 2  can be configured by switching between the supply mode PM, the discharge mode DM, and the shut-off mode SM. Further, the fluid circuit LC 2  is configured to operate (expand) the pressing cuff  30  and the auxiliary cuff  50  forming the pressing member, or deactivate the same (exhaust air from the pressing cuff  30  and the auxiliary cuff  50 ). 
     Specifically, the fluid circuit LC 2  according to the present embodiment includes the exhaust valve  72 , each of the on-off valves  80  to  83 , each of the pressure sensors  73  and  74 , and each of flow paths L 11  to L 16 . Here, air flows through each of the flow paths L 11  to L 16 . 
     As shown in  FIG. 19 , the flow path L 11  connects the pump  71  and the on-off valve  81 . The flow path L 12  connects the on-off valve  80  and the on-off valve  83  while merging with the flow path L 11 . The flow path L 13  connects the on-off valve  80  and the pressing cuff  30 . The flow path L 14  connects the on-off valve  81  and the sensing cuff  40 . The flow path L 15  connects the on-off valve  82  and the auxiliary cuff  50 . Further, the flow path L 16  connects the exhaust valve  72  and the flow path L 11 . The on-off valve  80  is inserted between the flow path L 12  and the flow path L 13 , the on-off valve  81  is inserted between the flow path L 11  and the flow path L 14 , and the on-off valve  82  is inserted between the flow path L 12  and the flow path L 15 . Further, the on-off valve  83  is inserted between the flow path L 12  and the atmosphere. 
     The first pressure sensor (pressing cuff pressure sensor)  73  is connected to the flow path L 13 . Further, the second pressure sensor (sensing cuff pressure sensor)  74  is connected to the flow path L 14 . 
     (Operation of sphygmomanometer according to the Second Embodiment) 
     After the sphygmomanometer  100  is worn around the wrist BW, the blood pressure measurement preparation processing (step S 1 ) and the blood pressure measurement processing (step S 2 ) shown in  FIG. 7  are also performed on the sphygmomanometer  100  according to the present embodiment. 
     (Operation of Blood Pressure Measurement Preparation Processing) 
     First, the details of the blood pressure measurement preparation processing (step S 1 ) according to the present embodiment is described.  FIG. 20  shows a specific flow of the blood pressure measurement preparation processing according to the present embodiment. 
     (1) In the state of the sphygmomanometer  100  being worn around the wrist BW, and with the fluid circuit LC 2  switched to the discharge mode DM, the first preparation processing unit  65 A of the control unit  65  operates (expands) the pressing cuff  30  to press the sensing cuff  40  to toward the wrist BW. Then, by the pressing, the air remaining in the sensing cuff  40  is discharged to the atmosphere through the fluid circuit LC 2 . More specific description is as follows. 
     First, in step S 31  of  FIG. 20 , the first preparation processing unit  65 A closes the on-off valves  81  to  83  (see the “x” marks of the on-off valves  81  to  83  in  FIG. 21 ). Further, in step S 32 , the first preparation processing unit  65 A opens the on-off valve  80 . 
     Next, in step S 33 , the first preparation processing unit  65 A turns the pump  71  to the ON state. Thereby, as shown by arrows W 11  in  FIG. 21 , the pump  71  can supply air to the pressing cuff  30  through the flow path L 11 , the on-off valve  80 , and the flow path L 13 . By the supply of air in step S 33 , the pressing cuff  30  is filled with air, and the pressing cuff  30  expands (which can be grasped as the operation of the pressing cuff  30 ). Then, the expansion of the pressing cuff  30  generates a pressing force on the sensing cuff  40 . 
     Next, in step S 34 , the first preparation processing unit  65 A determines whether or not the measurement result (pressure in the pressing cuff  30 ) of the first pressure sensor  73  has reached the first pressure threshold value Pth 1 . As in the first embodiment, any value may be adopted as the first pressure threshold value Pth 1 , and as an example, a value of 30 mmHg may be adopted. 
     If the measurement result of the first pressure sensor  73  is less than the first pressure threshold value Pth 1  (NO in step S 34 ), the air supply from the pump  71  to the pressing cuff  30  is continued, while the determination processing in step S 34  is also continued. On the other hand, if the measurement result of the first pressure sensor  73  has reached the first pressure threshold value Pth 1  (YES in step S 34 ), in step S 35 , the first preparation processing unit  65 A closes the on-off valve  80  (see the “x” mark of the on-off valve  80  in  FIG. 22 ). 
     Next, in step S 36 , the first preparation processing unit  65 A turns the pump  71  to the OFF state. As a result, the supply of air from the pump  71  to the pressing cuff  30  is stopped. As described above, the opening and closing of the exhaust valve  72  is controlled in conjunction with the ON/OFF of the pump  71 , and when the pump  71  is in the OFF state, the exhaust valve  72  is in the open state. Then, in step S 37 , the first preparation, processing unit  65 A opens the on-off valve  81 . With the stopping of the pump  71  (opening of the exhaust valve  72 ) and the opening the on-off valve  81 , the first preparation processing unit  65 A switches the fluid circuit LC 2  to the discharge mode DM. 
     In the discharge mode DM of the fluid circuit LC 2 , as described above, the pressing cuff  30  operates (expands) to press the sensing cuff  40 . Then, by the pressing, the air remaining in the sensing cuff  40  is discharged to the atmosphere through the flow path L 14 , the on-off valve  81 , the flow paths L 11  and L 16 , and the exhaust valve  72 , as shown by arrows W 12  in  FIG. 22 . In this way, the expansion of the pressing cuff  30  (the pressing force from the pressing cuff  30 ) is used to forcibly discharge an amount of air in the sensing cuff  40  from the sensing cuff  40  to the atmosphere, and thereby, an amount of remaining air in the sensing cuff  40  is brought close to zero. 
     (2) After the remaining air in the sensing cuff  40  is almost discharged to the atmosphere (after the operation of the first preparation processing unit  65 A of the control unit  65 ), and with the fluid circuit LC 2  switched to the supply mode PM, the second preparation processing unit  65 B of the control unit  65  causes the sensing cuff  40  to store a predetermined amount (appropriate amount) of the pressure transmitting air received from the pump  71  through the fluid circuit LC 2 . More specific description is as follows. 
     First, in step S 38  of  FIG. 20 , the second preparation processing unit  65 B turns ON the pump  71 . When the pump  71  is turned ON and the on-off valve  81  is opened, the second preparation processing unit  65 B switches the fluid circuit LC 2  to the supply mode PM. In the supply mode PM, as shown by arrows W 13  in  FIG. 23 , the pump  71  can supply air (which can be grasped as the appropriate amount of pressure transmitting fluid) to the sensing cuff  40  through the flow path L 11 , the on-off valve  81 , and the flow path L 14 . By the supply of air in step S 38 , the sensing cuff  40  is caused to store an appropriate amount of pressure transmitting air (see  FIG. 23 ). Note that an amount of the “appropriate amount” is described in, for example, JP 2018-102867 A which is already described. 
     Next, in step S 39 , the second preparation processing unit  65 B determines whether or not the measurement result (pressure in the sensing cuff  40 ) of the second pressure sensor  74  has reached the second pressure threshold value Pth 2 . Note that any value can be adopted for the second pressure threshold value Pth 2 . For example, as the second pressure threshold value Pth 2 , less than 40 mmHg (preferably 30 mmHg) is adopted. 
     If the measurement result of the second pressure sensor  74  is less than the second pressure threshold value Pth 2  (NO in step S 39 ), the air supply from the pump  71  to the sensing cuff  40  is continued, while the determination processing in step S 39  is also continued. 
     (3) On the other hand, if the measurement result of the second pressure sensor  74  has reached the second pressure threshold value Pth 2  (YES in step S 39 ), after the operation of the second preparation processing unit  65 B, the third preparation processing unit  65 C of the control unit  65  performs the following control before the blood pressure measurement. 
     Specifically, in step S 40  of  FIG. 20 , the third preparation processing unit  65 C closes the on-off valve  81  (see the “x” mark of the on-off valve  81  in  FIG. 24 ). With the closing of the on-off valve  81 , the fluid circuit LC 2  is switched to the shut-off mode SM. 
     Next, in step S 41 , the third preparation processing unit  65 C turns the pump  71  to the OFF state. Next, in step S 42 , the third preparation processing unit  65 C opens the on-off valve  80 . As shown by arrows W 14  in  FIG. 24 , this enables the air in the pressing cuff  30  which is not operating to be discharged to the atmosphere through the fluid circuit LC 2  (the flow path L 13 , the on-off valve  80 , the flow paths L 12 , L 11 , and L 16 , and the exhaust valve  72 ) which is in the shut-off mode SM. The above is the blood pressure measurement preparation processing (steps Si in  FIG. 7  and  FIG. 20 ) by the preparation processing units  65 A to  65 C of the control unit  65 . 
     As can be seen from the above, by the control of the control unit  65 , the fluid circuit LC 2  according to the present embodiment supplies the pressurizing air from the pump  71  to the pressing cuff  30  when the pressing cuff  30  is operating, and causes the pressing cuff  30  to expand ( FIG. 21 ). This enables the pressing cuff  30  to press the sensing cuff  40  toward the wrist BW. In addition, by the control of the control unit  65 , the fluid circuit LC 2  discharges the pressurizing air from the pressing cuff  30  to the atmosphere when the pressing cuff  30  is not operating ( FIG. 24 ). 
     (Operation of Blood Pressure Measurement Processing) 
     After step S 1  of  FIG. 7  (after the end of the flow of  FIG. 20 ), the measurement processing unit  65 D of the control unit  65  executes the blood pressure measurement processing (step S 2  of  FIG. 7 ).  FIG. 25  shows a specific flow of the blood pressure measurement processing according to the present embodiment. 
     Specifically, in step S 51  of  FIG. 25 , the measurement processing unit  65 D turns ON the pump  71  while maintaining the close state of the on-off valves  81  to  83  (the shut-off mode SM of the fluid circuit LC 2 ). As shown by arrows W 15  in  FIG. 26 , this enables the air to be sent into the pressing cuff  30  through the flow path L 11 , the on-off valve  80 , and the flow path L 13 . Therefore, the pressing cuff  30  can be operated (expanded). The expanded pressing cuff  30  presses the sensing cuff  40  toward the wrist BW through the belts  20   a  and  20   b    
     Next, in step S 52 , the measurement processing unit  65 D determines whether or not the measurement result (pressure in the sensing cuff  40 ) of the second pressure sensor  74  has reached the second pressure threshold value Pth 2 . If the measurement result of the second pressure sensor  74  is less than the second pressure threshold value Pth 2  (NO in step S 52 ), the air supply from the pump  71  to the pressing cuff  30  is continued, while the determination processing in step S 52  is also continued. On the other hand, if the measurement result of the second pressure sensor  74  has reached the second pressure threshold value Pth 2  (YES in step S 52 ), the measurement processing unit  65 D opens the on-off valve  82  (step S 53 ). 
     Thereby, as shown by arrows W 16  in  FIG. 27 , the air is supplied from the pump  71  into the pressing cuff  30  through the flow paths L 11  and L 12 , the on-off valve  80 , and the flow path L 13 . Further, as shown by arrows W 17  in  FIG. 27 , the air is supplied from the pump  71  into the auxiliary cuff  50  through the flow path L 11 , the on-off valve  82 , and the flow path L 15 . In this way, while pressurizing the pressing cuff  30  and the auxiliary cuff  50  gradually (that is, while causing the sensing cuff  40  to compress the wrist BW), based on the pressure of the pressure transmitting air stored in the sensing cuff  40 , the blood pressure of the wrist BW is calculated by the oscillometric method (step S 54 ). 
     After the calculation of blood pressure by the measurement processing unit  65 D is completed, in step S 55 , the measurement processing unit  65 D turns the on-off valve  83  to the open state. Next, in step S 56 , the measurement processing unit  85 D turns OFF the pump  71 . Thereby, for example, the air in the auxiliary cuff  50  is discharged to the atmosphere through the flow path L 15 , the on-off valve  82 , the flow path L 12 , and the on-off valve  83 , as shown by arrows W 18  in  FIG. 28 , and the air in the pressing cuff  30  is discharged to the atmosphere through the flow path L 13 , the on-off valve  80 , the flow path L 12 , L 11 , and L 16 , and the exhaust valve  72 , as shown by arrows W 19  in  FIG. 28 . Therefore, the pressure in the pressing cuff  30  and the pressure in the auxiliary cuff  50  become atmospheric pressure. 
     Next, in step S 57 , the measurement processing unit  65 D turns the on-off valve  81  to the open state. Thereby, for example, as indicated by arrows W 20  in  FIG. 29 , the air in the sensing cuff  40  is discharged to the atmosphere through the flow path L 14 , the on-off valve  81 , the flow paths L 11  and L 16 , and the exhaust valve  72 , and/or, through the flow path L 14 , the on-off valve  81 , the flow path L 12 , and the on-off valve  83 . Therefore, the pressure in the sensing cuff  40  becomes atmospheric pressure, and the blood pressure measurement processing ends. 
     (Effects) 
     The sphygmomanometer  100  according to the present embodiment has the following effects in addition to the effects described in the first embodiment. That is, in the sphygmomanometer  100  according to the present embodiment, the pressing cuff  30  is arranged at the portion of the inner circumferential side of the belts  20   a  and  20   b  that becomes opposite to the sensing cuff  40  in the worn state. Then, by the control of the control unit  65 , the fluid circuit LC 2  supplies the pressurizing fluid from the pump  71  to the pressing cuff  30  when the pressing cuff  30  is operating, and causes the pressing cuff  30  to expand. The expansion of the pressing cuff  30  causes the sensing cuff  40  to be pressed toward the wrist BW. On the other hand, by the control of the control unit  65 , the fluid circuit LC 2  discharges the pressurizing air from the pressing cuff  30  to the atmosphere when the pressing cuff  30  is not operating. 
     Thereby, the pressing cuff  30  can be driven (expanded or contracted) by the pump  71 , that is, by means common to the means for supplying the pressure transmitting air to the sensing cuff  40 . Therefore, the configuration of the sphygmomanometer  100  can be simplified as compared with the case in which, for example, the pressing member is constituted of a mechanical actuator. Further, the pressing cuff  30  is arranged at the portion of the inner circumferential side of the belts  20   a  and  20   b  that becomes opposite to the sensing cuff  40  in the worn state. For example, the pressing cuff  30  is arranged on the back side surface of the wrist (the surface corresponding to the back side of the hand) in the worn state, and is expanded to increase the tension of the belts  20   a  and  20   b . As a result, the portion of the belts  20   a  and  20   b  facing the sensing cuff  40  requires only a small amount of stroke to press the sensing cuff  40  toward the wrist BW. Therefore, an escaping distance of the arteries A 1  and A 2  (positioned in the wrist BW) pushed by the sensing cuff  40  is reduced (see, for example, JP 2017-006488 A). Therefore, the blood pressure can be calculated more accurately. 
     Further, also in the sphygmomanometer  100  according to the present embodiment, the main body  10  is arranged at the portion opposite to the sensing cuff  40  in the circumferential direction of the belts  20   a  and  20   b , as in the first embodiment. As described above, the pressing cuff  30  is arranged at the portion of the inner peripheral side of the belts  20   a  and  20   b  that becomes opposite to the sensing cuff  40 . Therefore, a distance from the pump  71  mounted on the main body  10  to the pressing cuff  30  can be shortened as much as possible, and the sphygmomanometer  100  can be made compact. 
     In each of the above embodiments, the control unit  65  includes the CPU, but the present invention is not limited to this. The control unit  65  may include a logic circuit (integrated circuit) such as a programmable logic device (PLD) or a field programmable gate array (FPGA). 
     As described above, a sphygmomanometer according to the present disclosure is a sphygmomanometer comprising: 
     a main body mounted with a pump; 
     a belt extending from the main body and worn around a measurement target site; 
     a sensing cuff arranged, in a worn state of the belt being worn around the measurement target site, at a portion of an inner circumferential side of the belt that crosses an artery passing portion of the measurement target site, and configured in a bag shape so as to allow storage of a pressure transmitting fluid; 
     a pressing member that presses the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site; 
     a fluid circuit that can be configured by switching among a supply mode of suppling the pressure transmitting fluid from the pump to the sensing cuff, a discharge mode of discharging the fluid from the sensing cuff to atmosphere, and a shut-off mode of shutting off fluid supply to the sensing cuff and fluid discharge from the sensing cuff; and 
     a control unit, wherein, 
     the control unit includes, in the worn state: 
     a first preparation processing unit that, with the fluid circuit switched to the discharge mode, operates the pressing member to press the sensing cuff toward the measurement target site and discharges a fluid remaining in the sensing cuff to the atmosphere through the fluid circuit; 
     a second preparation processing unit that, with the fluid circuit switched to the supply mode after operation of the first preparation processing unit, causes the sensing cuff to store a predetermined amount of the pressure transmitting fluid received from the pump through the fluid circuit; and 
     a measurement processing unit that, with the fluid circuit switched to the shut-off mode after operation of the second preparation processing unit, operates the pressing member to press the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site, and meanwhile, calculates a blood pressure of the measurement target site based on a pressure of the pressure transmitting fluid stored in the sensing cuff by an oscillometric method. 
     The “fluid” is typically air, but may be other gas or liquid. 
     The “inner circumferential side” of the belt refers to a side facing the measurement target site in the worn state wrapped around the measurement target site. 
     In the sphygmomanometer of the present disclosure, the control unit performs predetermined control in the worn state of the belt being worn around the measurement target site. That is, with the fluid circuit switched to the discharge mode, the first preparation processing unit included in the control unit operates the pressing member to press the sensing cuff and causes the fluid remaining in the sensing cuff to be discharged to the atmosphere through the fluid circuit. As a result, even if the fluid remains in the sensing cuff after the blood pressure measurement by the sphygmomanometer and before the next blood pressure measurement, the fluid is discharged from the sensing cuff. Next, after the operation of the first preparation processing unit, with the fluid circuit switched to the supply mode, the second preparation processing unit causes the sensing cuff to store the predetermined amount of the pressure transmitting fluid received from the pump through the fluid circuit. As a result, the pressure transmitting fluid is stored in the sensing cuff. At this time, because the remaining fluid has been discharged from the sensing cuff by the operation of the first preparation processing unit, the amount of the pressure transmitting fluid stored in the sensing cuff becomes constant. Next, after the operation of the second preparation processing unit, with the fluid circuit switched to the shut-off mode, the measurement processing unit operates the pressing member to press the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site, and meanwhile, calculates the blood pressure of the measurement target site based on a pressure of the pressure transmitting fluid stored in the sensing cuff by the oscillometric method. Thereby, for example, as disclosed in JP 2018-102868 A and JP 2018-102867 A, as a result of setting width dimensions of the belt, the pressing member, and the sensing cuff (as appropriate, these are collectively referred to as a “cuff”) to be small (for example, about 25 mm), the blood pressure of the measurement target site is calculated accurately even when the compression loss of the pressing member occurs during pressurization. In particular, as described above, because the amount of the pressure transmitting fluid stored in the sensing cuff becomes constant after the operation of the second preparation processing unit, the blood pressure is calculated accurately. 
     In the sphygmomanometer of one embodiment, 
     the pressing member includes a pressing cuff having a bag shape and arranged between the belt and the sensing cuff, and 
     under control of the control unit, when the pressing member is operating, the fluid circuit supplies a pressurizing fluid from the pump to the pressing cuff to expand the pressing cuff and causes the sensing cuff to press toward the measurement target site, and meanwhile, when the pressing member is not operating, the fluid circuit discharges the pressurizing fluid to the atmosphere from the pressing cuff. 
     In the sphygmomanometer of this one embodiment, the pressing cuff can be driven (expanded or contracted) by the pump, that is, by means common to the means for supplying the pressure transmitting fluid to the sensing cuff. Therefore, the configuration of the sphygmomanometer can be simplified as compared with the case in which, for example, the pressing member is constituted of such as a mechanical actuator. 
     In the sphygmomanometer of one embodiment, 
     the pressing member includes a pressing cuff having a bag shape and arranged at a portion of the inner circumferential side of the belt that becomes opposite to the sensing cuff in the worn state, and 
     under control of the control unit, when the pressing member is operating, the fluid circuit supplies a pressurizing fluid from the pump to the pressing cuff to expand the pressing cuff and causes the sensing cuff to press toward the measurement target site, and meanwhile, when the pressing member is not operating, the fluid circuit discharges the pressurizing fluid to the atmosphere from the pressing cuff. 
     In the sphygmomanometer of this one embodiment, the pressing cuff can be driven (expanded or contracted) by the pump, that is, by means common to the means for supplying the pressure transmitting fluid to the sensing cuff. Therefore, the configuration of the sphygmomanometer is simplified as compared with the case in which, for example, the pressing member is constituted of such as a mechanical actuator. Further, the pressing cuff is arranged at the portion of the inner circumferential side of the belt that becomes opposite to the sensing cuff in the worn state. For example, if the measurement target site is a wrist, the pressing cuff is arranged on a back side surface of the wrist (the surface corresponding to the back side of the hand) in the worn state, and is expanded to increase the tension of the belt. As a result, the portion of the belt facing the sensing cuff requires only a small amount of stroke to press the sensing cuff toward the measurement target site. Therefore, an escaping distance of the artery (positioned in the measurement target site) pushed by the sensing cuff is reduced (see, for example, JP 2017-006488 A). Therefore, the blood pressure is calculated more accurately. 
     In the sphygmomanometer of one embodiment, 
     the control unit includes a third preparation processing unit that operates after the operation of the second preparation processing unit and before operation of the measurement processing unit, and 
     with the fluid circuit switched to the shut-off mode, the third preparation processing unit deactivates the pressing member and discharges the pressurizing fluid from the pressing cuff to the atmosphere. 
     In the sphygmomanometer of this one embodiment, after the operation of the second preparation processing unit and before the operation of the measurement processing unit, with the fluid circuit switched to the shut-off mode, the third preparation processing unit deactivates the pressing member, and causes the pressurizing fluid to be discharged to the atmosphere from the pressing cuff As a result, the pressing applied to the sensing cuff by the pressing cuff is removed. Therefore, the pressure transmitting fluid stored in the sensing cuff by the second preparation processing unit can be distributed inside the sensing cuff. Therefore, when the blood pressure is measured by the measurement processing unit, the sensing cuff can correctly detect the pressure (pulse wave signal) generated by the artery at the measurement target site, making the accuracy of the blood pressure measurement improved. 
     The sphygmomanometer of one embodiment further comprises a pressing cuff pressure sensor configured to measure pressure in the pressing cuff. 
     In the sphygmomanometer of this one embodiment, the pressure in the pressing cuff can be measured by the pressing cuff pressure sensor. Therefore, the pressure in the pressing cuff can be controlled by using the output of the pressing cuff pressure sensor. This is particularly useful when the fluid remaining in the sensing cuff is discharged to the atmosphere by the first preparation processing unit and when the blood pressure is measured by the measurement processing unit. 
     The sphygmomanometer of one embodiment further comprises a sensing cuff pressure sensor configured to measure pressure in the sensing cuff. 
     In the sphygmomanometer of this one embodiment, the pressure in the sensing cuff can be measured by the sensing cuff pressure sensor. Therefore, the pressure in the sensing cuff can be controlled by using the output of the sensing cuff pressure sensor. This is particularly useful when the predetermined amount of pressure transmitting fluid is stored in the sensing cuff by the second preparation processing unit. 
     In the sphygmomanometer of one embodiment, the main body is arranged at a portion opposite to the sensing cuff in a circumferential direction of the belt. 
     In the sphygmomanometer of one embodiment, the main body is arranged at the portion opposite to the sensing cuff in the circumferential direction of the belt. Therefore, for example, when this sphygmomanometer constitutes a wrist-type sphygmomanometer, the main body is arranged on the back side surface of the wrist (the surface corresponding to the back side of the hand) in the worn state. As a result, the main body is less likely to interfere with the daily life of a user. Further, when the pressing cuff is arranged at the portion of the inner circumferential side of the belt that becomes opposite to the sensing cuff, a distance from the pump to the pressing cuff can be shortened as much as possible, and the sphygmomanometer can also be made compact. 
     In another aspect, a blood pressure measurement method according to the present disclosure is a blood pressure measurement method that uses a sphygmomanometer comprising: a main body mounted with a pump; a belt extending from the main body and worn around a measurement target site; a sensing cuff arranged, in a worn state of the belt being worn around the measurement target site, at a portion of an inner circumferential side of the belt that crosses an artery passing portion of the measurement target site, and configured in a bag shape so as to allow storage of a pressure transmitting fluid; a pressing member that presses the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site; and a fluid circuit that can be configured by switching among a supply mode of suppling the pressure transmitting fluid from the pump to the sensing cuff, a discharge mode of discharging the fluid from the sensing cuff to atmosphere, and a shut-off mode of shutting off fluid supply to the sensing cuff and fluid discharge from the sensing cuff, wherein, 
     the method comprising, in the worn state: 
     executing first preparation processing that, with the fluid circuit switched to the discharge mode, operates the pressing member to press the sensing cuff toward the measurement target site and discharges a fluid remaining in the sensing cuff to the atmosphere through the fluid circuit; 
     executing second preparation processing that, with the fluid circuit switched to the supply mode after the first preparation processing, causes the sensing cuff to store a predetermined amount of the pressure transmitting fluid received from the pump through the fluid circuit; and 
     executing measurement processing that, with the fluid circuit switched to the shut-off mode after the second preparation processing, operates the pressing member to press the sensing cuff toward the measurement target site and causes the sensing cuff to compress the measurement target site, and meanwhile, calculates a blood pressure of the measurement target site based on a pressure of the pressure transmitting fluid stored in the sensing cuff by an oscillometric method. 
     In the blood pressure measurement method of the present disclosure, the following processing is performed in the worn state of the belt being worn around the measurement target site. That is, with the fluid circuit switched to the discharge mode, the pressing member is operated to press the sensing cuff, and the fluid remaining in the sensing cuff is discharged to the atmosphere through the fluid circuit (first preparation processing). As a result, even if the fluid remains in the sensing cuff after the blood pressure measurement by the sphygmomanometer and before the next blood pressure measurement, the fluid is discharged from the sensing cuff. Next, after the first preparation processing, with the fluid circuit switched to the supply mode, the sensing cuff is caused to store the predetermined amount of pressure transmitting fluid received from the pump through the fluid circuit (second preparation processing). As a result, the pressure transmitting fluid is stored in the sensing cuff. At this time, because the remaining fluid has been discharged from the sensing cuff by the first preparation processing, the amount of pressure transmitting fluid stored in the sensing cuff becomes constant. Next, after the second preparation processing, with the fluid circuit switched to the shut-off mode, the pressing member operates to press the sensing cuff and causes the sensing cuff to compress the measurement target site, and meanwhile, the blood pressure of the measurement target site is calculated based on the pressure of the pressure transmitting fluid stored in the sensing cuff by the oscillometric method (measurement processing). Thereby, for example, as disclosed in JP  2018 - 102868  A and JP 2018-102867 A, as a result of setting the width dimensions of the belt, the pressing member, and the sensing cuff (as appropriate, these are collectively referred to as a “cuff”) to be small (for example, about 25 mm), the blood pressure of the measurement target site is calculated accurately even when the compression loss of the pressing member occurs during pressurization. In particular, as described above, because the amount of the pressure transmitting fluid stored in the sensing cuff becomes constant after the operation of the second preparation processing unit, the blood pressure is calculated accurately. 
     In yet another aspect, a computer-readable recording medium storing a program according to the present disclosure is a computer-readable recording medium non-transitorily storing a program for causing a computer to execute the above blood pressure measurement method. 
     By making a computer read the program stored in the computer-readable recording medium according to the present disclosure and causing the computer to execute the program, the above blood pressure measurement method can be implemented. 
     As is clear from the above, according to the sphygmomanometer and the blood pressure measurement method of the present disclosure, it becomes possible to create, before measuring a blood pressure, a state for making a blood pressure measurement accurate. In addition, by making a computer read the program stored in the computer-readable recording medium according to the present disclosure and causing the computer to execute the program, the above blood pressure measurement method can be implemented. 
     The above embodiments are illustrative, and are modifiable in a variety of ways without departing from the scope of this invention. It is to be noted that the various embodiments described above can be appreciated individually within each embodiment, but the embodiments can be combined together. It is also to be noted that the various features in different embodiments can be appreciated individually by its own, but the features in different embodiments can be combined.