Patent Publication Number: US-2023143560-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. 2020-126438 filed in Japan on Jul. 27, 2020, the entire content of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a sphygmomanometer, and more specifically to a sphygmomanometer that performs blood pressure measurement by temporarily compressing a measurement target site by a blood pressure measurement cuff. Furthermore, the present invention relates to a blood pressure measurement method for measuring a blood pressure by such a sphygmomanometer. Furthermore, the present invention relates to a computer-readable recording medium storing a program for causing a computer to execute such a blood pressure measurement method. 
     BACKGROUND ART 
     Conventionally, as this type of sphygmomanometer, for example, as disclosed in Patent Literature 1 (JP H03-23837 A), there has been known a sphygmomanometer including: a cuff (band) that compresses a living body; a measurement control unit that controls an operation of blood pressure measurement; a leak valve that leaks air from a pressurizing tube connected to the cuff during the blood pressure measurement; an emergency relief valve for relieving the pressurizing tube connected to the cuff in case of emergency; a safety control unit that operates the emergency relief valve in a case where the measurement control unit does not output a signal indicating measurement completion even after a lapse of a predetermined time after starting measurement. Furthermore, Patent Literature 1 discloses that an accident is prevented by confirming whether or not a power supply voltage value can be normally supplied to the measurement control unit and the safety control unit before starting measurement. 
     SUMMARY OF INVENTION 
     In Patent Literature 1, whether or not the power supply voltage value can be normally supplied is confirmed before starting the measurement, but the operation of the emergency relief valve is not confirmed. For this reason, in a case where the emergency relief valve itself has been failed, there is a problem that exhaust in an emergency (in case of emergency) is not performed. For example, in a sphygmomanometer such as a nighttime sphygmomanometer that starts measurement of a blood pressure according to a schedule set in advance while a subject is sleeping (nighttime), if the emergency relief valve is failed in case of emergency, a measurement target site is compressed for a long time while the subject is unconscious, and a state occurs in which an artery remains in an ischemic condition. 
     Therefore, an object of the present invention is to provide a sphygmomanometer and a blood pressure measurement method capable of reliably preventing occurrence of a state where a measurement target site remains compressed for a long time. Furthermore, 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 method. 
     In order to achieve the object, a sphygmomanometer of the present disclosure is a sphygmomanometer that performs blood pressure measurement by temporarily compressing a measurement target site by a blood pressure measurement cuff, the sphygmomanometer comprising:
         a pump that supplies a fluid to the cuff to pressurize the cuff;   a pressure sensor that detects a pressure of the cuff;   a first valve for regular measurement that discharges the fluid from the cuff to depressurize the cuff during blood pressure measurement;   a second valve for emergency exhaust that discharges the fluid from the cuff to depressurize the cuff when an abnormality occurs in which discharge of the fluid by the first valve is not normally performed;   a blood pressure measurement unit that controls operations of the pump and the first and second valves on a basis of the pressure of the cuff output from the pressure sensor to measure a blood pressure of the measurement target site; and   an abnormality determination unit that performs a determination process of supplying the fluid to the cuff by the pump in a state where a closing instruction is given to the first valve and an opening instruction is given to the second valve, and determining whether or not there is an abnormality in an emergency exhaust function according to a degree of increase in the pressure of the cuff.       

     In this specification, giving a “closing instruction” to a valve refers to controlling the valve to close regardless of whether the valve type is a normally open valve or a normally closed valve. Furthermore, giving an “opening instruction” to a valve refers to controlling the valve to open regardless of whether the valve type is a normally open valve or a normally closed valve. 
     In another aspect, a blood pressure measurement method of the present disclosure is a blood pressure measurement method for performing blood pressure measurement by temporarily compressing a measurement target site by a blood pressure measurement cuff, comprising:
         a pump that supplies a fluid to the cuff to pressurize the cuff;   a pressure sensor that detects a pressure of the cuff;   a first valve for regular measurement that discharges the fluid from the cuff to depressurize the cuff during blood pressure measurement; and   a second valve for emergency exhaust that discharges the fluid from the cuff to depressurize the cuff when an abnormality occurs in which discharge of the fluid by the first valve is not normally performed,   the blood pressure measurement method comprising:   a measurement step of measuring a blood pressure of the measurement target site by controlling operations of the pump and the first and second valves on a basis of the pressure of the cuff output from the pressure sensor; and   a determination step of supplying the fluid to the cuff by the pump in a state where a closing instruction is given to the first valve and an opening instruction is given to the second valve, and determining whether or not there is an abnormality in an emergency exhaust function according to a degree of increase in the pressure of the cuff, as a step performed prior to the measurement step each time the measurement step is performed.       

     In yet another aspect, a computer-readable recording medium according to the present disclosure is a non-transitorily computer-readable recording medium 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 view illustrating an external appearance of a wrist-type sphygmomanometer according to one embodiment of the present invention. 
         FIG.  2    is a diagram illustrating a block configuration of the sphygmomanometer. 
         FIG.  3    is a view illustrating a mode in which the sphygmomanometer is worn on a left wrist as a measurement target site. 
         FIG.  4 A  is a view illustrating a sitting position as a measurement posture. 
         FIG.  4 B  is a view illustrating a supine position as a measurement posture. 
         FIG.  5    is a diagram illustrating an operation flow in a case where the sphygmomanometer confirms an operation of a protection device unit in a regular blood pressure measurement mode. 
         FIG.  6    is a diagram illustrating an operation flow in a case where the sphygmomanometer performs determination of the presence or absence of an abnormality of an emergency exhaust function only in a nighttime blood pressure measurement mode. 
         FIG.  7    is a diagram illustrating a specific flow of a blood pressure measurement routine in the operation flows in  FIGS.  5  and  6   . 
         FIG.  8    is a diagram illustrating a specific flow of an operation confirmation routine of the protection device unit in the operation flows in  FIGS.  5  and  6   . 
         FIG.  9    is a diagram schematically illustrating how to determine whether or not there is an abnormality in the emergency exhaust function according to the degree of increase in the pressure of a cuff in the sphygmomanometer. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 
     (Configuration of Sphygmomanometer) 
       FIG.  1    illustrates an external appearance of a wrist-type sphygmomanometer  100  according to one embodiment of the present invention. The sphygmomanometer  100  roughly includes a blood pressure measurement cuff  20  that is to be worn on a left wrist  90  (see  FIG.  3    described later) as a measurement target site, and a main body  10  that is integrally attached to the cuff  20 . 
     The cuff  20  is a general one for a wrist-type sphygmomanometer, and has an elongated band shape so as to surround the left wrist  90  along its circumferential direction. The cuff  20  includes a fluid bag  22  (see  FIG.  2   ) therein for compressing the left wrist  90 . Note that, in order to maintain the cuff  20  in an annular shape at all times, a curler having appropriate flexibility may be provided in the cuff  20 . 
     As illustrated in  FIG.  3   , the main body  10  is integrally attached to a substantially center portion in a longitudinal direction of the band-shaped cuff  20 . In this example, the portion to which the main body  10  is attached is supposed to correspond to a palm-side surface (surface on a palm side of a hand)  90   a  of the left wrist  90  in a worn state. 
     The main body  10  has a flat substantially rectangular parallelepiped shape along an outer peripheral surface of the cuff  20 . The main body  10  is formed to be small and thin so as not to disturb the sleep of a user (in this example, referring to a subject, and the same applies hereinafter). Furthermore, corner portions of the main body  10  are rounded (the corners are rounded). 
     As illustrated in  FIG.  1   , the main body  10  is provided with, on a surface (top surface) on a side farthest from the left wrist  90  among outer surfaces thereof, a display  50  forming a display screen and an operation unit  52  for inputting an instruction from the user. 
     In this example, the display  50  is constituted of a liquid crystal display (LCD), and displays given information according to a control signal from a central processing unit (CPU)  110  described later. In this example, a maximum blood pressure (unit; mmHg), a minimum blood pressure (unit; mmHg), and a pulse (unit; beats/minute) are displayed. Note that the display  50  may be constituted of an organic electro luminescence (EL) display, or may include a light emitting diode (LED). 
     The operation unit  52  inputs an operation signal corresponding to an instruction from the user to the CPU  110  described later. In this example, the operation unit  52  includes a measurement switch  52 A as a measurement instruction input unit for receiving a blood pressure measurement instruction from the user, and a nighttime measurement switch  52 B as a mode operation unit for receiving an instruction to switch a mode between a regular blood pressure measurement mode and a nighttime blood pressure measurement mode. Here, the “regular blood pressure measurement mode” means a mode in which, when a blood pressure measurement instruction is input through the measurement switch  52 A, blood pressure measurement is performed in response to the blood pressure measurement instruction (however, as described later, the absence of an abnormality in an emergency exhaust function may be set as a condition for starting the blood pressure measurement). The “nighttime blood pressure measurement mode” means a mode (automatic measurement mode) in which blood pressure measurement is automatically started according to a schedule set in advance so that blood pressure values can be measured while the user is sleeping (however, as described later, the absence of an abnormality in the emergency exhaust function may be set as a condition for starting the blood pressure measurement). The schedule set in advance refers to a plan to measure at, for example, fixed clock times such as 1:00, 2:00, or 3:00, in the middle of the night, or a plan to measure, for example, once every two hours after the nighttime measurement switch  52 B being pressed. 
     Specifically, in this example, each of the measurement switch  52 A and the nighttime measurement switch  52 B is a momentary type (self-return type) switch, and is in an on-state only while being pressed down, and returns to an off-state when being released. 
     When the measurement switch  52 A is once pressed down while the sphygmomanometer  100  is in the regular blood pressure measurement mode, which means a blood pressure measurement instruction, the measurement target site (left wrist  90 ) is temporarily compressed by the cuff  20 , and blood pressure measurement is executed by an oscillometric method. When the measurement switch  52 A is pressed down again during the blood pressure measurement (for example, during pressurization of the cuff  20 ), which means an instruction to stop the blood pressure measurement, the blood pressure measurement is immediately stopped. 
     When the nighttime measurement switch  52 B is once pressed down while the sphygmomanometer  100  is in the regular blood pressure measurement mode, which means an instruction to transition to the nighttime blood pressure measurement mode, the sphygmomanometer  100  transitions from the regular blood pressure measurement mode to the nighttime blood pressure measurement mode (however, as described later, the absence of an abnormality in the emergency exhaust function may be set as a transition condition to the nighttime blood pressure measurement mode). In the nighttime blood pressure measurement mode, as described above, blood pressure measurement by the oscillometric method is automatically started according to the schedule set in advance. When the nighttime measurement switch  52 B is pressed down again while the sphygmomanometer  100  is in the nighttime blood pressure measurement mode, which means an instruction to stop the nighttime blood pressure measurement mode, the sphygmomanometer  100  transitions from the nighttime blood pressure measurement mode to the regular blood pressure measurement mode. 
       FIG.  2    illustrates a block configuration of the sphygmomanometer  100 . 
     As described above, the cuff  20  includes the fluid bag  22  for compressing the left wrist  90  as the measurement target site. The fluid bag  22  and the main body  10  are connected by an air pipe  39  so as to be capable of fluid communication. 
     The main body  10  is roughly equipped with a main unit  190  for blood pressure measurement and a protection device unit  200  for emergency exhaust. 
     The main unit  190  includes, in addition to the display  50  and the operation unit  52  described above, a first CPU  1100  that constitutes a part of the CPU  110  as a control unit, a memory  51  as a storage unit, a power supply unit  53 , a first pressure sensor  31 , a pump  32 , and a first valve  33  for blood pressure measurement. Furthermore, the main unit  190  includes a first A/D conversion circuit  310  that converts an output of the first pressure sensor  31  from an analog signal to a digital signal, a pump drive circuit  320  that drives the pump  32 , and a first valve drive circuit  330  that drives the first valve  33 . 
     The protection device unit  200  includes a second CPU  2100  that constitutes a part of the CPU  110  as the control unit, a second pressure sensor  231 , a second valve  233  for emergency exhaust, a second A/D conversion circuit  2310  that converts an output of the second pressure sensor  231  from an analog signal to a digital signal, and a second valve drive circuit  2330  that drives the second valve  233 . 
     The first pressure sensor  31 , the pump  32 , the first valve  33 , the second pressure sensor  231 , and the second valve  233  are commonly connected to the fluid bag  22  through the air pipe  39  so as to be capable of fluid communication. 
     The CPU  110  includes the first CPU  1100  as a first processor that mainly works for blood pressure measurement, and the second CPU  2100  as a second processor that mainly works for emergency exhaust, and controls the entire operation of the sphygmomanometer  100 . Specifically, the CPU  110  works as a pressure control unit according to a program for controlling the sphygmomanometer  100  stored in the memory  51 , and performs control to drive the pump  32 , the first valve  33 , and the second valve  233  in response to operation signals from the operation unit  52 . Furthermore, the CPU  110 , particularly the first CPU  1100  works as a blood pressure measurement unit, calculates blood pressure values by using an algorithm for blood pressure calculation by the oscillometric method, and controls the display  50  and the memory  51 . The CPU  110 , particularly the second CPU  2100  works as an abnormality determination unit, and confirms an operation of the protection device unit  200 . 
     The memory  51  stores a program for controlling the sphygmomanometer  100 , data used for controlling the sphygmomanometer  100 , setting data for setting various functions of the sphygmomanometer  100 , measurement result data of blood pressure values, and the like. Furthermore, the memory  51  is used as a work memory or the like when the program is executed. 
     In this example, the power supply unit  53  is constituted of a secondary battery, and supplies power to each unit of the CPU  110 , the first pressure sensor  31 , the pump  32 , the first valve  33 , the display  50 , the memory  51 , the first A/D conversion circuit  310 , the pump drive circuit  320 , the first valve drive circuit  330 , the second pressure sensor  231 , the second valve  233 , the second A/D conversion circuit  2310 , and the second valve drive circuit  2330 . 
     The pump  32  supplies air as a fluid to the fluid bag  22  through the air pipe  39  in order to pressurize the pressure (cuff pressure) in the fluid bag  22  included in the cuff  20 . The pump drive circuit  320  drives the pump  32  on the basis of a control signal given from the CPU  110 . 
     In this example, the first valve  33  is constituted of a normally open solenoid valve, and is opened and closed to discharge the air in the fluid bag  22  or to fill the air into the fluid bag  22  through the air pipe  39  in order to control the cuff pressure. The first valve drive circuit  330  opens and closes the first valve  33  on the basis of a control signal given from the first CPU  1100 . If the first valve  33  is normal, the first valve  33  becomes an open state upon receiving an opening instruction (de-energization), and becomes a closed state upon receiving a closing instruction (energization). 
     The first pressure sensor  31  and the first A/D conversion circuit  310  work as a pressure detection unit that detects the pressure of the cuff. In this example, the first pressure sensor  31  is a piezoresistive pressure sensor that detects the pressure (cuff pressure) in the fluid bag  22  included in the cuff  20  through the air pipe  39 , and outputs it as electrical resistance due to the piezoresistive effect. The first A/D conversion circuit  310  converts the output (electrical resistance) of the first pressure sensor  31  from an analog signal to a digital signal, and outputs the digital signal to the CPU  110 . In this example, the first CPU  1100  works as an oscillation circuit that oscillates at a frequency corresponding to the electrical resistance from the first pressure sensor  31 , and acquires a signal indicating the cuff pressure according to the oscillation frequency. 
     In this example, the second valve  233  is constituted of a normally closed solenoid valve, and is opened in order to perform emergency exhaust of the air in the fluid bag  22  through the air pipe  39  in an emergency (in case of emergency). The second valve drive circuit  2330  opens and closes the second valve  233  on the basis of a control signal given from the second CPU  2100 . If the second valve  233  is normal, the second valve  233  becomes an open state upon receiving an opening instruction (energization), and becomes a closed state upon receiving a closing instruction (de-energization). 
     The second pressure sensor  231  and the second A/D conversion circuit  2310  work as a pressure detection unit that detects the pressure of the cuff. In this example, the second pressure sensor  231  is a piezoresistive pressure sensor that detects the pressure (cuff pressure) in the fluid bag  22  included in the cuff  20  through the air pipe  39 , and outputs it as electrical resistance due to the piezoresistive effect. The second A/D conversion circuit  2310  converts the output (electrical resistance) of the second pressure sensor  231  from an analog signal to a digital signal, and outputs the digital signal to the CPU  110 . In this example, the second CPU  2100  works as an oscillation circuit that oscillates at a frequency corresponding to the electrical resistance from the second pressure sensor  231 , and acquires a signal indicating the cuff pressure according to the oscillation frequency. 
       FIGS.  4 A and  4 B  illustrate measurement postures of “sitting position” and “supine position”, respectively, which are recommended in a case where a subject performs blood pressure measurement by using the sphygmomanometer  100 . Here, as illustrated in  FIG.  4 A , the “sitting position” means a posture in which a user  80  wearing the sphygmomanometer  100  on the left wrist  90  sits on a chair  97  or the like, and holds the left wrist  90  (and the sphygmomanometer  100 ) at a height level of a heart  81  by raising the left wrist  90  obliquely (the hand is up, the elbow is down) in front of a body trunk with the left elbow placed on a table  98 . This posture eliminates the height difference between the left wrist  90  and the heart  81  of the user  80 , and thus is recommended in order to increase the blood pressure measurement accuracy in the regular blood pressure measurement mode. On the other hand, as illustrated in  FIG.  4 B , the “supine position” means a posture in which the user  80  wearing the sphygmomanometer  100  on the left wrist  90  lies on his/her back on a horizontal floor surface  99  or the like in a state where the left elbow is extended along the body trunk. In the nighttime blood pressure measurement mode, blood pressure measurement is started according to the schedule set in advance while the subject is sleeping (nighttime), so that the subject is supposed to take the measurement posture of the “supine position”. 
     (Blood pressure measurement method) In the sphygmomanometer  100 , there are a case where determination of the presence or absence of an abnormality of the emergency exhaust function is performed in the regular blood pressure measurement mode (an operation flow in  FIG.  5   ), and apart from the case, a case where determination of the presence or absence of an abnormality of the emergency exhaust function is performed only in the nighttime blood pressure measurement mode (an operation flow in  FIG.  6   ). Note that, hereinafter, the first CPU  1100  and the second CPU  2100  are collectively referred to as the CPU  110  except a case where they are specifically distinguished from each other. 
     (Case Where Abnormality Determination of Emergency Exhaust Function is Performed in Regular Blood Pressure Measurement Mode) 
       FIG.  5    illustrates an operation flow in a case where the sphygmomanometer  100  performs determination of the presence or absence of the abnormality of the emergency exhaust function in the regular blood pressure measurement mode. Note that, in this example, when the measurement switch  52 A is pressed in a power-off state, the power is turned on and the regular blood pressure measurement mode is set by default. 
     As illustrated in  FIG.  4 A , it is assumed that the user  80  wearing the sphygmomanometer  100  on the left wrist  90  is in a posture of the sitting position. 
     In this state, as shown in step Si in  FIG.  5   , when the user presses down the measurement switch  52 A provided on the main body  10  to input a blood pressure measurement instruction (YES in step S 1 ), the CPU  110  proceeds to step S 2  and enters into an operation confirmation routine of the protection device unit. 
     (Operation Confirmation Routine of Protection Device Unit) Specifically, in the operation confirmation routine of the protection device unit, as illustrated in  FIG.  8   , the CPU  110  gives a closing instruction (energization) to the first valve  33  via the first valve drive circuit  330  (step S 201 ), and gives an opening instruction (energization) to the second valve  233  via the second valve drive circuit  2330  (step S 202 ). In this state, the CPU  110  drives the pump  32  via the pump drive circuit  320 , and supplies air to the cuff  20  (fluid bag  22 ) through the air pipe  39  (step S 203 ). Then, the CPU  110  works as an abnormality determination unit, and performs a determination process of determining whether or not there is an abnormality in the emergency exhaust function according to the degree of increase in the pressure of the cuff  20  (steps S 204  and S 205 ). 
     Specifically, the CPU  110 , particularly the second CPU  2100  determines whether or not the cuff pressure is equal to or higher than a reference pressure Pref (in this example, Pref=5 mmHg) on the basis of an output of the second pressure sensor  231  (step S 204 ). Here, if the cuff pressure is less than the reference pressure Pref (NO in step S 204 ), the determination as to whether or not the cuff pressure is equal to or higher than the reference pressure Pref is continued until a reference time tref (in this example, tref=5 sec) elapses from the start of driving of the pump  32  (steps S 204  and S 205 ). Then, when the cuff pressure becomes equal to or higher than the reference pressure Pref by the time at which the reference time tref elapses from the start of driving of the pump  32  (YES in step S 204 ), it is determined that there is an abnormality in the emergency exhaust function. On the other hand, if the cuff pressure is less than the reference pressure Pref until the reference time tref elapses from the start of driving of the pump  32  (YES in step S 205 ), it is determined that there is no abnormality in the emergency exhaust function. Note that the value of the reference time tref and the value of the reference pressure Pref can each be variably set. 
     The reason for performing the determination process (steps S 204  and S 205 ) is as follows. 
     (i) For example, as a first case, if the first valve  33  is normal and in a closed state, and the second valve  233  is normal and in an open state, when the fluid is supplied to the cuff  20  by the pump  32 , as exemplified as a curved line C 1  indicated by a solid line in  FIG.  9   , the degree of increase in the pressure of the cuff  20  is low because the second valve  233  is in an open state. The second CPU  2100  determines that there is no abnormality in the emergency exhaust function according to the result of “low”. 
     (ii) Next, as a second case, if the first valve  33  is normal and in a closed state, and the second valve  233  is abnormal and in a closed state, when the fluid is supplied to the cuff  20  by the pump  32 , as exemplified as a curved line C 2  indicated by a broken line in  FIG.  9   , the degree of increase in the pressure of the cuff  20  is high because the first and second valves  33  and  233  are in a closed state. The second CPU  2100  determines that there is an abnormality in the emergency exhaust function according to the result of “high”. In the example in  FIG.  9   , it is determined that there is an abnormality in the emergency exhaust function at a point of time at which a time tf has elapsed from the start of driving of the pump  32 . 
     (iii) Next, as a third case, if the first valve  33  is abnormal and in an open state, and the second valve  233  is normal and in an open state, when the fluid is supplied to the cuff  20  by the pump  32 , the degree of increase in the pressure of the cuff  20  is low because the first valve  33  is in an open state. The second CPU  2100  determines that there is no abnormality in the emergency exhaust function according to the result of “low”. 
     (iv) Finally, as a fourth case, if the first valve  33  is abnormal and in an open state, and the second valve  233  is abnormal and in a closed state, when the fluid is supplied to the cuff  20  by the pump  32 , the degree of increase in the pressure of the cuff  20  is low because the first valve  33  is in an open state. The second CPU  2100  determines that there is no abnormality in the emergency exhaust function according to the result of “low”. 
     As a result, in the second case (ii), the CPU  110  can, for example, stop the blood pressure measurement for the measurement target site according to the determination result that there is an abnormality in the emergency exhaust function. Therefore, it is possible to prevent occurrence of a state where the measurement target site remains compressed for a long time. In the example in  FIG.  8   , the CPU  110  stops the pump  32  (step S 208 ), and gives an opening instruction (de-energization) to the first valve  33  to open the first valve  33  (step S 209 ). At this time, since the first valve  33  is a normally open solenoid valve, it is expected to open in response to the opening instruction. Subsequently, the CPU  110  works as a notification unit, and displays an error indication on the display  50  as a notification that there is an abnormality in the emergency exhaust function (step S 210 ). This error indication may be a message such as “abnormality occurs in emergency exhaust function”, or may be an error code such as “Eab” (ab representing numbers set in advance). The notification may be an alarm sound by a buzzer not illustrated. With this notification, the user (typically, the subject) knows that there is an abnormality in the emergency exhaust function, and for example, can take measures such as requesting a service department of a sphygmomanometer manufacturer to perform maintenance service. 
     On the other hand, in the first case (i), the third case (iii), and the fourth case (iv), the CPU  110  can start blood pressure measurement for the measurement target site according to the determination result that there is no abnormality in the emergency exhaust function. However, in the third case (iii) and the fourth case (iv), since the first valve  33  is abnormal and remains in an open state, the pressure of the cuff  20  does not increase even when the CPU  110  operates the pump  32  to supply the fluid to the cuff  20  for blood pressure measurement. Therefore, it is possible to prevent occurrence of a state where the measurement target site remains compressed for a long time. In this example, since the pressure of the cuff  20  does not increase, the CPU  110  determines that a measurement error has occurred, and stops the blood pressure measurement. 
     In the first case (i), the CPU  110  can measure the blood pressure of the measurement target site by controlling the operations of the pump  32  and the first and second valves  33  and  233  on the basis of the pressure of the cuff  20  output from the first and second pressure sensors  31  and  231 . In this case, since the second valve  233  is normal, emergency exhaust can be performed by making the second valve  233  in an open state in an emergency (in case of emergency). 
     In the example in  FIG.  8   , in order to start a blood pressure measurement routine, the CPU  110  once stops the pump  32  (step S 206 ), and gives a closing instruction (de-energization) to the second valve  233  to close the second valve  233  (step S 207 ). At this time, since the second valve  233  is a normally closed solenoid valve, it is expected to close in response to the closing instruction. Thereafter, the process returns to the flow in  FIG.  5    and enters into the blood pressure measurement routine (step S 3 ). 
     (Blood Pressure Measurement Routine) 
     As illustrated in  FIG.  7   , when the process enters into the blood pressure measurement routine, the CPU  110  initializes the first and second pressure sensors  31  and  231  (step S 101 ). Specifically, the CPU  110  initializes a processing memory area and stops the pump  32 , and gives an opening instruction (de-energization) and an opening instruction (energization) to the first valve  33  and the second valve  233 , respectively. At this time, since the first valve  33  is a normally open solenoid valve, it is expected to open in response to the opening instruction. When either the first valve  33  or the second valve  233  is normal and open, the cuff pressure becomes equal to the atmospheric pressure. In this state, 0 mmHg adjustment (the atmospheric pressure being set to 0 mmHg) of the first pressure sensor  31  and the second pressure sensor  231  is performed. 
     Next, the CPU  110  gives a closing instruction (energization) to the first valve  33  via the first valve drive circuit  330 , and gives a closing instruction (de-energization) to the second valve  233  via the second valve drive circuit  2330  (step S 102 ). At this time, it is unclear whether or not the first valve  33  closes in response to the closing instruction. However, since the second valve  233  is a normally closed solenoid valve, it is expected to close in response to the closing instruction. Subsequently, the CPU  110  drives the pump  32  via the pump drive circuit  320 , and starts pressurizing the cuff  20  (fluid bag  22 ) (step S 103 ). At this time, the CPU  110  controls the pressurization rate of the cuff pressure that is the pressure in the fluid bag  22  on the basis of the output of the first pressure sensor  31  in this example while supplying air from the pump  32  to the fluid bag  22  through the air pipe  39 . 
     Here, if the first valve  33  is abnormal and remains in an open state (the third case (iii) and the fourth case (iv) described above), the pressure of the cuff  20  does not increase even when the CPU  110  operates the pump  32  to supply the fluid to the cuff  20  for the blood pressure measurement. In this example, for example, as indicated by the curved line C 1  illustrated in  FIG.  9   , when the cuff pressure does not become equal to or higher than the reference pressure Pref (in this example, Pref=5 mmHg) even after a lapse of the reference time tref (in this example, tref=5 sec) set in advance from the start of driving of the pump  32 , a measurement error occurs, and the subsequent process is stopped (note that the value of the reference time tref and the value of the reference pressure Pref can each be variably set). Therefore, it is possible to prevent occurrence of a state where the measurement target site remains compressed for a long time. Note that, at this time, the CPU  110  may work as a notification unit, and display an error indication on the display  50  as a notification that there is an abnormality in the first valve  33 . This error indication may be a message such as “abnormality occurs in valve for blood pressure measurement”, or may be an error code such as “Ecd” (cd representing numbers set in advance). 
     Next, in step S 104  in  FIG.  7   , the CPU  110 , particularly the first CPU  1100  works as a blood pressure measurement unit, and attempts to calculate blood pressure values (the maximum blood pressure (systolic blood pressure) and the minimum blood pressure (diastolic blood pressure)) by using an algorithm stored in the memory  51  by a known oscillometric method on the basis of a pulse wave signal (fluctuation component due to a pulse wave included in the output of the first pressure sensor  31 ) acquired at this point of time. 
     At this point of time, in a case where the blood pressure values cannot be calculated yet due to lack of data (NO in step S 105 ), the process of steps S 103  to S 105  is repeated unless the cuff pressure reaches an upper limit pressure (for safety, for example, it is set in advance to 300 mmHg). 
     When the blood pressure values can be calculated in this manner (YES in step S 105 ), the CPU  110  stops the pump  32  (step S 106 ), and gives an opening instruction (de-energization) to the first valve  33  via the first valve drive circuit  330  (step S 107 ). At this time, since the first valve  33  is a normally open solenoid valve, it is expected to open in response to the opening instruction. Accordingly, control to exhaust the air in the cuff  20  (fluid bag  22 ) is performed. Furthermore, the CPU  110  displays the calculated blood pressure values on the display  50  (step S 108 ), and performs control to store the blood pressure values in the memory  51 . 
     Thereafter, the CPU  110 , particularly the second CPU  2100  determines whether or not the exhaust from the cuff  20  has been completed on the basis of the output of the second pressure sensor  231  (step S 109 ). Specifically, it is determined whether or not the cuff pressure becomes less than the pressure set in advance (for example,  5  mmHg) after a lapse of a time set in advance (for example,  10  seconds) from giving the opening instruction (de-energization) to the first valve  33 . Here, if the exhaust from the cuff  20  is not completed for some reason (NO in step S 109 ), the second CPU  2100  gives an opening instruction (energization) to the second valve  233  via the second valve drive circuit  2330  (step S 110 ). Here, it has been confirmed that the second valve  233  does not become abnormal and a closed state (the second case (ii) described above) in the immediately preceding operation confirmation routine of the protection device unit (FIG.  8 ). Therefore, the second valve  233  is reliably expected to open in response to the opening instruction (energization). Accordingly, the exhaust from the cuff  20  can be reliably completed. 
     When the exhaust from the cuff  20  is completed (YES in step S 109 ), the process returns to the operation flow in  FIG.  5   . In the example in  FIG.  5   , the operation flow ends as it is. 
     In this manner, according to the sphygmomanometer  100 , it is possible to reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     Furthermore, in the operation flow in  FIG.  5   , the second CPU  2100  performs the operation confirmation routine of the protection device unit (step S 2 ) prior to the blood pressure measurement routine (step S 3 ) each time the first CPU  1100  performs the blood pressure measurement routine. Therefore, it is possible to further reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     Furthermore, in the sphygmomanometer  100 , the first valve  33  and the second valve  233  are valves of types different from each other (normally open valve and normally closed valve). Accordingly, the probability of occurrence of an abnormality due to the same failure is low as compared with a case of valves of the same type. Therefore, the reliability of the sphygmomanometer  100  as a product can be enhanced. Furthermore, the first valve  33  for blood pressure measurement is a normally open solenoid valve. Accordingly, it is sufficient that the first valve  33  becomes a closed state upon receiving a closing instruction (actuation instruction, that is, energization) during the blood pressure measurement (a period in which the measurement target site is temporarily compressed by the cuff  20 ), and it is sufficient that the first valve  33  is not actuated (de-energized) and in an open state during a period other than during the blood pressure measurement. The second valve  233  for emergency exhaust is a normally closed solenoid valve. Accordingly, it is sufficient that the second valve  233  becomes an open state upon receiving an opening instruction (actuation instruction, that is, energization) during the emergency exhaust, and it is sufficient that the second valve  233  is not actuated (de-energized) and in a closed state during a period other than during the emergency exhaust. Therefore, the power consumption of the first valve  33  and the second valve  233  can be reduced. 
     (Case Where Abnormality Determination of Emergency Exhaust Function is Performed Only in Nighttime Blood Pressure Measurement Mode) 
       FIG.  6    illustrates an operation flow in a case where the sphygmomanometer  100  performs determination of the presence or absence of the abnormality of the emergency exhaust function only in the nighttime blood pressure measurement mode. It is assumed that the sphygmomanometer  100  is powered on at the start of the flow, and in the regular blood pressure measurement mode. 
     As illustrated in  FIG.  4 B , it is assumed that the user  80  wearing the sphygmomanometer  100  on the left wrist  90  is in a posture of the supine position. 
     As shown in step S 11  in  FIG.  6   , when the user presses down the nighttime measurement switch  52 B provided on the main body  10 , in this example, the sphygmomanometer  100  transitions from the regular blood pressure measurement mode to the nighttime blood pressure measurement mode in response to the pressing down. In this example, in the nighttime blood pressure measurement mode, it is assumed that a schedule is established to measure once every two hours until, for example, 7:00 a.m. after the nighttime measurement switch  52 B is pressed. Note that the schedule is not limited to this schedule, and may be established to measure at fixed clock times such as 1:00 a.m., 2:00 a.m., 3:00 a.m., or the like until, for example, 7:00 a.m. after the nighttime measurement switch  52 B is pressed. 
     Next, as shown in step S 12  in  FIG.  6   , the CPU  110  determines whether or not it is the measurement clock time set in the schedule (for the nighttime blood pressure measurement mode). If it is not the measurement clock time set in the schedule (NO in step S 12 ), the CPU  110  waits for the measurement clock time set in the schedule. 
     When the measurement clock time set in the schedule is reached (YES in step S 12 ), as shown in step S 13  in  FIG.  6   , the CPU  110  executes the operation confirmation routine of the protection device unit similarly to step S 2  in  FIG.  5   . That is, the CPU  110 , particularly the second CPU  2100  works as an abnormality determination unit, and performs a determination process of determining whether or not there is an abnormality in the emergency exhaust function according to the degree of increase in the pressure of the cuff  20 . Here, if there is an abnormality in the emergency exhaust function, the CPU  110  stops the blood pressure measurement for the measurement target site, and displays an error indication that there is an abnormality in the emergency exhaust function on the display  50  (in particular, steps S 208  to S 210  in  FIG.  8   ). 
     On the other hand, if there is no abnormality in the emergency exhaust function, as shown in step S 14  in  FIG.  6   , the blood pressure measurement routine is executed similarly to step S 3  in  FIG.  5   . That is, the CPU  110 , particularly the first CPU  1100  works as a blood pressure measurement unit, performs calculation of blood pressure values (the maximum blood pressure (systolic blood pressure) and the minimum blood pressure (diastolic blood pressure)) by using an algorithm stored in the memory  51  by a known oscillometric method on the basis of a pulse wave signal (fluctuation component due to a pulse wave included in the output of the first pressure sensor  31 ), and displays the calculated blood pressure values on the display  50 , or the like (in particular, steps S 101  to S 108  in  FIG.  7   ). Subsequently, if the exhaust from the cuff  20  is not completed for some reason (NO in step S 109  in  FIG.  7   ), the CPU  110 , particularly the second CPU  2100  gives an opening instruction (energization) to the second valve  233  via the second valve drive circuit  2330  (step S 110 ). Accordingly, the exhaust from the cuff  20  is reliably completed. 
     When one blood pressure measurement set in the schedule is completed in this manner, in step S 15 , the CPU  110  determines whether or not all the blood pressure measurement set in the schedule has been completed. Here, as long as the blood pressure measurement is still scheduled according to the schedule (NO in step S 15 ), the CPU  110  waits for the next measurement clock time set in the schedule. 
     When the next measurement clock time set in the schedule is reached (YES in step S 12 ), the CPU  110  repeats the process of steps S 13  to S 15 . Furthermore, in step S 15 , the CPU  110  determines whether or not all the blood pressure measurement set in the schedule has been completed. When all the blood pressure measurement set in the schedule is completed in this manner (YES in step S 15 ), the CPU  110  ends the nighttime blood pressure measurement mode. 
     In the nighttime blood pressure measurement mode, if the second valve  233  for emergency exhaust is failed in an emergency (in case of emergency), a state occurs where the measurement target site remains compressed for a long time while the subject is unconscious. Such a situation should reliably be prevented. Therefore, in the operation flow in  FIG.  6   , in the nighttime blood pressure measurement mode, the second CPU  2100  performs the operation confirmation routine of the protection device unit (step S 13 ) prior to the blood pressure measurement routine (step S 14 ) each time the first CPU  1100  performs the blood pressure measurement routine. Therefore, it is possible to further reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     On the other hand, in the operation flow in  FIG.  6   , the regular blood pressure measurement mode is maintained unless the nighttime measurement switch  52 B is pressed down (NO in step S 11 ). In this case, the CPU  110 , when the measurement switch  52 A is pressed down (YES in step S 21 ), the CPU  110  proceeds to step S 22  in response to the input blood pressure measurement instruction without entering into the operation confirmation routine of the protection device unit ( FIG.  8   ) (in short, without performing the determination process described above (steps S 204  and S 205 )), and executes the blood pressure measurement routine. Accordingly, the blood pressure of the measurement target site is measured. 
     The reason for omitting the operation confirmation routine of the protection device unit ( FIG.  8   ) in the regular blood pressure measurement mode (steps S 21  to S 22 ) in the operation flow in  FIG.  6    in this manner is as follows. Firstly, this is because, in the regular blood pressure measurement mode, if the operation confirmation routine of the protection device unit is performed prior to the blood pressure measurement routine each time the first CPU  1100  performs the blood pressure measurement routine, a time period required for one blood pressure measurement (here, it means a total time period of a time period required for the operation confirmation routine of the protection device unit and a time period required for an actual blood pressure measurement routine) becomes long as a whole. Secondly, this is because, in the regular blood pressure measurement mode, the subject is in an awake state, thus it can be said that performing the operation confirmation routine of the protection device unit (in short, the determination process described above (steps S 204  and S 205 )) is less significant than in the nighttime blood pressure measurement mode. 
     In the embodiment described above, a blood pressure measurement unit and the abnormality determination unit are constituted of a programmed first CPU  1100  and a programmed second CPU  2100  different from the first CPU  1100 . In addition, the first valve  33  is driven by the first CPU  1100  via the first valve drive circuit  330 , and the second valve  233  is driven by the second CPU  2100  via the second valve drive circuit  2330 . Therefore, even when an abnormality has occurred in either one of a set of the first CPU  1100 , the first valve drive circuit  330 , and the first valve  33  or a set of the second CPU  2100 , the second valve drive circuit  2330 , and the second valve  233 , if the other set is normal, the exhaust from the cuff  20  can be performed. Therefore, it is possible to further reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     (Modification) 
     In the operation flow in  FIG.  6   , as shown in step S 11 , when the user presses down the nighttime measurement switch  52 B provided on the main body  10 , the sphygmomanometer  100  immediately transitions from the regular blood pressure measurement mode to the nighttime blood pressure measurement mode in response to the pressing down. However, the present invention is not limited thereto. For example, when the user presses down the nighttime measurement switch  52 B provided on the main body  10  (step S 11 ), the CPU  110  may first execute the operation confirmation routine of the protection device unit ( FIG.  8   ) in response to the pressing down. Then, when determining that there is an abnormality in the emergency exhaust function, the CPU  100  may prohibit the sphygmomanometer  100  from transitioning to the nighttime blood pressure measurement mode, while when determining that there is no abnormality in the emergency exhaust function, the CPU  110  may allow the sphygmomanometer to transition to the nighttime blood pressure measurement mode. Accordingly, it is possible to further reliably prevent a situation in which a state occurs where the measurement target site remains compressed for a long time while the subject is unconscious. 
     In the embodiment described above, the first valve  33  is a normally open solenoid valve, and the second valve  233  is a normally closed solenoid valve, but the present invention is not limited thereto. The types of the first valve  33  and the second valve  233  (the normally open valve and the normally closed valve) may be any type. 
     Furthermore, the sphygmomanometer  100  is of a type that compresses a wrist (the left wrist  90  in the above example, but may be a right wrist) as the measurement target site. Accordingly, it is expected that the degree of disturbing the sleep of the user (subject) is less than that in a type that compresses an upper arm (Imai et al., “Development and evaluation of a home nocturnal blood pressure monitoring system using a wrist-cuff device”, Blood Pressure Monitoring 2018, 23, P318-326). Therefore, the sphygmomanometer  100  is suitable for nighttime blood pressure measurement. 
     Furthermore, the sphygmomanometer  100  is integrally and compactly formed as a wrist-type sphygmomanometer. Accordingly, handling by a user becomes convenient. 
     Furthermore, in the embodiment described above, a blood pressure is calculated in the pressurization process of the cuff  20  (fluid bag  22 ), but the present invention is not limited thereto. The blood pressure may be calculated in a depressurization process of the cuff  20 . 
     Furthermore, in the embodiment described above, the measurement switch  52 A and the nighttime measurement switch  52 B each provided on the main body  10  are provided as the operation unit, but the present invention is not limited thereto. The operation unit may be constituted of, for example, a communication unit that receives an instruction from a smartphone or the like existing outside the sphygmomanometer  100  via wireless communication. 
     Furthermore, in the embodiment described above, the main body  10  is provided integrally with the cuff  20 , but the present invention is not limited thereto. The main body  10  may be formed as a separate body from the cuff  20 , and may be connected to the cuff  20  (fluid bag  22 ) via a flexible air tube so as to be capable of fluid communication. 
     The above-described blood pressure measurement method (in particular, the operation flow of  FIGS.  5 - 8   ) may be recorded as software (a computer program) on a non-transitory recording medium capable of storing data, such as a compact disc (CD), a digital universal disc (DVD), or a flash memory. By installing software recorded on such a recording medium in a substantial computer device such as a personal computer, a personal digital assistant (PDA), or a smartphone, the computer device can be caused to execute the above-described blood pressure measurement method. 
     As described above, a sphygmomanometer of the present disclosure is a sphygmomanometer that performs blood pressure measurement by temporarily compressing a measurement target site by a blood pressure measurement cuff, the sphygmomanometer comprising:
         a pump that supplies a fluid to the cuff to pressurize the cuff;   a pressure sensor that detects a pressure of the cuff;   a first valve for regular measurement that discharges the fluid from the cuff to depressurize the cuff during blood pressure measurement;   a second valve for emergency exhaust that discharges the fluid from the cuff to depressurize the cuff when an abnormality occurs in which discharge of the fluid by the first valve is not normally performed;   a blood pressure measurement unit that controls operations of the pump and the first and second valves on a basis of the pressure of the cuff output from the pressure sensor to measure a blood pressure of the measurement target site; and   an abnormality determination unit that performs a determination process of supplying the fluid to the cuff by the pump in a state where a closing instruction is given to the first valve and an opening instruction is given to the second valve, and determining whether or not there is an abnormality in an emergency exhaust function according to a degree of increase in the pressure of the cuff.       

     In this specification, giving a “closing instruction” to a valve refers to controlling the valve to close regardless of whether the valve type is a normally open valve or a normally closed valve. Furthermore, giving an “opening instruction” to a valve refers to controlling the valve to open regardless of whether the valve type is a normally open valve or a normally closed valve. 
     In the sphygmomanometer of the present disclosure, the abnormality determination unit supplies the fluid to the cuff by the pump in a state where a closing instruction is given to the first valve and an opening instruction is given to the second valve. In this case: 
     (i) For example, as a first case, if the first valve is normal and in a closed state, and the second valve is normal and in an open state, when the fluid is supplied to the cuff by the pump, the degree of increase in the pressure of the cuff is low because the second valve is in an open state. The abnormality determination unit determines that there is no abnormality in the emergency exhaust function according to the result of “low”. 
     (ii) Next, as a second case, if the first valve is normal and in a closed state, and the second valve is abnormal and in a closed state, when the fluid is supplied to the cuff by the pump, the degree of increase in the pressure of the cuff is high because the first and second valves are in a closed state. The abnormality determination unit determines that there is an abnormality in the emergency exhaust function according to the result of “high”. 
     (iii) Next, as a third case, if the first valve is abnormal and in an open state, and the second valve is normal and in an open state, when the fluid is supplied to the cuff by the pump, the degree of increase in the pressure of the cuff is low because the first valve is in an open state. The abnormality determination unit determines that there is no abnormality in the emergency exhaust function according to the result of “low”. 
     (iv) Finally, as a fourth case, if the first valve is abnormal and in an open state, and the second valve is abnormal and in a closed state, when the fluid is supplied to the cuff by the pump, the degree of increase in the pressure of the cuff is low because the first valve is in an open state. The abnormality determination unit determines that there is no abnormality in the emergency exhaust function according to the result of “low”. 
     As a result, in the second case, the blood pressure measurement unit can, for example, stop the blood pressure measurement for the measurement target site according to the determination result that there is an abnormality in the emergency exhaust function. Therefore, it is possible to prevent occurrence of a state where the measurement target site remains compressed for a long time. On the other hand, in the first case, the third case, and the fourth case, the blood pressure measurement unit can start blood pressure measurement for the measurement target site according to the determination result that there is no abnormality in the emergency exhaust function. However, in the third case and the fourth case, since the first valve is abnormal and remains in an open state, the pressure of the cuff does not increase even when the blood pressure measurement unit operates the pump to supply the fluid to the cuff (typically, a measurement error occurs). Therefore, it is possible to prevent occurrence of a state where the measurement target site remains compressed for a long time. In the first case, the blood pressure measurement unit can measure the blood pressure of the measurement target site by controlling the operations of the pump and the first and second valves on the basis of the pressure of the cuff output from the pressure sensor. In this case, since the second valve is normal, emergency exhaust can be performed by making the second valve in an open state in an emergency (in case of emergency). In this manner, according to the sphygmomanometer, it is possible to reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     In the sphygmomanometer according to one embodiment, the abnormality determination unit performs the determination process prior to the blood pressure measurement each time the blood pressure measurement unit performs the blood pressure measurement. 
     In the sphygmomanometer according to this one embodiment, the abnormality determination unit performs the determination process prior to the blood pressure measurement each time the blood pressure measurement unit performs the blood pressure measurement. Therefore, it is possible to further reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     In the sphygmomanometer according to one embodiment, when the abnormality determination unit determines that there is an abnormality in the emergency exhaust function, the blood pressure measurement unit stops the blood pressure measurement for the measurement target site, while when the abnormality determination unit determines that there is no abnormality in the emergency exhaust function, the blood pressure measurement unit starts the blood pressure measurement. 
     In the sphygmomanometer according to this one embodiment, when the abnormality determination unit determines that there is an abnormality in the emergency exhaust function, the blood pressure measurement unit stops the blood pressure measurement for the measurement target site. Therefore, it is possible to reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. On the other hand, when the abnormality determination unit determines that there is no abnormality in the emergency exhaust function, the blood pressure measurement unit starts the blood pressure measurement. Here, in the third case and the fourth case, since the first valve is abnormal and remains in an open state, the pressure of the cuff does not increase even when the blood pressure measurement unit operates the pump to supply the fluid to the cuff. Therefore, the blood pressure measurement unit can determine that the first valve is abnormal and a measurement error has occurred according to the degree of increase in the pressure of the cuff, and can stop the measurement according to the determination result. In the first case, when the blood pressure measurement unit operates the pump to supply the fluid to the cuff, the pressure of the cuff increases normally, so that the blood pressure measurement unit can complete the blood pressure measurement. 
     In the sphygmomanometer according to one embodiment,
         the first valve is a normally open valve, and   the second valve is a normally closed valve.       

     In the sphygmomanometer according to this one embodiment, the first valve and the second valve are valves of types different from each other (normally open valve and normally closed valve). Accordingly, the probability of occurrence of an abnormality due to the same failure is low as compared with a case of valves of the same type. Therefore, the reliability of the sphygmomanometer as a product can be enhanced. Furthermore, the first valve for blood pressure measurement is a normally open solenoid valve. Accordingly, it is sufficient that the first valve becomes a closed state upon receiving a closing instruction (actuation instruction) during the blood pressure measurement (a period in which the measurement target site is temporarily compressed by the blood pressure measurement cuff), and it is sufficient that the first valve is not actuated and in an open state during a period other than during the blood pressure measurement. The second valve for emergency exhaust is a normally closed solenoid valve. Accordingly, it is sufficient that the second valve becomes an open state upon receiving an opening instruction (actuation instruction) during the emergency exhaust, and it is sufficient that the second valve is not actuated and in a closed state during a period other than during the emergency exhaust. Therefore, the power consumption of the first valve and the second valve can be reduced. 
     The sphygmomanometer according to one embodiment comprises an automatic measurement mode in which the blood pressure measurement is automatically started according to a schedule set in advance, wherein
         in the automatic measurement mode, the abnormality determination unit performs the determination process prior to the blood pressure measurement each time the blood pressure measurement unit performs the blood pressure measurement according to the schedule.       

     In the automatic measurement mode, if the second valve for emergency exhaust is failed in an emergency (in case of emergency), there is a possibility that a state occurs in which the measurement target site remains compressed for a long time. Therefore, in the sphygmomanometer according to this one embodiment, in the automatic measurement mode, the abnormality determination unit performs the determination process prior to the blood pressure measurement each time the blood pressure measurement unit performs the blood pressure measurement according to the schedule. Therefore, it is possible to reliably prevent a situation in which a state occurs where the measurement target site remains compressed for a long time while the subject is unconscious. 
     The sphygmomanometer according to one embodiment comprises a regular blood pressure measurement mode in which the blood pressure measurement is performed in response to an input blood pressure measurement instruction, wherein in the regular blood pressure measurement mode, the abnormality determination unit does not perform the determination process, and the blood pressure measurement unit measures the blood pressure of the measurement target site in response to the input blood pressure measurement instruction. 
     In the regular blood pressure measurement mode, if the abnormality determination unit performs the determination process prior to the blood pressure measurement each time the blood pressure measurement unit performs the blood pressure measurement, a time period required for one blood pressure measurement (here, it means a total time period of a time period required for the determination process and a time period required for an actual blood pressure measurement) becomes long as a whole. On the other hand, in the regular blood pressure measurement mode, since the measurement subject is in an awake state, it can be said that performing the determination process is less significant than in a case where the measurement of the blood pressure is started according to the schedule set in advance while a subject is sleeping (nighttime) as in the nighttime sphygmomanometer, for example. Therefore, in the sphygmomanometer according to this one embodiment, in the regular blood pressure measurement mode, the abnormality determination unit does not perform the determination process, and the blood pressure measurement unit measures the blood pressure of the measurement target site in response to the input blood pressure measurement instruction. Therefore, the time required for one blood pressure measurement becomes short as a whole as compared with the case where the abnormality determination unit performs the determination process prior to the blood pressure measurement each time the blood pressure measurement unit performs the blood pressure measurement. 
     In the sphygmomanometer according to one embodiment,
         when a transition instruction to transition to the automatic measurement mode is input, the abnormality determination unit performs the determination process in response to the transition instruction, and   when determining that there is an abnormality in the emergency exhaust function, the abnormality determination unit prohibits the sphygmomanometer from transitioning to the automatic measurement mode, while when determining that there is no abnormality in the emergency exhaust function, the abnormality determination unit allows the sphygmomanometer to transition to the automatic measurement mode.       

     In the sphygmomanometer according to this one embodiment, when a transition instruction to transition to the automatic measurement mode is input, the abnormality determination unit performs the determination process in response to the transition instruction. Then, when determining that there is an abnormality in the emergency exhaust function, the abnormality determination unit prohibits the sphygmomanometer from transitioning to the automatic measurement mode, while when determining that there is no abnormality in the emergency exhaust function, the abnormality determination unit allows the sphygmomanometer to transition to the automatic measurement mode. Therefore, it is possible to further reliably prevent a situation in which a state occurs where the measurement target site remains compressed for a long time while the subject is unconscious. 
     Note that, the “transition instruction” to transition to the automatic measurement mode is input via, for example, a switch as an operation unit provided on the main body of the sphygmomanometer. 
     The sphygmomanometer according to one embodiment comprises a notification unit that notifies that there is an abnormality in the emergency exhaust function when the abnormality determination unit determines that there is an abnormality in the emergency exhaust function. 
     In the sphygmomanometer according to this one embodiment, when the abnormality determination unit determines that there is an abnormality in the emergency exhaust function, the notification unit notifies that there is an abnormality in the emergency exhaust function. With this notification, the user (typically, the subject) knows that there is an abnormality in the emergency exhaust function, and for example, can take measures such as requesting a service department of a sphygmomanometer manufacturer to perform maintenance service. 
     In the sphygmomanometer according to one embodiment,
         the blood pressure measurement unit and the abnormality determination unit are constituted of a programmed first processor and a programmed second processor different from the first processor,   the first valve is driven by the first processor, and   the second valve is driven by the second processor.       

     In the sphygmomanometer according to this one embodiment, even when an abnormality has occurred in either one of a set of the first processor and the first valve or a set of the second processor and the second valve, if the other set is normal, the exhaust from the cuff can be performed. Therefore, it is possible to further reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     In another aspect, a blood pressure measurement method of the present disclosure is a blood pressure measurement method for performing blood pressure measurement by temporarily compressing a measurement target site by a blood pressure measurement cuff, comprising:
         a pump that supplies a fluid to the cuff to pressurize the cuff;   a pressure sensor that detects a pressure of the cuff;   a first valve for regular measurement that discharges the fluid from the cuff to depressurize the cuff during blood pressure measurement; and   a second valve for emergency exhaust that discharges the fluid from the cuff to depressurize the cuff when an abnormality occurs in which discharge of the fluid by the first valve is not normally performed,   the blood pressure measurement method comprising:   a measurement step of measuring a blood pressure of the measurement target site by controlling operations of the pump and the first and second valves on a basis of the pressure of the cuff output from the pressure sensor; and   a determination step of supplying the fluid to the cuff by the pump in a state where a closing instruction is given to the first valve and an opening instruction is given to the second valve, and determining whether or not there is an abnormality in an emergency exhaust function according to a degree of increase in the pressure of the cuff, as a step performed prior to the measurement step each time the measurement step is performed.       

     According to the blood pressure measurement method of the present disclosure, it is possible to reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. 
     In yet another aspect, a computer-readable recording medium according to the present disclosure is a non-transitorily computer-readable recording medium 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 a computer to execute the program, the 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 is possible to reliably prevent occurrence of a state where the measurement target site remains compressed for a long time. Furthermore, according to the program stored in the computer-readable recording medium of the present disclosure, it is possible to cause a computer to implement such a blood pressure measurement method. 
     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.