Patent Publication Number: US-2021161401-A1

Title: Electrocardiograph

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage application filed pursuant to 35 U.S.C. 365(c) and 120 as a continuation of International Patent Application No. PCT/JP2019/029028, filed Jul. 24, 2019, which application claims priority from Japanese Patent Application No. 2018-154494, filed Aug. 21, 2018, which applications are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     One aspect of the present invention relates to a portable electrocardiograph, for example. 
     BACKGROUND ART 
     To perform an examination regarding heart diseases such as atrial fibrillation, typically electrocardiographic information of a patient is measured over an extended period of time (e.g. 24 hours) using a portable electrocardiograph, such as a Holter electrocardiograph. To reduce a burden on the patient caused by attaching the electrocardiograph, an electrocardiograph in the form of a garment such as a shirt has been developed (see, for example, Patent Document 1). 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: JP 2014-226367 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In portable electrocardiographs, there is a demand to be able to reduce power consumption while collecting data of electrocardiographic information necessary for the examination regarding heart disease. 
     The present invention has been made with reference to the above circumstances, and an object of an aspect of the present invention is to provide an electrocardiograph that is capable of power saving. 
     Solution to Problem 
     The present invention adopts the following configurations in order to solve the above problems, for example. 
     An electrocardiograph according to an aspect includes an electrocardiographic measurement unit configured to measure electrocardiographic information of a user, a physiological indicator measurement unit configured to measure a physiological indicator of the user, the physiological indicator being different from the electrocardiographic information, a first determination unit configured to determine whether or not the user is in a relaxed state, on the basis of a measurement result of the physiological indicator, and a measurement control unit configured to control the electrocardiographic measurement unit on the basis of a determination result by the first determination unit. 
     Certain abnormalities in the heart, such as atrial fibrillation, are known to be prone to occur when the user is relaxing. The relaxed state refers to the condition in which the parasympathetic nerves are predominately working, or the parasympathetic nerves are estimated to be working predominately. According to the above-described configuration, the measurement of the electrocardiographic information is started when the user is determined to be in the relaxed state. This allows the electrocardiographic information to be measured when the user is in the relaxed state. 
     As a result, the power consumption can be reduced while acquiring data of electrocardiographic information necessary for an examination regarding cardiac abnormalities, such as atrial fibrillation. 
     In another aspect, the physiological indicator may be respiration rate, and the first determination unit may be configured to determine that the user is in the relaxed state in a case where the respiration rate is below a preset threshold and determine that the user is not in the relaxed state in a case where the respiration rate exceeds the threshold. 
     According to the above-described configuration, threshold processing on the measurement result of respiration rate is used to determine whether or not the user is in the relaxed state. Thus, the determination processing can be made simple, and the power consumed in the determination processing is reduced. 
     In another aspect, the measurement control unit may be configured to, in response to the first determination unit determining that the user is in the relaxed state, control the electrocardiographic measurement unit to start measuring the electrocardiographic information and, in response to the first determination unit determining that the user is not in the relaxed state, control the electrocardiographic measurement unit to stop measuring the electrocardiographic information. 
     According to the above-described configuration, it is possible to measure the electrocardiographic information when the user is in the relaxed state, and not to measure the electrocardiographic information when the user is not in the relaxed state. 
     Thus, the power consumption can be reduced while acquiring data of electrocardiographic information necessary for an examination regarding cardiac abnormalities, such as atrial fibrillation, which are prone to occur when the user is in the relaxed state. 
     In another aspect, the measurement control unit may be configured to control the physiological indicator measurement unit to continuously measure the physiological indicator in a time period in which the electrocardiographic measurement unit is not measuring the electrocardiographic information. 
     According to the above-described configuration, it is possible to quickly detect that the user has entered the relaxed state, compared to a configuration in which the physiological indicator is measured periodically. 
     In another aspect, the electrocardiograph may further include a second determination unit configured to determine whether or not the user is in the relaxed state, on the basis of a measurement result of the electrocardiographic information, and the measurement control unit may be configured to, in response to the first determination unit determining that the user is in the relaxed state, control the electrocardiographic measurement unit to start measuring the electrocardiographic information and, in response to the second determination unit determining that the user is not in the relaxed state, control the electrocardiographic measurement unit to stop measuring the electrocardiographic information. 
     According to the above-described configuration, it is determined whether the user is in a relaxed state, based on a measurement result of the electrocardiographic information during measurement of the electrocardiographic information. Therefore, there is no need to drive the physiological indicator measurement unit during measurement of the electrocardiographic information. As a result, power consumption can be reduced. 
     In another aspect, the electrocardiograph may further include a communication control unit configured to transmit a measurement result of the electrocardiographic information to an external device. 
     According to the above-described configuration, the amount of data of the electrocardiographic information is reduced, and thus, the power consumed to transmit the data of the electrocardiographic information is reduced. 
     In another aspect, the electrocardiograph may further include a first notification unit configured to notify the user of a determination result by the first determination unit. 
     According to the above-described configuration, the user can be informed that the user is not in the relaxed state. As a result, the user can be prompted to enter relaxed state. 
     In another aspect, the electrocardiograph may further include a second notification unit, and the physiological indicator measurement unit may be configured to measure a plurality of types of physiological indicators of the user, the plurality of types of physiological indicators being different from the electrocardiographic information, the first determination unit may be configured to, in a case where the first determination unit determines that the user is not in the relaxed state, generate determination information indicating a type of physiological indicator, from among the plurality of types of physiological indicators, being the cause of determination that the user is not in the relaxed state, and the second notification unit may be configured to notify the user of the type of physiological indicator, indicated by the determination information, being the cause of determination that the user is not in the relaxed state. 
     According to the above-described configuration, a user can be informed of the cause of why the user was determined to not be in the relaxed state. As a result, the user can be prompted to enter relaxed state. 
     Advantageous Effects of Invention 
     According to the present invention, an electrocardiograph capable of power saving can be provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram schematically illustrating an electrocardiograph according to an embodiment. 
         FIG. 2  is a block diagram illustrating a hardware configuration of the electrocardiograph illustrated in  FIG. 1 . 
         FIG. 3  is a diagram illustrating the appearance of the electrocardiograph illustrated in  FIG. 1 . 
         FIG. 4  is a block diagram illustrating a software configuration of the electrocardiograph illustrated in  FIG. 1 . 
         FIG. 5  is a flowchart illustrating a method for measuring electrocardiographic information executed by the electrocardiograph illustrated in  FIG. 1 . 
         FIG. 6  is a block diagram illustrating a software configuration of an electrocardiograph according to an embodiment. 
         FIG. 7  is a block diagram illustrating a software configuration of an electrocardiograph according to an embodiment. 
         FIG. 8  is a diagram schematically illustrating an electrocardiograph according to an embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
     Application Example 
     With reference to  FIG. 1 , an example of a case to which the present invention is applied will be described.  FIG. 1  illustrates an example of a portable electrocardiograph  10  according to an embodiment. The electrocardiograph  10  is configured to be attached to a user, for example. The electrocardiograph  10  includes an attachment member  20 , an electrocardiographic measurement unit  30 , a respiration rate measurement unit  40 , a determination unit  50 , and a measurement control unit  51 . 
     In the example of  FIG. 1 , the attachment member  20  is configured as a shirt worn on an upper body of a user and is used to attach the electrocardiograph  10  to a user. 
     The electrocardiographic measurement unit  30  measures the electrocardiographic information of the user. The respiration rate measurement unit  40  measures the respiration rate of the user. The respiration rate is the number of breaths per unit time. The respiration rate measurement unit  40  is an example of a physiological indicator measurement unit that measures a physiological indicator of a user which is different from the electrocardiographic information. The physiological indicator is an indicator associated with a biological information of the user. As described below, the measurement result of the physiological indicator is used to determine whether or not the user is in a relaxed state. Thus, the physiological indicator that is measured by the physiological indicator measurement unit is able to be used to determine whether or not the user is in a relaxed state and, for example, is respiration rate, pulse, heart rate, pulse wave, or the like. The relaxed state refers to the condition in which the parasympathetic nerves are predominately working, or the parasympathetic nerves are estimated to be working predominately. 
     The determination unit  50  determines whether or not the user is in the relaxed state on the basis of the measurement result of the respiration rate output from the respiration rate measurement unit  40 . Specifically, the determination unit  50  determines that the user is in the relaxed state in a case where the respiration rate is below a preset threshold and determines that the user is not in the relaxed state in a case where the respiration rate exceeds the threshold. 
     The measurement control unit  51  controls the electrocardiographic measurement unit  30  and the respiration rate measurement unit  40 . The measurement control unit  51  controls the electrocardiographic measurement unit  30  on the basis of the result of the determination by the determination unit  50 . As an example, the measurement control unit  51  controls the respiration rate measurement unit  40  so as to periodically perform the measurement and, in response to the determination unit  50  determining that the user is in the relaxed state, controls the electrocardiographic measurement unit  30  to start measuring electrocardiographic information and, in response to the determination unit  50  determining that the user is not in the relaxed state, controls the electrocardiographic measurement unit  30  to stop measuring electrocardiographic information. 
     According to the electrocardiograph  10  having the configuration described above, when the user is in the relaxed state, the electrocardiographic information is measured, and when the user is not in the relaxed state, the electrocardiographic information is not measured. Certain abnormalities in the heart, such as atrial fibrillation, are known to be prone to occur when the user is relaxing (when parasympathetic nerves are dominant). Accordingly, the electrocardiograph  10  is controlled to measure electrocardiographic information when atrial fibrillation is prone to occur. Thus, the power consumption can be reduced while acquiring data of electrocardiographic information necessary for an examination regarding cardiac abnormalities, such as atrial fibrillation. 
     Next, the electrocardiograph  10  will be described in detail. 
     Configuration Example 
     Hardware Configuration 
     An example of the hardware configuration of the electrocardiograph  10  will be described with reference to  FIGS. 2 and 3 . In the example of  FIG. 2 , the electrocardiograph  10  includes a control unit  11 , a storage unit  15 , a display device  16 , a power button  17 , a communication interface  18 , a battery  19 , the attachment member  20 , a case  21 , electrodes  31  and  32 , a signal processing circuit  33 , an acceleration sensor  41 , and a signal processing circuit  42 . As illustrated in  FIG. 3 , the case  21 , the electrodes  31  and  32 , and the acceleration sensor  41  are provided in the attachment member  20 . The control unit  11 , the storage unit  15 , the display device  16 , the power button  17 , the communication interface  18 , the battery  19 , the signal processing circuit  33 , and the signal processing circuit  42  are provided in the case  21 . 
     Referring to  FIG. 2 , the control unit  11  includes a central processing unit (CPU)  12 , a random access memory (RAM)  13 , a read only memory (ROM)  14 , and the like and controls each constituent element. For example, the storage unit  15  is an auxiliary storage device such as a semiconductor memory (for example, a flash memory) and stores, in a non-volatile manner, programs executed by the control unit  11 , settings data necessary for executing the programs, electrocardiographic information measurement data, and the like. A storage medium included in the storage unit  15  is a medium that accumulates information such as a program by electrical, magnetic, optical, mechanical, or chemical action so that a computer, a machine, or the like can read the information such as the program being recorded. Note that at least one or all of the programs may be stored in the ROM  14 . 
     The display device  16  includes, for example, one or more light emitting diode (LED) lamps that indicate an operating state. For example, the display device  16  includes an LED lamp that indicates whether or not power is on, an LED lamp that indicates whether or not a communication is possible state, and an LED lamp that indicates the determination result of whether or not the user is in the relaxed state. Note that the display device  16  may include an image display device such as a liquid crystal display device. The power button  17  is a button for switching the power on and off. 
     The communication interface  18  is an interface for communicating with an external device (for example, a smart phone of the user). Typically, the communication interface  18  includes a wireless module compliant with a low power wireless communication protocol such as Bluetooth (trade name). 
     The battery  19  supplies power to each of the constituent elements. Specifically, the battery  19  supplies power to the control unit  11 , the storage unit  15 , the display device  16 , the communication interface  18 , the signal processing circuit  33 , the acceleration sensor  41 , and the signal processing circuit  42 . The battery  19  may be a rechargeable battery. 
     Referring to  FIG. 3 , the electrodes  31  and  32  are provided on the inner circumferential surface of the attachment member  20 . The inner circumferential surface of the attachment member  20  refers to a portion of the surface of the attachment member  20  that faces the user in a state where the electrocardiograph  10  is attached to the user (hereinafter, simply referred to as an attachment state). In the attachment state, the electrodes  31  and  32  come into contact with the body surface of the user. The electrodes  31  and  32  are disposed on the attachment member  20  such that the heart of the user is located between the electrodes  31  and  32  in the attachment state. The electrodes  31  and  32  are formed using, for example, a fiber impregnated with an electrically conductive polymer. The electrodes  31  and  32  are connected to the signal processing circuit  33 . 
     Referring to  FIG. 2 , the signal processing circuit  33  includes an instrumentation amplifier  331 , a low pass filter (LPF)  332 , an amplifier  333 , and an analog-to-digital converter (ADC)  334 . The instrumentation amplifier  331  includes two input terminals, and the electrodes  31  and  32  are respectively connected to the input terminals. The instrumentation amplifier  331  performs differential amplification on the potential of the electrode  31  and the potential of the electrode  32 , and generates a potential difference signal in accordance with the potential difference between the electrode  31  and the electrode  32 . The instrumentation amplifier  331  is an example of a potential difference signal generation unit that generates a potential difference signal indicating the potential difference between the electrode  31  and the electrode  32 . The potential difference signal is filtered by the LPF  332 , amplified by the amplifier  333 , and converted into a digital signal by the ADC  334 . The control unit  11  acquires, as the electrocardiographic information measurement result, the potential difference signal output in a time series from the signal processing circuit  33 . The electrocardiographic information is a waveform signal that indicates the electrical activity of the heart of the user. In this example, the electrodes  31  and  32 , the signal processing circuit  33 , and the control unit  11  constitute the electrocardiograph measurement unit  30  illustrated in  FIG. 1 . 
     Note that the arrangement of the electrodes  31  and  32  is not limited to the example illustrated in  FIG. 3 . Furthermore, three or more electrodes may be provided on the inner circumferential surface of the attachment member  20 , and the electrocardiographic information may be measured using these electrodes. 
     Referring to  FIG. 3 , the acceleration sensor  41  is provided on a portion of the attachment member  20  corresponding to the chest. The acceleration sensor  41  is, for example, a triaxial acceleration sensor and generates an acceleration signal representing acceleration in three directions orthogonal to each other. The output of the acceleration sensor  41  is connected to the signal processing circuit  42 . 
     Referring to  FIG. 2 , the signal processing circuit  42  includes an LPF  421 , an amplifier  422 , and an ADC  423 . The acceleration signal is filtered by the LPF  421 , amplified by the amplifier  422 , and converted into a digital signal by the ADC  423 . The control unit  11  measures the respiration rate on the basis of the acceleration signal output in a time series from the signal processing circuit  42 . In this example, the acceleration sensor  41 , the signal processing circuit  42 , and the control unit  11  constitute the respiration rate measurement unit  40  illustrated in  FIG. 1 . 
     Note that other sensors such as a strain gauge or a piezoelectric sensor may be used instead of the acceleration sensor  41 . 
     Note that, with regard to a specific hardware configuration of the electrocardiograph  10 , constituent elements can be omitted, replaced, and added as appropriate according to the embodiment. For example, the control unit  11  may include a plurality of processors. 
     Software configuration 
     With reference to  FIG. 4 , an example of a software configuration of the electrocardiograph  10  will be described. In the example illustrated in  FIG. 4 , the electrocardiograph  10  includes the determination unit  50 , the measurement control unit  51 , an electrocardiographic information acquisition unit  52 , a respiration rate calculation unit  53 , a communication control unit  54 , a notification unit  55 , and an electrocardiographic information storage unit  57 . The determination unit  50 , the measurement control unit  51 , the electrocardiographic information acquisition unit  52 , the respiration rate calculation unit  53 , the communication control unit  54 , and the notification unit  55  execute the following processing by the control unit  11  of an electrocardiograph  10  executing a program stored in the storage unit  15 . When the control unit  11  executes the program, the control unit  11  deploys the program in the RAM  13 . Then, the control unit  11  causes the CPU  12  to interpret and execute the program deployed in the RAM  13  to control each of the constituent elements. The electrocardiographic information storage unit  57  is realized by the storage unit  15 . 
     The electrocardiographic information acquisition unit  52  acquires, as the electrocardiographic information, a potential difference signal indicating the potential difference between the electrode  31  and the electrode  32  output in a time series from the signal processing circuit  33 , and stores the data of the electrocardiographic information in the electrocardiographic information storage unit  57 . 
     The respiration rate calculation unit  53  calculates the respiration rate on the basis of the acceleration signal output in a time series from the signal processing circuit  42 . A known technique can be used as the method for calculating the respiration rate on the basis of the acceleration signal, and thus detailed descriptions thereof will be omitted. 
     The determination unit  50  determines whether or not the user is in the relaxed state on the basis of the respiration rate calculated by the respiration rate calculation unit  53 . For example, the determination unit  50  determines that the user is in the relaxed state in a case where the respiration rate is below a preset threshold and determines that the user is not in the relaxed state in a case where the respiration rate exceeds the threshold. The respiration rate is defined, for example, as the number of breaths per minute. The threshold is, for example, 13.5 (times/min). 
     The measurement control unit  51  controls the signal processing circuit  33 , the acceleration sensor  41 , and the signal processing circuit  42 . The measurement control unit  51  controls the operation of the acceleration sensor  41  and the signal processing circuit  42  in order to periodically measure the respiration rate. For example, the measurement control unit  51  repeats the process of driving the acceleration sensor  41  and the signal processing circuit  42  for one minute and then deactivating the acceleration sensor  41  and the signal processing circuit  42  for 14 minutes. As a result, the respiration rate is measured in a 15 minute period, and the determination unit  50  determines on the basis of the measurement result of the respiration rate. 
     In response to the determination unit  50  determining that the user is in the relaxed state, the measurement control unit  51  drives the signal processing circuit  33 , and in response to the determination unit  50  determining that the user is not in the relaxed state, the measurement control unit  51  stops the signal processing circuit  33 . The electrocardiographic information is measured during a period in which the signal processing circuit  33  is driven. 
     The communication control unit  54  controls the communication interface  18 . For example, the communication control unit  54  reads the data of the electrocardiographic information from the electrocardiographic information storage unit  57  and transmits the data of the electrocardiographic information to an external device via the communication interface  18 . 
     The notification unit  55  notifies the user of the result of the determination by the determination unit  50 , for example, via the display device  16 . For example, the LED lamp indicating the determination result included in the display device  16  emits blue when the user is in the relaxed state and emits red when the user is not in the relaxed state. Note that the LED lamp may emit light only when the user is not in the relaxed state. The notification unit  55  corresponds to a “first notification unit” of the present invention. 
     Note that, in the present embodiment, the example in which any of the functions of the electrocardiograph  10  is realized by a general-purpose processor is described. However, some or all of the functions may be implemented by one or more dedicated processors. 
     Operation Example 
       FIG. 5  illustrates an example of an operation flow when the electrocardiograph  10  measures electrocardiographic information. 
     In step S 11  of  FIG. 5 , the control unit  11  measures the respiration rate of the user. Specifically, the control unit  11  operates as the respiration rate calculation unit  53  and calculates the respiration rate of the user based on the output of the acceleration sensor  41 . The measurement of the respiration rate is performed periodically. 
     In step S 12 , the control unit  11  functions as the determination unit  50  and determines whether or not the user is in the relaxed state based on the measurement result of the respiration rate. Specifically, the control unit  11  determines that the user is in the relaxed state in the case where the respiratory rate is below a threshold, and otherwise determines that the user is not in the relaxed state. In a case where the control unit  11  determines that the user is in the relaxed state, the process proceeds to step S 13 , and in a case where the control unit  11  determines that the user is not in the relaxed state, the process returns to step S 11 . 
     In step S 13 , the control unit  11  measures the electrocardiographic information of the user. Specifically, the control unit  11  functions as the measurement control unit  51  and drives the signal processing circuit  33 . Then, the control unit  11  functions as the electrocardiographic information acquisition unit  52 , acquires, as the electrocardiographic information, a potential difference signal indicating the potential difference between the electrode  31  and the electrode  32  output from the signal processing circuit  33 , and stores in the electrocardiographic information storage unit  57 . 
     In step S 14 , the control unit  11  measures the respiration rate of the user. As described above, the measurement of the respiration rate is performed periodically. Accordingly, the measurement of the respiration rate is performed even during measurement of the electrocardiographic information. 
     In step S 15 , the control unit  11  functions as the determination unit  50  and determines whether or not the user is in the relaxed state based on the measurement result of the respiration rate. In a case where the control unit  11  determines that the user is in the relaxed state, the process returns to step S 13 , and in a case where the control unit  11  determines that the user is not in the relaxed state, the process proceeds to step S 16 . 
     In step S 16 , the control unit  11  finishes measuring the electrocardiographic information. Specifically, the control unit  11  functions as the measurement control unit  51  and stops the signal processing circuit  33 . Then, the process returns to step S 11 . The process from step S 11  to step S 16  is repeated until the power is turned off 
     In this way, the control unit  11  measures the electrocardiographic information of the user in a period from when it is determined that the user is in the relaxed state until when it is determined that the user is not in the relaxed state. 
     Furthermore, the process procedure illustrated in  FIG. 5  is merely an example and the process procedure and contents thereof can be appropriately changed. For example, the control unit  11  may operate as the communication control unit  54  and transmit the data of the electrocardiographic information obtained in step S 13  to the external device in real-time. 
     The control unit  11  can operate as the notification unit  55 . For example, the control unit  11  may turn on the LED lamp that indicates the determination result in red until it is determined that the user is in the relaxed state in step S 12 . The control unit  11  may turn on the LED that indicates the determination result in blue from when it is determined that the user is in the relaxed state in step S 12  until when it is determined that the user is not in the relaxed state step S 15 . The control unit  11  may turn on the LED lamp that indicates the determination result in red when it is determined that the user is not in the relaxed state in step S 15 . 
     Effects 
     As described above, the electrocardiograph  10  measures the respiration rate of the user and determines whether or not the user is in the relaxed state based on the measurement result of the respiration rate. Then, in a case where it is determined that the user is in the relaxed state, the electrocardiograph  10  starts measuring the electrocardiographic information and, in a case where it is determined that the user is not in the relaxed state, stops measuring the electrocardiographic information. In this manner, it is possible to make the electrocardiographic information to be measured in a time period in which atrial fibrillation is prone to occur, and the electrocardiographic information not measured in other time periods. As a result, data of the electrocardiographic information required for examination regarding atrial fibrillation can be collected while reducing power consumption. Because the amount of data of the electrocardiographic information is reduced, the power consumed to wirelessly transmit the data of the electrocardiographic information can be reduced. 
     Determination of whether the user is in the relaxed state is performed by threshold processing using the measurement result of the respiration rate. The determination processing can be made simple, and thus the power consumed in the determination processing can be reduced. 
     Furthermore, the determination result of whether or not the user is in the relaxed state is notified to the user. This allows the user to be informed that the user is not in the relaxed state. As a result, the user can be prompted to enter relaxed state so that the measurement of the electrocardiographic information is not insufficient. 
     Modified Examples 
     Note that the present invention is not limited to the embodiments described above. 
     In the embodiment described above, the measurement of the respiration rate is performed periodically. In one or more embodiments, the measurement of respiration rate may be performed continuously. In other words, the respiration rate of the user may be constantly monitored. In one or more embodiments, the measurement of the respiration rate may be performed continuously when measurement of the electrocardiographic information is not taking place, and the measurement of the respiration rate may be performed periodically during measurement of the electrocardiographic information. These embodiments are capable of quickly detecting that the user has entered the relaxed state. As a result, the reliability of measuring the electrocardiographic information when the user is in the relaxed state is improved. 
     In one or more embodiments, the electrocardiograph  10  may measure a plurality of types of physiological indicators that are different from the electrocardiographic information and determine whether or not the user is in the relaxed state based on the measurement results. In a case where the control unit  11  determines that the user is not in the relaxed state, the control unit  11  may generate determination information indicating a type of a physiological indicator, from among the plurality of types of physiological indicators, which is the cause of determination that the user is not in the relaxed state. The control unit  11  may operates as a second notification unit, and may notify the user, for example, via the display device  16 , of the type of physiological indicator, indicated by the determination information, which is the cause of determination that the user is not in the relaxed state. The notification may be made by changing the color of the LED lamp. In a case where the display device  16  includes an image display device, the control unit  11  may display, on the image display device, a character string identifying the type of physiological indicator that is the cause of determination that the user is not in the relaxed state. This allows the user to be informed of the cause of determination that the user is not in the relaxed state. As a result, the user can be prompted to enter relaxed state. For example, in a case where the user realizes that the respiration rate is the cause why the user is not in the relaxed state, the user can perform deep breathing or other such actions to enter the relaxed state. 
     In one or more embodiments, during measurement of the electrocardiographic information, whether or not the user is in the relaxed state may be determined on the basis of the measurement result of the electrocardiographic information. This embodiment will be simply described with reference to  FIG. 6 . 
       FIG. 6  illustrates an example of the software configuration of an electrocardiograph according to one or more embodiments. In the example illustrated in  FIG. 6 , the electrocardiograph includes the measurement control unit  51 , the electrocardiographic information acquisition unit  52 , the respiration rate calculation unit  53 , the communication control unit  54 , the notification unit  55 , a first determination unit  61 , a second determination unit  62 , and the electrocardiographic information storage unit  57 . In  FIG. 6 , elements similar to those illustrated in  FIG. 4  are given the same reference signs, and descriptions thereof will be omitted as appropriate. The measurement control unit  51 , the electrocardiographic information acquisition unit  52 , the respiration rate calculation unit  53 , the communication control unit  54 , the notification unit  55 , the first determination unit  61 , and the second determination unit  62  execute predetermined processing by the control unit of an electrocardiograph executing a program stored in the storage unit. 
     The first determination unit  61  corresponds to the determination unit  50  illustrated in  FIG. 4 . Specifically, the first determination unit  61  determines that the user is in the relaxed state in a case where the respiration rate calculated by the respiration rate calculation unit  53  is below a preset threshold, and determines that the user is not in the relaxed state in a case where the respiration rate exceeds the threshold. 
     The second determination unit  62  determines whether or not the user is in the relaxed state based on the electrocardiographic information acquired by the electrocardiographic information acquisition unit  52 . Specifically, the second determination unit  62  calculates an R-R Interval (RRI), which is an interval between adjacent R waves, from the electrocardiographic information, and generates time series data of RRI. Next, the second determination unit  62  calculates the power spectral density from the time series data of RRI using the autoregressive model, calculates the integrated value of power over the frequency range from 0.05 Hz to 0.15 Hz as LF, and calculates the integrated value of power over the frequency range from 0.15 Hz to 0.40 Hz as HF. LF/HF, which is the LF to HF ratio, represents a balance between sympathetic and parasympathetic nerves, with a higher value indicating a sympathetic nerve dominance and a lower value indicating a parasympathetic nerve dominance. The second determination unit  62  determines that the user is in the relaxed state in a case where the LF/HF is below a preset threshold, and determines that the user is not in the relaxed state in a case where the LF/HF is equal to or greater than the threshold. 
     Based on the result of the determination made by the first determination unit  61  and the result of the determination by the second determination unit  62 , the notification unit  55  notifies the user of the determination result of whether or not the user is in the relaxed state. 
     Note that the second determination unit  62  may calculate the heart rate from the electrocardiographic information, and may determine that the user is in the relaxed state in a case where the calculated heart rate value is below a preset threshold and determine that the user is not in the relaxed state in a case where the calculated heart rate value exceeds the threshold. The heart rate refers to the number of times of the heart beats per unit time. 
     The first determination unit  61  operates when the measurement of the electrocardiographic information is not being performed, and the second determination unit  62  operates during measurement of the electrocardiographic information. In this case, there is no need to measure the respiration rate during measurement of the electrocardiographic information. In other words, during measurement of the electrocardiographic information, it is not necessary to drive the signal processing circuit  42 , and no processing is performed by the respiration rate calculation unit  53 . In this manner, power consumption can be reduced. 
     In one or more embodiments, the electrocardiograph  10  may further include a detection unit  71  and a notification unit  72 , as illustrated in  FIG. 7 . The detection unit  71  and the notification unit  72  execute the following processing by the control unit  11  of the electrocardiograph  10  executing a program stored in the storage unit  15 . 
     The detection unit  71  detects that atrial fibrillation has occurred in the heart of the user, on the basis of the electrocardiographic information acquired by the electrocardiographic information acquisition unit  52 . The notification unit  72  notifies the user in response to the detection unit  71  detecting that atrial fibrillation has occurred. The notification can be performed by sound, light, vibration, or the like. This allows the user to realize that atrial fibrillation has occurred. 
     In the embodiment described above, the respiration rate is adopted as a physiological indicator different from the electrocardiographic information. In one or more embodiments, a pulse wave may be adopted as a physiological indicator. 
       FIG. 8  illustrates an example of the electrocardiograph  100  according to an embodiment. In the example of  FIG. 8 , the electrocardiograph  100  is configured to be attached to the upper arm of a user. The electrocardiograph  100  includes an attachment member  120 , an electrocardiographic measurement unit  130 , a pulse wave measurement unit  140 , a determination unit  150 , and a measurement control unit  151 . 
     The attachment member  120  is a member that is wound around the upper arm of the user, and has a band, belt, or roll shape. The electrocardiographic measurement unit  130 , the pulse wave measurement unit  140 , the determination unit  150 , and the measurement control unit  151  are provided in the attachment member  120 . 
     The electrocardiographic measurement unit  130  measures the electrocardiographic information of the user. The electrocardiographic measurement unit  130  includes at least two electrodes on an inner circumferential surface of the attachment member  120 , and the electrocardiographic information is measured using these electrodes. In the attachment state, the electrodes come into contact with the skin of the upper arm of the user. It is generally known that electrocardiographic information can be measured using only multiple electrodes each disposed on any one of the limbs. 
     The pulse measurement unit  140  measures a pulse wave of the user at the upper arm. In one example, the pulse wave measurement unit  140  includes a photoelectric sensor and measures a volume pulse wave with the photoelectric sensor. A known technique can be used as the method for measuring the pulse wave at the upper arm, and thus descriptions thereof will be omitted. The pulse measurement unit  140  outputs a pulse wave signal, which is a waveform signal indicating pulse wave fluctuation. 
     The determination unit  150  determines whether or not the user is in the relaxed state based on the pulse wave signal output from the pulse wave measurement unit  140 . Specifically, the determination unit  150  calculates a peak interval, which is an interval between adjacent peaks, on the basis of the pulse wave signal and generates time series data for the peak interval. Next, the determination unit  150  calculates the power spectral density from the time series data of the peak interval using the autoregressive model, calculates the integrated value of power over the frequency range from 0.05 Hz to 0.15 Hz as LF, and calculates the integrated value of power over the frequency range from 0.15 Hz to 0.40 Hz as HF. The determination unit  150  determines that the user is in the relaxed state in a case where the LF/HF, which is the LF to HF ratio, is below a preset threshold, and determines that the user is not in the relaxed state in a case where the LF/HF is equal to or greater than the threshold. 
     Note that the determination unit  150  may calculate the heart rate on the basis of the pulse wave signal, and may determine that the user is in the relaxed state in a case where the calculated heart rate value is below a preset threshold and determine that the user is not in the relaxed state in a case where the calculated heart rate value exceeds the threshold. 
     The measurement control unit  151  controls the electrocardiographic measurement unit  130  and the pulse wave measurement unit  140 . In response to the determination unit  150  determining that the user is in the relaxed state, the measurement control unit  151  controls the electrocardiographic measurement unit  130  to start measuring the electrocardiographic information. As an example, the measurement control unit  151  controls the pulse wave measurement unit  140  so as to periodically perform the measurement and, in response to the determination unit  150  determining that the user is in the relaxed state, controls the electrocardiographic measurement unit  130  to start measuring electrocardiographic information and, in response to the determination unit  150  determining that the user is not in the relaxed state, controls the electrocardiographic measurement unit  130  to stop measuring electrocardiographic information. 
     According to the electrocardiograph  100  having the configuration described above, the same effects as the electrocardiograph  10  illustrated in  FIG. 1  can be obtained. 
     In short, the present invention is not limited to the embodiment described above as is, and the constituent elements can be modified and embodied within a range that does not depart from the gist in a stage of implementation. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment described above. For example, some constituent elements may be omitted from the entire constituent elements shown in the embodiment. Furthermore, the constituent elements of different embodiments may be combined appropriately. 
     Supplementary Notes 
     A part or the entirety of the embodiment can be described, as described in the following supplementary notes in addition to the scope of the claims, but the present invention is not limited thereto. 
     (Supplementary Note 1) 
     An electrocardiograph ( 10 ), including an electrocardiographic measurement unit ( 30 ) configured to measure electrocardiographic information of a user, a physiological indicator measurement unit ( 40 ) configured to measure a physiological indicator of the user, the physiological indicator being different from the electrocardiographic information, a first determination unit ( 50 ) configured to determine whether or not the user is in a relaxed state on the basis of a measurement result of the physiological indicator, and a measurement control unit ( 51 ) configured to control the electrocardiographic measurement unit on the basis of a determination result by the first determination unit. 
     Reference Signs List 
       10  Electrocardiograph 
       11  Control unit 
       12  CPU 
       13  RAM 
       14  ROM 
       15  Storage unit 
       16  Display device 
       17  Power button 
       18  Communication interface 
       19  Battery 
       20  Attachment member 
       21  Case 
       30  Electrocardiographic measurement unit 
       31 ,  32  Electrode 
       33  Signal processing circuit 
       331  Instrumentation amplifier 
       332  Low pass filter 
       333  Amplifier 
       334  Analog-to-digital converter 
       40  Respiration rate measurement unit 
       41  Acceleration sensor 
       42  Signal processing circuit 
       421  Low pass filter 
       422  Amplifier 
       423  Analog-to-digital converter 
       50  Determination unit 
       51  Measurement control unit 
       52  Electrocardiographic information acquisition unit 
       53  Respiration rate calculation unit 
       54  Communication control unit 
       55  Notification unit 
       57  Electrocardiographic information storage unit 
       61  First determination unit 
       62  Second determination unit 
       71  Detection unit 
       72  Notification unit 
       100  Electrocardiograph 
       120  Attachment member 
       130  Electrocardiographic measurement unit 
       140  Pulse wave measurement unit 
       150  Determination unit 
       151  Measurement control unit