Patent Publication Number: US-2020303077-A1

Title: Monitoring apparatus, monitoring method, and monitoring program

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Japanese Patent Application No. 2017-181194 filed on Sep. 21, 2017, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a monitoring apparatus, a monitoring method, and a monitoring program. 
     BACKGROUND 
     Information provision systems which advise a user to stop movement based on biological information of the user and environmental information of the surroundings of the user are known (for example, see PTL 1). 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2013-220182 A 
     SUMMARY 
     A monitoring apparatus according to an embodiment of the present disclosure comprises an acquisition unit, a controller, and a notification interface. The acquisition unit is configured to acquire biological information of a subject. The controller is configured to determine whether the subject has disease development risk, based on a result of analyzing the biological information of the subject. The notification interface is configured to notify information about the disease development risk. 
     A monitoring method according to an embodiment of the present disclosure comprises: acquiring biological information of a subject; determining whether the subject has disease development risk, based on a result of analyzing the biological information of the subject; and notifying information about the disease development risk. 
     A monitoring program according to an embodiment of the present disclosure is configured to cause a processor to: acquire biological information of a subject; determine whether the subject has disease development risk, based on a result of analyzing the biological information of the subject; and notify information about the disease development risk. 
     A monitoring apparatus according to an embodiment of the present disclosure comprises an information acquisition unit, a notification interface, and a controller. The information acquisition unit is configured to acquire information about an altitude of a subject. The notification interface is configured to notify the subject of predetermined information. The controller is configured to control the notification interface to notify the subject of the predetermined information, in a case of determining, based on the information about the altitude, that the subject has disease development risk. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a block diagram illustrating an example of the schematic structure of a monitoring apparatus according to an embodiment; 
         FIG. 2  is a diagram illustrating an example of the connection between the monitoring apparatus and a sensor; 
         FIG. 3  is a flowchart illustrating an example of a procedure for a monitoring method; 
         FIG. 4  is a conceptual diagram illustrating an example of a data structure stored in a memory; 
         FIG. 5  is a conceptual diagram illustrating an example of the data structure stored in the memory; 
         FIG. 6  is a flowchart illustrating an example of a procedure for determining biological information in stages; 
         FIG. 7  is a flowchart illustrating an example of a procedure for determining development of mountain sickness; 
         FIG. 8  is a flowchart illustrating an example of a mountain sickness determination procedure according to the present disclosure; 
         FIG. 9  is a block diagram illustrating an example of a structure in which the monitoring apparatus and a server are connected; 
         FIG. 10  is a block diagram illustrating an example of the internal structure of the server illustrated in  FIG. 9 ; 
         FIG. 11  is a schematic diagram of a sensor of a first example used in the present disclosure; 
         FIG. 12  is a schematic diagram of a sensor of a second example used in the present disclosure; 
         FIG. 13  is a block diagram illustrating an example of the schematic structure of a monitoring apparatus according to another embodiment; 
         FIG. 14  is a flowchart illustrating an example of a procedure for a monitoring method; 
         FIG. 15  is a flowchart illustrating another example of the procedure for the monitoring method; and 
         FIG. 16  is a diagram illustrating an example of the correlation between altitude changes and SpO 2  changes. 
     
    
    
     DETAILED DESCRIPTION 
     Support for health management of a user is desired in order to enable the user to continue movement. The present disclosure relates to provision of a monitoring apparatus, a monitoring method, and a monitoring program that can support health management of a user. A monitoring apparatus, a monitoring method, and a monitoring program according to an embodiment can support health management of a user. Embodiments of the present disclosure will be described below, with reference to the drawings. 
     As illustrated in  FIG. 1 , a monitoring apparatus  1  according to an embodiment includes a controller  10 , a memory  12 , an acquisition unit  20 , and a notification interface  30 . The monitoring apparatus  1  may further include an input interface  40  that receives input from a user. The monitoring apparatus  1  is connected to an external sensor  50  via the acquisition unit  20 . The monitoring apparatus  1  may include the sensor  50 . The sensor  50  is worn by the user, and detects biological information of the user. The monitoring apparatus  1  can monitor changes in the body condition of the user, based on the biological information of the user detected by the sensor  50 . A user whose biological information is detected by the sensor  50  is also referred to as a subject. 
     The controller  10  can control or manage each component of the monitoring apparatus  1 . The controller  10  can transmit control information to each component of the monitoring apparatus  1 , and acquire control information from each component. The controller  10  may include at least one processor such as a central processing unit (CPU) for executing a program defining a control procedure. The controller  10  may store the program and the like in the memory  12 . The controller  10  may include the memory  12 . 
     The at least one processor may include a single integrated circuit (IC) or a plurality of communicably-connected ICs or discrete circuits. The at least one processor may be implemented based on various known technologies. For example, the processor may include one or more circuits or units configured to perform one or more processes based on instructions stored in the memory  12  or a storage medium. The processor may be implemented as firmware for performing one or more processes. The firmware may be, for example, a discreet logic component. 
     The processor may include one or more processors, controllers, microprocessors, microcontrollers, application specific ICs, digital signal processors, programmable logic devices, or field programmable gate arrays. The processor may include any combination of these devices or configurations or combinations of other known devices and configurations. 
     The memory  12  may be semiconductor memory, magnetic memory, or the like. The memory  12  may store various information used in the controller  10 , programs for operating the components in the monitoring apparatus  1 , and the like. The memory  12  may function as working memory of the controller  10 . 
     The acquisition unit  20  acquires the biological information of the subject from the sensor  50 , and outputs the biological information to the controller  10 . The controller  10  may store the biological information of the subject in the memory  12 . The controller  10  may store the biological information of the subject in the memory  12 , together with information about the time of detection by the sensor  50 . The acquisition unit  20  may include a communication device. The communication device may be, for example, a communication interface of a local area network (LAN) or the like. The communication device may be communicably connected to an external apparatus, by wire or wirelessly. The acquisition unit  20  may be communicably connected to the sensor  50  by the communication device. The acquisition unit  20  may be included in the controller  10 . 
     The sensor  50  may include a device that detects the breathing rate of the subject in a predetermined time period. The sensor  50  may include a device that detects the body temperature of the subject. The sensor  50  may include a device that detects the percutaneous oxygen saturation of the subject. The percutaneous oxygen saturation is also simply referred to as oxygen saturation. The percutaneous oxygen saturation is also referred to as SpO 2 . S represents saturation, p represents pulse oximeter (pulse oximetry) or percutaneous, and O 2  represents oxygen. The sensor  50  may include a device that detects the pulse rate of the subject in a predetermined time period. The sensor  50  may include a device that detects the blood pressure of the subject. The sensor  50  may include a device that detects the blood flow amount of the subject. The sensor  50  may include a device that detects the electrical resistance of the body surface. The sensor  50  may include a device that detects brain waves of the subject. 
     The device that detects the blood flow amount will be described below. In the tissues of the living body, scattered light scattered from moving blood cells undergoes a frequency shift by a Doppler effect proportional to the moving speed of the blood cells in the blood. The frequency shift by the Doppler effect is also referred to as a Doppler shift. The controller  10  detects a beat signal generated as a result of light interference between scattered light from static tissues and scattered light from moving blood cells. 
     The beat signal represents intensity as a function of time. The controller  10  converts the beat signal into a power spectrum which represents power as a function of frequency. In the power spectrum of the beat signal, the Doppler shift frequency is proportional to the speed of blood cells. In the power spectrum of the beat signal, the power corresponds to the amount of blood cells. The controller  10  obtains the blood flow amount by multiplying the power spectrum of the beat signal by the frequency and integrating the multiplication result. 
     The notification interface  30  notifies the subject of information based on control information acquired from the controller  10 . The notification interface  30  may include a display device. The display device may be, for example, a liquid crystal display, an organic electroluminescent (EL) display, or an inorganic EL display. The display device is not limited to such, and may be any other device. The notification interface  30  may display text, images, and the like on the display device, to notify the subject of the information based on the control information acquired from the controller  10 . 
     The notification interface  30  may include a light source such as a light emitting diode (LED) or a halogen lamp. The notification interface  30  may notify the surroundings of the information based on the control information acquired from the controller  10 , by illumination or blinking of the light source. The notification interface  30  may include a buzzer such as a piezoelectric buzzer or an electromagnetic buzzer, a speaker for generating predetermined sound, or the like. The notification interface  30  may notify to the surroundings of the information based on the control information acquired from the controller  10 , by buzzer ringing, sound generation, or the like. 
     The input interface  40  may include physical keys such as a keyboard, or a touch panel. The input interface  40  is not limited to such, and may include any of various input devices. 
     For example, the monitoring apparatus  1  may be a smartphone terminal  1   a  or a folding mobile phone terminal  1   b , as illustrated in  FIG. 2 . The monitoring apparatus  1  is not limited to such, and may be any of various types of terminals or devices such as pendant type, wristband type, and eyeglass type. The monitoring apparatus  1  may be a general-purpose terminal or device capable of various functions, or a special-purpose terminal or device. The monitoring apparatus  1  and the monitoring method according to the embodiment may be implemented by executing, in a terminal or a device, a program including a procedure for monitoring the body condition of the subject. The program including the procedure for monitoring the body condition of the subject is also referred to as a monitoring program. The sensor  50  is connected to the monitoring apparatus  1  via a network  80  (see  FIG. 9 ) that is wired, wireless, or a combination thereof, and information and the like are transmitted and received between the sensor  50  and the monitoring apparatus  1 . 
       FIG. 2  illustrates an example of a pulse oximeter of a type worn on the subject&#39;s ear as the sensor  50 . The pulse oximeter is not limited to a type worn on the ear, and may be of a type worn on other parts such as a finger. The sensor  50  is not limited to a pulse oximeter, and may be a device of any of other various types. The sensor  50  may be worn on such parts that do not interfere with the movement of the subject. The sensor  50  may be in a form that does not interfere with the movement of the subject. This improves user friendliness. In the present disclosure, the number of biological sensors provided as the sensor  50  is not limited to one, and a plurality of biological sensors may be provided. For example, the sensor  50  may include any combination of a breathing rate sensor, a SpO 2  sensor, a thermometer, a pulse sensor, a blood flow amount sensor, a blood pressure sensor, a heart rate sensor, and other appropriate biological sensors. These biological sensors may be separated between the sensor  50  and the monitoring apparatus  1  as appropriate. The monitoring apparatus  1  may include part of the biological sensors. For example, the breathing rate sensor may analyze vibrations in the pulse of the subject and detect the breathing rate. The breathing rate sensor may detect the movement of the human body, such as the abdomen, in contact with the human body or without contact, and detect the breathing rate. An example of the breathing sensor which does not contact the human body is an infrared sensor. 
     The monitoring apparatus  1  can monitor the condition of the subject according to the procedure of the flowchart illustrated in  FIG. 3 . As an example, suppose the monitoring apparatus  1  monitors the risk of the subject developing acute mountain sickness during climbing. Acute mountain sickness is also referred to as AMS. Acute mountain sickness is hereafter simply referred to as mountain sickness. Herein, the risk of developing each type of sickness such as mountain sickness or headache, ill health, injury, pain, malfunctioning of any part of the body, mental disturbance, or mental disorder is also referred to as disease development risk. What subsequently develops is referred to as the sickness, the disease, or the like. A person who has developed mountain sickness is unlikely to notice that he or she has developed mountain sickness. A person who has developed severe mountain sickness has a possibility of also developing brain edema, pulmonary edema, or the like concurrently, and slipping into critical condition. As a result of the subject being notified of the disease development risk before he or she develops mountain sickness or before the mountain sickness becomes severe, the subject can implement a coping measure to prevent development of severe mountain sickness. Thus, the health management of the subject can be supported, and the safety of the subject can be ensured easily. 
     The monitoring apparatus  1  is not limited to monitoring the risk of developing mountain sickness, and may monitor the risk of developing various diseases such as venous thrombosis. Venous thrombosis is also referred to as economy class syndrome. The monitoring apparatus  1  can monitor the risk of the subject developing a disease in the absence of subjective symptoms. The monitoring apparatus  1  can monitor the risk of the subject developing a disease that is difficult to recognize. By monitoring the disease development risk, the monitoring apparatus  1  can notify the subject of the risk before the subject develops the disease or before the disease becomes severe, and urge the subject to implement a coping measure. Consequently, the subject can prevent the development of the disease or prevent the disease from becoming severe. 
     The controller  10  sets parameters relating to control of each component in the monitoring apparatus  1  (step S 1 ). The controller  10  may store the set parameters in the memory  12 . The parameters may include a cycle for acquiring the biological information of the subject from the sensor  50 . For example, the cycle for acquiring the biological information may be set in seconds or in minutes, or set to 1 hour or more. The parameters may include information specifying one or more types of biological information to be acquired from the sensor  50 . The parameters may include one or more thresholds used for determination based on the biological information. The parameters are not limited to such, and may include various items. The controller  10  may set the parameters based on the defaults of the monitoring apparatus  1 . The controller  10  may set the parameters based on input from the subject. The controller  10  may set the parameters based on the height, weight, age, sex, etc. of the subject. The controller  10  may set the parameters based on past biological information of the subject stored in the memory  12 . 
     The controller  10  acquires the biological information of the subject from the sensor  50  (step S 2 ). The type(s) of the biological information acquired may be set by the parameters. The biological information may include, for example, the breathing rate, SpO 2 , body temperature, pulse rate, blood pressure, and/or blood flow amount of the subject. 
     Data stored in the memory  12  will be described below, with reference to  FIGS. 4 and 5 .  FIGS. 4 and 5  are conceptual diagrams illustrating an example of data structures  400  and  500  stored in the memory  12 . In the present disclosure, the data structures stored in the memory  12  are not limited to the data structures  400  and  500  illustrated in  FIGS. 4 and 5 . One or more other data elements may be added as appropriate to the data structures  400  and  500  illustrated in  FIGS. 4 and 5 . One or more data elements may be omitted as appropriate from the data structures  400  and  500  illustrated in  FIGS. 4 and 5 . 
     As illustrated in  FIG. 4 , the data structure  400  stored in the memory  12  may include user ID  410 , measurement date and time  412 , breathing rate  414 , SpO 2    416 , body temperature  418 , pulse rate  420 , blood pressure  422 , blood flow amount  424 , position  426 , etc., as data elements. In the data structure  400 , the user ID  410  and the measurement date and time  412  may be main keys. The user ID  410  may be data identifying the subject. The measurement date and time  412  may be data about the date and time of detection of the biological information of the subject. The breathing rate  414 , the SpO 2    416 , the body temperature  418 , the pulse rate  420 , the blood pressure  422 , and the blood flow amount  424  may be data about the breathing rate, SpO 2 , body temperature, pulse rate, blood pressure, and blood flow amount detected from the subject, respectively. The position  426  may be data about the current position of the subject. The current position of the subject may be expressed by latitude, altitude, longitude, or any combination thereof. The data elements included in the data structure  400  may be data about biological information of the subject. 
     As illustrated in  FIG. 5 , the data structure  500  stored in the memory  12  may include user ID  530 , name  532 , birth date  534 , age  536 , sex  538 , chronic disease  540 , climbing experience  542 , etc., as data elements. In the data structure  500 , the user ID  530  may be a main key. The data elements included in the data structure  500  may be items about personal information of the subject. The name  532 , the birth date  534 , the age  536 , and the sex  538  may be data about the name, birth date, age, and sex of the subject, respectively. The chronic disease  540  may be data about the name of any disease with which the subject was diagnosed, symptoms which the subject recognized, and the like. The climbing experience  542  may be data about the number of years of climbing experience of the subject, the names and/or number of mountains climbed, and the like. 
     The data elements included in the data structures  400  and  500  may be replaced with each other, or combined into one data structure  400  or  500 . 
     The controller  10  determines whether the subject has disease development risk, based on at least one piece of biological information (step S 3 ). The controller  10  may determine that the subject has disease development risk, in the case where the SpO 2  of the subject is less than a predetermined value. The predetermined value concerning SpO 2  may be, for example, 85%. The predetermined value is, however, not limited to such, and may be determined as appropriate. The controller  10  may determine that the subject has disease development risk, in the case where the body temperature of the subject is greater than or equal to a predetermined value. The predetermined value concerning body temperature may be, for example, 37.0° C. The predetermined value is, however, not limited to such, and may be determined as appropriate. The controller  10  may determine that the subject has disease development risk, in the case where the breathing rate of the subject is outside a predetermined range. That is, the controller  10  may determine that the subject has disease development risk, in the case where the breathing rate of the subject is excessively low or excessively high. The predetermined range concerning breathing rate may be, for example, a range of 10 to 25 per minute. The predetermined range is, however, not limited to such, and may be determined as appropriate. 
     The controller  10  may determine whether the subject has disease development risk, based on results of comparing a plurality of pieces of biological information with respective thresholds. The controller  10  may calculate a score quantifying the disease development risk, based on at least one piece of biological information. The controller  10  may determine that the subject has disease development risk, in the case where the score is greater than or equal to a predetermined value or in the case where the score is less than or equal to a predetermined value. The predetermined value concerning score may be determined as appropriate. 
     The controller  10  may determine whether the subject has disease development risk, based on a result of comparing biological information acquired before a predetermined time point and biological information acquired after the predetermined time point, which are stored in the memory  12 . The controller  10  may determine that the subject has disease development risk, in the case where the difference between the biological information acquired before the predetermined time point and the biological information acquired after the predetermined time point is greater than or equal to a predetermined value. That is, the controller  10  may determine that the subject has disease development risk, in the case where the amount of change of biological information is greater than or equal to the predetermined value. The predetermined value concerning the amount of change of biological information may be determined as appropriate. 
     In the case where the subject does not have disease development risk (step S 3 : NO), the controller  10  returns to step S 2 . In the case where the subject has disease development risk (step S 3 : YES), the controller  10  causes the notification interface  30  to notify the subject of information about the disease development risk (step S 4 ). The information about the disease development risk may include the determination result that the subject has disease development risk. The information about the disease development risk may include information about a coping measure for the disease development risk of mountain sickness. For example, the coping measure may be to urge the subject to use a breathing technique that improves the symptoms of mountain sickness, or to urge the subject to descend the mountain. The coping measure for mountain sickness is not limited to such, and may be any of various measures. The controller  10  may output control information including the contents of the notification to the notification interface  30 . The notification interface  30  may notify the subject of the contents based on the control information, or notify a person in the vicinity of the subject of the contents. After step S 4 , the controller  10  ends the procedure of the flowchart in  FIG. 3 . After step S 4 , the controller  10  may return to step S 1  or S 2 . 
     Examples of the coping measure for the disease development risk of mountain sickness include information regarding a massage technique, information regarding fluid intake, information regarding resting time, and information regarding resting attitude. 
     The monitoring apparatus  1  can notify the subject of information in stages based on the biological information of the subject, according to the procedure of the flowchart illustrated in  FIG. 6 . The monitoring apparatus  1  may notify the subject of information in stages based on comparison results of the SpO 2  of the subject and a plurality of thresholds. The monitoring apparatus  1  may notify the subject of information in stages based on comparison between various biological information other than SpO 2  and a plurality of thresholds. The order of the steps in the flowchart illustrated in  FIG. 6  may be changed as appropriate. 
     The controller  10  sets parameters relating to control of each component in the monitoring apparatus  1  (step S 11 ). The controller  10  may set a threshold to be compared with the SpO 2  of the subject, as a parameter. The controller  10  may set a first threshold, a second threshold, and a third threshold. The number of thresholds is not limited to three, and may be two or less, or four or more. The first threshold is less than the second threshold. The second threshold is less than the third threshold. For example, the first threshold, the second threshold, and the third threshold may be respectively set to 70%, 80%, and 90%. These threshold values are based on the result of demonstration experiments conducted by the inventors at high altitude. The thresholds are not limited to these values, and may be set to other values. 
     The controller  10  acquires the SpO 2  of the subject from the sensor  50  (step S 12 ). 
     The controller  10  determines whether the SpO 2  is less than the first threshold (step S 13 ). In the case where the SpO 2  is less than the first threshold (step S 13 : YES), the controller  10  causes the notification interface  30  to notify first information (step S 14 ). The first information may include information urging the subject to stop climbing and descend the mountain. The first information may include other information. After step S 14 , the controller  10  returns to step S 12 . 
     In the case where the SpO 2  is not less than the first threshold (step S 13 : NO), the controller  10  determines whether the SpO 2  is less than the second threshold (step S 15 ). In the case where the SpO 2  is less than the second threshold (step S 15 : YES), the controller  10  causes the notification interface  30  to notify second information (step S 16 ). The second information may include information urging the subject to use a breathing technique that prevents development of mountain sickness. The breathing technique may be, for example, a pressure breathing technique or an abdominal breathing technique. The breathing technique is not limited to such, and may be any of other various techniques. The second information may include information indicating a specific procedure of the breathing technique. The second information is not limited to these information, and may include other information. After step S 16 , the controller  10  returns to step S 12 . The second information may include information regarding a massage technique, information regarding fluid intake, information regarding resting time, information regarding resting attitude, etc. 
     In the case where the SpO 2  is not less than the second threshold (step S 15 : NO), the controller  10  determines whether the SpO 2  is less than the third threshold (step S 17 ). In the case where the SpO 2  is less than the third threshold (step S 17 : YES), the controller  10  causes the notification interface  30  to notify third information (step S 18 ). The third information may include information urging the subject to rest in order to prevent development of mountain sickness. The third information may include information urging the subject to exercise. The third information may include information urging the subject to receive hydration. The third information is not limited to these information, and may include other information. After step S 18 , the controller  10  returns to step S 12 . In the case where the SpO 2  is not less than the third threshold (step S 17 : NO), the controller  10  returns to step S 12 . The third information may include information regarding a massage technique, information regarding fluid intake, information regarding resting time, information regarding resting attitude, etc. 
     The monitoring apparatus  1  can notify information suitable for the condition of the subject, by determining the biological information based on the thresholds in stages. 
     The monitoring apparatus  1  can perform a more detailed determination of whether the subject has disease development risk based on the biological information of the subject, according to the procedure of the flowchart illustrated in  FIG. 7 . 
     The controller  10  sets parameters relating to control of each component in the monitoring apparatus  1  (step S 21 ). The controller  10  may perform a procedure that is the same as or similar to step S 1  in  FIG. 3 . 
     The controller  10  acquires the biological information of the subject from the sensor  50  (step S 22 ). The controller  10  may perform a procedure that is the same as or similar to step S 2  in  FIG. 3 . 
     The controller  10  determines whether the biological information satisfies a first criterion (step S 23 ). The first criterion may include the breathing rate of the subject being greater than or equal to a predetermined threshold. In the case where the breathing rate of the subject is greater than or equal to the predetermined threshold, there is a possibility that the subject is in a state of hyperpnea. The first criterion may include the breathing rate of the subject being less than a predetermined threshold. In the case where the breathing rate of the subject is less than the predetermined threshold, there is a possibility that the subject is in a state of apnea. The first criterion may include the SpO 2  of the subject being less than a predetermined threshold. In the case where the SpO 2  of the subject is less than the predetermined threshold, there is a possibility that the subject is in a state of hypoxia. The first criterion may include the body temperature of the subject being greater than or equal to a predetermined threshold. In the case where the body temperature of the subject is greater than or equal to the predetermined threshold, there is a possibility that the subject is in a state of feverishness. The first criterion may include the body temperature of the subject being less than a predetermined threshold. In the case where the body temperature of the subject is less than the predetermined threshold, there is a possibility that the subject is in a state of hypothermia. The first criterion is not limited to such, and may include various conditions, and may be a combination of a plurality of conditions. 
     In the case where the biological information does not satisfy the first criterion (step S 23 : NO), the controller  10  returns to step S 22 . In the case where the biological information satisfies the first criterion (step S 23 : YES), the controller  10  determines whether the biological information satisfies a second criterion (step S 24 ). The second criterion may include the same condition as that included in the first criterion, or include a different condition from that included in the first criterion. The second criterion may include the pulse rate of the subject being greater than or equal to a predetermined threshold. In the case where the pulse rate of the subject is greater than or equal to the predetermined threshold, there is a possibility that the subject is in a state of hypoxia. The second criterion may include a condition relating to the autonomic nerve state. The autonomic nerve state can be represented by the balance between the strength of sympathetic nerve activity and the strength of parasympathetic nerve activity. The second criterion may include the difference between the strength of sympathetic nerve activity and the strength of parasympathetic nerve activity being greater than or equal to a predetermined value. The controller  10  may determine the autonomic nerve state based on the biological information of the subject. The controller  10  may determine the autonomic nerve state based on the variation in heartbeat. The controller  10  may determine the autonomic nerve state based on the variation in the electrical resistance of the body surface of the subject. 
     In the case where the biological information does not satisfy the second criterion (step S 24 : NO), the controller  10  returns to step S 22 . In the case where the biological information satisfies the second criterion (step S 24 : YES), the controller  10  causes the notification interface  30  to notify the subject of information about the disease development risk (step S 25 ). The controller  10  may cause the notification interface  30  to notify information urging the subject to input subjective symptoms. 
     The controller  10  receives input of subjective symptoms from the subject by the input interface  40  (step S 26 ). The controller  10  may cause the notification interface  30  to produce a display requesting the subject to answer questions based on the Lake Louise Score (LLS). The questions which the subject is requested to answer are not limited to the LLS-based questions, and may be other various questions. Examples of the subjective symptoms of the subject include physical pain such as headache, decreased appetite, fatigue or a feeling of weariness, dizziness or lightheadedness, and a sleeping state. In the present disclosure, the controller  10  may cause the notification interface  30  to produce a display requesting the subject to answer questions other than the LLS-based questions. 
     The controller  10  determines whether the subject is developing mountain sickness, based on the subjective symptoms of the subject (step S 27 ). The controller  10  may calculate a score quantifying the subjective symptoms of the subject. The controller  10  may calculate a score quantifying the answers of the subject to the LLS-based questions. The controller  10  may determine whether the subject is developing mountain sickness, based on the calculated score. The controller  10  may determine the severity of the mountain sickness developed by the subject, based on the calculated score. 
     In the case where the controller  10  does not determine that the subject is developing mountain sickness (step S 27 : NO), the controller  10  returns to step S 22 . In this case, the controller  10  may cause the notification interface  30  to notify that the likelihood of the subject developing mountain sickness is low. Given that the subject satisfies the second criterion (step S 24 ), for example, the controller  10  may determine that the subject is predicted to develop mountain sickness. Given that the subject satisfies the second criterion (step S 24 ), for example, the controller  10  may cause the notification interface  30  to notify a coping measure for the disease development risk. 
     In the case where the controller  10  determines that the subject is developing mountain sickness (step S 27 : YES), the controller  10  determines the severity of the mountain sickness based on the biological information (step S 28 ). The controller  10  may determine the severity of the mountain sickness based on the blood pressure or blood flow amount of the subject. For example, the controller  10  may determine the severity of the mountain sickness to be higher when the blood pressure of the subject is lower. For example, the controller  10  may determine the severity of the mountain sickness to be higher when the blood flow amount to the brain of the subject is larger. The controller  10  may determine the severity of the mountain sickness based on other various biological information, without being limited to these biological information. The controller  10  may determine the severity of the mountain sickness in stages, by comparing the biological information with a plurality of thresholds as in the procedure of the flowchart in  FIG. 6 . 
     The controller  10  causes the notification interface  30  to notify information about the coping measure for the subject based on the determination result on the severity of the mountain sickness (step S 29 ). The coping measure may be based on the severity of the mountain sickness. For example, the coping measure may be to urge the subject to descend the mountain, to urge the subject or another person to report, or to urge the subject to use a breathing technique that improves the symptoms of mountain sickness. The coping measure for mountain sickness is not limited to such, and may be any of other various measures. After step S 29 , the controller  10  ends the procedure of the flowchart in  FIG. 7 . 
     In the flowchart in  FIG. 7 , any one of steps S 23  and S 24  may be omitted. That is, the controller  10  may advance to step S 25  to notify the disease development risk, in the case where one of the first criterion and the second criterion is satisfied. 
     The monitoring apparatus  1  may determine whether the subject has risk of developing economy class syndrome. The monitoring apparatus  1  may determine whether the subject has risk of developing economy class syndrome, based on the blood flow amount of the subject. The monitoring apparatus  1  may determine whether the subject has risk of developing economy class syndrome based on other various biological information, without being limited to the blood flow amount of the subject. In the case where the subject has risk of developing economy class syndrome, the monitoring apparatus  1  may notify a coping measure to urge the subject to exercise or to urge the subject to receive hydration. The coping measure for economy class syndrome is not limited to such, and may be any of other various measures. 
     A specific mountain sickness determination process will be further described below, with reference to  FIG. 8 .  FIG. 8  is a flowchart of mountain sickness determination according to the present disclosure. The measurement order in the flowchart in  FIG. 8  is an example, and may be changed as appropriate. 
     The controller  10  performs a determination based on the breathing rate, SpO 2 , or body temperature of the subject (step S 701 ). The controller  10  may determine whether the subject is in a state of hyperpnea or apnea, based on the breathing rate of the subject (step S 711 ). The controller  10  may determine the SpO 2  decrease rate, based on the SpO 2  of the subject (step S 713 ). The controller  10  may determine whether the subject is in a state of hypothermia or hyperthermia, based on the body temperature of the subject (step S 715 ). The steps included in step S 701  may be performed in a different order, and any of the steps may be skipped as appropriate. In the case where at least one determination of the determinations in the steps included in step S 701  satisfies the condition, the controller  10  may advance to step S 703 . The controller  10  may store the determination result in each step included in step S 701  or a value obtained by converting the determination result into a score, in the memory  12 . After storing the determination result in the memory  12 , the controller  10  may advance to step S 703  regardless of whether the determination in each step included in step S 701  satisfies the condition. 
     The controller  10  performs the determination based on the autonomic nerve state or pulse rate of the subject (step S 703 ). The controller  10  may determine the degree of relaxation or the decrease rate of the degree of relaxation, based on the autonomic nerve state of the subject (step S 717 ). The controller  10  may determine the condition of the subject, based on the pulse rate of the subject (step S 719 ). The steps included in step S 703  may be performed in a different order, and any of the steps may be skipped as appropriate. In the case where at least one determination of the determinations in the steps included in step S 703  satisfies the condition, the controller  10  may advance to step S 705 . The controller  10  may store the determination result in each step included in step S 703  or a value obtained by converting the determination result into a score, in the memory  12 . After storing the determination result in the memory  12 , the controller  10  may advance to step S 705  regardless of whether the determination in each step included in step S 703  satisfies the condition. 
     The controller  10  performs the determination based on the chief complaint of the subject (step S 705 ). The controller  10  may perform LLS determination based on the chief complaint of the subject (step S 721 ). The controller  10  may advance to step S 707  in the case where the determination in step S 721  satisfies the condition. The controller  10  may store the determination result in step S 721  in the memory  12 , or convert the determination result into a score and store the score in the memory  12 . After storing the determination result in the memory  12 , the controller  10  may advance to step S 707  regardless of whether the determination in step S 721  satisfies the condition. 
     The controller  10  performs the determination based on the blood pressure or blood flow of the subject (step S 707 ). The controller  10  may determine the severity of the subject based on the blood pressure of the subject (step S 723 ). The controller  10  may determine the severity of the subject based on the blood flow of the subject (step S 725 ). The steps included in step S 707  may be performed in a different order, and any of the steps may be skipped as appropriate. In the case where at least one determination of the determinations in the steps included in step S 707  satisfies the condition, the controller  10  may determine that the subject has severe mountain sickness, and end the procedure of the flowchart in  FIG. 8 . The controller  10  may store the determination result in each step included in step S 707  or a value obtained by converting the determination result into a score, in the memory  12 . After storing the determination result in the memory  12 , the controller  10  may end the procedure of the flowchart in  FIG. 8  regardless of whether the determination in each step included in step S 707  satisfies the condition. The controller  10  may advance to the next step after performing the steps included in steps S 701 , S 703 , S 705 , and S 707 . 
     As illustrated in  FIG. 9 , each monitoring apparatus  1  connected to a sensor  50  may be communicably connected to a server  70  via the network  80 . The number of servers  70  is not limited to one, and may be two or more. The number of monitoring apparatuses  1  and the number of sensors  50  are each not limited to two, and may be one, or three or more. The number of sensors  50  connected to one monitoring apparatus  1  is not limited to one, and may be two or more. In the present disclosure, the sensor  50  may be connected to the server  70  without the monitoring apparatus  1  therebetween. The network  80  may be a wired network, a wireless network, or a combination thereof. 
     The server  70  can acquire biological information of a subject detected by a sensor  50 , from each monitoring apparatus  1 . The server  70  may acquire biological information of a plurality of subjects. The server  70  may analyze the acquired biological information using various calculations such as averaging. The server  70  may analyze the acquired biological information by a statistical technique. The server  70  may transmit the analysis result of the biological information to each monitoring apparatus  1 . The monitoring apparatus  1  may set parameters relating to control of each component in the monitoring apparatus  1 , based on the analysis result of the biological information. The server  70  may determine the disease development risk of the subject based on the biological information of the subject, and transmit the determination result to the monitoring apparatus  1 . The monitoring apparatus  1  may notify information based on the determination result of the disease development risk by the server  70 . The server  70  may generate information about a coping measure for the subject based on the biological information of the subject, and transmit the generated information to the monitoring apparatus  1 . The monitoring apparatus  1  may notify the subject of the information about the coping measure generated by the server  70 . 
     The internal structure of the server  70  will be described below, with reference to  FIG. 10 .  FIG. 10  is a block diagram illustrating an example of the internal structure of the server  70  illustrated in  FIG. 9 . 
     The server  70  includes a server controller  71 , a server communication interface  73 , and a server memory  72 . 
     The server controller  71  is a processor that controls and manages the whole server  70 , e.g. each functional block in the server  70 . The server controller  71  includes a processor such as a CPU that executes a program defining a control procedure. Such a program is, for example, stored in the server memory  72  or an external storage medium connected to the server  70 . 
     The server controller  71  includes at least one server processor  711  to provide control and throughput for executing various functions, as described in more detail below. 
     In various embodiments, at least one server processor  711  may be implemented as a single integrated circuit (IC), or as a plurality of ICs and/or discrete circuits communicably connected to one another. At least one server processor  711  can be implemented according to various known technologies. 
     In one embodiment, the server processor  711  includes, for example, one or more circuits or units configured to perform one or more data calculation procedures or processes by executing instructions stored in related memory. In another embodiment, the server processor  711  may be firmware configured to perform one or more data calculation procedures or processes. The firmware may be, for example, a discrete logic component. 
     In various embodiments, the server processor  711  may include one or more processors, controllers, microprocessors, microcontrollers, application specific integrated circuits (ASICs), digital signal processors, programmable logic devices, field programmable gate arrays, or any combination of these devices or structures, or any combination of other known devices or structures, to perform the functions of the server controller  71  described below. 
     The server memory  72  may be semiconductor memory, magnetic memory, or the like. The server memory  72  stores various information, programs for operating the server  70 , and the like. The server memory  72  may function as working memory. 
     Data stored in the server memory  72  may be the same as the data elements in the data structures  400  and  500  illustrated in  FIGS. 4 and 5 . Besides the data illustrated in  FIGS. 4 and 5 , the server memory  72  may store various control programs, application programs, and the like. The server  70  may acquire data from separate subjects each using a sensor  50 . That is, the server memory  72  in the server  70  may store the data illustrated in  FIGS. 4 and 5  for each of a plurality of subjects. 
     Some of the information stored in the server memory  72  may be acquired from a monitoring apparatus  1  or a sensor  50 . Some of the information stored in the server memory  72  may be acquired from another server  70  connected to the server  70  via the network  80 . 
     The server  70  may acquire a result of determining whether a subject has disease development risk, from each monitoring apparatus  1 . The server  70  may acquire disease development risk determination results for a plurality of subjects. The server  70  may analyze each determination result by a statistical method. The server  70  may transmit a result of analyzing the determination result to the monitoring apparatus  1 . The server  70  may generate information to be notified to the subject based on the result of analyzing the determination result, and transmit the generated information to the monitoring apparatus  1 . 
     As a result of the server  70  analyzing biological information of a plurality of subjects, the disease development risk determination accuracy in the monitoring apparatus  1  can be enhanced. 
     The monitoring apparatus  1  may include a position sensor for detecting the position of the monitoring apparatus  1 . The position sensor may acquire the position information of the monitoring apparatus  1  based on, for example, global navigation satellite system (GNSS) technologies including satellite navigation systems such as Global Positioning System (GPS), GLONASS, Galileo, and Quasi-Zenith Satellite System (QZSS). The monitoring apparatus  1  may transmit the position information of the monitoring apparatus  1  to the server  70 . The position information includes latitude, longitude, and altitude information. 
     The server  70  may determine whether the monitoring apparatus  1  is located in a predetermined range, based on the position information of the monitoring apparatus  1 . The server  70  may analyze biological information of a subject or a determination result based on the biological information acquired from each monitoring apparatus  1  located in the predetermined range, by a statistical method. By analyzing whether the determination results in the predetermined range exhibit bias, the possibility that an event which affects the determination results is occurring in the predetermined range can be detected. Consequently, the disease development risk of each subject present in the predetermined range can be determined with higher accuracy. 
     (First Example of Sensor  50 ) 
     The sensor  50  used in the present disclosure is not limited to that illustrated in  FIG. 2 . A sensor  50  of a first example used in the present disclosure will be described below, with reference to  FIG. 11 . 
     As illustrated in  FIG. 11 , the sensor  50  includes a holder  203 L held on the auricle of the left ear of the subject. The sensor  50  also includes a housing  205 L provided at the holder  203 L on the occipital region side of the left ear of the subject. The sensor  50  also includes a measurement unit  201 L provided at the holder  203 L on the face side of the left ear of the subject. The sensor  50  also includes a sensor communication interface  209  having a cable  105  to be connected to a smartphone. In the example in  FIG. 11 , the sensor communication interface  209  is covered by the housing  205 L. Accordingly, the cable  105  extends from the housing  205 L. The cable  105  may be provided at a part other than the housing  205 L. 
     As illustrated in  FIG. 11 , the sensor  50  includes a holder  203 R held on the auricle of the right ear of the subject. The sensor  50  also includes a housing  205 R provided at the holder  203 R on the occipital region side of the right ear of the subject. The sensor  50  also includes a measurement unit  201 R provided at the holder  203 R on the face side of the right ear of the subject. At least one of the measurement units  201 L and  201 R is located, for example, at the temporal region. At least one of the measurement units  201 L and  201 R may be located at a part other than the temporal region. 
     The sensor  50  illustrated in  FIG. 11  also includes a connector  207  connecting the housings  205 L and  205 R. The holder  203 L, the holder  203 R, and the connector  207  may be made of plastic, rubber, cloth, paper, resin, iron, or other material, or any combination thereof. At least one of the housings  205 L and  205 R is located, for example, at the mastoid region. At least one of the housings  205 L and  205 R may be located at a part other than the mastoid region. 
     The sensor  50  in the present disclosure may have, for example, a structure in which at least one of the measurement unit  201 R and the housing  205 R is omitted from the structure illustrated in  FIG. 11 . The sensor  50  in the present disclosure may have, for example, a structure in which at least one of the measurement unit  201 L and the housing  205 L is omitted from the structure illustrated in  FIG. 11 . The sensor  50  in the present disclosure may have, for example, a structure in which the measurement unit  201 R and the housing  205 L are omitted from the structure illustrated in  FIG. 11 . The sensor  50  in the present disclosure may have, for example, a structure in which the measurement unit  201 L and the housing  205 R are omitted from the structure illustrated in  FIG. 11 . 
     At least one of the measurement units  201 L and  201 R includes a breathing rate sensor, a SpO 2  sensor, a body temperature sensor, a pulse wave rate sensor, a blood flow amount sensor, a pulse wave sensor, a heart rate sensor, and the like. 
     (Second Example of Sensor  50 ) 
     A sensor  50  of a second example used in the present disclosure will be described below, with reference to  FIG. 12 . As illustrated in  FIG. 12 , the sensor  50  of the second example is of wristwatch type. The sensor  50  includes a measurement unit  201  located on the side of the body surface of the subject, and a holder  203  worn on the arm of the subject. The measurement unit  201  may be in contact with the body surface of the subject. The measurement unit  201  may include a breathing rate sensor, a SpO 2  sensor, a body temperature sensor, a pulse wave rate sensor, a blood flow amount sensor, a pulse wave sensor, a heart rate sensor, and the like. The holder  203  may be a belt wrapped around the arm of the subject, or have any other form that can be worn by the subject. The holder  203  may be made of plastic, rubber, cloth, paper, resin, iron, or other material, or any combination thereof. 
     The sensor  50  used in the present disclosure is not limited to the foregoing forms. For example, the sensor  50  may be included in any appropriate object such as a wristwatch, a cane, a flashlight, a hat, clothes, pants, shoes, eyeglasses, a helmet, a rucksack, a bag, a water bottle, a compass, a bicycle, an automobile, or a motorcycle. The sensor  50  in the present disclosure may have any appropriate shape such as a clip shape or a band shape. 
     In the sensor  50  in the present disclosure, a breathing rate sensor, a SpO 2  sensor, a body temperature sensor, a pulse wave rate sensor, a blood flow amount sensor, a pulse wave sensor, a heart rate sensor, and the like may be included in one device, or separated between a plurality of devices. 
     The monitoring apparatus  1  in the present disclosure may monitor the physical condition of the user as the subject, by appropriately using information other than biological information, such as position information, atmospheric temperature information, humidity information, weather information, time information, headache frequency, moving distance, and fluid intake. 
     (Notification Destination of Monitoring Apparatus  1 ) 
     In the present disclosure, for example, in the case where the physical condition of the user changes and the determination in step S 13 , S 15 , or S 17  in  FIG. 6  results in YES to thus indicate that the subject is at risk of having symptoms of mountain sickness or the like, the monitoring apparatus  1  or the sensor  50  may notify not only the user but also a person other than the user, a device, a server, and the like. In the case where the determination in step S 13 , S 15 , or S 17  in  FIG. 6  results in YES to thus indicate that the subject is at risk of having symptoms of mountain sickness or the like, the monitoring apparatus  1  may notify, for example, the first information, the second information, or the third information in  FIG. 6  to a person other than the user in a group to which the user using the sensor  50  belongs, a family or a friend of the user using the sensor  50 , a medical institution, an administrative body, or the like. The person other than the user in the group to which the user using the sensor  50  belongs may be, for example, a leader of the group to which the user using the sensor  50  belongs. For example, in the case where the user using the sensor  50  is traveling, the leader may be a tour guide. In the case where the determination in step S 13 , S 15 , or S 17  in  FIG. 6  or step S 27  results in YES to thus indicate that the subject is at some risk of having symptoms of mountain sickness or the like, the monitoring apparatus  1  may notify, for example, information about the risk to a server, a security alarm, a personal computer, a smartphone, a mobile phone, etc. of a person other than the user in a group to which the user using the sensor  50  belongs, a family or a friend of the user using the sensor  50 , a medical institution, an administrative body, or the like. 
     Each sensor  50  described above may be connected to not only a smartphone but also a mobile phone, a music player, a game machine, a personal computer, a server, a tablet terminal, or the like. 
     For example, the presently disclosed technique may be used in situations in which the user is climbing, jogging, running, walking, driving an automobile, driving a motorcycle, driving a bicycle, flying an airplane, steering a ship, or sightseeing. The presently disclosed technique may be used in situations in which the user is driving or riding a train, a bus, an automobile, a motorcycle, a bicycle, an airplane, or a ship. Situations in which the presently disclosed technique is used are not limited to such. 
     (Monitoring Apparatus According to Another Embodiment) 
     A monitoring apparatus according to another embodiment will be described below. 
     As illustrated in  FIG. 13 , a monitoring apparatus  1  according to an embodiment is the same as the monitoring apparatus  1  illustrated in  FIG. 1  in that it includes a controller  10  and a notification interface  30 . The monitoring apparatus  1  illustrated in  FIG. 13  may further include a memory  12 , an acquisition unit  20 , and an input interface  40 , as in the monitoring apparatus  1  illustrated in  FIG. 1 . The monitoring apparatus  1  illustrated in  FIG. 13  is connected to an external sensor  50  via the acquisition unit  20 , as in the monitoring apparatus  1  illustrated in  FIG. 1 . The monitoring apparatus  1  illustrated in  FIG. 13  can monitor changes in the body condition of the user based on the biological information of the user detected by the sensor  50 , as in the monitoring apparatus  1  illustrated in  FIG. 1 . These functional units may be the same as the functional units included in the monitoring apparatus  1  illustrated in  FIG. 1 . Description of parts same as or similar to those described above with regard to the monitoring apparatus  1  illustrated in  FIG. 1  is simplified or omitted as appropriate. 
     The monitoring apparatus  1  illustrated in  FIG. 13  further includes an information acquisition unit  60 . In the monitoring apparatus  1  according to the embodiment, the information acquisition unit  60  acquires information about the altitude of the subject. The information acquisition unit  60  may be a position sensor for detecting the position of the monitoring apparatus  1 , such as a GPS module. The position sensor may acquire the position information of the monitoring apparatus  1  based on, for example, GNSS technologies including satellite navigation systems such as GPS, GLONASS, Galileo, and QZSS, as mentioned above. In this case, the position information acquired by the information acquisition unit  60  includes latitude, longitude, and altitude information. The information acquisition unit  60  can thus acquire the information about the altitude of the subject. 
     The information acquisition unit  60  may estimate the information about the altitude of the subject, by acquiring information of latitude and longitude. For example, with information based on a topographical map of an area including the position of the subject, the information about the altitude of the subject can be estimated from the information of the position (latitude and longitude) of the subject. To enable such estimation, position information and altitude information are associated with each other. For example, information associating position and altitude with each other may be stored in the memory  12  in the monitoring apparatus  1 . In this case, the controller  10  may estimate the information about the altitude of the subject, based on the information of the position (latitude and longitude) acquired by the information acquisition unit  60 . For example, the information associating position and altitude with each other may be stored in the server memory  72  (see  FIG. 10 ). In this case, the information acquisition unit  60  may transmit the acquired information of the position (latitude and longitude) to the server  70 , and the server controller  71  may estimate the information about the altitude of the subject. 
     The information acquisition unit  60  may estimate the information about the altitude of the subject, by acquiring information of the atmospheric pressure of the ambient environment like, for example, an atmospheric pressure sensor. The information acquisition unit  60  may have any structure capable of acquiring the information about the altitude of the subject. 
     Operation of the monitoring apparatus  1  illustrated in  FIG. 13  will be described below. 
     Mountain sickness is known to be likely to occur when the subject enters a state of hypoxia, e.g. when SpO 2  decreases. In particular, the risk of developing mountain sickness is high when the altitude changes (increases or decreases) rapidly while climbing, driving an automobile on mountain roads, or the like. Accordingly, the monitoring apparatus  1  according to the embodiment monitors at least one of the altitude of the subject and/or the biological information of the subject, and notifies predetermined information such as a warning or an alarm in the case where the subject is determined to have disease development risk of mountain sickness. 
     The monitoring apparatus  1  can monitor the condition of the subject according to the procedure of the flowchart illustrated in  FIG. 14 . As an example, suppose the monitoring apparatus  1  monitors the risk of the subject developing mountain sickness during climbing or the like. 
     The controller  10  sets parameters relating to control of each component in the monitoring apparatus  1  (step S 31 ). The controller  10  may store the set parameters in the memory  12 . The parameter setting in step S 31  may be performed in a way same as or similar to the parameter setting in step S 1  in  FIG. 3 . 
     The controller  10  acquires information about the altitude of the subject from the information acquisition unit  60  (step S 32 ). The information about the altitude of the subject may be, for example, information of height such as elevation. For example, in the case where the information acquisition unit  60  is an atmospheric pressure sensor, the information acquisition unit  60  may acquire information of the atmospheric pressure of the ambient environment of the monitoring apparatus  1  including the information acquisition unit  60 . Thus, information of altitude (height) estimated from the information of the atmospheric pressure acquired by the information acquisition unit  60  may be used as the information about the altitude of the subject. 
     The controller  10  determines whether the subject has disease development risk of mountain sickness, based on the information about the altitude of the subject (step S 33 ). The controller  10  may determine that the subject has disease development risk, in the case where the altitude of the subject is greater than or equal to a predetermined altitude, for example, the altitude is 2000 m or more. Thus, the controller  10  may determine that the subject has disease development risk based on the information about the altitude. The controller  10  may determine that the subject has disease development risk, in the case where the altitude of the subject changes (increases or decreases) by a predetermined amount or more, for example, the altitude changes by 200 m or more with respect to 1500 m. Thus, the controller  10  may determine that the subject has disease development risk based on the information about the change of the altitude. The controller  10  may determine that the subject has disease development risk, in the case where the altitude of the subject changes (increases or decreases) by a predetermined amount or more within a predetermined time period, for example, the altitude changes by 300 m or more with respect to 2000 m within 30 minutes. Thus, the controller  10  may determine that the subject has disease development risk based on the information about the change of the altitude within the predetermined time period. In particular, the controller  10  may determine that the subject has disease development risk, in the case where the change of the altitude within the predetermined time period is the predetermined amount or more. 
     In the case where the subject does not have disease development risk (step S 33 : NO), the controller  10  returns to step S 32 . In the case where the subject has disease development risk (step S 33 : YES), the controller  10  causes the notification interface  30  to notify the subject of predetermined information such as information about the disease development risk (step S 34 ). Thus, in the monitoring apparatus  1  according to the embodiment, in the case where the controller  10  determines that the subject has disease development risk based on, for example, the information about the altitude, the controller  10  may control the notification interface  30  to notify the subject of the predetermined information. 
     In step S 34 , the controller  10  may notify, from the notification interface  30 , the subject that the subject has disease development risk, as information such as sound (speech) and/or display (warning light). In step S 34 , the controller  10  may notify, from the notification interface  30 , tactile information such as vibration, instead of or in addition to auditory information and/or visual information. As an example, the controller  10  may notify, from the notification interface  30 , the subject of a message such as “You have risk of mountain sickness” by speech and/or display. As another example, the controller  10  may notify, from the notification interface  30 , the subject of a message such as “Please rest awhile” by speech and/or display. As yet another example, the controller  10  may notify, from the notification interface  30 , the subject of a message such as “Please increase your breathing rate/Please take . . . deep breaths” by speech and/or display. 
     In step S 34 , for example, the controller  10  may notify the server  70  that the subject has risk of mountain sickness. In step S 34 , for example, the controller  10  may notify an external medical institution or clinic that the subject has risk of mountain sickness. 
     Hence, the monitoring apparatus  1  according to the embodiment can reduce the risk of the subject developing mountain sickness during climbing or the like. The monitoring apparatus  1  according to the embodiment can therefore support the health management of the user. 
     The monitoring apparatus  1  may monitor the condition of the subject according to the procedure of the flowchart illustrated in  FIG. 15 . As an example, suppose the monitoring apparatus  1  monitors the risk of the subject developing mountain sickness during climbing or the like in  FIG. 15 , as in  FIG. 14 . 
     The procedure of the flowchart in  FIG. 15  differs from the procedure of the flowchart in  FIG. 14  in that the process of step S 41  is added and the process of step S 33  is changed. 
     The controller  10  sets parameters relating to control of each component in the monitoring apparatus  1  (step S 31 ). The controller  10  may store the set parameters in the memory  12 . The parameter setting in step S 31  may be performed in a way same as or similar to the parameter setting in step S 1  in  FIG. 3 . 
     The controller  10  acquires the biological information of the subject from the sensor  50  (step S 41 ). In step S 41 , the controller  10  may control the acquisition unit  20  to acquire the biological information of the subject from the sensor  50 . That is, the acquisition unit  20  may acquire the biological information of the subject. The type(s) of the biological information acquired may be set by the parameters. The biological information may include at least one of the breathing rate, SpO 2 , oxygen saturation, body temperature, pulse rate, blood pressure, and blood flow amount of the subject. 
     In  FIG. 15 , the process of step S 32  and the process of step S 41  may be performed in reverse order. 
     The controller  10  determines whether the subject has disease development risk, based on at least one piece of biological information (step S 33 ). In step S 33 , the controller  10  may determine whether the subject has disease development risk, based on at least one of the biological information of the subject and the information about the altitude of the subject. 
     The controller  10  may determine that the subject has disease development risk, in the case where the SpO 2  of the subject is less than or equal to a predetermined value, for example, the SpO 2  is 85% or less. Thus, the controller  10  may determine that the subject has disease development risk based on the biological information. The controller  10  may determine that the subject has disease development risk, in the case where the SpO 2  of the subject changes (increases or decreases) by a predetermined amount or more, for example, the SpO 2  changes by 10% or more with respect to 95%. Thus, the controller  10  may determine that the subject has disease development risk based on the change of the biological information. The controller  10  may determine that the subject has disease development risk, in the case where the SpO 2  of the subject changes (increases or decreases) by a predetermined amount or more within a predetermined time period, for example, the SpO 2  changes by 5% or more with respect to 95% within 20 minutes. Thus, the controller  10  may determine that the subject has disease development risk based on the change of the biological information within the predetermined time period. In particular, the controller  10  may determine that the subject has disease development risk, in the case where the change of the biological information within the predetermined time period is the predetermined amount or more. 
     In the case where the subject does not have disease development risk (step S 33 : NO), the controller  10  returns to step S 32 . In the case where the subject has disease development risk (step S 33 : YES), the controller  10  causes the notification interface  30  to notify the subject of predetermined information such as information about the disease development risk (step S 34 ). Thus, in the monitoring apparatus  1  according to the embodiment, in the case where the controller  10  determines that the subject has disease development risk based on, for example, the biological information of the subject such as SpO 2 , the controller  10  may control the notification interface  30  to notify the subject of the predetermined information. 
     In step S 33 , the controller  10  may determine whether the subject has disease development risk, by comparing the biological information acquired by the acquisition unit  20  (from the sensor  50 ) with estimated biological information. 
     As illustrated in  FIG. 16 , in the monitoring apparatus  1  according to the embodiment, the biological information of the subject may be estimated from the information about the altitude of the subject. The upper graph in  FIG. 16  illustrates temporal changes of the altitude of the subject. The controller  10  can recognize temporal changes of the altitude of the subject, by acquiring the information about the altitude of the subject from the information acquisition unit  60  continuously (or at predetermined timings). The altitude of the subject increases until about time t 1 , as illustrated in the upper graph in  FIG. 16 . The altitude of the subject gently decreases after about time t 1 , as illustrated in the upper graph in  FIG. 16 . 
     The controller  10  may estimate SpO 2  illustrated in the lower graph in  FIG. 16 , based on the temporal changes of the altitude of the subject illustrated in the upper graph in  FIG. 16 . In the lower graph in  FIG. 16 , “estimated SpO 2 ” denotes SpO 2  estimated by the controller  10 . The estimated SpO 2  is a result of estimating SpO 2  which the subject is expected to have when undergoing the temporal changes of the altitude illustrated in the upper graph in  FIG. 16 . In  FIG. 16 , SpO 2  is plotted with a dashed line. In the case where, when the subject is undergoing the temporal changes of the altitude illustrated in the upper graph in  FIG. 16 , the SpO 2  of the subject changes like the estimated SpO 2  illustrated in the lower graph in  FIG. 16 , the disease development risk of the subject can be determined to be low. The controller  10  may estimate the SpO 2 , or acquire the SpO 2  estimated by the server  70 . 
     The estimated SpO 2  may be obtained, for example, with reference to past data of the subject. For example, if there is a value of SpO 2  detected when the subject was at the same altitude in the past, the value may be taken to be the estimated SpO 2 . The estimated SpO 2  may be calculated, for example, based on past data of the subject. For example, if there is no value of SpO 2  detected when the subject was at the same altitude in the past but there is a value of SpO 2  detected when the subject was at another altitude, the value of the SpO 2  of the subject at the predetermined altitude may be estimated from such a value and taken to be the estimated SpO 2 . 
     The estimated SpO 2  may be, for example, customized for each subject. In the case where appropriate information of the subject cannot be acquired, a value serving as a model of normal people may be calculated and taken to be the estimated SpO 2 . In this case, for example, the estimated SpO 2  may be calculated based on the sex, age, etc. of the subject. 
     In the lower graph in  FIG. 16 , “acquired SpO 2 ” denotes SpO 2  acquired by the acquisition unit  20  (from the sensor  50 ). 
     In the example in  FIG. 16 , the acquired SpO 2  is greater than the estimated SpO 2  until about time t 1 . In this case, the controller  10  may determine that the disease development risk of the subject is low. In the example in  FIG. 16 , the acquired SpO 2  is less than the estimated SpO 2  from about time t 1  to about time t 2 . In this case, the controller  10  may determine that the disease development risk of the subject is high. In the example in  FIG. 16 , the acquired SpO 2  is greater than the estimated SpO 2  from about time t 2 . In this case, the controller  10  may determine that the disease development risk of the subject is low. Thus, the controller  10  may determine that the subject has disease development risk, based on the estimated biological information of the subject and the biological information of the subject acquired by the acquisition unit  20 . 
     The controller  10  may determine, for example, whether the extent to which the acquired SpO 2  is less than the estimated SpO 2  is greater than or equal to a predetermined value, instead of determining whether the acquired SpO 2  is greater than the estimated SpO 2  or less than the estimated SpO 2 . For example, in the case where the acquired SpO 2  is less than the estimated SpO 2  by 8%, the controller  10  may determine that the disease development risk of the subject is high. Thus, the controller  10  may determine that the subject has disease development risk, in the case where the difference between the estimated biological information and the acquired biological information is greater than or equal to the predetermined value. 
     As a modification of the operation illustrated in  FIG. 15 , the controller  10 , without initially performing detection of biological information by the sensor  50 , may turn the sensor  50  on and start detection when a predetermined altitude, altitude change, or the like is detected. With such control, the sensor  50  need not be constantly on, so that the power consumption of the monitoring apparatus  1  (or the sensor  50 ) can be reduced. 
     Although the embodiments according to the present disclosure have been described by way of the drawings and examples, various changes or modifications may be easily made by those of ordinary skill in the art based on the present disclosure. Such various changes or modifications are therefore included in the scope of the present disclosure. For example, the functions included in the components, steps, etc. may be rearranged without logical inconsistency, and a plurality of components, steps, etc. may be combined into one component, step, etc. and a component, step, etc. may be divided into a plurality of components, steps, etc. Although apparatuses have been mainly described in the embodiments according to the present disclosure, the embodiments according to the present disclosure can also be implemented as methods including the steps executed by the components included in the apparatuses. The embodiments according to the present disclosure can also be implemented as methods or programs executed by processors included in the apparatuses or storage media storing such programs, which are also included in the scope of the present disclosure. 
     Terms such as “first” and “second” in the present disclosure are identifiers for distinguishing components. Components distinguished by terms such as “first” and “second” in the present disclosure may have their numbers interchanged with each other. For example, the identifier “first” of the “first information” and the identifier “second” of the “second information” may be interchanged with each other. The identifiers are replaced with each other simultaneously. The components are distinguishable even after their identifiers are interchanged. The identifiers may be omitted. Components from which identifiers are omitted are distinguished by reference signs. Description of identifiers such as “first” and “second” in the present disclosure alone should not be used for interpretation of order of components or reasoning based on one identifier being smaller than another identifier. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  monitoring apparatus 
               10  controller 
               12  memory 
               20  acquisition unit 
               30  notification interface 
               40  input interface 
               50  sensor 
               60  information acquisition unit 
               70  server 
               71  server controller 
               711  server processor 
               72  server memory 
               73  server communication interface 
               80  network 
               201 ,  201 L,  201 R measurement unit 
               203 ,  203 L,  203 R holder 
               205 ,  205 L,  205 R housing 
               207  connector 
               209  sensor communication interface 
               400 ,  500  data structure