Patent Publication Number: US-2020283150-A1

Title: G tolerance improvement device and control method

Description:
TECHNICAL FIELD 
     The present invention relates to a G tolerance improvement device and a control method thereof. 
     Priority is claimed on Japanese Patent Application No. 2017-181382, filed Sep. 21, 2017, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     Conventionally, airplane pilots sometimes experience abnormal conditions such as decreased visual acuity, loss of consciousness, and central nervous system disorders during airplane turns. These abnormal states (hereinafter referred to as “hypoxic brain conditions”) are caused by the fact that centrifugal acceleration exceeding an allowable amount caused by the turning of an airplane reduces venous return, leading to sufficient oxygen not being supplied to the brain. Therefore, in order to suppress the occurrence of a hypoxic brain state, a device (hereinafter referred to as a “G tolerance improvement device”) that increases the pilot&#39;s resistance to centrifugal acceleration (hereinafter referred to as “G tolerance”) has been used. The G tolerance improvement device is a device including clothing that increases G tolerance, such as a suit that increases G tolerance of the lower body, a vest that increases G tolerance of the upper body, and a helmet that increases G tolerance of the head. In particular, a suit that increases G tolerance is called a G suit. The G tolerance improvement device may also be, for example, a COMBAT EDGE (Combined Advanced Technology Enhanced Design G Ensemble). The airplane may for example be a fighter. 
     A conventional G tolerance improvement device suppresses the occurrence of a hypoxic brain state by sending compressed air into clothing and compressing the pilot. Specifically, for example, the G suit of the G tolerance improvement device has a structure like a trouser-shaped floating ring or life jacket, and is connected to a connector in the cockpit by a hose when boarding. The G tolerance improvement device is provided with an accelerometer, and when the acceleration measured by the accelerometer exceeds a predetermined magnitude, compressed air is fed into the G suit. Such a G tolerance improvement device compresses the lower body of the pilot by sending compressed air into the G suit, thereby lessening a lowering of the blood and so suppressing the occurrence of decreased visual acuity, loss of consciousness, and central nervous system disorders. 
     The G tolerance improvement device provides the same function as such a G suit in clothing such as a vest and a helmet. In this way, the G tolerance improvement device exerts pressure on the lower body, upper body, and head, thereby suppressing the occurrence of a hypoxic brain state. 
     CITATION LIST 
     Non-Patent Document 
     
         
         Non-patent Document 1: Maruyama S., Takahata T., Shoji I., Manabe T., Nishida Y., “Aiming to improve pilot G tolerance” The 19th Annual Meeting of Society of Pathophysiology, Japanese journal of pathophysiology 18(1), 39-41, 2009-05-20 
         Non-patent Document 2: “G-suit.” Wikipedia: Japanese-language version. Retrieved Aug. 23, 2017, from https://ja.wikipedia.org/wiki/%E8%80%90G%E3%82%B9%E3%83% BC%E3%83%84 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, a conventional G tolerance improvement device may not recognize the pilot&#39;s state. For this reason, there was a problem that pressure could not be applied appropriately to the pilot. 
     In view of the above circumstances, the object of the present invention is to provide a technique capable of appropriately applying pressure to a user such as a pilot. 
     Means for Solving the Problems 
     One aspect of the present invention is a G tolerance improvement device includes: an estimation unit that estimates either or both of a body fluid volume in the head of a user and a change amount of the body fluid volume; and a pressurization unit that applies pressure to the user based on either or both of the body fluid volume and the change amount estimated by the estimation unit. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, further provided with: a first electrode unit provided with a first electrode that makes contact with the head of the user; and a second electrode unit provided with a second electrode that makes contact with the user at a location different from the location where the first electrode makes contact, in which the estimation unit estimates either or both of the body fluid volume and the change amount based on the impedance between the first electrode unit and the second electrode unit. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which either one or both of the first electrode unit and the second electrode unit are provided with two or more electrodes. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the head with which the first electrode makes contact is either one or both of the crown or temple region of the head of the user. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the location that the second electrode makes contact with is any one or all of the head, neck, chest, abdomen, waist, and buttocks of the user. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the body fluid volume estimated by the estimation unit is the body fluid volume in the cranium of the user. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the change amount is the venous return. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the estimation unit estimates the body fluid volume, and the pressurization unit applies pressure to the user when the body fluid volume is equal to or less than a first threshold value. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the estimation unit further estimates the change amount, and the pressurization unit applies pressure to the user when the change amount exceeds a second threshold even when the body fluid volume is greater than the first threshold value. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the estimation unit estimates the change amount, and the pressurization unit applies pressure to the user when the change amount exceeds a second threshold value. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the pressurization unit applies pressure to any of the neck, armpits, lower limbs, abdomen, waist, chest, and upper limbs of the user. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the pressurization unit reduces the pressurization amount when the period of applying pressure reaches a predetermined period. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, in which the pressurization unit reduces the pressurization amount when the body fluid volume is equal to or greater than a third threshold value. 
     One aspect of the present invention is the aforementioned G tolerance improvement device, further provided with an accelerometer that measures acceleration applied to the user, in which the estimation unit estimates either or both of the body fluid volume or the change amount when the acceleration is greater than a fourth threshold value. 
     One aspect of the present invention is a control method including: estimating either of a body fluid volume in the head of a user or a change amount of the body fluid volume, and applying pressure to the user on the basis of either or both of the estimated body fluid volume and the change amount. 
     Effects of the Invention 
     With the present invention it is possible to appropriately apply pressure to a user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing showing an example of use of a G tolerance improvement device  1  according to the embodiment. 
         FIG. 2  is a diagram showing a specific example of the configuration of the G tolerance improvement device  1  of the embodiment. 
         FIG. 3  is a flowchart showing a specific processing flow in which the G tolerance improvement device  1  according to the embodiment applies pressure to the user&#39;s neck. 
         FIG. 4  is a diagram illustrating a specific example of a functional configuration when the G tolerance improvement device  1  according to the embodiment is provided with a safety mechanism  1 . 
         FIG. 5  is a flowchart showing a specific processing flow in which the G tolerance improvement device  1  of the embodiment is provided with the first safety mechanism and pressurizes the user&#39;s neck. 
         FIG. 6  is a flowchart showing a specific processing flow in which the G tolerance improvement device  1  of the embodiment is provided with a second safety mechanism and pressurizes the user&#39;s neck. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
       FIG. 1  is a drawing showing an example of use of a G tolerance improvement device  1  of the embodiment. The G tolerance improvement device  1  of the embodiment applies a current or voltage to the head of a user  91  via an electrode to acquire the impedance of the head and thereby estimates the body fluid volume in the cranium and a change amount thereof. The G tolerance improvement device  1  of the embodiment applies a pressure based on the estimated body fluid volume and change amount thereof to the neck of the user  91  to suppress a lowering of the blood, and maintains the body fluid volume of the head of the user  91  at an appropriate amount. Blood volume is an amount having a high correlation to the body fluid volume in the cranium. Therefore, the body fluid volume in the cranium may be, for example, the amount of blood in the cranium. 
     The G tolerance improvement device  1  according to the embodiment is provided with a first electrode unit  11 , a second electrode unit  12 , an accelerometer  13 , a control device  14 , and a pressurization unit  15 . 
     The first electrode unit  11  is provided with an electrode that makes contact with the head of the user  91 . More specifically, the first electrode unit  11  is provided with a first application electrode  111  and a first measurement electrode  112 . The first measurement electrode  112  is located between the first application electrode  111  and a second electrode unit  12 . Provided the first application electrode  111  and the first measurement electrode  112  are in contact with the head of the user  91 , contact may be made by any method. For example, the first application electrode  111  and the first measurement electrode  112  may be in contact with the head of the user  91  wearing a helmet  92  by being attached to the crown of the helmet  92 . Alternatively, the first application electrode  111  and the first measurement electrode  112  may be attached to the helmet  92  and an ear muff  93  of a headphone to make contact with a temple region of the user  91 . By the helmet  92  and the ear muff  93  of the headphone covering a temple region of the user  91 , the first application electrode  111  and the first measurement electrode  112  make contact with a temple region of the user  91 . In addition, for example, by being attached to the crown of a face mask, the first application electrode  111  and the first measurement electrode  112  may make contact with the head of the user  91  wearing the face mask. The helmet  92  is an impact absorbing protector used in an environment where impacts are received. The helmet  92  is not only provided so that the first application electrode  111  and the first measurement electrode  112  are in contact with the user  91 , but is also a head protecting member that protects the user  91  in an environment where impacts are received. 
     In addition, the user  91  may bring the first application electrode  111  and the first measurement electrode  112  into contact with his body by wearing a hood-like cloth to which the first application electrode  111  and the first measurement electrode  112  are attached, and then wear the helmet  92  thereon. 
     A voltage is applied between the first application electrode  111  and the second electrode unit  12  in order to measure the impedance of the head of the user  91 . Therefore, when the first measurement electrode  112  is located between the first application electrode  111  and the second electrode unit  12 , the impedance of the head is measured with high accuracy compared to the case where the first measurement electrode  112  is not located between the first application electrode  111  and the second electrode unit  12 . 
     Note that the first measurement electrode  112  is located between the first application electrode  111  and the second electrode unit  12  means the following. A curve connecting the center point of the first application electrode  111  and the center point of the second electrode unit  12  and parallel to the surface of the head of the user  91  is assumed to be an H line. Being located between the first application electrode  111  and the second electrode unit  12  means that a part of the first measurement electrode  112  is located on the H line sandwiched between the center point of the first application electrode  111  and the center point of the second electrode unit  12 . That is, the first measurement electrode  112  may be located at a position below the position shown in  FIG. 1 . 
     However, the first measurement electrode  112  is not necessarily located between the first application electrode  111  and the second electrode unit  12 , and may be located at any position in consideration of the impedance measurement accuracy provided the impedance of the head can be measured. 
     In the G tolerance improvement device  1  of the present embodiment, it is desirable that the first measurement electrode  112  is located between the first application electrode  111  and the second electrode unit  12 . 
     The second electrode unit  12  is provided with an electrode that contacts the neck of the user  91 . More specifically, the second electrode unit  12  is provided with a second application electrode  121  and a second measurement electrode  122 . The second measurement electrode  122  may be located between the second application electrode  121  and the first electrode unit  11 . The second electrode unit  12  does not necessarily need to contact the neck, and may make contact with any location provided the location is one at which the impedance of the head can be measured. For example, the second electrode unit  12  may be attached to the chest, abdomen, waist, or buttocks of the user  91 . Further, the second electrode unit  12  may be attached to any place on the head that differs from the first electrode unit. 
     A voltage is applied between the second application electrode  121  and the first electrode unit  11  in order to measure the impedance of the head of the user  91 . Therefore, when the second measurement electrode  122  is located between the second application electrode  121  and the first electrode unit  11 , the impedance of the head is measured with high accuracy compared with the case where the second measurement electrode  122  is not located between the second application electrode  121  and the first electrode unit  11 . 
     Note that the second measurement electrode  122  being located between the second application electrode  121  and the first electrode unit  11  means the following. A curve connecting the center point of the second application electrode  121  and the center point of the first electrode unit  11  and parallel to the surface of the head of the user  91  is assumed to be an I line. Being located between the second application electrode  121  and the first electrode unit  11  means that a part of the second measurement electrode  122  is located on the I line sandwiched between the center point of the second application electrode  121  and the center point of the first electrode unit  11 . That is, the second measurement electrode  122  may located at a position above the position shown in  FIG. 1 . 
     However, the second measurement electrode  122  is not necessarily located between the second application electrode  121  and the first electrode unit  11 , and may be located at any position in consideration of the impedance measurement accuracy provided the position is one at which the impedance of the head can be measured. 
     In the G tolerance improvement device  1  of the present embodiment, it is desirable that the second measurement electrode  122  is located between the second application electrode  121  and the first electrode unit  11 . 
     The accelerometer  13  measures the acceleration applied thereto and outputs a signal indicating the magnitude of the acceleration (hereinafter referred to as “acceleration signal”). The accelerometer  13  may be located at any position as long as the accelerometer  13  is installed at a location subjected to substantially the same acceleration as that applied to the user  91 . 
     For example, the accelerometer  13  may be attached to the helmet  92  worn by the user  91 , or may be attached to an object that is subjected to substantially the same acceleration as the user  91 , such as a seat of an airplane on which the user  91  has boarded. 
     The control device  14  is electrically connected to the first electrode unit  11  and the second electrode unit  12  and controls the first electrode unit  11  and the second electrode unit  12 . On the basis of the current flowing through the first electrode unit  11  and the second electrode unit  12  and the acceleration signal output from the accelerometer  13 , the control device  14  performs control so that the pressurization unit  15  applies pressure of a predetermined level determined in advance at a location in contact with the pressurization unit  15 . 
     The pressurization unit  15  makes contact with the neck of the user  91  and applies pressure to the neck of the user  91  under the control of the control device  14 . The region to which pressure is applied is not limited to the example of  FIG. 1 . The pressurization unit  15  may apply pressure to other regions instead of the neck or in addition to the neck. Other regions are, for example, the armpits, the lower limbs, the abdomen, the waist, the chest, the upper limbs, and the like. The lower limbs, abdomen, waist, chest, and upper limbs may be pressurized with, for example, a G suit. The region to which pressure is applied may be any of the neck, armpits, lower limbs, abdomen, waist, chest, and upper limbs, or a combination thereof. 
     By the pressurization unit  15  applying pressure to the neck of the user  91  and the like, a decrease in the body fluid volume in the cranium of the user  91  is suppressed, and so the occurrence of an abnormal state in the user  91  such as decreased visual acuity, loss of consciousness, or a central nervous system disorder is suppressed. The pressurization unit  15  may be any unit that applies pressure to the neck of the user  91  and the like. For example, the pressurization unit  15  may be an airbag. The pressurization unit  15  may pressurize the entire circumference of the neck uniformly, may selectively pressurize the front surface of the neck (front neck portion), and may selectively pressurize around the jugular vein. 
       FIG. 2  is a diagram showing a specific example of the configuration of the G tolerance improvement device  1  according to the embodiment. 
     The control device  14  is provided with an application unit  141 , an impedance measurement unit  142 , and a pressurization control unit  143 . 
     The application unit  141  applies a voltage between the first application electrode  111  and the second application electrode  121 . The application unit  141  may be any device as long as a voltage can be applied between the first application electrode  111  and the second application electrode  121 . For example, the application unit  141  may be a voltage source. 
     The impedance measurement unit  142  measures the impedance between the first measurement electrode  112  and the second measurement electrode  122  by acquiring the current flowing through the first measurement electrode  112  and the second measurement electrode  122 . 
     The pressurization control unit  143  controls the pressure applied by the pressurization unit  15  to the user  91  on the basis of the acceleration signal output from the accelerometer  13  and the impedance measured by the impedance measurement unit  142 . More specifically, the pressurization control unit  143  estimates the body fluid volume in the cranium of the user  91  and a change amount of the body fluid volume per unit time based on the impedance measured by the impedance measurement unit  142 . The pressurization control unit  143  controls whether or not the pressurization unit  15  applies pressure to the user  91  on the basis of the estimated body fluid volume and the change amount of the body fluid volume per unit time. The change amount of the body fluid volume may be, for example, the venous return. 
     Note that when the body fluid volume in the cranium is small, since it is difficult for current to flow through the cranium, the impedance of the head becomes larger compared to the case of the body fluid volume being large. Therefore, for example, the pressurization control unit  143  estimates the body fluid volume in the cranium to be small when the impedance measured by the impedance measurement unit  142  is larger than a predetermined impedance. 
       FIG. 3  is a flowchart illustrating a specific processing flow in which the G tolerance improvement device  1  according to the embodiment pressurizes the user&#39;s neck. 
     The accelerometer  13  measures the acceleration and outputs an acceleration signal (Step S 101 ). The pressurization control unit  143  acquires the acceleration signal and determines whether or not the acceleration signal is less than a predetermined value (hereinafter referred to as “reference acceleration”) (Step S 102 ). When the acceleration is equal to or greater than the reference acceleration (Step S 102 : No), the application unit  141  applies a voltage between the first application electrode  111  and the second application electrode  121  (Step S 103 ). The impedance measurement unit  142  acquires a current flowing through the first measurement electrode  112  and the second measurement electrode  122 . The current flowing through the first measurement electrode  112  and the second measurement electrode  122  is a current generated by the voltage applied by the application unit  141 . The impedance measurement unit  142  measures the impedance between the first measurement electrode  112  and the second measurement electrode  122  on the basis of the current value of the acquired current and the voltage applied by the application unit  141  (Step S 104 ). 
     The pressurization control unit  143  acquires the impedance measured by the impedance measurement unit  142 , and estimates the body fluid volume in the cranium of the user  91  and the change amount per unit time (Step S 105 ). The pressurization control unit  143  determines whether or not the body fluid volume that has been estimated (hereinafter referred to as “estimated body fluid volume”) is greater than a predetermined body fluid volume (hereinafter referred to as “reference body fluid volume”) (Step S 106 ). 
     When the estimated body fluid volume is greater than the reference body fluid volume (Step S 106 : Yes), the pressurization control unit  143  determines whether or not the estimated change amount in the body fluid volume (hereinafter referred to as “estimated change amount”) is greater than a predetermined value (hereinafter referred to as “minimum allowable change amount”) (Step S 107 ). 
     The estimated change amount may indicate a decrease amount or an increase amount. When the estimated change amount indicates a decrease amount, the minimum allowable change amount is an amount indicating that, when the estimated change amount is larger than the minimum allowable change amount, there is a high risk of decreased visual acuity, loss of consciousness, a central nervous system disorder, or the like occurring in the user  91 . When the estimated change amount indicates an increase amount, the minimum allowable change amount is an amount indicating that, when the estimated change amount is larger than the minimum allowable change amount, there is a high risk of an increase in intracranial pressure, brain damage, or the like occurring in the user  91 . When inverse G occurs, the body fluid volume may increase rapidly. Reverse G indicates upward G. 
     When the estimated change amount is larger than the minimum allowable change amount (Step S 107 : Yes), the pressurization control unit  143  controls the pressurization unit  15  to apply pressure to the user  91  (Step S 108 ). 
     More specifically, when downward G is applied and the estimated change amount indicates a decrease amount, the pressurization control unit  143  applies pressure to the user  91 . Alternatively, when pressure is already being applied, the pressurization control unit  143  increases the pressurization amount. When upward G (reverse G) is applied and the estimated change amount indicates an increase amount, the pressurization control unit  143  applies pressure to the user  91 . Alternatively, when pressure is already being applied, the pressurization control unit  143  increases the pressurization amount. 
     In this way, even if the estimated body fluid volume is larger than the reference body fluid volume, the pressurization control unit  143  increases the pressurization amount applied to the user  91  when the estimated change amount is larger than the minimum allowable change amount. This suppresses the movement of body fluid to the head. Based on the change amount of the body fluid volume, the pressurization amount can be appropriately controlled without being affected by individual differences in body fluid volume. 
     It should be noted that the pressurization unit  15  may adjust the region to which pressure is applied and the manner in which the pressure is applied depending on whether the estimated change amount indicates a decrease amount or an increase amount. For example, when reverse G is applied and the estimated change amount indicates an increase amount, the pressurization unit  15  applies pressure to both sides of the neck. In this case, the pressurization unit  15  may apply pressure to both sides of the neck and reduce the pressurization amount to the lower limbs and the abdomen. Thereby, movement of bodily fluid can be appropriately suppressed. 
     On the other hand, in Step S 106 , when the estimated body fluid volume is equal to or less than the reference body fluid volume (Step S 106 : No), the pressurization control unit  143  controls the pressurization unit  15  to apply pressure to the user  91  (Step S 108 ). 
     In this way, the pressurization control unit  143  applies pressure to the user  91  when the estimated body fluid volume is equal to or less than the reference body fluid volume or when the estimated change amount is larger than the minimum allowable change amount. 
     On the other hand, when the estimated change amount is equal to or less than the minimum allowable change amount in Step S 107  (Step S 107 : No), the pressurization control unit  143  controls the pressurization unit  15  so that the pressurization unit  15  lowers the pressure applied to the user  91  (Step S 109 ). In addition, when the pressurization unit  15  does not apply pressure to the user  91 , the pressure of the pressurization unit  15  does not become lower than that. 
     In this way, when pressure is applied to the user  91 , the pressurization control unit  143  decreases the pressurization amount when the estimated change amount is less than or equal to the minimum allowable change amount. Alternatively, when no pressure is applied to the user  91 , the pressurization control unit  143  does not apply pressure to the user  91  while the estimated change amount is less than or equal to the minimum allowable change amount. 
     On the other hand, when the acceleration is smaller than the reference acceleration in Step S 102  (Step S 102 : Yes), the pressurization control unit  143  controls the pressurization unit  15  to reduce the pressure applied to the user  91  by the pressurization unit  15  (Step S 109 ). In addition, when the pressurization unit  15  does not apply pressure to the user  91 , the pressure of the pressurization unit  15  does not become lower than that. 
     In this way, when the acceleration is equal to or greater than the reference acceleration, the pressurization control unit  143  applies pressure to the user  91  in accordance with the estimated body fluid volume and change amount. Accordingly, it is possible to suppress the application of pressure to the user  91  when the acceleration is less than the reference acceleration. Further, the pressurization control unit  143  can reduce the processing load when the acceleration is less than the reference acceleration. 
     If pressure is applied from the pressurization unit  15  to the neck continuously for a long time, excessive body fluid builds up in the head and neck, leading to the possibility of the user  91  entering a dangerous state. For this reason, the G tolerance improvement device  1  is further provided with a timer  144  in addition to the functional parts of  FIG. 3 . It is desirable that the G tolerance improvement device  1  be provided with a safety mechanism (hereinafter referred to as a “first safety mechanism”) that automatically reduces the pressurization amount by the pressurizing unit  14  after a certain time (hereinafter referred to as a “limit time”) has elapsed from the start of pressurization according to the timer. Further, it is desirable that the G tolerance improvement device  1  be provided with a safety mechanism (hereinafter referred to as a “second safety mechanism”) that quickly decreases the pressurization amount when excessive buildup of body fluid is detected on the basis of the impedance value. Thereby, the possibility that the user  91  will be in the above dangerous state can be reduced. The excessive buildup of body fluid means that body fluid exceeding a predetermined body fluid volume is built up in the skull (hereinafter referred to as “allowable body fluid volume”). 
       FIG. 4  is a diagram illustrating a specific example of a functional configuration when the G tolerance improvement device  1  of the embodiment is provided with the safety mechanism  1 . 
     The G tolerance improvement device  1  provided with the safety mechanism  1  is provided with a timer  144  in addition to the functional units shown in  FIG. 2 . The timer  144  measures the time from the time origin, with the time at which the G tolerance improvement device  1  started applying pressure to the user  91  serving as the time origin. The timer  144  outputs the measured time to the pressurization control unit  143 . For example, the timer  144  measures the time from the time origin, with the time at which the pressurization control unit  143  started controlling the pressurization unit  15  being the time origin. 
       FIG. 5  is a flowchart showing a specific processing flow of applying pressure to the user&#39;s neck when the G tolerance improvement device  1  of the embodiment is provided with the first safety mechanism. The flowchart of  FIG. 5  differs from the flowchart of  FIG. 3  on the point of the process of Step S 110  being provided immediately after the process of Step S 108  in the flowchart of  FIG. 3 . It should be noted that in the processing of  FIG. 5 , the same processes as those in  FIG. 3  are denoted by the same reference numerals, with descriptions thereof being omitted. 
     In Step  108 , after the pressurization control unit  143  controls the pressurization unit  15  to apply pressure to the user  91 , the pressurization control unit  143  acquires the time measured by the timer  144  (hereinafter referred to as “timer time”). The pressurization control unit  143  determines whether or not the timer time is equal to or longer than the limit time (Step S 110 ). When the timer time is equal to or longer than the limit time (Step S 110 : Yes), the pressurization control unit  143  controls the pressurization unit  15  to reduce the pressure applied to the user  91  by the pressurization unit  15  (Step S 109 ). On the other hand, when the timer time is shorter than the limit time (Step S 110 : No), the processing of the G tolerance improvement device  1  returns to the process of Step S 101 . 
       FIG. 6  is a flowchart showing a specific processing flow of applying pressure to the user&#39;s neck when the G tolerance improvement device  1  of the embodiment is provided with the second safety mechanism. The flowchart of  FIG. 6  differs from the flowchart of  FIG. 3  on the point of the process of Step S 111  being provided between the process of Step S 106  and the process of Step S 107  in the flowchart of  FIG. 3 . It should be noted that in the processing of  FIG. 6 , the same processes as those in  FIG. 3  are denoted by the same reference numerals, with descriptions thereof being omitted. 
     When it is determined in Step S 106  that the estimated body fluid volume is greater than the reference body fluid volume (Step S 106 : Yes), the pressurization control unit  143  determines whether or not the estimated body fluid volume is equal to or greater than the allowable body fluid volume (Step S 111 ). As described above, the allowable body fluid volume is a limit amount when body fluid is excessively built up in the cranium. When downward G is applied and the estimated body fluid volume is equal to or greater than the allowable body fluid volume (Step S 111 : Yes), the pressurization control unit  143  controls the pressurization unit  15  to lower the pressure applied by the pressurization unit  15  to the user  91  (Step S 109 ). In this way, it is possible to achieve a reduction in the body fluid by detecting that an excessive buildup of body fluid in the cranium has been detected and reducing the pressurization amount. On the other hand, when the estimated body fluid volume is a value smaller than the allowable body fluid volume (Step S 111 : No), the G tolerance improvement device  1  performs the process of Step S 107 . 
     The G tolerance improvement device  1  of the embodiment configured as described above is provided with the pressurization unit  15  in contact with the user&#39;s neck and the impedance measurement unit  142  that measures the impedance of the head of the user  91 . The G tolerance improvement device  1  is further provided with the pressurization control unit  143  that estimates the body fluid volume in the cranium of the user  91  and the change amount per unit time on the basis of the measured impedance, and controls the pressurization unit  15  on the basis of the estimated values. For this reason, it is possible to apply pressure to a pilot according to the physical condition of each pilot. 
     (Modification) 
     The G tolerance improvement device  1  need not necessarily have the second electrode unit  12  in contact with the neck, and may have the second electrode unit  12  in contact with the abdomen or waist. 
     The first electrode unit  11  of the G tolerance improvement device  1  need not necessarily be provided with two electrodes, and may also be one electrode having the same function as the first application electrode  111  and the first measurement electrode  112 . In addition, the second electrode unit  12  of the G tolerance improvement device  1  need not necessarily be provided with two electrodes, and may also be one electrode having the same function as the second application electrode  121  and the second measurement electrode  122 . 
     Furthermore, the first electrode unit  11  of the G tolerance improvement device  1  need not necessarily be provided with two electrodes, and may be provided with three or more. 
     Furthermore, the second electrode unit  12  of the G tolerance improvement device  1  need not necessarily be provided with two electrodes, and may be provided with three or more. 
     Although the impedance measurement method of the embodiment is a so-called four-terminal method, the impedance measurement method in the case where each of the first electrode unit  11  and the second electrode unit  12  is provided with only one electrode is a so-called two-terminal method. 
     In addition, the G tolerance improvement device  1  need not necessarily be provided with two electrode units, and may be provided with one or three or more. 
     Note that the application unit  141 , the impedance measurement unit  142 , and the pressurization control unit  143  need not necessarily be mounted as a single housing, and some or all of the function units may be individually mounted. 
     Note that the application of the voltage in Step S 103  of  FIG. 3  need not necessarily be performed in Step S 103 , and may be performed any time provided the application is before the impedance measurement in Step S 104 . 
     Note that a voltage need not necessarily be applied between the first measurement electrode  112  and the second measurement electrode  122 , and a current may be applied. Further, the impedance measurement unit  142  need not necessarily measure the impedance by acquiring the current flowing through the first measurement electrode  112  and the second measurement electrode  122 . The impedance measurement unit  142  may measure the impedance by acquiring the voltage flowing through the first measurement electrode  112  and the second measurement electrode  122 . 
     The method of estimating the body fluid volume by the G tolerance improvement device  1  is not necessarily a method based on impedance, and may be any method provided the method is capable of estimating the body fluid volume of the head of the user  91 . The body fluid volume of the head of the user  91  may be estimated by, for example, a change in reflectance or transmittance of electromagnetic waves such as infrared rays irradiated on the head of the user  91 . 
     In the estimation method using electromagnetic waves such as infrared rays, the G tolerance improvement device  1  may be provided with a light receiving element instead of the first electrode unit  11 , the second electrode unit  12 , and the impedance measurement unit  142 . In the estimation method using electromagnetic waves such as infrared rays, the G tolerance improvement device  1  may be provided with a light source that emits electromagnetic waves such as infrared rays instead of the application unit  141 . Moreover, in the estimation method using electromagnetic waves such as infrared rays, the G tolerance improvement device  1  may be provided with a pressurization control unit  143   a  instead of the pressurization control unit  143 . The light receiving element receives the electromagnetic waves emitted from the light source and reflected off the head of the user  91 . The light receiving element outputs a signal indicating the intensity of the received light. The pressurization control unit  143   a  controls the pressure applied by the pressurization unit  15  to the user  91  on the basis of the acceleration signal output by the accelerometer  13  and the signal output by the light receiving element. 
     For example, the pressurization control unit  143   a  estimates the body fluid volume in the cranium on the basis of the intensity of electromagnetic waves received by the light receiving element. The body fluid volume estimated by the pressurization control unit  143   a  is estimated by an estimation method based on the following physical phenomenon. That is, since electromagnetic waves such as infrared rays emitted from the light source are absorbed by the body fluid in the cranium, the intensity of the electromagnetic waves received by the light receiving element is subject to a phenomenon in which there is the more body fluid in the cranium, the weaker the intensity becomes. 
     Further, the method of estimating the body fluid volume by the G tolerance improvement device  1  may be an estimation method employing not only electromagnetic waves but also ultrasonic waves. In the estimation method using ultrasound, the diameter of a blood vessel in the neck or head, blood flow, pressure, the size of the sinus and cerebrospinal fluid space, and the like may be measured by ultrasound, and the body fluid volume of the head measured on the basis of the measurement data. Specifically, a body fluid volume estimation method using ultrasonic waves may be a method represented by ultrasonic echo sounding. For example, the method may be one that estimates the body fluid volume on the basis of a reflection point in the body, or a temporal change in the depth or distance, or one that estimates the body fluid volume on the basis of a flow velocity or pressure differential due to a Doppler echo. 
     In the above-described embodiment, the case where the pressurization control unit  143  acquires the estimated body fluid volume and the estimated change amount is illustrated. However, the pressurization control unit  143  does not necessarily need to estimate the body fluid volume in the cranium and the change amount per unit time, and may estimate only one of them. Further, the pressurization control unit  143  need not necessarily control the pressurization unit  15  on the basis of the body fluid volume in the cranium and the change amount per unit time, and may control the pressurization unit  15  on the basis of only either one. 
     Furthermore, the present invention is not limited to a special high G environment such as an aircraft, but can be used for avoiding dizziness and fainting associated with a decrease in blood volume in the head. The present invention can also be used for patients with reduced G tolerance, which gives rise to fainting attacks caused by relatively minor G changes such as standing up and ascending in an elevator, which is seen in patients with blood pressure regulation dysfunction due to Sphaet-Drager syndrome, diabetic neuropathy, or the like. 
     The impedance measurement unit  142  and the pressurization control unit  143  in embodiment described above may be realized by a computer. In that case, a program for realizing these functions may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM or a CD-ROM, and a hard disk incorporated in the computer system. Furthermore, the “computer-readable recording medium” may include one that dynamically holds a program for a short time, such as a communication line in the case where a program is transmitted via a network such as the Internet or a communication line such as a telephone circuit, or one that holds a program for a predetermined time like a volatile memory in a computer system serving as a server or a client in that case. The program may be configured to realize some of the above-mentioned functions, may be configured to realize the above-mentioned functions by combination with a program recorded in advance in a computer system, and may be realized using a programmable logic device such as a field programmable gate array (FPGA) or the like. 
     The impedance measurement unit  142  and the pressurization control unit  143  are examples of an estimation unit. 
     The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configurations are not limited to this embodiment, and designs or the like within a scope not departing from the gist of the present invention are also included. 
     INDUSTRIAL APPLICABILITY 
     It is possible to appropriately apply pressure to a user. 
     REFERENCE SYMBOLS 
     
         
         
           
               1 : G tolerance improvement device 
               11 : First electrode unit 
               12 : Second electrode unit 
               13 : Accelerometer 
               14 : Control device 
               15 : Pressurization unit 
               111 : First application electrode 
               112 : First measurement electrode 
               121 : Second application electrode 
               122 : Second measurement electrode 
               141 : Application unit 
               142 : Impedance measurement unit 
               143 : Pressurization control unit 
               91 : User 
               92 : Helmet 
               93 : Ear muff