Stress assessment device, vehicle seat, stress assessment method and program

Abstract

To improve determination accuracy for a stress state of a subject.SOLUTION: A stress determination ECU 26 acquires a base heart rate HR0 of a subject measured by a base heart rate acquisition device 46, and calculates a heart rate HR of a driver 20 on the basis of a heartbeat signal input from a heartbeat measuring device 24. The stress determination ECU determines a stress state of the subject on the basis of the time that the heart rate HR of the subject satisfies the formula (1) HR≥ch×HR0 (ch being a coefficient) and the time that the heart rate index (e.g., the ratio LF / HF of frequency components of a heartbeat interval of the subject and variations RMSSD of the heartbeat interval of the subject) other than the base heart rate HR0 of the subject satisfies a predetermined stress determination condition using the heart rate index.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a stress assessment device, a seat for a vehicle, a stress assessment method, and a stress assessment program. [Background technology]

[0002] Patent document 1 describes a technology in which a pressure sensor is used to detect the internal pressure that changes due to the body movement caused by the breathing of an occupant on the intake and exhaust path of a massage air bag, and if the measured change in internal pressure is equal to or greater than a threshold value α, the occupant is estimated to be in a state of tension (stress). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-052332 [Non-patent literature]

[0004] [Non-Patent Document 1] Haruko Takada, Mikio Takada, Ai Kanayama, Significance of LF and HF Components in Heart Rate Variability Frequency Analysis and the Coefficient of Heart Rate Variability, HEP Vol.32, No.6, 2005 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology in Patent Document 1 detects breathing depth and pitch by detecting changes in the internal pressure of an air bag, which changes due to the body movement caused by the occupant's breathing. However, the subject's breathing can be intentionally controlled by the subject, for example, and therefore has a relatively small correlation with the subject's stress state (state of the autonomic nervous system). In addition, there are individual differences in the fluctuations in breathing depth and pitch under stress. For this reason, the technology described in Patent Document 1 has the problem of insufficient accuracy in determining the subject's stress state.

[0006] The present disclosure has been made in consideration of the above facts, and aims to provide a stress assessment device, a seat for a vehicle, a stress assessment method, and a stress assessment program that can improve the accuracy of assessing a subject's stress state. [Means for solving the problem]

[0007] The stress assessment device according to the first aspect of the present invention is configured by setting the heart rate of the subject as HR, the basal heart rate of the subject as HR0, and the coefficient as c h When HR ≥ c h ×HR0…(1) and a judgment unit that judges the stress state of the subject based on the time during which the subject's heart rate HR satisfies the above formula (1) and the time during which the subject's heart rate index other than the basal heart rate HR0 satisfies a predetermined stress judgment condition using the heart rate index.

[0008] The basal heart rate HR0 is the lowest heart rate when the heart rate drops during sleep. The basal heart rate HR0 is a value specific to each individual, and is stable with little daily fluctuation, making it suitable for correcting individual differences. Based on this, in the first aspect, the stress state of the subject is determined using the time that satisfies the above formula (1), which uses the basal heart rate HR0 as the criterion for determining the stress state of the subject. This makes it possible to reduce the variation in the determination of the stress state of the subject due to individual differences.

[0009] Furthermore, in the first aspect, the subject's stress state is determined using the time during which a heart rate index other than the basal heart rate HR0 satisfies a predetermined stress determination condition using that heart rate index. In this way, by using a heart rate index other than the basal heart rate HR0 that is more likely to reflect the stress state than body movement due to breathing, the accuracy of determining the subject's stress state can be improved. Therefore, according to the first aspect, the accuracy of determining the subject's stress state can be improved.

[0010] In a second aspect, in the first aspect, the determination unit determines a ratio of frequency components of the heartbeat interval of the subject as LF / HF as a heartbeat index other than the basal heart rate HR0, and determines a threshold value for determining LF / HF as c f When LF / HF≦c f …(2) The stress state of the subject is judged taking into consideration the time during which the ratio LF / HF of the frequency components of the subject's heartbeat intervals satisfies the above formula (2) as the predetermined stress judgment condition.

[0011] The ratio LF / HF of the frequency components of the subject's heartbeat interval is a heartbeat index that more easily reflects the subject's stress state than body movement due to breathing. In the second aspect, the subject's stress state is determined taking into consideration the time that satisfies the above-mentioned formula (2) using the ratio LF / HF of the frequency components of the subject's heartbeat interval, thereby further improving the accuracy of determining the subject's stress state.

[0012] In a third aspect, in the first aspect, the determination unit determines the variation in the heartbeat intervals of the subject as an RMSSD (Root Mean Square Successive Differences) as a heartbeat index other than the basal heart rate HR0, and sets a determination threshold for the RMSSD as c v When RMSSD ≤ c v …(3) The stress state of the subject is determined taking into consideration the time during which the RMSSD of the subject's heartbeat intervals satisfies the above formula (3) as the predetermined stress determination condition.

[0013] The RMSSD, which is the variation in the subject's heartbeat intervals, is also a heart rate index that more easily reflects the stress state than body movement due to breathing. In the third aspect, the stress state of the subject is determined taking into consideration the time when the RMSSD, which is the variation in the subject's heartbeat intervals, satisfies the above-mentioned formula (3), thereby further improving the accuracy of determining the stress state of the subject.

[0014] In a fourth aspect, in the second aspect, the determination unit determines whether the duration T1 when the state satisfying the formula (1) continues is equal to or exceeds a predetermined value c t1 As described above, the duration T2 when the state satisfying the formula (2) continues is equal to or exceeds a predetermined value c t1 When the first condition above is satisfied, it is determined that the stress of the subject is higher than when the first condition is not satisfied.

[0015] The first condition in the fourth aspect is that the duration T1 when the state satisfying the formula (1) continues and the duration T2 when the state satisfying the formula (2) continue are each a predetermined value c t1 This condition is that, for example, at least one of the durations T1 and T2 is equal to or greater than a predetermined value c t1 If the durations T1 and T2 are less than the predetermined value c t1 In the above cases, the subject is determined to be under high stress. Therefore, according to the fourth aspect, the subject's stress state can be appropriately determined based on the duration T1 of the subject's heart rate HR and the duration T2 of the ratio LF / HF of the frequency components of the subject's heartbeat intervals.

[0016] In a fifth aspect, in the third aspect, the determination unit determines whether the duration T1 when the state satisfying the formula (1) continues is equal to or exceeds a predetermined value c t1 As described above, the duration T3 when the state satisfying the formula (3) continues is equal to or exceeds a predetermined value c t1 If the second condition above is satisfied, it is determined that the stress of the subject is higher than if the second condition is not satisfied.

[0017] The second condition in the fifth aspect is that the duration T1 when the state satisfying the formula (1) continues and the duration T3 when the state satisfying the formula (3) continue are each a predetermined value c t1 This condition is that, for example, at least one of the durations T1 and T3 is equal to or greater than a predetermined value ct1 If the durations T1 and T3 are less than the predetermined value c t1 In the above cases, the subject is determined to be under high stress. Therefore, according to the fifth aspect, the subject's stress state can be appropriately determined based on the duration T1 of the subject's heart rate HR and the duration T3 of the subject's heartbeat interval variability RMSSD.

[0018] In a sixth aspect, in the second aspect, the determination unit determines whether an integrated time t1, which is the time when the state satisfying the formula (1) is reached within a predetermined determination time, is equal to or exceeds a predetermined value c t2 In the above, the time when the formula (2) is satisfied is the time when the formula (2) is satisfied within the predetermined judgment time. The accumulated time t2 is a predetermined value c t2 When the third condition above is satisfied, it is determined that the stress of the subject is higher than when the third condition is not satisfied.

[0019] The third condition in the sixth aspect is that the integrated time t1 obtained by integrating the time during which the state satisfying the formula (1) within a predetermined judgment time and the integrated time t2 obtained by integrating the time during which the state satisfying the formula (2) within a predetermined judgment time are each a predetermined value c t2 This condition is that, for example, at least one of the integrated times t1 and t2 is equal to or greater than a predetermined value c t2 If the accumulated times t1 and t2 are less than the predetermined value c, the stress of the subject is judged to be low. t2 In the above cases, the subject is determined to be under high stress. Therefore, according to the sixth aspect, the subject's stress state can be appropriately determined based on the integration time t1 of the subject's heart rate HR and the integration time t2 of the ratio of frequency components of the subject's heartbeat intervals LF / HF.

[0020] In a seventh aspect, in the third aspect, the determination unit determines whether an integrated time t1, which is the time when the state satisfying the formula (1) is reached within a predetermined determination time, is equal to or exceeds a predetermined value c t2In the above, the time when the formula (3) is satisfied is the time when the formula (3) is satisfied within the predetermined judgment time. The accumulated time t3 is a predetermined value c t2 If the above fourth condition is met, it is determined that the stress of the subject is higher than if the fourth condition is not met.

[0021] The fourth condition in the seventh aspect is that the integrated time t1 obtained by integrating the time during which the state satisfying the formula (1) within a predetermined judgment time and the integrated time t3 obtained by integrating the time during which the state satisfying the formula (3) within a predetermined judgment time are each a predetermined value c t2 This condition is that, for example, at least one of the integrated times t1 and t3 is equal to or greater than a predetermined value c t2 If the accumulated times t1 and t3 are less than the predetermined value c t2 In the above cases, the subject is determined to be under high stress. Therefore, according to the seventh aspect, the stress state of the subject can be appropriately determined based on the integration time t1 of the subject's heart rate HR and the integration time t3 of the subject's heartbeat interval variability RMSSD.

[0022] A seat for a moving body according to an eighth aspect includes a seat body on which an occupant of the moving body sits, and the stress assessment device according to any one of the first to seventh aspects.

[0023] The eighth aspect includes the stress assessment device according to any one of the first to seventh aspects, and thus, like the first aspect, the accuracy of assessing the stress state of the subject can be improved.

[0024] A stress assessment method according to a ninth aspect of the present invention is a method for assessing stress by using a heart rate of a subject as HR, a basal heart rate of the subject as HR0, a coefficient as c h When HR ≥ c h ×HR0…(1) The computer is caused to execute a process that includes determining the stress state of the subject based on the time during which the subject's heart rate HR satisfies the above formula (1) and the time during which the subject's heart rate index other than the basal heart rate HR0 satisfies a predetermined stress determination condition using the heart rate index.

[0025] According to the ninth aspect, similarly to the first aspect, it is possible to improve the accuracy of determining the stress state of the subject.

[0026] The stress assessment program according to the tenth aspect of the present invention is a stress assessment program for causing a computer to calculate a heart rate of a subject as HR, a basal heart rate of the subject as HR0, a coefficient as c h When HR ≥ c h ×HR0…(1) A process is executed that includes determining the stress state of the subject based on the time during which the subject's heart rate HR satisfies the above formula (1) and the time during which the subject's heart rate index other than the basal heart rate HR0 satisfies a predetermined stress determination condition using that heart rate index.

[0027] According to the tenth aspect, similarly to the first aspect, it is possible to improve the accuracy of determining the stress state of the subject. [Effects of the Invention]

[0028] The present disclosure has an effect of improving the accuracy of determining a subject's stress state. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a side view of a vehicle seat according to an embodiment; [Figure 2] FIG. 2 is a block diagram showing a schematic configuration of a stress determination ECU and its periphery. [Figure 3] FIG. 2 is a functional block diagram of a stress determination ECU according to the first embodiment. [Figure 4] FIG. 10 is a diagram showing an example of the transition of the RRI value. [Figure 5]4 is a flowchart showing a stress assessment process according to the first embodiment. [Figure 6] 10 is a table showing a comprehensive stress assessment in the first embodiment. [Figure 7] FIG. 10 is a functional block diagram of a stress determination ECU according to a second embodiment. [Figure 8] 10 is a flowchart showing a stress assessment process according to the second embodiment. [Figure 9] 10 is a table showing a comprehensive stress assessment in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, an example of an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0031] [First embodiment] The vehicle seat 10 shown in Fig. 1 includes a seat body 12. The seat body 12 is provided in a driver's seat of a vehicle, which is an example of a moving body, and is seated by a vehicle driver 20, which is an example of a test subject. The driver 20 seated in the seat body 12 operates a steering wheel 22 and pedals (not shown) to drive the vehicle when the vehicle is traveling. The vehicle seat 10 is an example of a moving body seat according to the present disclosure.

[0032] The seat body 12 includes a seat cushion portion 14, a seat back portion 16, and a headrest portion 18. The headrest portion 18 is attached to the upper end portion of the seat back portion 16 in the vertical direction of the vehicle so as to be slidable along the length of the seat back portion 16. The lower end portion of the seat back portion 16 in the vertical direction of the vehicle is attached to the rear end portion of the seat cushion portion 14 in the longitudinal direction of the vehicle via a rotation mechanism (not shown), and is rotatable relative to the seat cushion portion 14 around an axis along the width direction of the vehicle.

[0033] The vehicle seat 10 also includes a heart rate measuring device 24 and a stress determination ECU (Electronic Control Unit) 26. The heart rate measuring device 24 is, for example, a radio wave or optical heart rate monitor, and is worn, for example, on the chest of a driver 20 of the vehicle seated in the seat body 12. The heart rate measuring device 24 measures the heart rate of the driver 20 while worn on the chest of the driver 20, and generates a heart rate signal (see also FIG. 4) representing the measured heart rate. of The heart rate measuring device 24 is output to the stress determination ECU 26. The heart rate measuring device 24 is not limited to being worn on the chest of the driver 20, but may be provided on the seat back 16, or may be wrapped around the arm of the driver 20, for example.

[0034] The stress determination ECU 26 is housed in the seat cushion portion 14. The stress determination ECU 26 is a device that determines the stress state of the vehicle driver 20 from the heart rate signal and basal heart rate HR0 of the driver 20, and outputs a stress detection signal if it determines that the driver 20 is stressed.

[0035] 2, the stress assessment ECU 26 includes a CPU (Central Processing Unit) 28, a memory 30 such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and a non-volatile storage unit 32 such as a HDD (Hard Disk Drive) or an SSD (Solid State Drive). The stress assessment ECU 26 also includes a communication I / F (Interface) 34 and an input / output I / F 36. The CPU 28, memory 30, storage unit 32, communication I / F 34, and input / output I / F 36 are connected to each other via an internal bus 38 so as to be able to communicate with each other.

[0036] The communication I / F 34 includes an interface for connecting to a network (not shown). This network is, for example, a wired or wireless communication network using a public line such as the Internet. For the interface, for example, a communication standard such as LTE or Wi-Fi (registered trademark) is used. The stress determination ECU 26 is connected to the basal heart rate acquisition device 46 and the biological data accumulation device 48 via the network so as to be able to communicate with each other.

[0037] The basal heart rate acquisition device 46 is, for example, a heart rate sensor mounted on a wearable device or the like, and measures the basal heart rate HR0 of the driver 20 (subject) while the subject is asleep, for example, immediately before getting into the vehicle. When acquiring the basal heart rate HR0, a value corresponding to the 1st to 3rd percentile of the distribution (i.e., histogram) of heart rates during sleep is acquired, taking into account the measurement error of the basal heart rate acquisition device 46. The basal heart rate HR0 data measured by the basal heart rate acquisition device 46 is transmitted directly to the stress assessment ECU 26 via a network, or indirectly via a biological data accumulation device 48. The biological data accumulation device 48 is, for example, a smartphone or a data server. The biological data accumulation device 48 accumulates the basal heart rate HR0 data for each subject.

[0038] The input / output I / F 36 is connected to the heart rate measuring device 24, the warning device 50, and other devices 56. The warning device 50 includes a vibration generating unit and a sound generating unit. In this embodiment, when it is determined that the driver 20 is stressed, a warning signal including a vibration signal portion for causing the vibration generating unit to generate vibrations and a sound signal portion for causing the sound generating unit to generate sound is output from the warning device 50 of the stress determination ECU 26. The vibration signal portion of the warning signal is input to the vibration generating unit, and the sound signal portion of the warning signal is input to the sound generating unit.

[0039] The vibration generating unit includes a piezoelectric element built into the seat cushion 14 and the seat back 16 of the vehicle seat 10, and applies a warning vibration to the driver 20 in accordance with the vibration signal portion of the warning signal. The audio generating unit includes a speaker provided in the vehicle cabin, and generates a warning sound in accordance with the audio signal portion of the warning signal. The audio signal portion is a voice that reads out a message such as "Stress has been detected. We recommend you take a break," and is stored as audio data in the memory unit 32. The other device 56 is, for example, a vehicle control device that controls automatic driving of the vehicle, or a display control device that controls a display device installed in the vehicle.

[0040] The memory unit 32 of the stress assessment ECU 26 also stores a stress assessment program 40. The stress assessment ECU 26 reads the stress assessment program 40 from the memory unit 32 and loads it into the memory 30, and the stress assessment program 40 loaded into the memory 30 is executed by the CPU 28, whereby the stress assessment ECU 26 functions as a assessment unit 60 shown in Fig. 3. The assessment unit 60 assesses the stress state of the driver 20 of the vehicle based on the heart rate signal and basal heart rate HR0 of the driver 20.

[0041] 3, the judgment unit 60 includes a basal heart rate HR0 acquisition unit 62, a heart rate HR calculation unit 64, a heart rate interval frequency component ratio LF / HF calculation unit 66, a heart rate interval variation RMSSD calculation unit 68, a duration T1 calculation unit 70, a duration T2 calculation unit 72, a duration T3 calculation unit 74, a first condition judgment unit 76, a second condition judgment unit 78, and a comprehensive judgment unit 80. The stress judgment ECU 26 is an example of a stress judgment device according to the present disclosure.

[0042] The basal heart rate HR0 acquisition unit 62 acquires the basal heart rate HR0 measured by the basal heart rate acquisition device 46 and stores the acquired basal heart rate HR0 in the memory unit 32 or the like. In this case, the basal heart rate HR0 acquisition unit 62 may store data on the basal heart rate HR0 for each of a plurality of subjects in the memory unit 32 or the like. Note that in this embodiment, the basal heart rate acquisition device 46 measures the heart rate of the subject while the subject is sleeping to acquire the basal heart rate HR0 of the driver 20, i.e., the subject, but this is not limited to this. If there is a method for measuring the basal heart rate HR0 other than while the subject is sleeping, that method may be used.

[0043] The heart rate HR calculation unit 64 calculates the heart rate HR of the driver 20 based on the heart rate signal input from the heart rate measuring device 24. One example of the heart rate HR is the instantaneous heart rate, which is the heart rate measured in the smallest time unit, but the heart rate HR is not limited to this. The heart rate HR may also be a moving average of the instantaneous heart rate for each predetermined time period longer than the smallest time unit (for example, about 5 seconds). Alternatively, the interval between R waves in the heart rate signal (the so-called RRI (RR Interval): see also FIG. 4) may be measured, and the heart rate (bpm) may be calculated from the heart rate interval RRI by the formula: heart rate (bpm) = 60 / RRI (seconds).

[0044] The heartbeat interval frequency component ratio LF / HF calculation unit 66 extracts the low frequency component LF and the high frequency component HF of the heartbeat interval from the heartbeat signal input from the heartbeat measuring device 24, and calculates the ratio LF / HF. An example of the frequency of the low frequency component LF is 0.02 to 0.15 Hz, and an example of the frequency of the high frequency component HF is 0.15 to 0.50 Hz (see also Non-Patent Document 1).

[0045] The heartbeat interval variation RMSSD calculation unit 68 calculates the RRI value (for example, 900 ms, 910 ms, 950 ms, etc. shown in FIG. 4) from the heartbeat signal input from the heartbeat measuring device 24, and calculates the heartbeat interval variation RMSSD by substituting the calculated RRI value into the following equation (4).

[0046]

number

[0047] In equation (4), N is the number of RRIs in a unit time (an example of a unit time is 30 to 60 seconds), and x i is the i-th RRI value.

[0048] The duration T1 calculation unit 70 calculates the duration T1 based on the basal heart rate HR0 acquired by the basal heart rate HR0 acquisition unit 62 and the heart rate HR calculated by the heart rate HR calculation unit 64. HR ≥ c h ×HR0…(1) The duration T1 during which the heart rate HR of the driver 20 continues to satisfy the above formula (1) is calculated. h is a coefficient, and a value of about 1.6 to 1.7 can be used, for example.

[0049] The duration T2 calculation unit 72 calculates the following based on the ratio LF / HF of the frequency components of the heartbeat interval calculated by the ratio LF / HF of the frequency components of the heartbeat interval calculation unit 66: LF / HF≦c f …(2) The duration T2 when the ratio LF / HF of the frequency components of the heartbeat interval of the driver 20 continues to satisfy the above formula (2) is calculated. f is a threshold value for determining the ratio LF / HF of frequency components of the heartbeat interval.

[0050] The duration T3 calculation unit 74 calculates, based on the heartbeat interval variation RMSSD calculated by the heartbeat interval variation RMSSD calculation unit 68, RMSSD ≤ c v …(3) The duration T3 during which the RMSSD of the heartbeat intervals of the driver 20 continues to satisfy the above formula (3) is calculated. v is the threshold for determining the RMSSD of the heartbeat intervals.

[0051] The first condition determination unit 76 determines whether the duration T1 is equal to or exceeds a predetermined value c based on the duration T1 calculated by the duration T1 calculation unit 70 and the duration T2 calculated by the duration T2 calculation unit 72. t1 or more and the duration T2 is equal to or greater than the predetermined value c t1 It is determined whether the first condition, that is, the predetermined value c t1 An example is a time of about 30 to 60 seconds.

[0052] The second condition determination unit 78 determines whether the duration T1 is equal to or greater than a predetermined value c based on the duration T1 calculated by the duration T1 calculation unit 70 and the duration T3 calculated by the duration T3 calculation unit 74. t1 or more and the duration T3 is equal to or greater than the predetermined value c t1 It is determined whether the second condition, ie, the above condition, is satisfied.

[0053] The comprehensive judgment unit 80 judges the stress state of the driver 20 into three levels: "no stress," "low stress," and "high stress," based on the judgment result of the first condition by the first condition judgment unit 76 and the judgment result of the second condition by the second condition judgment unit 78. When the comprehensive judgment unit 80 judges the stress state of the driver 20 to be "low stress" or "high stress," it outputs a stress detection signal.

[0054] Next, as an operation of the first embodiment, a stress determination process executed by the stress determination ECU 26 while the ignition switch of the vehicle is on, for example, will be described with reference to FIG.

[0055] In step 100 of the stress assessment processing, the basal heart rate HR0 acquisition unit 62 acquires the basal heart rate HR0 of the driver 20 from the basal heart rate acquisition device 46. In step 102, the assessment unit 60 sets each of the durations T1, T2, and T3 to 0. In step 104, the heart rate HR calculation unit 64 calculates the heart rate HR of the driver 20 based on the heart rate signal input from the heart rate measuring device 24. In step 106, the heart rate interval frequency component ratio LF / HF calculation unit 66 calculates the heart rate interval frequency component ratio LF / HF from the heart rate signal input from the heart rate measuring device 24. In step 108, the heart rate interval variance RMSSD calculation unit 68 calculates the heart rate interval variance RMSSD from the heart rate signal input from the heart rate measuring device 24.

[0056] In step 110, the duration T1 calculation unit 70 determines whether or not the heart rate HR of the driver 20 satisfies the above-mentioned formula (1) based on the basal heart rate HR0 acquired by the basal heart rate HR0 acquisition unit 62 and the heart rate HR calculated by the heart rate HR calculation unit 64. If the determination in step 110 is negative, the process proceeds to step 112, where the duration T1 calculation unit 70 sets the duration T1 to 0. If the determination in step 110 is positive, the process proceeds to step 114, where the duration T1 calculation unit 70 adds the execution period x of the main routine (steps 104 to 138) to the duration T1.

[0057] As a result, the duration T1 is set to the duration when the heart rate HR of the driver 20 continues to satisfy the above-mentioned formula (1) by repeating the main routine.

[0058] In step 116, the duration T2 calculation unit 72 determines whether or not the ratio LF / HF of the frequency components of the heartbeat intervals of the driver 20 satisfies the above-mentioned formula (2), based on the ratio LF / HF of the frequency components of the heartbeat intervals calculated by the ratio LF / HF of the frequency components of the heartbeat intervals calculation unit 66. If the determination in step 116 is negative, the process proceeds to step 118, where in step 112 the duration T2 calculation unit 72 sets the duration T2 to 0. If the determination in step 116 is positive, the process proceeds to step 120, where in step 120 the duration T2 calculation unit 72 adds the execution period x of the main routine to the duration T2.

[0059] As a result, the duration T2 is set to the duration when the ratio LF / HF of the frequency components of the heartbeat intervals of the driver 20 continues to satisfy the above-mentioned formula (2) by repeating the main routine.

[0060] In step 122, the duration T3 calculation unit 74 determines whether the heartbeat interval variation RMSSD of the driver 20 satisfies the above-mentioned formula (3) based on the heartbeat interval variation RMSSD calculated by the heartbeat interval variation RMSSD calculation unit 68. If the determination in step 122 is negative, the process proceeds to step 124, where the duration T3 calculation unit 74 sets the duration T3 to 0. If the determination in step 122 is positive, the process proceeds to step 126, where the duration T3 calculation unit 74 adds the execution period x of the main routine to the duration T3.

[0061] As a result, the duration T3 is set to the duration when the main routine is repeated and the state in which the variation RMSSD in the heartbeat intervals of the driver 20 satisfies the above-mentioned formula (3) continues.

[0062] In step 128, the first condition determination unit 76 determines whether the duration T1 is equal to or greater than a predetermined value c t1 or more and the duration T2 is equal to or greater than the predetermined value c t1If the determination in step 128 is negative (if the first condition is not satisfied), the process proceeds to step 130.

[0063] In step 130, the second condition determination unit 78 determines whether the duration T1 is equal to or greater than a predetermined value c t1 or more and the duration T3 is equal to or greater than the predetermined value c t1 If the determination in step 130 is negative (if the second condition is not satisfied), the process proceeds to step 134.

[0064] As described above, if the determinations at steps 128 and 130 are both negative, the first and second conditions are not satisfied, and therefore the comprehensive determination section 80 determines that there is no stress in step 134. In this case, no stress detection signal is output.

[0065] If the determination in step 130 is positive (if the second condition is satisfied), the process proceeds to step 136. If the determination in step 128 is negative and the determination in step 130 is positive, the first condition is not satisfied but the second condition is satisfied, so in step 136 the comprehensive determination unit 80 determines that the stress is low. In this case, a stress detection signal is output.

[0066] On the other hand, if the determination in step 128 is affirmative (if the first condition is satisfied), the process proceeds to step 132. In step 132, the second condition determination unit 78 determines whether the duration T1 is equal to or greater than the predetermined value c t1 or more and the duration T3 is equal to or greater than the predetermined value c t1 If the determination in step 132 is negative (if the second condition is not satisfied), the process proceeds to step 136.

[0067] As described above, if the determination in step 128 is positive and the determination in step 132 is negative, the first condition is met but the second condition is not, and therefore the comprehensive determination unit 80 determines that the stress is low in step 136. In this case, a stress detection signal is output.

[0068] If the determination in step 132 is affirmative (if the second condition is satisfied), the process proceeds to step 138. If the determinations in steps 128 and 132 are both affirmative, the first condition and the second condition are both satisfied, and therefore, in step 138, the comprehensive determination unit 80 determines that the stress is high. In this case, a stress detection signal is output.

[0069] The determination made by the comprehensive determination unit 80 described above can be tabulated as shown in Figure 6. After the processing of step 134, step 136 or step 138 is completed, the process returns to step 104, and the processing from step 104 onwards is repeated.

[0070] As described above, in the first embodiment, the judgment unit 60 judges the stress state of the driver 20 based on the time during which the heart rate HR of the driver 20 satisfies the above-mentioned formula (1) and the time during which a heart rate index other than the basal heart rate HR0 of the driver 20 satisfies a predetermined stress judgment condition using that heart rate index. This makes it possible to improve the accuracy of judging the stress state of the driver 20.

[0071] In the first embodiment, the determination unit 60 also determines the stress state of the driver 20 by taking into consideration the time during which the ratio LF / HF of the frequency components of the heartbeat intervals of the driver 20, which is a heartbeat index other than the basal heart rate HR0, satisfies the above-mentioned formula (2) as a predetermined stress determination condition. This further improves the accuracy of the determination of the stress state of the driver 20.

[0072] In the first embodiment, the determination unit 60 determines the stress state of the driver 20 by taking into consideration the time during which the variability in heartbeat intervals RMSSD of the driver 20, which is a heart rate index other than the basal heart rate HR0, satisfies the above-mentioned formula (3) as the predetermined stress determination condition. This further improves the accuracy of determining the stress state of the driver 20.

[0073] In the first embodiment, the determination unit 60 determines whether the duration T1 when the state satisfying the above-mentioned formula (1) continues is equal to or exceeds a predetermined value c t1 When the state satisfying the above formula (2) continues, the duration T2 is equal to or exceeds the predetermined value c t1 When the above first condition is satisfied, it is determined that the stress of the driver 20 is higher than when the first condition is not satisfied. This makes it possible to appropriately determine the stress state of the driver 20 based on the duration T1 of the heart rate HR of the driver 20 and the duration T2 of the ratio LF / HF of the frequency components of the heartbeat intervals of the driver 20.

[0074] In the first embodiment, the determination unit 60 determines whether the duration T1 when the state satisfying the above-mentioned formula (1) continues is equal to or exceeds a predetermined value c t1 When the state satisfying the above formula (3) continues, the duration T3 is equal to or exceeds the predetermined value c t1 When the above second condition is satisfied, it is determined that the stress of the driver 20 is higher than when the second condition is not satisfied. This makes it possible to appropriately determine the stress state of the driver 20 based on the duration T1 of the heart rate HR of the driver 20 and the duration T3 of the heart rate interval variability RMSSD of the driver 20.

[0075] Second Embodiment Next, a second embodiment of the present disclosure will be described. Note that the same parts as those in the first embodiment are given the same reference numerals and descriptions thereof will be omitted.

[0076] As shown in FIG. 7, the judgment unit 60 according to the second embodiment includes an accumulated time t1 calculation unit 82, an accumulated time t2 calculation unit 84, an accumulated time t3 calculation unit 86, a third condition judgment unit 88, and a fourth condition judgment unit 90, instead of the duration T1 calculation unit 70, duration T2 calculation unit 72, duration T3 calculation unit 74, first condition judgment unit 76, and second condition judgment unit 78 described in the first embodiment.

[0077] The integrated time t1 calculation unit 82 calculates an integrated time t1 by accumulating the time during which the heart rate HR of the driver 20 satisfies the above-mentioned formula (1) within a predetermined determination time, based on the basal heart rate HR0 acquired by the basal heart rate HR0 acquisition unit 62 and the heart rate HR calculated by the heart rate HR calculation unit 64. An example of the predetermined determination time is approximately 30 to 60 seconds.

[0078] Based on the ratio LF / HF of the frequency components of the heartbeat interval calculated by the ratio LF / HF of the frequency components of the heartbeat interval calculation unit 66, the cumulative time t2 calculation unit 84 calculates the cumulative time t2 by accumulating the time during which the ratio LF / HF of the frequency components of the heartbeat interval of the driver 20 satisfies the above-mentioned equation (2) within a predetermined determination time.

[0079] Based on the heartbeat interval variation RMSSD calculated by the heartbeat interval variation RMSSD calculation unit 68, the cumulative time t3 calculation unit 86 calculates the cumulative time t3 by accumulating the time during which the heartbeat interval variation RMSSD of the driver 20 satisfies the above-mentioned equation (3) within a predetermined judgment time.

[0080] The third condition determination unit 88 determines whether the integrated time t1 is equal to or exceeds a predetermined value c based on the integrated time t1 calculated by the integrated time t1 calculation unit 82 and the integrated time t2 calculated by the integrated time t2 calculation unit 84. t2 or more and the cumulative time t2 is equal to or greater than the predetermined value c t2 It is determined whether the third condition, i.e., the predetermined value c t2 An example is a time of about 15 seconds or more.

[0081] The fourth condition determination unit 90 determines whether the integrated time t1 is equal to or exceeds a predetermined value c based on the integrated time t1 calculated by the integrated time t1 calculation unit 82 and the integrated time t3 calculated by the integrated time t3 calculation unit 86. t2 or more and the cumulative time t3 is equal to or greater than the predetermined value c t2 It is determined whether the fourth condition, ie, the above condition, is satisfied.

[0082] The comprehensive judgment unit 80 judges the stress state of the driver 20 into three levels: "no stress," "low stress," and "high stress," based on the judgment result of the third condition by the third condition judgment unit 88 and the judgment result of the fourth condition by the fourth condition judgment unit 90. When the comprehensive judgment unit 80 judges the stress state of the driver 20 to be "low stress" or "high stress," it outputs a stress detection signal.

[0083] Next, as an operation of the second embodiment, the stress assessment process according to the second embodiment will be described with reference to FIG. 8. In step 150, the basal heart rate HR0 acquisition unit 62 acquires the basal heart rate HR0 of the driver 20 from the basal heart rate acquisition device 46. In step 152, the assessment unit 60 sets the integrated times t1, t2, and t3 to 0. In addition, in step 154, the assessment unit 60 starts a timer that measures a predetermined assessment time. An example of the predetermined assessment time is approximately 30 to 60 seconds.

[0084] In step 156, the heart rate HR calculation unit 64 calculates the heart rate HR of the driver 20 based on the heart rate signal input from the heart rate measuring device 24. In step 158, the heart rate interval frequency component ratio LF / HF calculation unit 66 calculates the heart rate interval frequency component ratio LF / HF from the heart rate signal input from the heart rate measuring device 24. In step 160, the heart rate interval variance RMSSD calculation unit 68 calculates the heart rate interval variance RMSSD from the heart rate signal input from the heart rate measuring device 24.

[0085] In step 162, the integrated time t1 calculation unit 82 determines whether the heart rate HR of the driver 20 satisfies the above-mentioned formula (1) based on the basal heart rate HR0 acquired by the basal heart rate HR0 acquisition unit 62 and the heart rate HR calculated by the heart rate HR calculation unit 64. If the determination in step 162 is affirmative, the process proceeds to step 164, where the integrated time t1 calculation unit 82 adds the execution cycle x of the main routine (steps 156 to 174) to the integrated time t1. If the determination in step 162 is negative, step 164 is skipped.

[0086] As a result, the cumulative time t1 is set to the cumulative time obtained by repeating the main routine and accumulating the time during which the driver's 20 heart rate HR satisfies the above-mentioned equation (1) within a predetermined judgment time.

[0087] In step 166, the integrated time t2 calculation unit 84 determines whether the ratio LF / HF of the frequency components of the heartbeat intervals of the driver 20 satisfies the above-mentioned formula (2) based on the ratio LF / HF of the frequency components of the heartbeat intervals calculated by the ratio LF / HF of the frequency components of the heartbeat intervals calculation unit 66. If the determination in step 166 is positive, the process proceeds to step 168, where the integrated time t2 calculation unit 84 adds the execution period x of the main routine to the integrated time t2. If the determination in step 166 is negative, step 168 is skipped.

[0088] As a result, the main routine is repeated and the accumulated time t2 is set to the accumulated time during which the ratio LF / HF of the frequency components of the heartbeat intervals of the driver 20 satisfies the above-mentioned equation (2) within a predetermined judgment time.

[0089] In step 170, the integrated time t3 calculation unit 86 determines whether the heartbeat interval variation RMSSD of the driver 20 satisfies the above-mentioned formula (3) based on the heartbeat interval variation RMSSD calculated by the heartbeat interval variation RMSSD calculation unit 68. If the determination in step 170 is affirmative, the process proceeds to step 172, where the integrated time t3 calculation unit 86 adds the execution period x of the main routine to the integrated time t3. If the determination in step 170 is negative, step 172 is skipped.

[0090] As a result, the main routine is repeated and the accumulated time t3 is set to the accumulated time during which the variation RMSSD in the heartbeat intervals of the driver 20 satisfies the above-mentioned equation (3) within a predetermined judgment time.

[0091] In step 174, the determination unit 60 determines whether the timer has timed out. If the determination in step 174 is negative, the process returns to step 156, and steps 156 to 174 are repeated until the determination in step 174 is positive. If the determination in step 174 is positive, the process proceeds to step 176.

[0092] In step 176, the third condition determination unit 88 determines whether the integrated time t1 is equal to or greater than a predetermined value c t2 or more and the cumulative time t2 is equal to or greater than the predetermined value c t2 If the determination in step 176 is negative (if the third condition is not satisfied), the process proceeds to step 178.

[0093] In step 178, the fourth condition determination unit 90 determines whether the integration time t1 is equal to or exceeds a predetermined value c t2 or more and the cumulative time t3 is equal to or greater than the predetermined value c t2 If the determination in step 178 is negative (if the second condition is not satisfied), the process proceeds to step 182.

[0094] As described above, if the determinations at steps 176 and 178 are both negative, the third and fourth conditions are not satisfied, and therefore the comprehensive determination unit 80 determines that there is no stress in step 182. In this case, no stress detection signal is output.

[0095] If the determination in step 178 is positive (if the fourth condition is satisfied), the process proceeds to step 184. If the determination in step 176 is negative and the determination in step 178 is positive, the third condition is not satisfied but the fourth condition is satisfied, so in step 184, the comprehensive determination unit 80 determines that the stress is low. In this case, a stress detection signal is output.

[0096] On the other hand, if the determination in step 176 is affirmative (if the third condition is satisfied), the process proceeds to step 180. In step 180, the fourth condition determination unit 90 determines whether the integrated time t1 is equal to or exceeds a predetermined value c t2 or more and the cumulative time t3 is equal to or greater than the predetermined value c t2 If the determination in step 180 is negative (if the fourth condition is not satisfied), the process proceeds to step 184.

[0097] As described above, if the determination in step 176 is positive and the determination in step 180 is negative, the third condition is satisfied but the fourth condition is not, and therefore the comprehensive determination unit 80 determines that the stress is low in step 184. In this case, a stress detection signal is output.

[0098] If the determination in step 180 is affirmative (if the fourth condition is satisfied), the process proceeds to step 186. If the determinations in steps 176 and 180 are both affirmative, the third and fourth conditions are both satisfied, and therefore, in step 186, the comprehensive determination unit 80 determines that the stress is high. In this case, a stress detection signal is output.

[0099] The determination made by the comprehensive determination unit 80 described above can be tabulated as shown in Figure 9. After the processing of step 182, step 184 or step 186 is completed, the process returns to step 152, and the processing from step 152 onwards is repeated.

[0100] In this way, in the second embodiment, the judgment unit 60 judges whether the accumulated time t1, which is the time during which the state satisfying the above-mentioned formula (1) is reached within a predetermined judgment time, is equal to or exceeds a predetermined value c t2 The cumulative time t2 obtained by accumulating the time during which the state satisfying the above-mentioned formula (2) within the predetermined judgment time is equal to or exceeds a predetermined value c t2 When the above third condition is satisfied, it is determined that the stress of the driver 20 is higher than when the third condition is not satisfied. This makes it possible to appropriately determine the stress state of the driver 20 based on the integrated time t1 for the heart rate HR of the driver 20 and the integrated time t2 for the ratio LF / HF of the frequency components of the heartbeat intervals of the driver 20.

[0101] In the second embodiment, the determination unit 60 determines whether the accumulated time t1, which is the time during which the state satisfying the above-described formula (1) is reached within a predetermined determination time, is equal to or exceeds a predetermined value c t2 The cumulative time t3 obtained by accumulating the time during which the state satisfying the above-mentioned formula (3) within the predetermined judgment time is equal to or exceeds a predetermined value c t2 When the above fourth condition is satisfied, it is determined that the stress of the driver 20 is higher than when the fourth condition is not satisfied. This makes it possible to appropriately determine the stress state of the driver 20 based on the integration time t1 for the heart rate HR of the driver 20 and the integration time t3 for the heart rate interval variation RMSSD of the driver 20.

[0102] In the above embodiment, the ratio of frequency components of heartbeat intervals (LF / HF) and the variability of heartbeat intervals (RMSSD) are used as examples of heartbeat indices other than the basal heart rate (HR0) in the present disclosure. However, in the present disclosure, the heartbeat indices other than the basal heart rate (HR0) are not limited to these, and other indices such as the standard deviation of heart rates may also be used.

[0103] In the above embodiment, when the driver 20 is determined to be stressed, the driver is notified by voice and vibration, but the present disclosure is not limited to this. For example, when the driver 20 is determined to be stressed, a massage mechanism provided in the seat body 12 may be activated, or music may be played on an audio device provided in the vehicle.

[0104] In the above embodiment, the present disclosure is described as being applied to a driver's seat of a vehicle, but the present disclosure is not limited to this and may be applied to seats other than the driver's seat of a vehicle. Furthermore, the moving body to which the present disclosure relates is not limited to a vehicle, and the present disclosure may be applied to seats of moving bodies such as trains, airplanes, and ships.

[0105] Furthermore, although the above describes a state in which the stress assessment program 40 as an example of a stress assessment program according to the present disclosure is pre-stored (installed) in the memory unit 32, the stress assessment program according to the present disclosure can also be provided in a form in which it is recorded on a non-temporary recording medium such as an HDD, SSD, or DVD. [Explanation of symbols]

[0106] 10 Vehicle seats 12 Seat body 20 Driver 24 Heart rate monitor 26 Stress Judgment ECU 40 Stress Assessment Program 46 Basal Heart Rate Acquisition Device 48 Biometric data collection device 60 Judgment section

Claims

1. The subject's heart rate is HR, the subject's basal heart rate is HR ０ , coefficient c ｈ When HR≧c ｈ ×HR ０ …(1) When the duration T1 during which the state in which the heart rate HR of the subject satisfies the above formula (1) continues is equal to or longer than a predetermined value c t1 , and the ratio of frequency components of the heart rate interval of the subject is LF / HF and the threshold value for determining LF / HF is c f , LF / HF≦c f…(2) It is determined whether a first condition is satisfied, that is, a duration T2 when a state in which the ratio LF / HF of the frequency components of the heartbeat interval of the subject satisfies the above formula (2) continues is equal to or greater than a predetermined value c t1 , and when the duration T1 is equal to or greater than the predetermined value c t1 and the variation in the heartbeat interval of the subject is RMSSD and a threshold value for determining the RMSSD is c v , RMSSD≦c v…(3) A stress assessment device including a assessment unit that determines whether a second condition is met, that is, the duration T3 when the RMSSD of the subject's heart rate intervals continues to satisfy the above equation (3) is greater than or equal to a predetermined value c t1, ​​and that assesses the subject's stress state as no stress if both the first condition and the second condition are not met, that assesses the subject's stress state as low stress if either the first condition or the second condition is met, and that assesses the subject's stress state as high stress if both the first condition and the second condition are met.

2. When the subject's heart rate is HR, the subject's basal heart rate is HR 0 , and the coefficient is c h , HR≧c h ×HR 0…(1) When the integrated time t1, which is the time during which the heart rate HR of the subject satisfies the above formula (1) within a predetermined judgment time, is equal to or greater than a predetermined value c t2 , and the ratio of the frequency components of the heart rate interval of the subject is LF / HF and the threshold value for LF / HF judgment is c f , LF / HF≦c f…(2) It is determined whether or not a third condition is satisfied, that is, an integrated time t2 obtained by accumulating the time during which the ratio LF / HF of the frequency components of the heartbeat intervals of the subject satisfies the above formula (2) within a predetermined judgment time is equal to or greater than a predetermined value c t2 , and when the integrated time t1 is equal to or greater than the predetermined value c t2 and the variation in the heartbeat intervals of the subject is RMSSD and the judgment threshold for the RMSSD is c v , RMSSD≦c v…(3) A stress assessment device including a assessment unit that determines whether a fourth condition, that is, the accumulated time t3 obtained by accumulating the time during which the RMSSD of the subject's heart rate intervals satisfies the above equation (3) within a predetermined assessment time, is greater than or equal to a predetermined value c t2, satisfies the fourth condition, and determines the subject's stress state to be no stress if both the third and fourth conditions are not met, determines the subject's stress state to be low stress if either the third or fourth condition is met, and determines the subject's stress state to be high stress if both the third and fourth conditions are met.

3. A seat body on which a passenger of a moving body sits; The stress assessment device according to claim 1 or 2; A seat for a vehicle including:

4. When the subject's heart rate is HR, the subject's basal heart rate is HR 0 , and the coefficient is c h , HR≧c h ×HR 0…(1) When the duration T1 during which the state in which the heart rate HR of the subject satisfies the above formula (1) continues is equal to or longer than a predetermined value c t1 , and the ratio of frequency components of the heart rate interval of the subject is LF / HF and the threshold value for determining LF / HF is c f , LF / HF≦c f…(2) It is determined whether a first condition is satisfied, that is, a duration T2 when a state in which the ratio LF / HF of the frequency components of the heartbeat interval of the subject satisfies the above formula (2) continues is equal to or greater than a predetermined value c t1 , and when the duration T1 is equal to or greater than the predetermined value c t1 and the variation in the heartbeat interval of the subject is RMSSD and a threshold value for determining the RMSSD is c v , RMSSD≦c v…(3) A stress assessment method in which a computer executes processing including: determining whether a second condition is met, that is, the duration T3 when the state in which the variation in the heart rate interval of the subject satisfies the above equation (3) continues is equal to or greater than a predetermined value c t1; judging the stress state of the subject to be no stress if both the first condition and the second condition are not met; judging the stress state of the subject to be low stress if either the first condition or the second condition is met; and judging the stress state of the subject to be high stress if both the first condition and the second condition are met.

5. The subject's heart rate is HR, the subject's basal heart rate is HR ０ , coefficient c ｈ When HR≧c ｈ ×HR ０ …(1) The time t1 during which the subject's heart rate HR satisfies the above formula (1) within a predetermined determination time is equal to or exceeds a predetermined value c ｔ２ The ratio of the frequency components of the subject's heartbeat interval is LF / HF, and the threshold for determining LF / HF is c ｆ When LF / HF≦c ｆ …(2) The integrated time t2 obtained by accumulating the time during which the ratio LF / HF of the frequency components of the heartbeat interval of the subject satisfies the above formula (2) within a predetermined judgment time is equal to or greater than a predetermined value c ｔ２ and determining whether the third condition is satisfied, and whether the integrated time t1 is equal to or greater than a predetermined value c ｔ２ The above, and the variability of the heart rate interval of the subject is RMSSD, and the threshold for determining the RMSSD is c ｖ When RMSSD≦c ｖ …(3) The integrated time t3 obtained by integrating the time during which the RMSSD of the subject's heartbeat intervals satisfies the above formula (3) within a predetermined determination time is equal to or greater than a predetermined value c ｔ２ A stress assessment method in which a computer executes processing including determining whether a fourth condition, namely, the above, is met, and if both the third condition and the fourth condition are not met, determining the stress state of the subject to be no stress, if either the third condition or the fourth condition is met, determining the stress state of the subject to be low stress, and if both the third condition and the fourth condition are met, determining the stress state of the subject to be high stress.

6. A computer, When the subject's heart rate is HR, the subject's basal heart rate is HR 0 , and the coefficient is c h , HR≧c h ×HR 0…(1) When the duration T1 during which the state in which the heart rate HR of the subject satisfies the above formula (1) continues is equal to or longer than a predetermined value c t1 , and the ratio of frequency components of the heart rate interval of the subject is LF / HF and the threshold value for determining LF / HF is c f , LF / HF≦c f…(2) It is determined whether a first condition is satisfied, that is, a duration T2 when a state in which the ratio LF / HF of the frequency components of the heartbeat interval of the subject satisfies the above formula (2) continues is equal to or greater than a predetermined value c t1 , and when the duration T1 is equal to or greater than the predetermined value c t1 and the variation in the heartbeat interval of the subject is RMSSD and a threshold value for determining the RMSSD is c v , RMSSD≦c v…(3) A stress assessment program for executing processing including determining whether a second condition is met, that is, whether the duration T3 when the RMSSD of the subject's heart rate intervals continues to satisfy the above equation (3) is greater than or equal to a predetermined value c t1 , and judging the subject's stress state to be no stress if both the first condition and the second condition are not met, judging the subject's stress state to be low stress if either the first condition or the second condition is met, and judging the subject's stress state to be high stress if both the first condition and the second condition are met.

7. A computer, When the subject's heart rate is HR, the subject's basal heart rate is HR 0 , and the coefficient is c h , HR≧c h ×HR 0…(1) When the integrated time t1, which is the time during which the heart rate HR of the subject satisfies the above formula (1) within a predetermined judgment time, is equal to or greater than a predetermined value c t2 , and the ratio of the frequency components of the heart rate interval of the subject is LF / HF and the threshold value for LF / HF judgment is c f , LF / HF≦c f…(2) It is determined whether or not a third condition is satisfied, that is, an integrated time t2 obtained by accumulating the time during which the ratio LF / HF of the frequency components of the heartbeat intervals of the subject satisfies the above formula (2) within a predetermined judgment time is equal to or greater than a predetermined value c t2 , and when the integrated time t1 is equal to or greater than the predetermined value c t2 and the variation in the heartbeat intervals of the subject is RMSSD and the judgment threshold for the RMSSD is c v , RMSSD≦c v…(3) A stress assessment program for executing processing including: determining whether a fourth condition is met, namely, whether the accumulated time t3, which is the time during which the RMSSD of the subject's heart rate interval variation satisfies the above equation (3) within a predetermined assessment time, is greater than or equal to a predetermined value c t2; judging the subject's stress state to be no stress if both the third and fourth conditions are not met; judging the subject's stress state to be low stress if either the third or fourth condition is met; and judging the subject's stress state to be high stress if both the third and fourth conditions are met.

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