JP7701201B2 - Method and system for determining driver's mental and physical state - Google Patents

Description

The present invention relates to a method and system for determining the mental and physical state of a driver while driving a railway vehicle, and in particular to a method and system for determining the mental and physical state of the driver from both measured heart rate and respiratory data of the driver.

The human autonomic nervous system is composed of the sympathetic nervous system and the parasympathetic nervous system, and by balancing these, the body and mind are kept in a normal state to cope with various aspects of daily life. Here, heart rate variability (HRV) contains both components that reflect the activity of the sympathetic nervous system, which reflects the state of mental and physical tension, and the activity of the parasympathetic nervous system, which leads to a calm state. Therefore, a system has been proposed that determines the activity state of the driver's autonomic nervous system from changes in the driver's heart rate while driving a vehicle, and reflects this in the vehicle's driving control or issues a warning.

For example, Patent Document 1 discloses a method for detecting changes in a driver's heart rate and judging the activity state of the driver's autonomic nerves. In this method, the driver's heart rate is measured using electrodes attached to the steering wheel of the vehicle, and the grip state of the steering wheel, which is equipped with multiple electrodes, is detected. Furthermore, an image of the driver is taken to detect the driver's posture, and from the heart rate and the driver's appearance, the activity state of the autonomic nerves can be judged, that is, a state requiring caution when driving the vehicle, such as tension, drowsiness, restlessness, fatigue, or absent-mindedness (distraction).

In addition, breathing, like heart rate, is related to the autonomic nervous system, but because breathing can be changed by a person's will, it is very difficult to determine the activity state of a driver's autonomic nervous system from biological cycle information measured only from breathing.

For example, Patent Document 2 discloses a method for determining the driver's level of psychological agitation by measuring changes in driving state in accordance with changes in breathing. A breathing signal is extracted from a body pressure signal from a pressure sensor attached to the back of the seat and the driving state quantities of the accelerator and brake. Since the body pressure signal contains body pressure fluctuations based on the operation of the accelerator and brake, an accurate breathing signal is obtained by removing the body pressure fluctuations from the body pressure signal using the driving state quantities.

Patent Document 3 also discloses a method for determining the degree of alertness, which is an index of the activity state of the autonomic nerves such as "dozing off," by numerically filtering the beat-to-beat interval (RRI) at which respiratory fluctuations are expected to occur for the measured heart rate, and detecting whether the fluctuation state of the RRI is that of a normal driving state or a simple increase or decrease corresponding to a sudden change in mental load. Here, the reference line f(n) corresponding to the fluctuation of the RRI is changed between the normal state and when there is a simple increase or decrease, and the variance RRVn of the RRI relative to this reference line f(n) is calculated, and the degree of alertness is detected based on the variance RRVn.

International Publication No. 2007/111223 JP 2006-042903 A JP 2007-044154 A

It has been proposed to extract a component corresponding to respiratory sinus arrhythmia (RSA) from the measured heart rate variability (HRV) and determine the activity state of the autonomic nerves. Here, it is difficult to determine the activity state of the autonomic nerves of a driver from biological cycle information of only the measured respiration or only the heart rate, but it is expected that by measuring respiration variability simultaneously with the heart rate and removing noise by performing a specified filter process, it is possible to analyze both the heart rate and respiration data together and obtain an evaluation of the response to various situations while driving a vehicle.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a method and system for determining the mental and physical state of a driver from both the measured heart rate and breathing data of the driver.

The method for determining the mental and physical state of a driver while driving a vehicle according to the present invention is a method for determining the mental and physical state of a driver while driving a railway vehicle by calculating an RSA value as a respiratory sinus arrhythmia (RSA) component of the heart rate from the correspondence using the time fluctuations of the heart rate and breathing measured in the driver while driving the railway vehicle, and by measuring the time fluctuations in the heart rate and breathing, and calculating the RSA value as the respiratory sinus arrhythmia (RSA) component of the heart rate from the correspondence. The method is characterized in that the time fluctuations are measured in a simulated driving section including a stressful task, and for physiological indices including breathing length and/or breathing amplitude and RSA value, reference values including reference breathing length and/or reference breathing amplitude are determined along with a reference RSA value that serves as a reference for each driver, and while measuring the time fluctuations in an actual driving section, if the RSA value is lower than the reference RSA value at a specific position for determining the mental and physical state, the driver's state of tension is determined from the fluctuation range of the physiological indices from the reference values.

This feature makes it possible to more clearly determine the driver's physical and mental state from both the measured heart rate and breathing data.

In the above-mentioned invention, a reference heart rate may be determined in accordance with the reference respiratory length and/or the reference respiratory amplitude in addition to the reference RSA value, and the state of tension may be determined by further combining the range of fluctuation of the heart rate from the reference heart rate and/or the range of fluctuation of the RSA value from the reference RSA value.

In the above-mentioned invention, the reference value may be determined as an arithmetic average of the corresponding physiological index throughout the simulated driving section.

In the above-mentioned invention, the determination of the state of tension may be characterized by determining the magnitude of the fluctuation range relative to the standard deviation of the physiological index throughout the simulated driving section.

In the above-mentioned invention, the RSA value may be calculated from the heart rate corresponding to one breath of the breath.

The invention described above may be characterized in that, from the physiological indices further including the heart rate, the rate of change of the heart rate, and the rate of change of the respiration length, one or more are selected for each driver along with the respiration length as a specific physiological indices, and respective reference values for the specific physiological indices are determined from measurements in the simulated driving section, and the state of tension is judged based on the fluctuation range of the specific physiological indices relative to the corresponding reference value.

In the above-mentioned invention, the simulated driving section may include a non-stress task, and one or more of the physiological indices corresponding to the non-stress task may be selected for each driver along with the respiratory length as a second specific physiological indices, and reference values for the second specific physiological indices may be determined from measurements in the simulated driving section, and when the RSA value is higher than the reference RSA value, the judgment may be made based on the fluctuation range of the second specific physiological indices relative to the corresponding reference value.

The above-mentioned invention may be characterized in that the fluctuation range from the reference RSA value is corrected by multiplying a correction coefficient determined by comparing the one-breath respiratory waveform and the one-breath heart rate variability waveform, which correspond to one breath of the respiratory waveform and the heart rate variability waveform, respectively.

In the above-mentioned invention, the simulated driving section may be provided by a driving simulator. With this feature, the time fluctuation of the heart rate and breathing during the simulated driving section can be easily measured, and the mental and physical state of the driver can be easily determined.

In the above-mentioned invention, the time variation of the respiration may be obtained by measuring the chest circumference or waist circumference of the driver. With this feature, the respiration data can be easily obtained, and the mental and physical state of the driver can be easily determined.

The system for determining the mental and physical state of a driver while driving a vehicle according to the present invention is a system that uses the time fluctuations of the heart rate and breathing measured in a driver while driving a railway vehicle to calculate an RSA value as a respiratory sinus arrhythmia (RSA) component of the heart rate from the correspondence and determines the mental and physical state of the driver, and includes a measurement unit including a sensor that measures the time fluctuations, and a control unit that calculates physiological indicators including breathing length and/or breathing amplitude and an RSA value from the time fluctuations measured by the measurement unit, and the control unit determines each of the reference values of the reference breathing length and/or reference breathing amplitude for the physiological indicators from the time fluctuations measured by the measurement unit in a simulated driving section including a tension task, as well as a reference RSA value that serves as a reference for each driver, and while measuring the time fluctuations in an actual driving section using the measurement unit, determines the driver's state of tension from the fluctuation range of the physiological indicators from each reference value when the RSA value is lower than the reference RSA value at a specific position for mental and physical state determination.

This feature makes it possible to more clearly determine the driver's physical and mental state from both the measured heart rate and breathing data.

In the above-mentioned invention, a reference heart rate may be determined in accordance with the reference respiratory length and/or the reference respiratory amplitude in addition to the reference RSA value, and the determination of the state of tension may be further made by combining the range of fluctuation of the heart rate from the reference heart rate and/or the range of fluctuation of the RSA value from the reference RSA value.

In the above-mentioned invention, the control unit may select one or more of the physiological indices, which further include the heart rate, the rate of change of the heart rate, and the rate of change of the respiratory length, for each driver and store them as specific physiological indices, determine reference values for the specific physiological indices from measurements in the simulated driving section, and make a judgment on the state of tension based on the range of fluctuation of the specific physiological indices from the corresponding reference value.

In the above-mentioned invention, the control unit may be characterized in that, based on the time fluctuations measured by the measurement unit in the simulated driving section further including a non-stress task, the control unit selects one or more from the physiological indices corresponding to the non-stress task for each driver together with the respiratory length and stores them as second specific physiological indices, determines reference values for the second specific physiological indices, and, when the RSA value is higher than the reference RSA value at a specific position for mental and physical state judgment, makes the judgment based on the fluctuation range from the corresponding reference value for the second specific physiological indices.

FIG. 1 is a block diagram of a system according to a representative example of the present invention. 1 is waveform data of the driver's heart rate and breathing. This is a graph showing the occurrence rate of RSA by score during stopping operations and station stops in a simulated train operation. 13 is a graph showing the occurrence rate for each score of (a) heart rate, (b) respiratory length, and (c) respiratory amplitude during a stopping operation and a station stop in a simulated train operation. 13 is a graph showing the occurrence rate for each score of the overall judgment during stopping operations and while stopping at stations in a simulated train operation. 13 is a graph showing (a) the occurrence rate of non-tension tendencies and tension tendencies for each physiological index for multiple tension and non-tension tasks in a simulated driving test, and (b) the occurrence rate when the physiological indexes are combined and judged comprehensively.

Below, a specific embodiment of a method and system for determining the mental and physical state of a driver while driving a vehicle according to a representative example of the present invention will be described with reference to Figures 1 to 5.

As shown in FIG. 1, the system 1 for determining the mental and physical state of a driver while driving a vehicle includes a waveform measurement unit 10 that measures the time variations of the driver's heart rate and breathing as waveforms, and a control unit 20 that includes a function for receiving and analyzing the waveform data of the time variations from the waveform measurement unit 10.

The waveform measurement unit 10 is, for example, a belt-like elastic device that can be worn on the driver's chest or abdomen, and includes a heart rate measurement sensor 11 that measures the heart rate, and a respiration measurement sensor 12 that measures the breathing state. Here, the heart rate measurement sensor 11 can acquire the time variation of the heart rate, i.e., the heart rate variation waveform HRV, using multiple electrocardiogram electrodes, etc. The respiration measurement sensor 12 can acquire the respiration waveform, which is the time variation of breathing, using a displacement sensor or the like that detects changes in the driver's chest or abdominal circumference, i.e., the circumference of the chest or abdomen. In this way, the waveform measurement unit 10 can be, for example, a wearable sensor, and can simultaneously and closely measure the time variation of the heart rate and breathing without restricting the driver's movements.

The control unit 20 controls the operation of the entire determination system 1, and includes a control device 21, a determination device 22, and a storage device 23. The control device 21 can instruct the waveform measurement unit 10 to measure the time variation of the heart rate and breathing and receive the waveform data. The determination device 22 can analyze the waveform data transferred from the control device 21 to determine the mental and physical state of the driver. The storage device 23 can store the programs executed by the determination device 22 and the waveform data received from the waveform measurement unit 10. The control unit 20 may further include an output device (not shown), such as a monitor.

The judgment device 22 measures the time fluctuations of heart rate and respiration in, for example, waveform data measured by the waveform measurement unit 10 using a predetermined judgment program, and obtains the heart rate (heart beat interval), heart beat amplitude, respiration length, and respiration amplitude as physiological indices along with the RSA (respiratory sinus arrhythmia) component, and can use these time fluctuations to comprehensively judge the driver's mental and physical state, particularly whether he is in a tense or non-tensioned state. The heart beat interval is obtained as the reciprocal of the heart rate. Among these physiological indices, the heart beat amplitude and respiration amplitude are standardized, including the measurement method and the method of quantifying the amplitude. For example, these amplitudes are calculated as one value per breath, and the amplitude when the driver is in the mental and physical state closest to the normal state is set to 1, and each amplitude can be expressed as a relative value to this.

The relative magnitude and change of the RSA value is said to indicate the activity state of the parasympathetic nervous system, and as the state of tension increases, the RSA value tends to become relatively lower. Therefore, a reference RSA value that serves as a benchmark for the RSA value can be set, and it can be determined that a state of tension exists when the RSA value measured drops from the reference RSA value. However, it is difficult to determine a state of tension with high accuracy using only the RSA value as an indicator.

In this embodiment, the state of tension is judged as follows. As described above, the RSA value tends to decrease in a state of tension. Therefore, when the RSA value is lowered below the reference RSA value, the probability that the driver's mental and physical state is in a state of tension increases. Therefore, when the RSA value is lowered below the reference RSA value, the relative strength of the state of tension is judged based on the breathing length and/or breathing amplitude, which are breathing components. When the state of tension is increased, both the breathing length and breathing amplitude tend to decrease. Therefore, when the breathing length and breathing amplitude are smaller than a predetermined reference breathing length and reference breathing amplitude, it is highly likely that the state of tension is stronger than the reference state of tension (the state of tension that should correspond to the reference RSA value), and the strength of the state of tension is judged based on the fluctuation range from the reference breathing length and reference breathing amplitude. In other words, the judgment is made based on the breathing length and breathing amplitude, which are values related to breathing, using the RSA value, which is a value related to the heart rate, as a trigger.

The standard RSA value, standard respiration length, and standard respiration amplitude are all determined for each driver by measuring the time fluctuations in heart rate and respiration during a simulated driving section that includes a task that causes stress. In other words, the fluctuations in heart rate and respiration in response to stress differ from driver to driver, and by determining standard values for each individual driver, the accuracy of the assessment of the state of stress is ensured.

In addition to respiratory length and respiratory amplitude, heart rate, heart rate amplitude, and RSA value may also be used in determining the state of tension. For example, a reference heart rate may also be determined for the heart rate, and the range of fluctuation of the heart rate from the reference heart rate may be determined and combined with the determination. Similarly, the range of fluctuation of the heart rate amplitude from the reference heart rate amplitude and the range of fluctuation of the RSA value from the reference RSA value may also be combined with the determination. This is expected to improve the accuracy of the determination.

The method for determining the reference values (reference RSA value, reference respiration length, reference respiration amplitude, reference heart rate, reference heart rate amplitude) varies depending on the type of tension state that is to be judged. For example, if it is desired to judge only a relatively strong state of tension, the reference value may be set small (and the heart rate large). In addition, by setting a value corresponding to a specific task in the simulated driving section as the reference value, it becomes possible to judge the strength of the tension state in comparison with the tension state for that specific task.

Furthermore, it has been confirmed that the correlation between the combination of physiological indices RSA value, respiration length, respiration amplitude, heart rate, and heart rate amplitude in a tense or non-tense state tends to differ for each driver. Such a tendency can be derived from the results of the simulated driving section described above, and a combination of physiological indices can be selected based on strong correlation, i.e., on the tendency to reproduce changes, and this can be used to determine the mental and physical state of the driver while driving a vehicle. This allows for a clearer state determination, making it possible to determine not only a tense state, but also a non-tense state.

Next, we will explain an example of actually determining the mental and physical state of a driver using the determination system 1.

Here, we assessed the mental and physical state, particularly the state of tension, of a driver while driving a railway vehicle. To this end, we used the assessment system 1 described above to measure the heart rate and respiration of the driver while driving a vehicle in a simulated driving section that included a task that caused tension (tension task), and found the time variations in these.

In the simulated driving section, a driving simulator was used to measure the heart rate and breathing of the driver while driving. Specifically, a simple railway driving simulator consisting of a large TV monitor and a one-handle controller was used. In the simulated driving, the driver repeated driving tasks a set number of times with breaks in between. A driving section between four stations, with a driving time of approximately 10 minutes, was set as the driving task. The driving tasks included stressful tasks such as the driving action of stopping a moving vehicle at a designated position. In order to allow the driver to concentrate on the simulated driving, the driver was instructed to drive at the specified speed limit according to the timetable. Here, the measurement results of the simulated driving repeatedly performed by one driver are explained.

As shown in FIG. 2, first, the heart rate variability waveform HRV and the respiration waveform BW were arranged on the same time axis for the measured waveform data. The heart rate variability waveform HRV was cut out for each time range corresponding to the respiration interval T separated by the respiration start point S of the respiration waveform BW. At this time, there was synchronism between the heart rate variability waveform HRV and the respiration interval T. The amplitude of the heart rate variability waveform HRV in each respiration interval T was taken as the RSA value. In other words, the RSA value was calculated from the heartbeat corresponding to one respiration. Note that the RSA value is preferably calculated after a conversion process in which line data connecting points on the heart rate variability waveform HRV that correspond in time to each respiration start point S is defined and this line data is subtracted from the heart rate variability waveform HRV. This conversion process can remove blood pressure variability system components that are affected by both the sympathetic and parasympathetic nerves.

For example, here, the arithmetic averages of the RSA value, heart rate, respiration length, and respiration amplitude obtained through the above-mentioned simulated operation section were used as the respective reference values, and the standard deviation from the average values was calculated for each value except for the respiration amplitude. The reference values were called the reference RSA value, reference heart rate, reference respiration length, and reference respiration amplitude, respectively. In addition, from the simulated operation section, the RSA value, heart rate, respiration length, and respiration amplitude corresponding to the positions during the stopping operation (20 seconds before the train stops at the station) and the positions during the train's stop at the station, which is less likely to cause tension, were extracted, and these were used as comparison targets and compared with the reference values to determine scores as follows.

That is, as shown in Figure 3, when the RSA value was more than a standard deviation higher than the reference RSA value, +1 point was assigned, when it was more than twice the standard deviation, +2 points were assigned, when it was more than twice the standard deviation, -1 point was assigned, and when it was more than twice the standard deviation, -2 points were assigned. Results other than 0 points were shown as the occurrence rate during stopping operations and when the train was stopped at a station. In other words, the range of variation from the reference RSA value was determined by judging whether the RSA value was large or small relative to the standard deviation or twice that value. As a result, it was found that the RSA value tends to be small during stopping operations, which are likely to cause stress. However, the RSA value often also became small even during stopping at a station, which is less likely to cause stress, and it was found that it is difficult to judge the state of stress based on the RSA value alone.

As shown in Figure 4(a), when the heart rate was higher than the reference heart rate by more than the standard deviation, +1 point was given, when it was higher than twice the standard deviation, +2 points, when it was lower than the standard deviation, -1 point, when it was lower than twice the standard deviation, -2 points, and results other than 0 points were shown as the occurrence rate during the stopping operation and while the train was stopped at the station. Heart rate tended to increase during the stopping operation, which is likely to cause stress.

As shown in Figure 4(b), when the breathing length was larger than the reference breathing length by more than the standard deviation, +1 point was given, when it was larger than twice the standard deviation, +2 points were given, when it was smaller than the standard deviation, -1 point was given, and when it was smaller than twice the standard deviation, -2 points were given. Results other than 0 points were shown as the occurrence rate during the stopping operation and while the train was stopped at the station. Breathing length tended to be smaller during the stopping operation, which is likely to cause stress.

As shown in Figure 4 (c), a score of +1 was assigned if the respiration amplitude was more than twice the reference respiration amplitude, and a score of -1 was assigned if the respiration amplitude was less than half the reference amplitude. Results other than 0 points were shown as the occurrence rate during the stopping operation and while the train was stopped at the station. The respiration amplitude tended to be smaller during the stopping operation, which is likely to cause stress.

However, it was found that determining the state of tension using heart rate, respiratory length, and respiratory amplitude alone was more difficult than using the RSA value described above.

Therefore, the signs of the scores for RSA, heart rate, respiratory length, and respiratory amplitude were changed so that the score that is more likely to occur under stress was positive; in other words, the scores for RSA value, respiratory length, and respiratory amplitude were multiplied by -1, and the individual scores were added up to determine an overall judgment.

As shown in Figure 5, in the overall assessment, a score of "3" was given almost exclusively to drivers during the stopping operation, and the driver's mental and physical state was considered to be in a relatively strong state of tension. On the other hand, in the assessments that gave negative scores, there were almost no instances of drivers during the stopping operation, and it was considered very likely that the driver was in a relatively weak state of tension.

As described above, the relative strength of tension in the mental and physical state of the driver can be determined from both the measured heart rate and respiration data. In particular, since the determination is made based on the difference between a reference value and a predetermined value relative thereto, such as using a reference RSA value and a standard deviation, the determination can be made based only on the relative numerical changes in the heart rate variability waveform and the respiration waveform. In other words, the accuracy of the absolute value of the measured value is not required. Therefore, the detailed calculation method of the RSA value is not particularly limited, and it is sufficient that one is set throughout the entire process from the simulated driving to the determination of the mental and physical state of the driver. In addition, it is meaningful to determine the mental and physical state of the driver from both the heart rate and respiration data, and the mental and physical state can be determined at least more accurately than a determination based on the RSA value alone by simply combining the determination of either the respiration length or the respiration amplitude with the trigger of the determination based on the RSA value. In addition, it is preferable to make a determination that combines both the respiration length and the respiration amplitude, and further, as described above, a determination that combines the heart rate, the RSA value, and the heart rate amplitude can also be made.

In addition, as mentioned above, since the measurement does not require absolute precision, obtaining the respiratory waveform can be a simple measurement method that simply detects changes in the driver's chest or waist circumference, and a wearable sensor can be used for the measurement.

In the above example, the RSA value, heart rate, heart rate amplitude, respiration length, and respiration amplitude during the stop operation and station stop were extracted from the simulated operation section and judged, but the reference value and standard deviation obtained in the simulated operation section can be used to measure the time fluctuation of the driver's heart rate and respiration in the actual operation section and judge the driver's mental and physical state. In other words, by calculating the reference RSA value, reference respiration length, reference respiration amplitude and their respective standard deviations, as well as the reference heart rate and reference heart rate amplitude in the simulated operation and storing them in the storage device 23, the driver's mental and physical state can be judged in real time at a specific position in other operation sections such as the subsequent actual operation section. The specific position is the position at which the driver's mental and physical state is to be judged, and is the position on the time axis where the time fluctuation of the heart rate and respiration was measured, but it can also be a spatial position by corresponding the spatial position in the operation section to the time axis. In particular, in the case of railways, the running schedule of vehicles on the operation section is set, and for example, the mental and physical state of the driver can be judged even just before a specific section such as a station or a railroad crossing, and an alarm can be issued in some cases. As mentioned above, these reference values and standard deviations include individual differences between drivers, so they are determined and used for each driver.

In the above example, the reference RSA value, reference heart rate, reference heart rate amplitude, reference respiration length, and reference respiration amplitude were determined as arithmetic averages over the simulated driving section, but they may be determined in other ways. For example, if the reference RSA value is determined to be the maximum value of the values obtained in the simulated driving section, the reference RSA value can be assumed to be an almost completely relaxed state. The state of tension is then scored in stages based on the range of decrease in the RSA value from the reference RSA value, and this can be combined with a determination of the range of change from the reference value, such as respiration length, in the same manner as above, to determine the driver's physical and mental state.

Furthermore, when the mental and physical state is judged by combining the fluctuation range of the RSA value from the reference RSA value, there is also a method of correcting such fluctuation range. First, the respiratory waveform and the heart rate variability waveform corresponding to one breath are respectively set as the one-breath respiratory waveform and the one-breath heart rate variability waveform. At this time, the one-breath respiratory waveform and the one-breath heart rate variability waveform are compared, and a correction coefficient is determined that is closer to 1 the higher the correlation between them and closer to 0 the lower the correlation. Such a correction coefficient can be calculated, for example, using the correlation coefficient or phase difference between the one-breath respiratory waveform and the one-breath heart rate variability waveform. If the correlation coefficient is used, the absolute value of the correlation coefficient can be used as the correction coefficient. If the phase difference is used, the absolute value of (π-phase difference)/π can be used as the correction coefficient. The integrated value of these two values may be used as the correction coefficient. Then, the correction is performed by multiplying the correction coefficient by the fluctuation range from the reference RSA value, and the judgment is performed in the same manner as above. The higher the correlation between the one-breath respiratory waveform and the one-breath heart rate variability waveform, the higher the reliability of the RSA value tends to be, so by making such a correction, the reliability of the RSA value can be reflected and the driver's mental and physical state can be judged with high accuracy.

In the above embodiment, the state of tension at a certain point in time was determined based on the time fluctuation of the heart rate and breathing at that point in time, but the mental and physical state can also be determined based on the temporal context. For example, if the RSA value is very high (for example, four times or more the reference RSA value) and the fluctuation range (distance) from the reference RSA value in the next breathing section T (see FIG. 2) falls significantly below the standard deviation, it can be determined that the driver is in a state of extreme tension or psychological agitation. In addition, when the driver is breathing regularly, it is highly likely that the driver is in a moderate state of tension that is favorable for driving operations, or in a state of reduced arousal. Therefore, if the distance between the breathing length and the reference breathing length is 10% or less in any of four consecutive breathing sections T, it is deemed to be regular breathing, and if the heart rate is constant or increasing at a value greater than the reference heart rate, it is determined to be moderate tension, and if the heart rate is constant or decreasing at a value less than the reference heart rate, it is determined to be a state of weaker tension (or a state of reduced arousal). In addition, if a person takes a deep breath, such as when the breathing amplitude exceeds twice the reference breathing amplitude or when the breathing length is more than twice the standard deviation of the reference breathing length, it can be determined that a change in mental and physical state has occurred around that time.

Here, it was found that in the five physiological indices, which are the three physiological indices of RSA value, respiration length, and heart rate, plus the respiration length change rate and heart rate change rate, there are differences in the tendency for changes to be reproduced in response to stressful tasks for each individual driver, while the change in respiration length in response to stressful tasks is consistent regardless of the individual driver. Therefore, by determining the state of tension using respiration length and another physiological indice in combination with it that has a high tendency to reproduce changes in response to stressful tasks that differ for each individual driver, a more accurate determination can be made.

In other words, the determination system 1 selects and stores, in the control unit 20, one or more physiological indices that show a tendency to reproduce changes in the respiratory length change rate, heart rate (heart beat interval), and heart rate change rate (heart beat interval change rate) RSA value corresponding to the tension task, that is, the same changes repeatedly, together with the respiratory length, as specific physiological indices for each driver. Such selection may be performed by setting a change range in advance and automatically filtering, or other known methods may be used. Then, along with the reference RSA value and reference respiratory length that serve as the reference for each driver, the reference values for each specific physiological indices are determined in the same manner as described above. Then, in determining the state of tension, the range of fluctuation from the corresponding reference value for the specific physiological indices including the respiratory length is combined, as described above, to determine the state of tension.

Figure 6(a) shows an example of the occurrence rate of non-tension and tension tendencies for each physiological index in response to tension tasks in a simulated driving session that includes multiple tension and non-tension tasks. The left side of the bar graph for each physiological index is the occurrence rate that indicates a tendency toward a non-tension state, i.e., an error in judging a state as non-tension despite the task being tension-related, and the right side of the bar graph is the occurrence rate that indicates a tendency toward a tension state, i.e., the correct answer.

The heartbeat interval change rate and respiration length change rate were calculated and evaluated as follows. In detail, the heartbeat interval calculated when the driver is estimated to be in the mental and physical state closest to normal is set as "1" in advance. Then, if the difference between the second to fourth heartbeat intervals excluding the first one out of the four consecutive heartbeat intervals calculated for each breath and the previous one (the difference between the first one in the case of the second one) is all "0.25" or less, the heartbeat interval is evaluated as stable and regular, and this is used to judge the mental and physical state. In other words, the standard heartbeat interval change rate is set to "0.25" or less, and the change rate per breath of four consecutive heartbeat intervals is evaluated. The respiration length change rate can be calculated and evaluated in the same way as the heartbeat interval change rate.

According to this, the heart beat interval tends to indicate the correct answer along with the respiratory length. Therefore, as described above, compared to the overall judgment B (see FIG. 6(b)) which combines the fluctuation range of the respiratory length from the reference respiratory length and the fluctuation range of the respiratory length change rate from the reference respiratory length change rate, the overall judgment A (see FIG. 6(b)) which combines the fluctuation range of the respiratory length from the reference respiratory length and the fluctuation range of the heart beat interval from the reference heart beat interval more correctly indicates the tendency to be in a tense state.

Although it has been difficult to determine a non-stressed state, similar to the above, by selecting a second specific physiological index, including respiratory length, that has a high tendency to reproduce changes in response to non-stress tasks that differ for each individual driver (e.g., while the train is stopped at a station), it becomes possible to determine the stressed state using these.

Although the representative embodiment of the present invention has been described above, the present invention is not necessarily limited to this embodiment, and may be modified as appropriate by those skilled in the art. In other words, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the scope of the appended claims.

1 Determination system 10 Waveform measurement unit 11 Heart rate measurement sensor 12 Respiration measurement sensor 20 Control unit 21 Control device 22 Determination device 23 Storage device

Claims (10)

A method for judging a mental and physical state of a driver by calculating a respiratory sinus arrhythmia (RSA) value as a RSA component of a heart rate from a correspondence between the time fluctuations of the heart rate and the respiration measured in the driver while driving a railway vehicle, comprising:
The time variation is measured in a simulated driving section including a tension task, and for physiological indices including a respiratory length, a respiratory amplitude, and an RSA value, a reference RSA value serving as a reference for each driver and each reference value including a reference respiratory length and a reference respiratory amplitude are determined;
A method for determining the mental and physical state of a driver while driving a vehicle, characterized in that while measuring the time fluctuations in an actual driving section, if the RSA value is lower than the standard RSA value at a specific position for determining the mental and physical state, the RSA value, the respiratory length and the respiratory amplitude are given positive or negative values for the fluctuation range from the standard RSA value, the standard respiratory length and the standard respiratory amplitude, respectively, and the sum of these values is standardized to determine the driver's state of tension before and after the stopping operation. determining a reference heart rate and a reference heart rate amplitude in accordance with the reference respiratory length and the reference respiratory amplitude;
2. The method for determining the mental and physical state of a driver while driving a vehicle according to claim 1, further comprising the steps of: giving a positive or negative value to one or more of the range of fluctuation of the heart rate from the reference heart rate and the range of fluctuation of the heart rate amplitude from the reference heart rate amplitude, standardizing the range and adding the value to the range of fluctuation of the heart rate and the reference heart rate amplitude. The method for determining the mental and physical state of a driver while driving a vehicle according to claim 2, characterized in that the reference RSA value, the reference respiration length, the reference heart rate, and the reference heart rate amplitude are determined as the arithmetic averages of the RSA value, the respiration length, the heart rate, and the heart rate amplitude, respectively, throughout the simulated driving section. 4. A method for determining the mental and physical state of a driver while driving a vehicle as claimed in claim 3, characterized in that the standard deviations of the RSA value, the respiratory length, and the heart rate throughout the simulated driving section are calculated, and when the fluctuation range relative to the standard deviation is small, they are not added to the value. The method for determining the mental and physical state of a driver while driving a vehicle according to any one of claims 1 to 4, characterized in that the RSA value is calculated from the heart rate corresponding to one breath of the breath. A method for determining the physical and mental state of a driver while driving a vehicle as described in claim 2, characterized in that a correction coefficient determined by comparing a one-breath respiratory waveform and a one-breath heart rate variability waveform corresponding to one breath of the respiratory waveform and the heart rate variability waveform, respectively, is multiplied by the range of fluctuation of the RSA value from the standard RSA value to determine the range of fluctuation from the standard RSA value. The method for determining the mental and physical state of a driver while driving a vehicle according to any one of claims 1 to 6, characterized in that the simulated driving section is provided by a driving simulator. The method for determining the mental and physical state of a driver while driving a vehicle according to any one of claims 1 to 7, characterized in that the time variation in breathing is obtained by measuring the driver's chest circumference or waist circumference. A system for judging a mental and physical state of a driver by calculating a respiratory sinus arrhythmia (RSA) value as a component of a heart rate from a correspondence between the time fluctuations of a heart rate and a respiration measured in the driver while the driver is driving a railway vehicle, the system comprising:
A measurement unit including a sensor for measuring the time variation;
A control unit that calculates physiological indices including a respiratory length, a respiratory amplitude, and an RSA value from the time variation measured by the measurement unit;
The control unit
From the time variation measured by the measurement unit in the simulated driving section including the stress task, a reference RSA value is determined as a reference for each driver, along with reference values including a reference respiration length and a reference respiration amplitude;
A system for determining the mental and physical state of a driver while driving a vehicle, characterized in that while the measurement unit measures the time fluctuations in an actual driving section, if the RSA value is lower than the reference RSA value at a specific position for determining the mental and physical state, the RSA value, the respiratory length and the respiratory amplitude are standardized by giving positive or negative values to the fluctuation ranges from the reference RSA value, the reference respiratory length and the reference respiratory amplitude, respectively, and the total value is used to determine the driver's state of tension before and after the stopping operation. determining a reference heart rate and a reference heart rate amplitude in accordance with the reference respiratory length and the reference respiratory amplitude;
The system for determining the mental and physical state of a driver while driving a vehicle as described in claim 9, characterized in that at least one of the range of fluctuation of the heart rate from the reference heart rate and the range of fluctuation of the heart rate amplitude from the reference heart rate amplitude is further given a positive or negative value to be standardized and summed to the value.

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