## 3 Results and Discussion
### Correlation between the Intervention Event and the HRV Change Ratio  
During all four sessions, the subject self-reported his traumatic event five times. Among the five trauma tellings, abrupt negative emotion changes within five minutes of the trauma tellings were observed four times. In the case of the only trauma telling not related to abrupt negative emotion change, the psychotherapist performed the stabilizing technique right after the trauma telling. Among the ten stabilizing techniques used in all four sessions, abrupt positive emotion change within five minutes was observed once. The trauma telling appears to have altered the subject's psychological status. To statistically evaluate the relationship between the intervention events (trauma telling, stabilization technique, positive emotion change, and negative emotion change) and the subject's psychological and physical status, the change ratios of the calculated HRV factors (RMSSD, SDNN, VLF, LF, HF, and Ratio) were analyzed. The change ratios of the HRV factors were used instead of their absolute values because the change trends are more meaningful than the absolute values. First, with respect to the cases marked as no intervention event, the change ratios of the HRV factors were calculated. In all four sessions, the time-zero HRV change ratios of  
Figure 4: Each 5 min SDNN and RMSSD in the fourth session. The 3 min data from the session start are omitted as being part of the stabilization period. The “P” marks are the positive emotion changing abruptly. The “N” mark is the negative emotion changing abruptly. The “S” mark is the stabilization technique. the non-noteworthy events were counted as 39. The five-min-later HRV change ratios were 23. The standard deviations of the RMSSD and SDNN were under 0.327, much smaller than the other standard deviations. The standard deviation range of the other HRV factors ranged from 0.489 to 1.803 and their average was 0.934. The average change ratios of the RMSSD and SDNN were \(-0.3\%\) and \(-10.2\%\) at time 0 and \(1.1\%\) and \(-11.9\%\) five minutes later, respectively. The RMSSD showed almost no change during the ordinary status, but the SDNN showed a gradual decrease of approximately 10%. Figure 5 exhibits the change ratio of the HRV factors when the subject described his traumatic event at time 0. In all four sessions, the trauma telling happened five times. The RMSSD and SDNN showed only reliable standard deviations. The SDNN increased by 10% at time 0 of the trauma telling and then decreased by 10% five minutes later. In relation to the average SDNN change ratio of the ordinary status (around \(-10\%\)), it appears that parasympathetic change occurred due to the trauma telling and then returned to the ordinary status. Considering the above-mentioned relation between the trauma telling and the abrupt negative emotional change, the SDNN change ratio according to the trauma telling can be explained. Even though the standard deviation of the RMSSD was the least among all the HRV factors, its change ratio (under 10%) was negligible compared to its change ratio at the ordinary status (around 0%). The change ratio of the HRV factors when the psychotherapist performed the stabilizing technique at time 0 was as shown in Figure 6. In all four sessions, the stabilizing technique was performed ten times. The RMSSD and SDNN showed only reliable standard deviations. The SDNN increased by about 23% at time 0 and then exhibited almost no change five minutes later. It is inferred that the stabilizing technique facilitated autonomic flexibility. Even though the standard deviation of the RMSSD was the least among all the HRV factors, its change ratio (under 10%) was negligible compared to its change ratio at the ordinary status (around 0%). Figure 5: Change ratio of the HRV when the subject described his trauma at time 0. During all the 4 sessions, the subject described his trauma 5 times. Figure 7 shows the change ratio of the HRV factors when the subject's abrupt positive emotion change was observed at time 0.