Abstract: Studies indicated that psychological stress may result in increase or decrease in target-specific sympathetic outputs, increase or decrease in certain vagal outputs. The altered responses may be less efficient and less adaptive and, thus, on a long-term basis, unfavorable to health. Evidence of disordered autonomic function has also been observed in patients with various somatic disorders, for instance, functional bowel disorders headaches, or cardiac arrhythmias. In order to clarify the relations between psychological stress and autonomic nervous system, in the present study, we examined the effect of different psychological stressors on the sympathetic and parasympathetic activities and other cardiovascular activities.
Method
Twenty four healthy female undergraduates participated in the study. The participants were requested to complete baseline rest, cancellation test, mirror-tracing task, arithmetic task and speech-preparation, and simultaneously recorded spectrum domain of HRV（TP: total power, HF: high frequency , LF: low frequency and LF/HF: low- to high-frequency ratio）, averaged R-R interval and blood pressure. The different components of HRV allow to observe sympathetic and parasympathetic function non-invasively and independently of each other. The data obtained were analyzed by SPSS 10.0. The order of the stressors presentation were counterbalanced in order to avoid order effect.
Results
One-way analysis of variance for repeated measures showed the values of TP and LF during speech-preparation were significantly increased than baseline and other tasks, HF was increased significantly than cancellation test and arithmetic and there was no difference compared to baseline. During other three tasks LF decreased compared to baseline, the values of TP, LF and HF were no difference between them. The values of LF/HF didn’t show main effect between any tasks. Compared to the baseline，any of the four psychological stressors induced a decrease for Averaged R-R interval, and an increase for the systolic pressure. No differences were observed for the diastolic pressure. Subjective experience of stress was not consistent with its physiological responses.
Conclusions
The findings indicated that the activities in sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) decreased during cancellation test, mirror-tracing task and arithmetic task. However, the activities of SNS and PNS during speech-preparation was stronger than other tasks. The autonomic nervous activities during speech-preparation were different from those on the other three tasks. Averaged R-R interval and Blood pressure were both sensitive to the differences between the baseline and the tasks. The differences of ANS activities during different tasks supported strongly for Berntson’s theory that proposed there were nine changeable modes of ANS. It was still not clear that the mental mechanism resulted in such differences

Key words: stress, autonomic nerve system activities, heart rate variability (HRV)