Abstract
The objective of the study was to monitor changes in physiological parameters (SYS, DIA, HR, HRV, LF(AU), LF(NU), HF(AU), HF(NU), LF/HF, VLF(AU), TRP and TLP, a total of 12 parameters), subjective fatigue feeling (by questionnaire), and blood pressure waveforms before and after an indoor simulated driving task for 90 to 120 minutes and conducted in the three time zones (morning, afternoon, and evening), with or without an exercise break. The results show that the time zone and the exercise break each had a significant effect on the changes of the whole set of the twelve physiological parameters based upon one-way MANOVA. Further, from two-way MANOVA (time zone and driving task), the driving task (90 or 120 mins) had very significant effect on the changes of the twelve physiological parameters. Moreover, from paired-t test (before vs. after driving), HRV, VLF(AU) and HF(AU) showed an increase while HR, TLP and TRP showed a decrease after driving, regardless of time zone or exercise break. In contrast, LF(NU), HF(NU) and LF/HF had opposite changes between the afternoon and the evening session and between with-exercise-break and without-exercise-break. Systolic pressure and radial artery waveform were better maintained in the state of homeostasis in the morning session than the afternoon or evening sessions, thanks to the activation of sympathetic nervous system. Exercise break had the similar effect. Driving task is a demanding activity both mentally and physically. Autonomic nervous system (ANS) activation may overcome some fatigue symptoms, but the recovery is nonetheless incomplete. Exercise break was shown to be an effective remedy, especially when accompanied by the ANS actions. Based upon the results of the study, the normalized parasympathetic index HF(NU), the normalized sympathetic index LF(NU) and the sympatho-vagal balance index LF/HF are three promising parameters that could be further developed for the monitoring of driver fatigue.