Changes in Physiological Parameters Induced by Simulated Driving Tasks: Morning vs. Afternoon Session

Introduction: Driving fatigue is one of the most common causes for traffic accidents. Immobilization of legs, hip, and waist is thought to play a major role in driving fatigue, as it hinders blood circulation and induce hemodynamic changes. Objective: the objective of the study was to monitor changes in physiological parameters before and after in-door simulated driving tasks conducted in the morning as well as afternoon sessions. Methods: 40 young male subjects were randomly divided into morning (group A) and afternoon (group B) sessions and participated in the 90-min simulated in-door driving task. Before and after the task, blood pressure (BP), heart rate (HR), and heart rate variability (HRV) parameters were measured using a novel wrist monitor ANSWatch® which utilized built-in bio-sensors in the cuff to acquire radial pulse waves directly. Palm temperatures were measured by a high-precision thermometer. A questionnaire ranking driving fatigue was filled by each volunteer before and after the driving task. Results: (1) From paired t-tests, both the morning and afternoon driving tasks caused decreases in HR and palm temperatures, and increases in HRV and VLF(AU) (Very low frequency(absolute unit)); For the morning session, LF(AU) (Low frequency(absolute unit)) and LF(NU)(Low frequency(normalized unit)) increased while HF(NU) (High frequency(normalized unit)) decreased; In contrast, LF(NU) and LF/HF decreased while HF(NU) increased for the afternoon session (all changes p<0.05). Systolic pressure was maintained in the morning session but dropped in the afternoon session (p<0.05). (2) From one-way and two-way MANOVA analyses, there was no significant difference between morning and afternoon session for the entire group of physiological parameters measured before or after driving tasks; However, LF(AU), LF(NU), and LF/HF three individual parameters measured before driving were higher in the afternoon session than in the morning session (p<0.05). (3) From written questionnaire, all subjects felt some degree of fatigue following the driving task. No statistical difference existed between the two driving sessions in terms of fatigue score baseline or score change due to driving. Conclusion: Multiple physiological parameters showed significant changes after simulated driving tasks. Distinct trends were found between the two driving sessions. In the morning session, poor circulation in the lower body (limbs, abdomen, and hip) caused decrease in palm temperatures and HR, but BP were maintained due to activation of the sympathetic nervous system as evidenced by increased HRV, LF(AU), and LF(NU). For the afternoon session, palm temperatures, HR and systolic pressure were all lowered. Parasympathetic nervous system was activated [indicated by increased HF(NU)] prompting the body to enter a sleepy state, which greatly increases accident risks in actual road driving. Monitoring of multiple physiological parameters in the study had gained great insight into mechanisms of homeo-stasis and provided a foundation in the future work to quantify driving fatigue in terms of degree of deviation from homeostatic states.