The Effects of Sleep Apnea on Heart Rate Variability in a Simulator

Heart rate variability has been used as a measure of mental workload, stress, and fatigue in drivers. The main goal of this study was to evaluate whether drivers with obstructive sleep apnea syndrome (OSAS) may have significantly different heart rate variability from those who do not have OSAS. Such a condition may indicate lower stress levels and an increase in crash risk due to sleepiness. This study also evaluates whether significant deviations in HRV may occur as drivers become drowsier over time. Eleven drivers with OSAS were compared to twelve other drivers with no known sleep disorder. All were tested in a driving simulator over a 60-minute period that consisted of three uneventful drive segments on two-lane rural roads. Heart rates were collected using electrocardiogram (ECG). The variability of heart rate was computed for each subsequent five-minute interval by calculating the standard deviations of the R-R intervals (i.e., the time duration between two consecutive R waves of the ECG) within that time. Results showed that there were no significant differences in HRV over time for the comparison group. However, HRV for drivers with OSAS increased by each subsequent time interval. Drivers with OSAS also had significantly higher mean heart rate variability over the course of the drive. Specifically, based on the second regression model, the difference in heart rate variability between drivers with OSAS and the comparison group significantly increased after about 25 minutes of driving. This likely reflects the physiological effects of increased fatigue, which would lead to inattention to the driving environment and increased crash risk.