O078 A Comparison of Subjective Sleepiness and Subjective driving Performance between People Vulnerable Versus Resistant to Driving Impairment following Extended Wakefulness.

INTRODUCTION: Subjective sleepiness and driving performance are generally associated but show inter-individual variability. Specifically, some people are more vulnerable, while others are more resistant to driving impairment during extended wakefulness. We examined the relationship between subjective sleepiness and driving performance in groups resistant versus vulnerable to driving impairment during extended wakefulness. METHODS: Thirty-two adults (female=18, mean age=33.0yrs, SD=14.6) completed five 60-minute driving simulator assessments across 29 hours of extended wakefulness. Perceived sleepiness (Karolinska sleepiness scale, KSS) and driving performance (nine-point Likert scale) were assessed at 10-minute intervals while driving. Through cluster analysis, participants were categorised as vulnerable (n=16) or resistant (n=16) using steering deviation and crash data. Correlations, stepwise regressions, and ROC curves were used to identify predictors of driving impairment. RESULTS: Perceived sleepiness and driving impairment increased across the drives during wakefulness and within drives, regardless of grouping (p<0.001). The exception was the drive at 25-hours into wakefulness, where the vulnerable group showed higher perceived driving impairment within the drive (p=0.001). Pre-drive KSS, total sleep time, age and gender were not significant predictors of crashes at drives undertaken at 1-hour, 7-hours, 13-hours, or 25-hours, but were significant at 19-hours into wakefulness, together explaining 44% of the variance in crashes. DISCUSSION: Self-reports are sensitive to driving impairment but not differential vulnerability to performance decrements during extended wakefulness. However, the findings support that both groups can perceive their sleepiness and ideally employ appropriate countermeasures (e.g., stop driving, nap, caffeine). Future studies should target more objective predictors of vulnerable versus resistant groups.