The deterioration of driving performance over time in drivers with untreated sleep apnea

Sleep apnea increases risk of driving crashes when left untreated. This study examined the driving performance decrements of untreated, undiagnosed sleep apnea drivers compared with healthy controls in a monotonous highway driving simulator task. It was hypothesized that the sleep apnea group would perform worse during a driving simulator test compared with the control group. A significant group by time interaction occurred indicating that sleep apnea participants’ performance degraded more quickly over the course of the drive. In contrast with previous studies, this sleep apnea group did not include sleep disorder center patients, but rather community volunteers whose screening indicated a significant apnea/hypopnea index of 15 or greater. There may be inherent differences between patients and nonpatients with sleep apnea, as patients may have a more significant impact on their quality of life, causing them to seek treatment. Still, the results are clear that although the sleep apnea group drove similarly to the control group at the start of the drive, they are sensitive to time on task effects. These results support the need to diagnose and treat sleep apnea.     

Investigating the relative effects of sleep deprivation and time of day on fatigue and performance

Time of day and the time since last sleep are acknowledged causes of fatigue, but comparatively little is known about how they interact. This study examines the relative effects of time of day and sleep deprivation on fatigue and performance. Two independent groups were exposed to 28 h of sleep deprivation beginning at 06:00 h for one group (n = 39) and at 00:00 h for the other (n = 22). By varying the start time for the two groups, but keeping constant the duration of sleep deprivation, the effects of variations in the time of day of testing could be examined. For the 06:00 h start group the longest period without sleep occurred close to the low point of the circadian rhythm. For the 00:00 h start group the circadian low point coincided with only two to six hours of sleep deprivation. Performance was evaluated two-hourly using eight computer-based tests and subjective fatigue ratings. The results showed a clear interaction effect. Both time of day and sleep deprivation affected performance but only in combination; neither had independent effects. These findings have implications for fatigue management.     

The distribution of sleepiness,sleep and work hours during a long distance morning trip: A comparison between night- and non-night workers

Few studies have examined the extent of driver sleepiness during a long distance morning trip. Sleepiness at this time may be high because of night work, waking early to commence work or travel, sleep disorders and the monotony of driving long distances. The objective of this study was to estimate the prevalence of chronic sleepiness (Epworth sleepiness score ≥ 10) and sleep restriction (≤5 h) in a sample of 649 drivers. Participants driving between 08:00 and 10:00 on three highways in regional Australia participated in a telephone interview. Approximately 18% of drivers reported chronic sleepiness. The proportions of night workers (NW) and non-night workers (NNW) with chronic sleepiness were not significantly different but males reported a significantly greater proportion of chronic sleepiness than females. The NW group had a significantly greater proportion of drivers with ≤5 h of sleep in the previous 24 and 48 h, fewer nights of full sleep (≤4), acute sleepiness and longer weekly work hours. The NW group reported driving a significantly longer distance at Time 1 (Mean = 140.29 ± 72.17 km, versus 117.55 ± 89.74 km) and an additional longer distance to complete the journey (Mean = 89.33 ± 95.23 km, versus 64.77 ± 94.07 km). The high proportions of sleep restriction and acute sleepiness among the NW group, and the amount of chronic sleepiness in the NW and NNW groups reported during a long distance morning trip may be of concern for driver safety.     

An assessment of the relevance of laboratory and motorcycling tests for investigating time of day and sleep deprivation influences on motorcycling performance

The aim of this study was to assess time of day and sleep deprivation impacts on motorcycling performance taking into consideration key variables, such as reaction time, motor coordination and vigilance that are principally involved in a riding task. Eight subjects participated in different tests sessions planned at 06:00 and 18:00h after a normal night's sleep and after a night of total sleep deprivation. During each session all subjects completed "laboratory" and "motorcycling" tests that were designed to assess each of the variables tested. As classically observed in sport performance, motorcycling performance demonstrates a time of day fluctuation by increasing from 06:00 to 18:00h during the day after a normal night's sleep. For each variable tested, the effects of sleep deprivation depend on the design of the test conditions. Thus, the data collected in laboratory specific conditions are more affected than those noted in arranged motorcycling situations. Taking into account that the sample size used in this study was limited, which may limit the results interpretations, these discrepancies suggest that during complex tasks, compensation mechanisms may be set up between different resources so as to maintain a good level of performance.     

Cognitive components of simulated driving performance: Sleep loss effects and predictors

Driving is a complex task, which can be broken down into specific cognitive processes. In order to determine which components contribute to drowsy driving impairments, the current study examined simulated driving and neurocognitive performance after one night of sleep deprivation. Nineteen professional drivers (age 45.3 ± 9.1) underwent two experimental sessions in randomised order: one after normal sleep and one after 27 h total sleep deprivation. A simulated driving task (AusEd), the psychomotor vigilance test (PVT), and neurocognitive tasks selected from the Cognitive Drug Research computerised neurocognitive assessment battery (simple and choice RT, Stroop Task, Digit Symbol Substitution Task, and Digit Vigilance Task) were administered at 10:00 h in both sessions. Mixed-effects ANOVAs were performed to examine the effect of sleep deprivation versus normal sleep on performance measures. To determine if any neurocognitive tests predicted driving performance (lane position variability, speed variability, braking RT), neurocognitive measures that were significantly affected by sleep deprivation were then added as a covariate to the ANOVAs for driving performance. Simulated driving performance and neurocognitive measures of vigilance and reaction time were impaired after sleep deprivation (p < 0.05), whereas tasks examining processing speed and executive functioning were not significantly affected by sleep loss. PVT performance significantly predicted specific aspects of simulated driving performance. Thus, psychomotor vigilance impairment may be a key cognitive component of driving impairment when sleep deprived. The generalisability of this finding to real-world driving remains to be investigated.     

Effects of THC on driving performance, physiological state and subjective feelings relative to alcohol

BACKGROUND: The effects of marijuana or THC on driving has been tested in several studies, but usually not in conjunction with physiological and subjective responses and not in comparison to alcohol effects on all three types of measures. OBJECTIVE: To assess the effects of two dosages of THC relative to alcohol on driving performance, physiological strain, and subjective feelings. METHOD: We tested the subjective feelings and driving abilities after placebo, smoking two dosages of THC (13 mg and 17 mg), drinking (0.05% BAC) and 24 h after smoking the high dose THC cigarette, while monitoring physiological activity of the drugs by heart rate. Fourteen healthy students, all recreational marijuana users, participated in the study. RESULTS: Both levels of THC cigarettes significantly affected the subjects in a dose-dependent manner. The moderate dose of alcohol and the low THC dose were equally detrimental to some of the driving abilities, with some differences between the two drugs. THC primarily caused elevation in physical effort and physical discomfort during the drive while alcohol tended to affect sleepiness level. After THC administration, subjects drove significantly slower than in the control condition, while after alcohol ingestion, subjects drove significantly faster than in the control condition. No THC effects were observed after 24 h on any of the measures.