Mild hypohydration increases the frequency of driver errors during a prolonged, monotonous driving task.

UNLABELLED: The aim of the present study was to examine the effect of mild hypohydration on performance during a prolonged, monotonous driving task. METHODS: Eleven healthy males (age 22±4y) were instructed to consume a volume of fluid in line with published guidelines (HYD trial) or 25% of this intake (FR trial) in a crossover manner. Participants came to the laboratory the following morning after an overnight fast. One hour following a standard breakfast, a 120min driving simulation task began. Driver errors, including instances of lane drifting or late breaking, EEG and heart rate were recorded throughout the driving task RESULTS: Pre-trial body mass (P=0.692), urine osmolality (P=0.838) and serum osmolality (P=0.574) were the same on both trials. FR resulted in a 1.1±0.7% reduction in body mass, compared to -0.1±0.6% in the HYD trial (P=0.002). Urine and serum osmolality were both increased following FR (P<0.05). There was a progressive increase in the total number of driver errors observed during both the HYD and FR trials, but significantly more incidents were recorded throughout the FR trial (HYD 47±44, FR 101±84; ES=0.81; P=0.006) CONCLUSIONS: The results of the present study suggest that mild hypohydration, produced a significant increase in minor driving errors during a prolonged, monotonous drive, compared to that observed while performing the same task in a hydrated condition. The magnitude of decrement reported, was similar to that observed following the ingestion of an alcoholic beverage resulting in a blood alcohol content of approximately 0.08% (the current UK legal driving limit), or while sleep deprived.

Driver sleepiness-comparisons between young and older men during a monotonous afternoon simulated drive.

Young men figure prominently in sleep-related road crashes. Non-driving studies show them to be particularly vulnerable to sleep loss, compared with older men. We assessed the effect of a normal night's sleep vs. prior sleep restricted to 5h, in a counterbalanced design, on prolonged (2 h) afternoon simulated driving in 20 younger (av. 23 y) and 19 older (av. 67 y) healthy men. Driving was monitored for sleepiness related lane deviations, EEGs were recorded continuously and subjective ratings of sleepiness taken every 200 s. Following normal sleep there were no differences between groups for any measure. After sleep restriction younger drivers showed significantly more sleepiness-related deviations and greater 4-11 Hz EEG power, indicative of sleepiness. There was a near significant increase in subjective sleepiness. Correlations between the EEG and subjective measures were highly significant for both groups, indicating good self-insight into increasing sleepiness. We confirm the greater vulnerability of younger drivers to sleep loss under prolonged afternoon driving.

One night's CPAP withdrawal in otherwise compliant OSA patients: marked driving impairment but good awareness of increased sleepiness.

PURPOSE: Obstructive sleep apnoea (OSA) patients effectively treated by and compliant with continuous positive air pressure (CPAP) occasionally miss a night's treatment. The purpose of this study was to use a real car interactive driving simulator to assess the effects of such an occurrence on the next day's driving, including the extent to which these drivers are aware of increased sleepiness. METHODS: Eleven long-term compliant CPAP-treated 50-75-year-old male OSA participants completed a 2-h afternoon, simulated, realistic monotonous drive in an instrumented car, twice, following one night: (1) normal sleep with CPAP and (2) nil CPAP. Drifting out of road lane ('incidents'), subjective sleepiness every 200 s and continuous electroencephalogram (EEG) activities indicative of sleepiness and compensatory effort were monitored. RESULTS: Withdrawal of CPAP markedly increased sleep disturbance and led to significantly more incidents, a shorter 'safe' driving duration, increased alpha and theta EEG power and greater subjective sleepiness. However, increased EEG beta activity indicated that more compensatory effort was being applied. Importantly, under both conditions, there was a highly significant correlation between subjective and EEG measures of sleepiness, to the extent that participants were well aware of the effects of nil CPAP. CONCLUSIONS: Patients should be aware that compliance with treatment every night is crucial for safe driving.

Moderate sleep restriction in treated older male OSA participants: greater impairment during monotonous driving compared with controls.

OBJECTIVES: To examine the effects on monotonous driving of normal sleep versus one night of sleep restriction in continuous positive airway pressure (CPAP) treated obstructive sleep apnoea (OSA) patients compared with age matched healthy controls. METHODS: Nineteen CPAP treated compliant male OSA patients (OSA-treated patients (OPs)), aged 50-75 years, and 20 healthy age-matched controls underwent both a normal night's sleep and sleep restriction to 5h (OPs remained on CPAP) in a counterbalanced design. All participants completed a 2h afternoon monotonous drive in a realistic car simulator. Driving was monitored for sleepiness-related minor and major lane deviations, with 'safe' driving time being total time driven prior to first major lane deviation. EEGs were recorded continuously, and subjective sleepiness ratings were taken at regular intervals throughout the drive. RESULTS: After a normal night's sleep, OPs and controls did not differ in terms of driving performance or in their ability to assess the levels of their own sleepiness, with both groups driving 'safely' for approximately 90 min. However, after sleep restriction, OPs had a significantly shorter (65 min) safe driving time and had to apply more compensatory effort to maintain their alertness compared with controls. They also underestimated the enhanced sleepiness. Nevertheless, apart from this caveat, there were generally close associations between subjective sleepiness, likelihood of a major lane deviation and EEG changes indicative of sleepiness. CONCLUSIONS: With a normal night's sleep, effectively treated older men with OSA drive as safely as healthy men of the same age. However, after restricted sleep, driving impairment is worse than that of controls. This suggests that, although successful CPAP treatment can alleviate potential detrimental effects of OSA on monotonous driving following normal sleep, these patients remain more vulnerable to sleep restriction.

Early evening low alcohol intake also worsens sleepiness-related driving impairment.

Following night-time sleep restriction, afternoon driving performance during the bi-circadian surge in afternoon sleepiness is markedly worsened by blood alcohol concentrations (BACs) well under most national driving limits. This study assessed how driving with this same sleep restriction and BACs (av 40 mg and 28 mg alcohol/100 ml blood at the beginning and end of drive, respectively) respond during the evening circadian rise in alertness. In a 2 x 2 (alcohol versus control drink [double blind] x normal night sleep versus sleep restricted), repeated-measures design, eight healthy young men drove for 2 h from 18:00 h, in a real-car simulator, on a monotonous, simulated highway. Driving impairment (lane drifting), subjective sleepiness and EEG measures of sleepiness were recorded. While sleep restriction alone produced significant impairments to evening driving and subjective sleepiness, alcohol alone did not. However, alcohol combined with sleep restriction significantly worsened all indices, although, this was less than that found for afternoon driving with identical interventions. Whereas low BACs may not affect driving in normally alert drivers in the early evening, the addition of moderate sleep restriction still produces a dangerous combination. Probably, there is no 'safe' level of alcohol intake for otherwise sleepy drivers, at any time of the day.

Sleepiness combined with low alcohol intake in women drivers: greater impairment but better perception than men?

OBJECTIVES: We have previously shown that low blood alcohol concentrations (BAC) (at approximately half the legal driving limit in both the United Kingdom and in most states in the United States) exacerbate moderate sleepiness (sleep during the night restricted to 5 hours) and markedly impair driving ability in young men. There are distinct physiologic sex differences in the absorption, metabolism, and central nervous system effects of alcohol; therefore, we replicated this earlier study, this time using women and using similar BAC to provide a comparison. DESIGN: 2 x 2 repeated-measures counterbalanced. SETTING: 2-hour drive from 2:00 pm in an instrumented car on a simulated highway. INTERVENTIONS: Alcohol versus control and normal sleep versus sleep restricted to 5 hours. MEASUREMENTS AND RESULTS: Driving impairment (lane drifting), subjective sleepiness, and electroencephalographic measures of sleepiness. Sleep restriction significantly worsened driving performance and subjective sleepiness as it had in men. Surprisingly, unlike men, women showed no apparent adverse effects of alcohol alone on these indexes; they seemingly compensated for the effects of alcohol. However, alcohol's effects were profound when alcohol was combined with sleep restriction; nevertheless, women, unlike men, were aware of this enhanced sleepiness. After alcohol ingestion, the electroencephalogram showed increased beta activity, an effect not seen in men, indicating a differential pharmacokinetic effect of alcohol on the central nervous system, compensatory effort, or both. Debriefing questionnaires indicated that women were aware of the varying risks of driving under these different conditions. CONCLUSIONS: Legally "safe" BAC markedly worsen sleepiness-impaired driving in women. However, they seem to be aware of their impaired driving and are able to judge the degree of risk entailed. Such an attitude may contribute to the lower incidence of sleep- or alcohol-related crashes in women compared with men.