Early morning driver sleepiness: effectiveness of 200 mg caffeine

Sleep-related vehicle accidents are prevalent early morning, especially in younger drivers. In two independent studies following a night of either restricted or nil sleep, young experienced drivers drove for 2 hr (0600-0800 h) continuously in an immobile car on an interactive, computer-generated, dull, and monotonous roadway. This exercise followed ingestion (at 0530 h) of 200 mg caffeine (= 2-3 cups coffee) versus placebo, counterbalanced, double blind. Driving incidents (lane drifting), subjective sleepiness, and 4-11 Hz electroencephalogram (EEG) activity were logged. In Study 1 (sleeping 0000-0500 h), caffeine significantly reduced incidents and subjective sleepiness throughout the 2-hr drive, and EEG power for the second 30-min period. In Study 2 (no sleep), sleepiness affected all measures profoundly, and driving was terminated after 1 hr. Nevertheless, caffeine reduced incidents significantly for the first 30 min and subjective sleepiness for the hour. This caffeine dose, feasibly taken via coffee, effectively reduces early morning driver sleepiness for about 30 min following nil sleep, and for around 2 hr after sleep restriction.     

Effects of moderate sleep deprivation and low-dose alcohol on driving simulator performance and perception in young men

STUDY OBJECTIVE: To determine the combined effects of sleep restriction and low-dose alcohol on driving simulator performance, EEG, and subjective levels of sleepiness and performance in the mid-afternoon. DESIGN: Repeated measures with 4 experimental conditions. Normal sleep without alcohol, sleep restriction alone (4 hours) and sleep restriction in combination with 2 different low blood alcohol concentrations (0.025 g/dL and 0.035 g/dL). SETTING: Sleep Laboratory, Adelaide Institute for Sleep Health. PARTICIPANTS: Twenty-one healthy young men, aged 18-30 years, mean (+/-SD) = 22.5(+/-3.7) years, BMI = 25(+/-6.7) kg/m2; all had normal sleep patterns and were free of sleep disorders. MEASUREMENTS: Participants completed a 70-minute simulated driving session, commencing at 14:00. Driving parameters included steering deviation, braking reaction time, and number of collisions. Alpha and theta EEG activity and subjective driving performance and sleepiness were also measured throughout the driving task. RESULTS: All measures were significantly affected by time. Steering deviation increased significantly when sleep restriction was combined with the higher dose alcohol. This combination also resulted in a significant increase in alpha/theta EEG activity throughout the drive, as well as greater subjective sleepiness and negative driving performance ratings compared to control or sleep restriction alone. DISCUSSION: These data indicate that combining low-dose alcohol with moderate sleep restriction results in significant decrements to subjective alertness and performance as well as to some driving performance and EEG parameters. This highlights the potential risks of driving after consumption of low and legal doses of alcohol when also sleep restricted.     

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.     

Sharp and sleepy: evidence for dissociation between sleep pressure and nocturnal performance

While sleep restriction decreases performance, not all individuals are equal with regard to sensitivity to sleep loss. We tested the hypothesis that performance could be independent of sleep pressure as defined by EEG alpha-theta power. Twenty healthy subjects (10 vulnerable and 10 resistant) underwent sleep deprivation for 25 h. Subjects had to rate their sleepiness (Karolinska Sleepiness Scale) and to perform a 10-min psychomotor vigilance task (PVT) every 2 h (20:00-08:00 hours). Sleep pressure was measured by EEG power spectral analysis (alpha-theta band 6.0-9.0 Hz). Initial performance, EEG spectral power and KSS score were equal in both groups (ANOVA, NS). The performance of vulnerable subjects significantly increased during the night (rANOVA, P < 0.01), whereas resistant subjects globally sustained their performance. Homeostatic pressure and subjective sleepiness significantly increased during the night (rANOVA, P < 0.01) identically in both categories (rANOVA, NS). Resistant subjects sustained their reaction time independently of the increase in homeostatic pressure. The phenotypic determinants of vulnerability to extended wakefulness remain unknown.     

Having to stop driving at night because of dangerous sleepiness – awareness,physiology and behaviour

A large number of accidents are due to the driver falling asleep at the wheel, but details of this link have not been studied on a real road. The purpose of the present study was to describe the development of sleepiness indicators, leading to the drive being terminated prematurely by the onboard expert driving instructor because of imminent danger. Eighteen individuals participated during a day drive and a night drive on a motorway (both 90 min). Eight drivers terminated (N) prematurely (after 43 min) because of sleep‐related imminent danger [according to the driving instructor or their own judgement (two cases)]. The results showed very high sleepiness ratings (8.5 units on the Karolinska Sleepiness Scale) immediately before termination (<7 at a similar time interval for those 10 who completed the drive). Group N also showed significantly higher levels of sleep intrusions on the electroencephalography/electro‐oculography (EEG/EOG) than those who completed the drive (group C). The sleep intrusions were increased in group N during the first 40 min of the night drive. During the day drive, sleep intrusions were increased significantly in group N. The night drive showed significant increases of all sleepiness indicators compared to the day drive, but also reduced speed and driving to the left in the lane. It was concluded that 44% of drivers during late‐night driving became dangerously sleepy, and that this group showed higher perceived sleepiness and more sleep intrusions in the EEG/EOG.     

'Post-lunch' sleepiness during prolonged, monotonous driving - effects of meal size

The 'post-lunch' dip is a bi-circadian phenomenon, largely unrelated to lunch, and worsened by a disturbed prior night's sleep. Despite anecdotal claims of adverse effects of larger lunches on afternoon driving ability, there is little actual driving data to support this belief. Although there have been various (non-driving) laboratory studies assessing meal size and micronutrient effects on psychological performance tests, findings are mixed. Moreover, most have not utilised heightened afternoon sleepiness after a shortened night's sleep, and few tested beyond 20 min. Using a real car interactive simulator having full size screen projection, we compared the effects on a 2h monotonous afternoon drive, of two very similar, palatable lunches ('light': 305 cal vs 'heavy': 922 cal [having 3× fat and 2× carbohydrate contents]), given double blind in a repeated measures counterbalanced design, to 12 young male drivers whose prior night's sleep had been restricted to 5h. Sleepiness-related lane drifting ('incidents'), subjective sleepiness and EEG (4-11 Hz power - indicative of sleepiness) were logged throughout. The heavy lunch caused significant increases to both incidents and EEG power, and a trend for greater subjective sleepiness. All three indices showed a significant worsening of sleepiness over the drive under both lunch conditions. Whilst there were no significant condition×time interactions, there was no difference between lunches for at least the first 30 min of the drive when, thereafter, the differences appeared. Ours was a realistic driving study, utilising typical lunches, following an unexceptional level of prior sleep loss, and where a heavy lunch exacerbated inherent sleepiness, to further impair monotonous driving.     

Temporal profile of prolonged, night-time driving performance: breaks from driving temporarily reduce time-on-task fatigue but not sleepiness

Breaks are often used by drivers to counteract sleepiness and time-on-task fatigue during prolonged driving. We examined the temporal profile of changes in driving performance, electroencephalogram (EEG) activity and subjective measures of sleepiness and fatigue during prolonged nocturnal driving in a car simulator. In addition, the study examined the impact of regular breaks from driving on performance, sleepiness and fatigue. Healthy volunteers (n=12, 23-45 years) maintained a regular sleep-wake pattern for 14 days and were then in a laboratory from 21:00 to 08:30 hours. The driving simulator scene was designed to simulate monotonous night-time rural driving. Participants drove 4 × 2-h test sessions, with a break from driving of 1 h between each session. During the break participants performed tests assessing sleepiness and fatigue, and psychomotor performance (~30 mins), and then were permitted to sit quietly. They were monitored for wakefulness, and not permitted to nap or ingest caffeine. EEG was recorded during the driving task, and subjective assessments of sleepiness and fatigue were obtained at the start and completion of each session. We found that driving performance deteriorated (2.5-fold), EEG delta, theta and alpha activity increased, and subjective sleepiness and fatigue ratings increased across the testing period. Driving performance and fatigue ratings improved following the scheduled breaks from driving, while the breaks did not affect EEG activity and subjective sleepiness. Time-on-task effects increased through the testing period, indicating that these effects are exacerbated by increasing sleepiness. Breaks from driving without sleep temporarily ameliorate time-on-task fatigue, but provide little benefit to the sleepy driver.     

Suppression of sleepiness in drivers: Combination of caffeine with a short nap

Previous research has shown that caffeine and a<15-min nap effectively and separately reduce sleepiness in drivers for I hr. In the present study, we examined in 12 sleepy individuals the treatments combined, taken during a 30-min break, prior to a longer (2 hr) continuous monotonous afternoon drive in a car simulator. Nonnap comparisons were 200 mg caffeine only and placebo. For placebo, driving incidents. Subjective and electroencephalographic measures of sleepiness all reflected a mid-afternoon peak'. This peak was significantly reduced by caffeine and eliminated by the combined treatment, which reduced incidents to 9% of placebo levels versus 34% of placebo levels for caffeine alone. Naps comprising “nonsleep dozing” were still effective.     

Task-dependent differences in subjective fatigue scores

The aim of the present study was to evaluate time-on-task effects on subjective fatigue in two different tasks of varying monotony during night-time testing (20:00 to 4:00 hours) in a sleep deprivation intervention. The experiment included eight test runs separated by breaks of approximately 20 min. Twenty healthy volunteers performed a driving simulator and the Mackworth clock vigilance task in four of the test runs each. Sequence of tasks was varied across subjects. Before and after each task, subjective sleepiness was assessed by means of the Karolinska sleepiness scale and subjective fatigue was rated on the Samn-Perelli checklist. Fatigue and sleepiness significantly increased over the course of the night. Both tasks led to an increase in fatigue and sleepiness across test runs. However, this time-on-task effect was larger in the vigilance than in the driving simulator task. It is important to note that fatigue and sleepiness in one test run were not influenced by the task performed in the preceding test run, that is there were no cross-over effects. The results suggest that time-on-task effects superimpose circadian and sleep-related factors affecting fatigue. They depend on the monotony of the task and can be quantified by means of a design including separate test runs divided by breaks.     

CNS arousal and neurobehavioral performance in a short-term sleep restriction paradigm

Few studies have investigated waking electrophysiological measures of arousal during sleep restriction. This study examined electroencephalogram (EEG) activity and performance during a 96-hour laboratory protocol where participants slept a baseline night (8 h), were randomly assigned to 3-, 5-, or 8-hour sleep groups for the next two nights sleep restriction (SR1, SR2), and then slept a recovery night (8 h). There were dose-dependent deficits on measures of mood, sleepiness, and reaction time that were apparent during this short-term bout of sleep restriction. The ratio of alpha to theta EEG recorded at rest indicated dose-dependent changes in CNS arousal. At 9:00 hours, both the 3- and 5-hour groups showed EEG slowing (sleepiness) during restriction, with the 3-hour group exhibiting greater deficits. Later in the day at 13:00 hours, the 5-hour group no longer exhibited EEG slowing, but the extent of slowing was more widespread across the scalp for the 3-hour group. High-frequency EEG, a measure of effort, was greater on the mornings following sleep restriction. The 5-hour group had increased beta EEG at central-parietal sites following both nights of restriction, whereas the 3-hour group had increased beta and gamma EEG at occipital regions following the first night only. Short-term sleep restriction leads to deficits in performance as well as EEG slowing that correspond to the amount and duration of sleep loss. High-frequency EEG may be a marker of effort or compensation.     

Subjective sleepiness, simulated driving performance and blink duration: examining individual differences

The present study aimed to provide subject-specific estimates of the relation between subjective sleepiness measured with the Karolinska Sleepiness Scale (KSS) and blink duration (BLINKD) and lane drifting calculated as the standard deviation of the lateral position (SDLAT) in a high-fidelity moving base driving simulator. Five male and five female shift workers were recruited to participate in a 2-h drive (08:00-10:00 hours) after a normal night sleep and after working a night shift. Subjective sleepiness was rated on the KSS in 5-min intervals during the drive, electro-occulogram (EOG) was measured continuously to calculate BLINKD, and SDLAT was collected from the simulator. A mixed model anova showed a significant (P < 0.001) effect of the KSS for both dependent variables. A test for a quadratic trend suggests a curvilinear effect with a steeper increase at high KSS levels for both SDLAT (P < 0.001) and BLINKD (P = 0.003). Large individual differences were observed for the intercept (P < 0.001), suggesting that subjects differed in their overall driving performance and blink duration independent of sleepiness levels. The results have implications for any application that needs prediction at the subject level (e.g. driver fatigue warning systems) as well as for research design and the interpretation of group average data.     

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.     

The impact of driver sleepiness on fixation‐related brain potentials

The effects of driver sleepiness are often quantified as deteriorated driving performance, increased blink durations and high levels of subjective sleepiness. Driver sleepiness has also been associated with increasing levels of electroencephalogram (EEG) power, especially in the alpha range. The present exploratory study investigated a new measure of driver sleepiness, the EEG fixation‐related lambda response. Thirty young male drivers (23.6 ± 1.7 years old) participated in a driving simulator experiment in which they drove on rural and suburban roads in simulated daylight versus darkness during both the daytime (full sleep) and night‐time (sleep deprived). The results show lower lambda responses during night driving and with longer time on task, indicating that sleep deprivation and time on task cause a general decrement in cortical responsiveness to incoming visual stimuli. Levels of subjective sleepiness and line crossings were higher under the same conditions. Furthermore, results of a linear mixed‐effects model showed that low lambda responses are associated with high subjective sleepiness and more line crossings. We suggest that the fixation‐related lambda response can be used to investigate driving impairment induced by sleep deprivation while driving and that, after further refinement, it may be useful as an objective measure of driver sleepiness.     

Driver sleepiness--evaluation of reaction time measurement as a secondary task

The application of reaction time (RT) as a secondary task to determine sleepiness in drivers is of increasing interest, but is a problematic area. We assessed the extent to which RT reflected this sleepiness, and/or otherwise affected driving behaviour in sleep restricted, moderately sleepy people. They drove a real-car interactive simulator for two, two hour afternoon monotonous drives, with and without RT (counterbalanced). Simple auditory RT was used, with a semi-random inter-stimulus interval averaging 21/2 minutes. Lane wandering (driving "incidents"), subjective and EEG measures of sleepiness were obtained. For both conditions all three indices changed significantly during the course of the afternoon circadian "dip". However, this was not reflected in RT, which remained relatively stable. Nevertheless, RT provided more "stimulation" for the sleepy driver, and significantly reduced subjective sleepiness, with a trend for fewer incidents and a more alert EEG. Possible reasons for the disparity in sensitivity between RT and the other measures are discussed. Under this experimental protocol, RT did not provide a useful guide to driver sleepiness; it was merely a mechanism for increasing task load and reducing monotony. The drivers' own insight into their sleepiness had more validity as a tool for assessing sleepiness.     

Subjective sleepiness and accident risk avoiding the ecological fallacy

The present study of sleepiness and accident risk in a HI-FI car simulator aimed to provide subject-level relative risks (RR) with 95% confidence intervals (CI) for different levels of subjective sleepiness measured with the Karolinska Sleepiness Scale (KSS), 1 = very alert, 9 = very sleepy, fighting sleep, an effort to staying awake. Five male and five female shift workers, mean age 37 years, participated with a 2-h drive (08:00-10:00 hours) in a dynamic high-fidelity moving base driving simulator, after a night of work and after a night of sleep. Subjective sleepiness was measured with KSS every 5 min and events of incidents (two wheels outside the right lane), accidents (two wheels off the road or four wheels in opposite lane) and crashes (four wheels off the road) were recorded. The probability of an accident was modelled with a Generalized Linear Mixed Model approach to estimate subject-specific effects, rather than group average effects, to avoid the ecological fallacy. The results showed that sleepiness was strongly related to accident risk. An average subject was estimated at 28.2 times (95% CI RR = 10.7-74.1) increased risk at KSS = 8 and at 185 times (95% CI RR = 42-316) at KSS = 9 compared with KSS = 5. There were large individual differences in event propensity that complicates the prediction of absolute accident risk for individual subjects.     

Counteracting driver sleepiness: Effects of napping, caffeine, and placebo

Sleepy drivers should “take a break,” but the efficacy of feasible additional countermeasures that can be used during the break is unknown. We examined a shorter than 15 min nap, 150 mg of caffeine in coffee, and a coffee plalcebo, each given randomly across test sessions to 10 sleepy subjects during a 30-min rest period between two 1-hr monotonous early afternoon drives in a car simulator. Caffeine and nap significantly reduced driving impairments, subjective sleepiness, and electroencephalographic (EEG) activity indicating drowsiness. Blink rate was unaffected. Sleep during naps varied, whereas caffeine produced more consistent effects. Subjects acknowledged sleepiness when the EEG indicated drowsiness, and driving impairments were preceded by self-knowledge of sleepiness. Taking just a break proved ineffective.     

Sleepiness and performance of professional drivers in a truck simulator—comparisons between day and night driving

Previous research has shown that night driving performance may be seriously affected by sleepiness. The present study compared daytime and night-time performance of professional drivers on a simulated truck driving task. A secondary purpose was whether a nap or a rest pause would affect performance. Nine professional drivers participated in a counterbalanced design. The conditions were day driving (DAYDRIVE), night driving (NIGHTDRIVE), night driving with a 30 minute rest (NIGHTREST), and night driving with a 30 minute nap (NIGHTNAP). Each condition consisted of three consecutive 30-min periods. For the DAYDRIVE and NIGHTDRIVE all periods were spent driving while the second period was either a rest pause or a nap for the other two conditions. Mean speed, standard deviation of speed and, standard deviation for lane position were recorded. Self ratings of sleepiness were obtained before and after each 30-min period. Reaction time tests and 10 minute standardized EEG/EOG recordings were obtained before and after each condition. EEG/EOG were also recorded continuously during driving. The effects on driving were small but significant: night driving was slower, with a higher variability of speed, and had higher variability of lane position. Subjective and EEG/EOG sleepiness were clearly higher during the night conditions. Reaction time performance was not significantly affected by conditions. Neither the nap nor the rest pause had any effect.     

The impact of a nap opportunity during the night shift on the performance and alertness of 12-h shift workers

The purpose of this workplace evaluation was to assess the effects on performance, alertness and subsequent sleep of strategic napping on 12-h overnight shifts. In a counterbalanced crossover design, 24 male aircraft maintenance engineers working in a forward rotating 12-h shift pattern volunteered to take part in the study for two work weeks. During the experimental week, each subject was given the opportunity to take a 20-min nap at work between 01:00 and 03:00 h on each of their two overnight shifts. On the control week no naps were taken on the night shifts. A computerized neurobehavioural test battery was employed to assess performance and subjective levels of fatigue at the beginning and end of each night shift, and pre- and postnap. Subjects were also asked to rate how near they had come to falling asleep while driving to and from work. The results revealed that taking a single 20-min nap during the first night shift significantly improved speed of response on a vigilance task measured at the end of the shift compared with the control condition. On the second night shift there was no effect of the nap on performance. Taking a short nap during either night shift had no significant effect on subjective ratings of fatigue, the level of sleepiness reported while driving to and from work, or subsequent sleep duration and sleep quality. Overall the results suggest some promise for a short duration nap taken in the workplace to counteract performance deficits associated with the first night shift.     

Sleep-related myoclonus in rheumatic pain modulation disorder (fibrositis syndrome) and in excessive daytime somnolence

We describe a new syndrome, Rheumatic Pain Modulation Disorder (RPMD) ("fibrositis syndrome") with sleep-related myoclonus (involuntary periodic leg movements). Measures of sleepiness, fatigue and pain, before and after sleep, and aspects of sleep of nine subjects (Ss) with RPMD and sleep-related myoclonus were compared to nine subjects with excessive daytime somnolence and sleep-related myoclonus. In eight of the RPMD with sleep-related myoclonus and three of those with daytime sleepiness, an alpha (7.5-11 Hz) EEG Non-Rapid Eye Movement sleep disorder was demonstrated. The RPMD with sleep-related myoclonus group contained a greater number of women, more pain, morning fatigue, and disturbances in sleep (more stage changes and alpha EEG sleep prior to leg myoclonus); but in comparison to the sleep-related myoclonus, daytime somnolent group, there were no differences in evening and morning sleepiness, number of limb movements, movement arousals, awakenings after sleep onset, sleep duration, and percent sleep stages.     

Sleep extension versus nap or coffee,within the context of ‘sleep debt’

Though extended night‐time sleep mostly reduces the ‘afternoon dip’, little is known about evening benefits to alertness, or about comparisons with an afternoon nap or caffeine. Twenty healthy carefully screened adults, normal waking alertness levels, underwent four counterbalanced conditions: usual night sleep; night sleep extended<90 min (usual bed‐time); up to 20 min afternoon nap; and 150 mg afternoon caffeine (versus decaffeinated coffee). Sleepiness was measured by afternoon and evening multiple sleep latency test (MSLTs), longer psychomotor vigilance test (PVT) sessions and a subjective sleepiness scale. Sleep was extended by average of 74 min, and all participants could nap 15–20 min. Sleep extension had little effect on PVT determined modest levels of morning sleepiness. Afternoon and evening MSLTs showed all active treatments significantly reduced the ‘dip’, with nap most effective until mid‐evening; next effective was caffeine, then extension. Late evening sleepiness and subsequent sleep did not differ between conditions. Arguably, participants may have experienced some ‘sleep debt’, given they extended sleep and reflected some sleepiness within settings sensitive to sleepiness. Nevertheless, extended sleep seemed largely superfluous and inefficient in reducing modest levels of sleepiness when compared with a timely nap, and even caffeine. Sleep, such as food and fluid intakes, can be taken to excess of real biological needs, and for many healthy adults, there is a level of modest daytime sleepiness, only unmasked by very sensitive laboratory measures. It may reflect a requirement for more sleep or simply be within the bounds of normal acceptability.