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.     

睡眠剥夺对警觉能力的影响

为探讨不同睡眠剥夺（sleep deprivation，SD）时间对于警觉性的影响，将24名正常青年男性分为SD21h组、SD45h组、SD69h组，每组8名，主要应用三个字母（C、G、N）的划销测验来测查不同SD条件下的警觉能力。测试时间分别为每天的7：00、10：00、13：00、16：00、19：00、22：00、l：00、4：00，采用组间比较和自身前后比较。结果：sD后，完成时间、总击中数、假阳性数和倒数第二分钟击中数表现出成绩显著下降，并同SD时间有关；完成时间和总击中数表现出生物节律的作用；倒数第二分钟击中数同SD相关系数最高，为非常好地评定警觉性的指标。结论：SD后警觉水平下降，并且同SD时间长短有关；SD时，字母划销测验是非常好的测查警觉性的测验。     

Initial age of unlicensed motorcycling experience for a cohort of high school students

The aim of this study is to use retrospective data to examine the initial age of unlicensed motorcycling experience for a cohort of senior high school students in Taiwan. The life-table method was applied to estimate the probability of unlicensed motorcycling at different age intervals below the minimum licensing age. The results indicated that an increase in the prevalence of unlicensed teenage motorcycling began at 10 years of age and peaked in the ages between 16 and 17 years. Only 38% of students had no motorcycle riding experience when they reached the minimum licensing age of 18 years. Gender and parental attitude were the factors that had a significant influence on the initial motorcycling age. In addition, we observed a significant difference between licensed and unlicensed students in the following areas: parental attitude, proportion of students using borrowed motorcycles, and riding and accident frequency. The results reveal a number of important implications, such as the promotion of alternative modes of transport, increased parental monitoring, and penalty enhancement, that may help to suppress the tendency of teenagers' unlicensed motorcycling.     

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.     

Developing measures of fatigue using an alcohol comparison to validate the effects of fatigue on performance

The effects of 28 h of sleep deprivation were compared with varying doses of alcohol up to 0.1% blood alcohol concentration (BAC) in the same subjects. The study was conducted in the laboratory. Twenty long-haul truck drivers and 19 people not employed as professional drivers acted as subjects. Tests were selected that were likely to be affected by fatigue, including simple reaction time, unstable tracking, dual task, Mackworth clock vigilance test, symbol digit coding, visual search, sequential spatial memory and logical reasoning. While performance effects were seen due to alcohol for all tests, sleep deprivation affected performance on most tests, but had no effect on performance on the visual search and logical reasoning tests. Some tests showed evidence of a circadian rhythm effect on performance, in particular, simple reaction time, dual task, Mackworth clock vigilance, and symbol digit coding, but only for response speed and not response accuracy. Drivers were slower but more accurate than controls on the symbol digit test, suggesting that they took a more conservative approach to performance of this test. This study demonstrated which tests are most sensitive to sleep deprivation and fatigue. The study therefore has established a set of tests that can be used in evaluations of fatigue and fatigue countermeasures.     

Unlicensed motorcycling of high school adolescents in Dehaghan county (Isfahan Province of Iran)

Background

Unlicensed motorcycling increases the chances of accidents in adolescents. There are many behavioral and non-behavioral factors involved in adolescents’ unlicensed motorcycling which were not addressed in research yet completely.

Methods

The cross-sectional study aimed to determine prevalence and related factors of unlicensed motorcycling on 500 unlicensed male high school adolescents in Dehaghan, who entered in the study by census. Demographic and motorcycling information were collected via self-report questionnaire, and its content validity was approved by a panel of experts. The statistical analyses of the data included Pearson Correlation Coefficient, chi-square, independent samples t-test and ANOVA with Tukey post hoc test.

Results

The prevalence of unlicensed motorcycling among participants was 74.2% and mean age at first motorcycling experience was 11.97 ± 1.97 years ranged from 8 to 17. Of the motorcyclist participants, 59.6% owned their personal motorcycle. Most motorcycle passengers (62.8%) were adolescent’s friends, and the most frequently expressed reason for use of motorcycle was fun and entertainment (54.2%). Age at first motorcycling experience was lower among rural adolescents than urban adolescents. However, unlicensed motorcycling was more prevalent among urban adolescents than rural ones. The relationship between living status, father’s job, mother’s job and age at first motorcycling experience was insignificant (P > 0.05). However, mean age at first motorcycling experience among students of humanities, technical disciplines, and general first year was lower than that among students of natural sciences and math.

Conclusion

High prevalence of unlicensed motorcycling and significant role of family and social environments on adolescents’ high-risk motorcycling without license, is indicative of the need for interventions at all levels of peers, family, and schools and also establishing new driving regulations in Iran.     

Explaining two-lane highway crash rates using land use and hourly exposure

This paper describes the estimation of Poisson regression models for predicting both single and multi-vehicle highway crash rates as a function of traffic density and land use, as well as ambient light conditions and time of day. The study focuses on seventeen rural, two-lane highway segments, each one-half mile in length with varying land use patterns and where actual hourly exposure values are available in the form of observed traffic counts. Land-use effects are represented by the number of driveways of various types on each segment. Hourly exposure is represented for single-vehicle crashes as the total vehicle miles traveled and volume/capacity ratio; for multi-vehicle crashes it is the product of the hourly volumes on the main highway and the roads intersecting it along the study segment. For single-vehicle crashes, the following variables were found to be significant, with a positive or negative effect as noted: daytime (06:00–19:00 h, negative effect), the natural log of the segment volume/capacity ratio (negative), percent of the segment with no passing zones (positive), shoulder width (positive), number of intersections (negative), and driveways (mixed effects by type). Good multi-vehicle crash prediction models had quite different variables: daylight conditions from 10:00–15:00 and 15:00–19:00 h (positive), number of intersections (negative), and driveways (positive for all types). The results show that traffic intensity explains differences in crash rates even when controlling for time of day and light conditions, and that these effects are quite different for single and multi-vehicle crashes. Suggestions for future research are also given.     

Fatigue, sleep restriction and driving performance

We ran a randomized cross-over design study under sleep-deprived and non-sleep-deprived driving conditions to test the effects of sleep restriction on real driving performance. The study was performed in a sleep laboratory and on an open French highway. Twenty-two healthy male subjects (age = 21.5 +/- 2 years; distance driven per year = 12,225 +/- 4739 km (7641 +/- 2962 miles) [mean +/- S.D.]) drove 1000 km (625 miles) over 10 h during five 105 min sessions on an open highway. Self-rated fatigue and sleepiness before each session, number of inappropriate line crossings from video recordings and simple reaction time (RT) were measured. Total crossings increased after sleep restriction (535 crossings in the sleep-restricted condition versus 66 after non-restricted sleep (incidence rate ratio (IRR): 8.1; 95% confidence interval (95% CI): 3.2-20.5; p < 0.001)), from the first driving session. The interaction between the two factors (conditionxtime of day) was also significant (F(5, 105) = 3.229; p < 0.05). Increasing sleepiness score was associated with increasing crossings during the next driving session in the sleep-restricted (IRR: 1.9; 95% CI: 1.4-2.4) but not in the non-restricted condition (IRR: 1.0; 95% CI: 0.8-1.3). Increasing self-perceived fatigue was not associated with increasing crossings in either condition (IRR: 0.95; 95% CI: 0.93-0.98 and IRR: 1.0; 95% CI: 0.98-1.02). Rested subjects drove 1000 km with four shorts breaks with only a minor performance decrease. Sleep restriction induced important performance degradation even though time awake (8h) and session driving times (105 min) were relatively short. Major inter-individual differences were observed under sleep restriction. Performance degradation was associated with sleepiness and not fatigue. Sleepiness combined with fatigue significantly affected RT. Road safety campaigns should encourage drivers to avoid driving after sleep restriction, even on relatively short trips especially if they feel sleepy.     

不同时间的睡眠剥夺对视觉P300的影响

睡眠剥夺在日常生活工作中广泛存在，导致认知功能下降，其中警觉水平下降最为明显。实验采用Oddball范式辨别任务，研究了32名青年男性在不同睡眠剥夺条件（sleep deprivation，SD）下（SD21h、SD4Sh、SD69h、正常对照组）的事件相关电位（event—related potentials，ERPs）P300成分的变化。结果表明，随SD时间延长，P300波幅降低、潜伏期延长；P300是比较好的评价SD后脑功能变化的指标。     

Effect of Florida's graduated licensing program on the crash rate of teenage drivers

On 1 July 1996, Florida instituted a graduated licensing program for drivers younger than age 18. For the first 3 months, holders of learner's licenses are not allowed to drive at all between 19:00 and 06:00 h; thereafter, they may drive until 22:00 h. Learner's licenses must be held for 6 months prior to eligibility for the intermediate license. Sixteen-year-old intermediate license holders are not permitted to drive unsupervised from 23:00 to 06:00 h, 17 year-olds from 01:00 to 06:00 h. All drivers younger than 18 have strict limits on the number of traffic violations they can accumulate and, effective 1 January 1997, all drivers younger than 21 are subject to a zero tolerance law for drinking and driving. Florida crash data for 1995-1997 were obtained and compared with similar data from Alabama, a state that borders Florida but does not have graduated licensing. For 15, 16, and 17 year-olds combined, there was a 9% reduction in the fatal and injury crash involvement rate in Florida during 1997, the first full year of graduated licensing, compared with 1995. On a percentage basis, crashes declined most among 15 year-olds, followed by 16 year-olds and then 17 year-olds. Reductions were not seen among Alabama teenagers nor among 18 year-olds in Florida.     

Effects of an afternoon nap on nighttime alertness and performance in long-haul drivers

The effects of an afternoon nap on alertness and psychomotor performance were assessed during a simulated night shift. After a night of partial sleep restriction, eight professional long-haul drivers either slept (nap condition) or engaged in sedentary activities (no-nap condition) from 14:00 to 17:00 h. Alertness and performance testing sessions were conducted at 12:00 (pre-nap baseline), 24:00, 02:30, 05:00 and 07:30 h, and followed 2-h runs in a driving simulator. In the nap condition, the subjects showed lower subjective sleepiness and fatigue, as measured by visual analog scales, and faster reaction times and less variability on psychomotor performance tasks. Electrophysiological indices of arousal during the driving runs also reflected the beneficial effects of the afternoon nap, with lower spectral activity in the theta (4–7.75 Hz), alpha (8–11.75 Hz) and fast theta-slow alpha (6–9.75 Hz) frequency bands of the electroencephalogram, indicating higher arousal levels. Thus, a 3-h napping opportunity ending at 17:00 h improved significantly several indices of alertness and performance measured 7–14 h later.     

Diurnal variation in subsidiary reaction time in a long-term driving task

Traffic accidents show a marked diurnal rhythm, which is a seldom investigated phenomenon. One possible background factor examined in the present study is the biological circadian rhythm. Eight subjects drove for 3 hr, beginning at 0300, 0900, 1500 and 2100. During each session a subsidiary reaction time task was used as an indirect measure of driving performance. Critical confounding factors, such as lighting conditions, traffic intensity, amount of sleep preceding the session and temperature in the car were considered. The results showed that there were small differences in the level of performance among the four sessions. However, differences in the rate of performance deterioration were not observed. From these results it was concluded that biological rhythm as a single variable has only a minor influence on this type of performance. Consequently the diurnal rhythm of traffic accidents must be attributed to other factors such as long hours of driving and/or sleep deprivation which culminate during the morning hours.     

A Model of the Relationship Between Psychosocial Variables and Diurnal Cortisol Rhythm Under Chronic Stress by Using Structural Equations

By using structural equations, we investigated the effect of chronic stress on salivary cortisol rhythm and proposed a causal model of chronic stress by using psychosocial and physiological data. First, 111 healthy workers (48 males, 63 females) completed questionnaires on chronic stress and lifestyle habits. Then, they provided saliva samples and answered questionnaires that were prepared to assess their psychological states 5 times (on waking up and at 10:00, 11:40, 14:00, and 16:00) on workdays. Structural equation modeling (SEM) revealed that chronic stress and longer commuting time resulted in sleep irregularities and this disrupted the cortisol circadian rhythm. This suggests that chronic stress disrupts the cortisol circadian rhythm even in healthy individuals, and sleep regularity mediates the effect of chronic stress on the cortisol rhythm.

     

Parallel computation of a damage localization problem using parallel multifrontal solver

In this paper, nonlinear parallel structural analyses are performed using a distributed memory sparse direct multifrontal linear solver. The linear solver is fully parallel, working with substructures determined by a parallel graph partitioner. The parallel performance of the nonlinear parallel algorithm is demonstrated using damage localization problems for two and three dimensional crack models. Convergence studies of the predicted local variation of damage at the crack tip are performed using discretizations with up to one million degrees of freedom. Implementation issues for damage localization problems are discussed, including the selection of independent variables and the use of Riks continuation method.We acknowledge the financial support of Ministry of Science and Technology by National Research Laboratory program. (grant number 00-N-NL-01-C-026)     

Wakefulness in young and elderly subjects driving at night in a car simulator

Young drivers are over-represented in nighttime traffic accidents and several studies have suggested that many accidents are associated with elevated sleepiness levels. It has been suggested that there may be a connection between lowered wake capacity and functional sensory motor skills on the one hand and sleep deprivation at the circadian low in young drivers on the other.Performance during a 45/min evening and night drive among young (n = 10, age range 18–24 years) and elderly (n = 10, age range 55–64 years) subjects was studied using a moving base driving simulator. EEG was measured continuously. Every 5 min, subjects were rated on the Karolinska Sleepiness Scale (KSS). Saliva cortisol was assessed before and after each drive.The results showed that sleepiness increased across each drive and was higher among young drivers at night. Relative EEG power increased among older drivers for frequencies of 10–16 Hz. The sigma 1 frequency band (12–14 Hz) proved particularly sensitive to sustained driving, and was elevated among subjects in the elderly group. Cortisol levels before and after the evening and night drive showed higher mean levels for elderly subjects.The present study has demonstrated that young drivers were more sleepy while driving at night. The effects could represent a mobilization of effort and a reorganization of brain firing pattern among older subjects, possibly reflecting better ability and effort to resist sleepiness.     

Validation of the Chinese-language brief sensation seeking scale: Implications for risky riding behaviors of parental motorcyclists and their child passengers

Motorcycles are the leading cause of road traffic deaths in the Western Pacific and Southeast Asia, where Mandarin Chinese is the most commonly used language. Sensation seeking (SS) is reported to correlate with many risky motor vehicle behaviors, and therefore a culture-adapted Chinese instrument is needed to assess this personality trait in Chinese-speaking motorcycling populations. The standard front and blinded-backward process was carried out to formulate the Chinese-language Brief Sensation Seeking Scale (C-BSSS). 193 parental motorcyclists who rode with their young children were interviewed concerning their SS levels, demographics, riding behaviors, and the driving/riding experiences. A random sample of 30 subjects was re-interviewed 1–2 weeks later to examine the test-retest reliability. Psychometric analyses revealed satisfactory item characteristics, internal consistency, intraobserver reliability, and interobserver reliability. Additionally, parental motorcyclists who had the following characteristics were more likely to be the high sensation seekers (SSers), including male, younger age, presenting risky motor vehicle behaviors of themselves (e.g., higher riding speeds, operating after drinking, using a mobile phone while operating, and receiving a traffic ticket), and carrying child passengers who demonstrated dangerous motorcycling behaviors (e.g., a younger age, non-helmeted, and overloaded). We conclude that the C-BSSS is a useful and reliable measure of SS for ethnic Chinese populations. This instrument may be helpful to develop the future prevention strategy of motorcycle injuries in Chinese parental motorcyclists and their young child passengers.     

Specific sleepiness symptoms are indicators of performance impairment during sleep deprivation

Drivers are not always aware that they are becoming impaired as a result of sleepiness. Using specific symptoms of sleepiness might assist with recognition of drowsiness related impairment and help drivers judge whether they are safe to drive a vehicle, however this has not been evaluated. In this study, 20 healthy volunteer professional drivers completed two randomized sessions in the laboratory – one under 24 h of acute sleep deprivation, and one with alcohol. The Psychomotor Vigilance Task (PVT) and a 30 min simulated driving task (AusEdTM) were performed every 3–4 h in the sleep deprivation session, and at a BAC of 0.00% and 0.05% in the alcohol session, while electroencephalography (EEG) and eye movements were recorded. After each test session, drivers completed the Karolinska Sleepiness Scale (KSS) and the Sleepiness Symptoms Questionnaire (SSQ), which includes eight specific sleepiness and driving performance symptoms. A second baseline session was completed on a separate day by the professional drivers and in an additional 20 non-professional drivers for test–retest reliability. There was moderate test–retest agreement on the SSQ (r = 0.59). Significant correlations were identified between individual sleepiness symptoms and the KSS score (r values 0.50–0.74, p < 0.01 for all symptoms). The frequency of all SSQ items increased during sleep deprivation (χ² values of 28.4–80.2, p < 0.01 for all symptoms) and symptoms were related to increased subjective sleepiness and performance deterioration. The symptoms “struggling to keep your eyes open”, “difficulty maintaining correct speed”, “reactions were slow” and “head dropping down” were most closely related to increased alpha and theta activity on EEG (r values 0.49–0.59, p < 0.001) and “nodding off to sleep” and “struggling to keep your eyes open” were related to slow eye movements (r values 0.67 and 0.64, p < 0.001). Symptoms related to visual disturbance and impaired driving performance were most accurate at detecting severely impaired driving performance (AUC on ROC curve of 0.86–0.91 for detecting change in lateral lane position greater than the change at a BAC of 0.05%). Individual sleepiness symptoms are related to impairment during acute sleep deprivation and might be able to assist drivers in recognizing their own sleepiness and ability to drive safely.     

Sleepiness in professional drivers: effect of age and time of day

The effect of age and time of day on objective and subjective sleepiness in professional drivers was investigated during a simulated driving task. Thirty-six young and middle-aged professional males drivers, free from any sleep disorder, took part in two simulated driving sessions; one carried out in the afternoon (between 2 and 4 p.m.) the other in the evening (between 11 p.m. and 1 a.m.). Half of each age group drove in a low traffic condition while the second half drove in a heavy traffic condition. Throughout the driving task, subjects' electroencephalogram and Karolinska sleepiness scale (KSS) scores were recorded. Visual analog scales measuring alertness and sleepiness levels were also completed before and after the driving. After each session, subjects filled out the NASA-TLX questionnaire and were asked if they had felt sleepy during the driving. Young professional drivers presented a significant decrease in alertness (raise of the spectral power in the alpha band) in the low traffic condition and a strong propensity to sleep during the evening test in contrast to middle-aged professional drivers.