Göran Kecklund

Sleepiness in long distance truck driving : an ambulatory EEG study of night driving

Eighteen truck drivers had their EEG recorded continuously during a night or evening drive between southern Sweden and Stockholm (500 km). They also carried out self ratings of sleepiness and performance every hour. The EEG was subjected to spectral analysis. The drivers were divided into two groups with a night group (n = 7) who drove between 20:30 to 97:20 and an evening group (n = 11) who drove between 18:20 and 04:00. The night group showed higher subjective sleepiness and lower subjective performance, and increased alpha and theta burst activity during the last three hours of the drive. The groups did not differ for the first 2-3 h of the drive. For the night group, a significant intraindividual correlation was found between subjective sleepiness and EEG alpha burst activity. End-of-the-drive subjective sleepiness and alpha burst activity were significantly correlated with total work hours and arrival time but not with age, diurnal type, prior (rated) sleep length, total break time, drive time or prior time awake. A regression analysis showed that total work hours and total break time predicted 66% of the variance of alpha burst activity during the end of the drive.

Impaired alertness and performance driving home from the night shift: a driving simulator study

Driving in the early morning is associated with increased accident risk affecting not only professional drivers but also those who commute to work. The present study used a driving simulator to investigate the effects of driving home from a night shift. Ten shift workers participated after a normal night shift and after a normal night sleep. The results showed that driving home from the night shift was associated with an increased number of incidents (two wheels outside the lane marking, from 2.4 to 7.6 times), decreased time to first accident, increased lateral deviation (from 18 to 43 cm), increased eye closure duration (0.102 to 0.143 s), and increased subjective sleepiness. The results indicate severe postnight shift effects on sleepiness and driving performance.

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.

Effects of alternating 8- and 12-hour shifts on sleep, sleepiness, physical effort and performance

OBJECTIVES This study concerned the influence of 6 positions of the computer mouse on the work table on posture, muscular load, and perceived exertion during text editing. METHODS An optoelectronic 3-dimensional motion analysis system was used to register the postures of 10 men and 10 women using video display units. Muscular load was also registered (with electromyography), as was perceived exertion (with rating scales). RESULTS A neutral posture with a relaxed and supported arm showed the least perceived exertion, and the electromyographic results showed low activity in both trapezius muscles in this position. Short operators (all women) showed a numerically higher activity in the 4 examined muscles than the tall operators (all men, except 1). This finding could be related to lower muscle force among women and to anthropometric differences, which also influence biomechanic load moments. Narrow-shouldered operators (8 women and 1 man) and short operators worked with larger outward rotation and abduction of the shoulder in a position of the mouse lateral to the keyboard than the broad-shouldered (7 men and 2 women) and tall operators did. Arm support markedly reduced muscle load in the neck-shoulder region among the operators. CONCLUSIONS The operators using video display units in this study preferred to use the mouse on a table in a close to relaxed, neutral posture of the arm in combination with arm support. Short and narrow-shouldered operators worked in more strenuous postures of the arm when the mouse was located lateral to the keyboard.

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.

Impaired sleep after bedtime stress and worries

Stress is assumed to impair sleep, but there is very little empirical evidence for this using sleep recordings. Here, we recorded sleep (at home) in 33 normal participants on three nights, which followed days with low, high and intermediate stress. The participants made daily ratings of the level of stress/worries at bedtime and also two-hourly ratings of stress. Only those 16 individuals who differed in stress/worries between two nights were analysed. There was a significantly lower sleep efficiency (81.0% versus 85.2%) a higher percent Wake (22.6% versus 15.6%) and a longer latency to Stage 3 (33.9 versus 18.3 min) during the nights with a higher stress/worry bedtime rating. None of the other sleep variables were affected. Also mean daytime stress ratings were significantly higher on the day preceding and following the high stress/worries sleep. It was concluded that moderate increases in stress/worries at bedtime are associated with moderately impaired sleep.

Poor sleep increases the prospective risk for recurrent events in middle-aged women with coronary disease. The Stockholm Female Coronary Risk Study.

OBJECTIVE We investigated the prognostic impact of sleep complaints in women with CHD and also examined whether the association between sleep problems and cardiac events could be explained by depression. METHODS All women patients, aged 65 or under who were admitted with an acute coronary syndrome between 1991 and 1994 in Stockholm, were followed for 5 years for recurrent coronary events. Sleep complaints and depression were measured at baseline using standardized questionnaires. Quality of sleep, restorative function of sleep, and snoring were assessed by the Karolinska Sleep Questionnaire (KSQ), and depressive symptoms by a questionnaire developed by Pearlin. RESULTS Poor sleep quality was associated with recurrent cardiac events. After multivariate adjustment for age, and standard risk factors, the hazard ratio (HR) for women with poor as compared with good sleep quality was 2.5 (95% CI: 1.2-5.2). Controlling for depression did not change this result substantial. Not waking up well-rested yielded a similarly increased risk (HR = 2.4; 95% CI: 1.2-4.6). Women with both poor sleep quality and depression had a worse prognosis than women free from these complaints (HR = 2.6; 95% CI: 1.0-6.4). Heavy snoring was not related to prognosis. CONCLUSIONS Our results indicate that poor sleep and sleep without a restorative function are associated with poor prognosis in female coronary patients. This association is not explained by depressive symptoms or by standard coronary risk factors.

Day-to-day variation in saliva cortisol-Relation with sleep, stress and self-rated health.

The objective was to examine the day-to-day variation in cortisol among healthy individuals and its relation to the time of saliva sampling, work, stress and fatigue. During 4 consecutive weeks, 14 office workers provided saliva samples (at awakening, 15 min after awakening and at bedtime) and made diary ratings for each day. Results showed a variation in cortisol values between participants but also within individuals. After controlling for the individual differences, results showed that low cortisol levels in the morning were associated with sleepiness at awakening and anxiety, exhaustion, and poor health the day before. High evening levels of cortisol were associated with symptoms of stress and poor self-rated health. Further analysis of the cortisol awakening response (CAR) showed that all participants had a mixture of both a positive and negative responses. During mornings with a negative response participants stayed in bed for a longer time after the initial awakening, which might be a sign of snoozing, thus missing the awakening response.

Age, gender and early morning highway accidents

Accident register data, time budget studies and road traffic flow data were used to compute the age and gender‐dependent relative risk [odds ratio (OR)] of being involved in a driving accident in which the driver was injured or killed. Alcohol‐related accidents were excluded from the analysis. The results showed that the night‐time risk, compared with that of the forenoon, was dramatically increased (OR=5) for young drivers (18–24 years) and reduced for old (65+) drivers. In direct comparison, the young drivers had 5–10 times higher risk of being involved in an accident during late night than during the forenoon, with the excess risk during the daytime being considerably lower. Women had a less pronounced night‐time peak than men. In direct comparison, men had twice as high a risk as women during the late night hours. The results clearly demonstrate a strong effect of young age on night‐time accident risk, together with a moderate effect of (male) gender.

Predicting long‐term sickness absence from sleep and fatigue

Disturbed or shortened sleep is prospectively related to disease. One might also expect that sickness absence would be another consequence but very little data seem to exist. The present study used 8300 individuals in a national sample to obtain information on reports of disturbed sleep and fatigue 1 year and merged this with data on long‐term sickness absence 2 years later. A logistic regression analysis was applied to the data with adjustments for demographic and work environment variables. The results showed that individuals without registered sickness absence at the start had a higher probability of entering a period of long‐term (≥90 days, odds ratio [OR] = 1.24 with 95% confidence interval [CI] = 1.02–1.51) sickness absence 2 years later if they reported disturbed sleep at the start. The figure for fatigue was OR = 1.35 (CI = 1.14–1.60). When fatigue or disturbed sleep was separately excluded the OR increased to OR = 1.44 and OR = 1.47, respectively. Intermediate sickness absence (14–89 days) showed similar but slightly weaker results. The results indicate that disturbed sleep and fatigue are predictors of long‐term absence and it is suggested that impaired sleep may be part of a chain of causation, considering its effects on fatigue.