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Studies of driving and sleepiness indicators have mainly focused on prior sleep reduction. The present study sought to identify sleepiness indicators responsive to several potential regulators of sleepiness: sleep loss, time of day (TOD) and time on task (TOT) during simulator driving. Thirteen subjects drove a high-fidelity moving base simulator in six 1-h sessions across a 24-h period, after normal sleep duration (8 h) and after partial sleep deprivation (PSD; 4 h). The results showed clear main effects of TOD (night) and TOT but not for PSD, although the latter strongly interacted with TOD. The most sensitive variable was subjective sleepiness, the standard deviation of lateral position (SDLAT) and measures of eye closure [duration, speed (slow), amplitude (low)]. Measures of electroencephalography and line crossings (LCs) showed only modest responses. For most variables individual differences vastly exceeded those of the fixed effects, except for subjective sleepiness and SDLAT. In a multiple regression analysis, SDLAT, amplitude/peak eye-lid closing velocity and blink duration predicted subjective sleepiness bouts with a sensitivity and specificity of about 70%, but were mutually redundant. The prediction of LCs gave considerably weaker, but similar results. In summary, SDLAT and eye closure variables could be candidates for use in sleepiness-monitoring devices. However, individual differences are considerable and there is need for research on how to identify and predict individual differences in susceptibility to sleepiness.

Very little is known about the prevalence of morning work and its relationship with sleep and fatigue. The present study obtained data from a representative sample of the Swedish population (N = 5489) to address this limitation in the literature. The results show that 15% of the population commenced work, at least occasionally, before 05:30 h and approximately 2% did so most of the time. With the increasing phase advance of the start time, the time of rising also advanced, but bedtime changed very little. Thus, early start times were not compensated with earlier bedtimes. Total sleep time decreased as the work start time was advanced; sleep duration was <5 h for work start times between 03:00 and 04:30 h. The results also indicated that advanced start times were linked with increased fatigue, feelings of not being well rested, and reports of early start times as a rather large or very large problem. However, difficulties in waking and disturbed sleep did not change with advanced start times. It was concluded that early start times are common and are associated with sleep problems and fatigue.

Previous studies indicate that the effect of a given shift schedule may depend on individual factors. The aim of the present study was to investigate whether a misfit between individual preferences and actual working hours affected the association between working hours and self-reported indicators of health and well-being. The study population consisted of 173 female eldercare workers who mainly worked day or evening shifts. We combined self-reported questionnaire data on preferences with actual work schedules during a four-week period. The study showed that a misfit between preferences on one hand and "non-day work", "weekend work" or "only a few consecutive days off" on the other hand was associated with an increased dissatisfaction with working hours and/or an increase in the intention to leave the workplace due to one's working hours.

Background: It is well known that physicians' night-call duty may cause impaired performance and adverse effects on subjective health, but there is limited knowledge about effects on sleep duration and recovery time. In recent years occupational stress and impaired well-being among anaesthesiologists have been frequently reported for in the scientific literature. Given their main focus on handling patients with life-threatening conditions, when on call, one might expect sleep and recovery to be negatively affected by work, especially in this specialist group. The aim of the present study was to examine whether a 16-hour night-call schedule allowed for sufficient recovery in anaesthesiologists compared with other physician specialists handling less life-threatening conditions, when on call. Methods: Sleep, monitored by actigraphy and Karolinska Sleep Diary/Sleepiness Scale on one night after daytime work, one night call, the following first and second nights post-call, and a Saturday night, was compared between 15 anaesthesiologists and 17 paediatricians and ear, nose, and throat surgeons. Results: Recovery patterns over the days after night call did not differ between groups, but between days. Mean night sleep for all physicians was 3 hours when on call, 7 h both nights post-call and Saturday, and 6 h after daytime work (p < 0.001). Scores for mental fatigue and feeling well rested were poorer post-call, but returned to Sunday morning levels after two nights' sleep. Conclusions: Despite considerable sleep loss during work on night call, and unexpectedly short sleep after ordinary day work, the physicians' self-reports indicate full recovery after two nights' sleep. We conclude that these 16-hour night duties were compatible with a short-term recovery in both physician groups, but the limited sleep duration in general still implies a long-term health concern. These results may contribute to the establishment of safe working hours for night-call duty in physicians

In this narrative review, we examined what level of research evidence is available that shift workers' sleep-wake disturbances can be minimized through ergonomic shift scheduling. We classified the pertinent studies conducted on real shift workers in field conditions by the type of shift system and study design (ie, whether the shift systems were modified or not - "treatment" versus "no treatment"). The results of the observational studies in which no changes to the shift system were made (ie, no treatment) showed that, irrespective of the shift system, night and early-morning shifts and quick returns are associated with short sleep and increases in sleepiness. The same is true for very long shifts (>16 hours) and extremely long weekly working hours (>55 hours). For all categories of shift systems, there was a lack of controlled intervention studies, limiting the possibility to provide solution-focused recommendations for shift scheduling. Most of the controlled intervention studies had been conducted on workers under regular 3-shift systems. These studies suggested that a change from slowly backward-rotating shifts to rapidly forward-rotating shifts is advantageous for alertness and, to some degree, sleep. We also found that a change from an 8- to 12-hour shift system does not necessarily result in impairments in the sleep-wake pattern. The level of research evidence was affected by many of the studies' frequent methodological limitations in measuring sleep and sleepiness. In all, to have reliable and solution-focused recommendations for shift scheduling, methodologically sound controlled intervention studies are required in different categories of shift systems.

Cox proportional hazard models were used to study relationships between the event that a driver is leaving the lane caused by sleepiness and different indicators of sleepiness. In order to elucidate different indicators' performance, five different models developed by Cox proportional hazard on a data set from a simulator study were used. The models consisted of physiological indicators and indicators from driving data both as stand alone and in combination. The different models were compared on two different data sets by means of sensitivity and specificity and the models' ability to predict lane departure was studied. In conclusion, a combination of blink indicators based on the ratio between blink amplitude and peak closing velocity of eyelid (A/PCV) (or blink amplitude and peak opening velocity of eyelid (A/POV)), standard deviation of lateral position and standard deviation of lateral acceleration relative road (ddy) was the most sensitive approach with sensitivity 0.80. This is also supported by the fact that driving data only shows the impairment of driving performance while blink data have a closer relation to sleepiness. Thus, an effective sleepiness warning system may be based on a combination of lane variability measures and variables related to eye movements (particularly slow eye closure) in order to have both high sensitivity (many correct warnings) and acceptable specificity (few false alarms).

Long-term sickness absence has doubled in Sweden, as has complaints of disturbed sleep. The present study sought to investigate the prospective link between long-term sickness absence and disturbed sleep or fatigue. Sleep and fatigue from a representative national sample was followed up 1.5-2 yr later in terms of return from long-term (>or=90 d) and intermediate term (14-89 d) sickness absence. 8,300 individuals participated in the survey, out of which 372 were on long-term and 1,423 were on intermediate term sick leave. The data was analyzed using logistic regression analysis with adjustment for background and work environment variables. Separate analyses were carried out for disturbed sleep and fatigue since they were correlated. The results showed that those with disturbed sleep at the start had an Odds Ratio (OR) of 0.56 (95% Confidence Interval (CI)=0.35-0.90) for returning from long-term sickness absence. For fatigue the results were OR=0.56 (CI=0.34-0.90). Intermediate term sickness absence showed similar, but slightly weaker, results. The results indicate that disturbed sleep and fatigue are predictors of lack of return from long term and intermediate term sickness absence.

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 poorhealth the day before. High evening levels of cortisol were associated with symptoms ofstress 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., QC 20120215

STUDY OBJECTIVES: Sleep reduction normally causes a homeostatic response during subsequent recovery sleep, but this does not seem to be true for repeated partial sleep loss. The aim of the present study was to test the response to repeated partial sleep loss through detailed focus on spectral data and parts of sleep. DESIGN: The experiment involved 4 h of sleep across 5 days in the laboratory (partial sleep deprivation [PSD]), followed by 3 days of recovery sleep. PSD was achieved through a delayed bedtime. Nine individuals participated. To avoid "laboratory monotony," subjects were permitted to leave the lab for a few hours each day. MEASUREMENTS AND RESULTS: All sleep stages and the latencies to sleep and slow wave sleep (SWS) showed a significant reduction during PSD. However, SWS and TST (total sleep time) during the first half of sleep increased gradually across days with PSD. During the first recovery sleep, SWS was significantly increased, while stage 1 and latency to stage 3 were reduced. All were back to baseline on the second night of recovery sleep. Summed spectral power during the first 3.8 h of sleep showed a gradual and robust increase (50% above baseline) in the range 1.25-7.25 Hz across days with PSD up to first recovery sleep and then returned to baseline. CONCLUSIONS: SWS and summed power density in a broad low-frequency band respond to repeated partial sleep deprivation in a dose-response fashion during the first 4 h sleep, apparently reflecting a robust and stable homeostatic response to sleep loss.

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 10-16Hz. The sigma 1 frequency band (12-14Hz) 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.

Almost all studies of sleepy driving are carried out in driving simulators and with monotonous road conditions (no interaction with other cars). The present study investigated indicators of sleepy driving in a more challenging scenario after a night awake. 17 participants drove a high fidelity moving base driving simulator experiment while sleepiness was monitored physiologically and behaviourally. Short periods of situations of free driving (no other vehicles) alternated with short periods of following another vehicle (car following) with and without the possibility to overtake. The result showed that a night of prior sleep loss increased sleepiness levels at the wheel (eye closure duration and lateral variability) compared to after a night of normal sleep. Blink duration while overtaking was significantly lower compared to the other situations, it was at the same level as after night sleep. Speed when passing a stopped school bus was not significantly affected by sleepiness. However the warning caused a more rapid reduction of speed. In conclusion, a moderately challenging driving contest did not affect sleepiness indicators, but a very challenging one did so (overtaking). This suggests that it is important to monitor the driving situation in field operational tests of sleepy driving.

Very little is known about differences in sleep between day and shift workers in representative samples of the population. This study compared a national representative sample (N=3400) of shift (with night shifts) and day workers regarding the different types of sleep disturbances and also the level of sleep symptoms with that of insomnia patients. The results showed very few differences between shift and day workers; only too little sleep and nodding off at work were marginally higher among shift workers. The results also showed that the complaints of insomnia patients for most sleep disturbances corresponded to the 2nd-16th percentile of the shift workers' levels of complaints. The results suggest, at least with the present questionnaire methodology, that shift work does not appear to be a major source of sleep disturbances and that their complaint levels bear no resemblance to those seen in insomniac patients., Conference Information: 18th International Symposium on Shift Work and Working TimeYeppoon, AUSTRALIA, AUG, 2007

Sleepiness is a major cause of lower productivity and higher risk of accidents in various work situations. Developing sleepiness monitoring techniques is important to improve work efficiency and to reduce accident risk, so that people can take a rest/break in appropriate timing before an accident or a mistake occurs. The aims of the present study are (1) to explain subjective sleepiness using sleep-related symptoms, and (2) to examine which symptoms are useful to predict performance errors. Participants were healthy paid volunteers (six males, six females; mean +/- SD, 31.5 +/- 10.74 years). Participants took part in 26-h sleep deprivation. During sleep deprivation, they carried out several performance tasks every 3 h and an hourly rating of questionnaires to evaluate subjective symptoms including two types of Karolinska sleepiness scale (KSS). The present study confirmed that performance errors can be predicted by subjective symptoms. While mental fatigue was correlated to KSS scores linearly, eye-related subjective symptoms showed quadratic correlations to KSS. By taking into consideration this noteworthy relationship between subjective symptoms and sleepiness, more accurate introspection of sleepiness and performance errors prediction (detection) may be possible.

Relatively few studies have tried to relate subjective sleep quality to objective sleep parameters and most have been carried out in laboratory settings and often with patients and usually only for a single night. The present study used a group of 33 subjects who had sleep polysomnographically recorded in their homes for three nights during a period of several weeks. First a multiple regression analysis was carried out for each night with a 4-item sleep quality index as the dependent variable and conventional sleep parameters as predictors. This yielded a significant beta value for percent Stage O for each of the three nights. Sleep efficiency showed a significant correlation with sleep quality for two nights but did not enter the regression. When the night with the best and poorest sleep were compared, the only significant variable became percent SWS. It was suggested that the differing results may have been due to the large age span confusing SWS/quality correlations., Internt publ.nr. P2677

Driver impairment at night and its relation to physiological sleepiness. Anund A, Kecklund G, Peters B, Forsman A, Lowden A, Akerstedt T. VTI, S-581 95 Linköping, Sweden. anna.anund@vti.se. OBJECTIVES: Studies of devices detecting sleepiness need reference points of physiological sleepiness. The present study sought to validate the Karolinska drowsiness score (KDS) as an indicator of physiological sleepiness against driving impairment and eye blink duration during a 45-minute drive in an advanced moving-base driving simulator. METHODS: Data from 19 persons were used in the analysis. Electrooculography, electroencephalography, and electromyography were administered continuously. Physiological sleepiness was quantified by scoring the percentage (0-100%) of the scoring epoch with alpha and theta activity and slow eye movements (KDS). Lateral position and speed were used as measures of driving behavior. Lane departure was defined as two wheels touching the lane markers. Blink duration was used as a secondary indicator of sleepiness. RESULTS: The results showed that, for young drivers, sleepiness increased with time in the task with higher levels. The variability of the lateral position and the mean and variability of the blink duration significantly changed when sleepiness increased to KDS >/=20%. Furthermore, there was an increase in the risk of lane departure for KDS >/=30%. CONCLUSIONS: The results suggest that KDS scoring is a reasonable procedure for estimating physiological sleepiness under conditions of driving. The results also indicate that a younger age is associated with greater sensitivity to sleepiness at the wheel., Internt publ.nr. P2662

Accounting for partial sleep deprivation and cumulative sleepiness in the Three-Process Model of alertness regulation. Akerstedt T, Ingre M, Kecklund G, Folkard S, Axelsson J. Stress Research Institute, University of Stockholm, Stockholm, Sweden. torbjorn.akerstedt@ki.se Mathematical models designed to predict alertness or performance have been developed primarily as tools for evaluating work and/or sleep-wake schedules that deviate from the traditional daytime orientation. In general, these models cope well with the acute changes resulting from an abnormal sleep but have difficulties handling sleep restriction across longer periods. The reason is that the function representing recovery is too steep--usually exponentially so--and with increasing sleep loss, the steepness increases, resulting in too rapid recovery. The present study focused on refining the Three-Process Model of alertness regulation. We used an experiment with 4 h of sleep/night (nine participants) that included subjective self-ratings of sleepiness every hour. To evaluate the model at the individual subject level, a set of mixed-effect regression analyses were performed using subjective sleepiness as the dependent variable. These mixed models estimate a fixed effect (group mean) and a random effect that accounts for heterogeneity between participants in the overall level of sleepiness (i.e., a random intercept). Using this technique, a point was sought on the exponential recovery function that would explain maximum variance in subjective sleepiness by switching to a linear function. The resulting point explaining the highest amount of variance was 12.2 on the 1-21 unit scale. It was concluded that the accumulation of sleep loss effects on subjective sleepiness may be accounted for by making the recovery function linear below a certain point on the otherwise exponential function., Internt publ.nr. P2657

Sleepiness and performance in response to repeated sleep restriction and subsequent recovery during semi-laboratory conditions. Axelsson J, Kecklund G, Akerstedt T, Donofrio P, Lekander M, Ingre M. Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. john.axelsson@ki.se There is an ongoing debate of how best to measure the effects of sleep loss in a reliable and feasible way, partly because well controlled laboratory studies and field studies have come to different conclusions. The aims of the present study were to investigate both sleepiness and performance in response to long-term sleep restriction and recovery in a semi-laboratory environment, investigate order effects (i.e., whether levels return to baseline) in a study with seven days of recovery, and characterize individual differences in tolerance to restricted sleep. Nine healthy men (age 23-28 yrs) participated in the protocol, which included one habituation day (sleep 23:00-07:00 h), two baseline days (23:00-07:00 h), five days with restricted sleep (03:00-07:00 h), and seven recovery days (23:00-07:00 h). Participants went outdoors at least twice each day. Reaction-time tests were performed at 08:00, 14:00, and 20:00 h each day in the laboratory. Sleepiness was self-rated by the Karolinska Sleepiness Scale (KSS)after each test. The mixed-effect regression models showed that each day of restricted sleep resulted in an increase of sleepiness by 0.64+/- .05 KSS units (a nine-step scale, p < .001), increase of median reaction times of 6.6+/- 1.6 ms ( p = .003), and increase of lapses/test of 0.69 +/- .16 ms ( p < .001). Seven days of recovery allowed participants to return to the baseline for sleepiness and median reaction time, but not for lapses.The individual differences were larger for performance measures than for sleepiness; the between-subject standard deviation for the random intercept was in the magnitude of the effects of 1.1 days of restricted sleep for sleepiness, 6, Internt publ.nr. P2656

Sleep length as a function of morning shift-start time in irregular shift schedules for train drivers: self-rated health and individual differences. Ingre M, Kecklund G, Akerstedt T, Söderström M, Kecklund L. Stress Research Institute, Stockholm University, Sweden. michael.ingre@stressforskning.su.se Forty-six male train drivers (mean age = 46.5, SD = 5.1) were recruited to participate in a diary study for 14 consecutive days with questions about their sleep and working hours. A polynomial mixed-effect regression model showed a curvilinear relation ( p < .001) between shift-start time and sleep duration for shifts starting at 03:00-12:00 hand with a near linear increase for ones starting between 04:30 and 09:00 h of approximately 0.7 h for every 1 h the shift was delayed. The longest sleeps were estimated at approximately 8 h before shifts that started at approximately 10:00 h. The shortest sleeps were found for shifts that started before 04:30 h and were estimated at approximately 5 h. Individual differences were estimated with a random-effect standard deviation of 0.51 h, independent of shift start time ( p = .005). One-half of the between-subject variance was explained by subjective health. A one-step decrease in health was associated with a 26 min increase in sleep length. The results have practical implications for constructing shift schedules. Early morning shifts reduced sleep length substantially and should be mixed with later start hours to avoid the accumulation of sleep dept. Delaying the shift-start past 10:00 h had little effect on sleep opportunity; however, delaying shift-start to between 04:30 and 9:00 h had a strong impact on sleep length, with 70% of the extra time used for sleep, suggesting large positive effects for this range of shift-start times., Internt publ.nr P2659

Police officers attitude to different shift systems: Association with age, present shift schedule, health and sleep/wake complaints. Kecklund G, Eriksen CA, Akerstedt T. Stress Research Institute, Stockholm University, SE-106 91 Stockholm, Sweden; Department of Clinical Neuroscience, Karolinska Institutet, Sweden. It is often claimed that shift workers give priority to long series of days off and therefore prefer compressed work schedules at the expense of what is optimal for long-term health. The aim of the present study was to evaluate the attitude to six new shift systems among a randomly selected sample of police officers. The results showed that the most popular shift system was a rapidly, forward, rotating schedule with at least 16h of rest between shifts, despite that it had fewer days off compared with some of the compressed shift systems. However, the individual differences were large and many individuals (32%) disliked the rapidly rotating shift system. Young age was associated with a positive attitude to the rapidly rotating shift system. The attitude to the shift system was also influenced by the present schedule, and shift systems that were similar to the present work hours received more positive evaluation. Sleep and health complaints showed no association with the attitude to the shift systems. In conclusion, the shift workers attitude to the new schedules was partly in agreement with the ergonomic recommendations of the design of three-shift systems that will facilitate sufficient sleep and minimize negative health consequences., Internt publ.nr. P2660

Effects of context on sleepiness self-ratings during repeated partial sleep deprivation. Akerstedt T, Kecklund G, Axelsson J. Stress Research Institute, Stockholm University, Stockholm, Sweden. torbjorn.akerstedt@ki.se Ratings of subjective sleepiness are often used in laboratory and field studies of sleep loss and shifted sleep hours. Some studies suggest that such ratings might fail to reflect sleepiness as shown in physiology or performance. One reason for this may be the influence of the context of the rating. Social interaction or physical activity may mask latent sleepiness. The present study attempted to approach this question. Nine subjects participated in a partial sleep-deprivation experiment (five days of 4 h of time in bed [TIB]), preceded by two baseline days (8 h TIB) and followed by three recovery days (8 h TIB). Sleepiness was self-rated on the Karolinska Sleepiness Scale (KSS; scores of 1-9) after a period of relaxation, after a reaction-time test, and after 30 min of free activities. The results showed a strong increase in subjective sleepiness during sleep restriction and a significant difference between conditions. Free activity reduced the self-rated subjective sleepiness by 1.1 KSS units compared to the level of sleepiness self-rated at the end of the reaction-time test. Thus, the results of this study indicate that the context of a sleepiness rating affects the outcome of the rating., Internt publ.nr. P2655

Internt publ.nr. P2690

Predicting road crashes from a mathematical model of alertness regulation--The Sleep/Wake Predictor. Akerstedt T, Connor J, Gray A, Kecklund G. Stress Research Institute, Stockholm University and Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. torbjorn.akerstedt@ki.se Sleepiness is related to factors such as the time of day, the time since awakening and the duration of prior sleep. The present study investigated whether actual road crashes could be predicted from a mathematical model based on these three factors (the Sleep/Wake Predictor-SWP). Data were derived from a population-based case-control study of serious injury crashes. Data on accident time (or control sampling time) and start and end of prior sleep were entered into the model (blind). The predicted sleepiness values were used in logistic regressions. The results showed a highly significant odds ratio (OR)=1.72 (confidence interval=1.41-2.09) for each incremental step of sleepiness on the output sleepiness scale (nine steps). There was also a significant interaction with blood alcohol level, showing high OR values for high sleepiness levels and alcohol levels above 50 mg% (0.05 g/dl). It was concluded that the model is a good predictor of road crashes beyond that of alcohol level, and that interaction between the two carries a very high risk., Internt publ.nr. P2667

The alerting effect of hitting a rumble strip--a simulator study with sleepy drivers. Anund A, Kecklund G, Vadeby A, Hjälmdahl M, Akerstedt T. Clinical Neuroscience, Karolinska Institutet, SE-177 71 Stockholm, Sweden. anna.anund@vti.se A moving base driving simulator experiment was carried out in order to investigate the effects of milled rumble strips on driver fatigue. There were rumble strips both at the edge line and centre line. Four different physical designs of milled rumble strips (yielding noise values from 1.5 to 16 dBA) and two placements on shoulder were used in the experiment. Sound and vibrations from real milled rumble strips were reproduced in the simulator. In total 35 regular shift workers drove during the morning hours after a full night shift. The main results showed an increase in sleepiness indicators (EEG alpha/theta activity, eye closure duration, standard deviation of lateral position, subjective sleepiness) from start to before hitting the rumble strip, an alerting effect in most parameters (not subjective sleepiness) after hitting the strip. The alertness enhancing effect was, however, short and the sleepiness signs returned 5 min after the rumble strip hit. Essentially no effects were seen due to type of strip. It was concluded that various aspects of sleepiness are increased before hitting a rumble strip and that the effect is very short-lived. Type of strip, as used in the present study did not have any effect., Internt publ.nr. P2713

Several mathematical models for prediction of sleepiness have been developed. Few validations on individual levels are available. Background The present study was designed to provide validation on the individual level of predictions using the Three Process-Model of alertness regulation. Model predictions of sleep timing were also tested. Method Sixteen shift workers participated in the study. Ratings of sleepiness were made every 2h across three shifts. The model was used to predict empirical ratings using as input only information of beginning and end of work shifts, as well as using information on sleep from actigraphs (in a separate analysis). Results The prediction using only information on work shifts correlated r=0.55 (p<0.001) with empirical ratings. Predictions were generally within ±1 confidence interval of the ratings. Adding actigraphy sleep data improved predictions marginally. The model predictions of onset and offset of sleep were generally close to the target. Conclusion It was concluded that model predictions have a rather high validity both with respect to sleepiness and to sleep timing. It is probable that other information on individual differences will further improve predictability., P2630

Akerstedt T, Kecklund G, Axelsson J. torbjorn.akerstedt@stressforskning.su.se 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. PMID: 17884278 [PubMed - in process], P2628

Sleep, sleepiness and health complaints in police officers: the effects of a flexible shift system. Eriksen CA, Kecklund G. National Institute for Psychosocial Medicine (IPM), Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden. The aim of the study was to study the effects of a flexible shift system (based on self-determined work hours) with respect to sleep/wake complaints and subjective health. The comparison group was a rapidly rotating shift system, with frequently occurring quick returns. A secondary aim was to examine the relation between work hour characteristics indicating compressed or difficult rosters (e.g. number of workdays in a row, frequency of quick returns and long work shifts) and subjective sleep and sleepiness, within the flexible shift system group. The sample of the analysis included 533 randomly selected police officers, of which 26% were females. The participants answered a questionnaire. The results showed that the flexible shift system group did not differ with respect to sleep/wake complaints and subjective health. However, the flexible shift group obtained more sleep in connection with the shifts, probably because of longer rest time between shifts. Thus, they worked less quick returns and long work shifts. The association between work hour characteristics and sleep/wake complaints was weak in the flexible shift group. Instead, sleep/wake problems were mainly associated with the attitude to work hours. PMID: 17485872 [PubMed - indexed for MEDLINE], P2638

Sleep and sleepiness in relation to stress and displaced work hours. Akerstedt T, Kecklund G, Gillberg M. Karolinska Institutet, Institute for Psychosocial Medicine Box 230, S-171 77 Stockholm, Sweden. torbjorn.akerstedt@ipm.ki.se Sleep is an important factor in relation to accidents, long-term health and mortality. Our group has had a long-term commitment to research on sleep regulation and its consequences. Over the years we have demonstrated pronounced effects of night work on sleep and alertness, including electroencephalographically determined sleep during work. We have also demonstrated that experimental displacement of sleep will result in short sleep at daytime and increased physiological sleepiness at night and developed mathematical models for prediction of sleep duration, as well as of sleepiness and risk of sleep-related accidents. We have also looked at the concept of sleep quality and found it dependent on sleep duration, sleep continuity and content of sleep stages 3 and 4. Sleep is also clearly disturbed in patients on long-term sick leave for burnout or in non-patients with high burnout scores, in particular sleep fragmentation is increased and sleep efficiency and sleep stages 3 and 4 (SWS--deep sleep) decreased. The fragmentation in turn seems related to endocrine changes. Present work is focused on bringing this work together, connecting the links from stress to sleep to metabolic changes to disease and long-term sickness absence. PMID: 17585960 [PubMed - indexed for MEDLINE], P2631

Objectives Previous studies of long workhours and their effects on stress, sleep, and health show inconclusive results. This inconclusiveness may be partly due to methodological problems such as the use of between-group designs or comparisons before and after reorganizations. In addition, stress is usually a confounder. A within-person design was used to examine the effects of working 8- or 12-hour shifts in the absence of additional stress. Methods In an experimental field study, 16 white-collar workers [9 women, mean age 45.9 (SD 15) years] undertook one workweek with normal workhours (8 hours) and 1 week of overtime with 4 extra hours of regular worktasks (12 hours). The participants wore actigraphs, rated sleepiness (Karolinska Sleepiness Scale) and stress throughout the day, and rated workload and how exhausted they felt. Saliva samples were collected on Mondays and Thursdays for cortisol analysis. On these days, ambulatory heart rate and blood pressure were also measured for 24 hours. Results Overtime was associated with higher levels of exhaustion. Sleepiness showed a significant interaction between conditions, with higher levels at the end of the workweek featuring overtime. Total sleep time was shorter in the overtime week. There were no significant differences between ratings of stress and workload. Cortisol showed a circadian variation but no main effect of condition. Conclusions One week of overtime work with a moderate workload produced no main effects on physiological stress markers. Nevertheless, sleep was negatively affected, with shorter sleeps during overtime work and greater problems with fatigue and sleepiness., QC 20120305

Objectives The aim of the study was to relate different levels of work stress to measures of sleep and the diurnal pattern of salivary cortisol and subjective sleepiness. Methods Thirty-four white-collar workers participated under two different conditions. One workweek with a relatively high stress level (H) and one with a lower stress level (L) as measured through self-rated stress during workdays. The workers wore activity monitors, filled out a sleep diary, gave saliva samples (for cortisol), and rated their sleepiness and stress during one workday and one free day. Results During the week with stress the number of workhours increased and total sleep time decreased. Sleepiness showed a significant interaction between weeks and time of day, with particularly high levels towards the evenings of the stress week. Cortisol also showed a significant interaction, with a more flattened pattern, probably due to increased evening levels during the stress week. Stress (restlessness) at bedtime was significantly increased during the stress week. Conclusion The results demonstrate that a workweek with a high workload and much stress increases sleepiness and workhours, impairs sleep, and affects the pattern of diurnal cortisol secretion., QC 20120305