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Biomedical subjects

Torbjörn Akerstedt

Publications and source records attributed to Torbjörn Akerstedt.

At least 19 recordsLinked to original sources
PubMed2006

Altered sleep/wake patterns and mental performance.

Altered sleep/wake patterns involve, by definition, displaced sleep. The present review concludes that mental performance is strongly influenced by many forms of displaced sleep. Being exposed to the circadian low (during work/activity), extended time awake or reduced duration of sleep will impair performance. The effect is most pronounced in the laboratory setting, however, even if a number of studies have shown effects of for example night work on neuropsychological tests, and simulated work. In real shift work situations performance changes have been less pronounced. No studies have evaluated the effects on production, but accidents and serious mistakes have been clearly established in road transport and there seems to be clear effects also in health care. The effects are similar in connection with flights across several time zones (jet lag) but less data are available. It is suggested that there is a need for establishing the significance of impaired performance due to work hours in white collar and service work. Also the notion of individual differences in performance impairment is an important issue.

Circadian Rhythm↗
PubMed2006

Validation of the Karolinska sleepiness scale against performance and EEG variables.

OBJECTIVE: The Karolinska sleepiness scale (KSS) is frequently used for evaluating subjective sleepiness. The main aim of the present study was to investigate the validity and reliability of the KSS with electroencephalographic, behavioral and other subjective indicators of sleepiness. METHODS: Participants were 16 healthy females aged 33-43 (38.1+/-2.68) years. The experiment involved 8 measurement sessions per day for 3 consecutive days. Each session contained the psychomotor vigilance task (PVT), the Karolinska drowsiness test (KDT-EEG alpha & theta power), the alpha attenuation test (AAT-alpha power ratio open/closed eyes) and the KSS. RESULTS: Median reaction time, number of lapses, alpha and theta power density and the alpha attenuation coefficients (AAC) showed highly significant increase with increasing KSS. The same variables were also significantly correlated with KSS, with a mean value for lapses (r=0.56). CONCLUSIONS: The KSS was closely related to EEG and behavioral variables, indicating a high validity in measuring sleepiness. SIGNIFICANCE: KSS ratings may be a useful proxy for EEG or behavioral indicators of sleepiness.

Adult↗
PubMed2006

Aircrew fatigue in trans-Atlantic morning and evening flights.

The aim of the investigation was to compare sleepiness and sleep on westward morning and evening flights. Seven morning-crew pilots and seven evening-crew pilots participated. Data were collected before, during, and after outward-bound (westward) and homeward-bound (eastward) flights across six time zones. A sleep/wake diary (with repeated sleepiness and performance ratings) and wrist actigraphy were used for data collection. Maximum sleep was obtained after return and minimum sleep before the outward-bound flights. Actigraphy measures and sleep efficiency over the course of the study showed no significant differences between the morning and evening crews. There was a trend for a significant effect of morning vs. evening flight for time with heavy eyelids, with the homeward-bound flight showing more time with heavy eyelids. There were no significant differences between morning and evening crews with regard to napping during the flight. The duration of wakefulness was longer for the evening flight crew. There were significant interactions for Karolinska sleepiness scale (KSS) self-ratings on both the outward-bound and homeward-bound flights, and KSS was elevated during a considerable portion of the evening flights. Rated performance showed a significant time effect, but there was no difference in self-ratings between morning and evening crews. Evening flights involve higher levels of sleepiness than morning flights, presumably because of the close proximity in time to the circadian trough of alertness.

Adult↗
PubMed2006

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.

Adult↗
PubMed2006

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.

Accidents, Traffic↗
PubMed2006

Overtime work and its effects on sleep, sleepiness, cortisol and blood pressure in an experimental field study.

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.

Adult↗
PubMed2006

Disturbed sleep and fatigue in occupational burnout.

OBJECTIVES: The purpose of this study was to investigate sleep with polysomnography and self-ratings and the diurnal pattern of sleepiness and fatigue in a group suffering from severe occupational burnout. METHOD: Twelve white-collar workers on long-term sick leave (>3 months) and 12 healthy controls with high and low scores on the Shirom Melamed Burnout Questionnaire (SMBQ) were included. A 1-night polysomnographic recording (after habituation) was carried out at home, and sleepiness and mental fatigue were rated at different times of the day for weekdays and the weekend. Precipitating factors at the time of the illness at work and real life were considered, and different dimensions of occupational fatigue were described. A repeated-measures analysis of variance using two or three within group factors was used to analyze the data. RESULTS: The main polysomnographic findings were more arousals and sleep fragmentation, more wake time and stage-1 sleep, lower sleep efficiency, less slow wave sleep and rapid eye movement sleep, and a lower delta power density in non-rapid eye movement sleep in the burnout group. The burnout patients showed pronounced sleepiness and mental fatigue at most times of the day for weekdays without reduction during weekends. The precipitating factor was occupational stress (psychiatric interview), and work stress indicators were increased. CONCLUSIONS: Occupational burnout is characterized by impaired sleep. It is suggested that impaired sleep may play a role in the development of fatigue or exhaustion in burnout.

Burnout, Professional↗
PubMed2006

Fatigue in trans-Atlantic airline operations: diaries and actigraphy for two- vs. three-pilot crews.

INTRODUCTION: The aim was to compare intercontinental flights with two-pilot and three-pilot crews with respect to fatigue/sleepiness and sleep, as there is considerable economic pressure on the airlines to use two-pilot crews. METHODS: Twenty pilots participated. Data were collected before, during, and after outbound and homebound flights using a sleep/wake diary (sleepiness ratings every 2-3 h) and wrist actigraphy. The duration of flights was approximately 8 h, and six time zones were crossed. The same pilots participated in both conditions. RESULTS: Napping during the outbound flight was 26 min for the two-pilot crew, and 48 min for the three-pilot crew. Napping during the homebound flight was 54 min and 1 h 6 min, respectively, and the difference was directly related to the time allotted for sleep. Subjective sleepiness was significantly higher for the two-pilot condition in both directions, peaking a few hours into the flight. Performance at top of descent for the two-pilot condition was rated as lower than the three-pilot condition. In the overall evaluation questionnaire there was a significant negative attitude toward two-crew operations. Sleep, sleepiness, subjective performance, boredom, mood, and layover sleep were assessed as having deteriorated in the two-pilot condition. The homebound flight was associated with considerably higher levels of sleepiness than the outbound flight. DISCUSSION: The study indicates that the reduction of crew size by one pilot is associated with moderately increased levels of sleepiness. It is also suggested that time allotted to sleep in the two-pilot condition might be somewhat extended to improve alertness.

Adult↗
PubMed2006

Impact of an 84-hour workweek on biomarkers for stress, metabolic processes and diurnal rhythm.

OBJECTIVES: This study examined the degree to which long workhours in combination with an extended workweek (12 hours/7 days) with permanent day shifts (0700-1900), as requested by the workers, influenced biomarkers for stress, metabolic processes, and diurnal rhythm. METHODS: Construction workers (N=50) working 84 hours a week, with alternate weeks off, were compared with construction workers (N=25) having a traditional 40-hour work schedule. The participants were all male and between the ages of 21 to 65 years. Blood samples were obtained in the morning immediately prior to the start of work on workday 1, 5, and 7 to assess cholesterol, cortisol, dehydroepiandrosterone, melatonin, prolactin, testosterone, and uric acid. Psychosocial circumstances were assessed with a questionnaire. RESULTS: The 84-hour group had higher melatonin concentrations and reported higher job-control scores than the 40-hour group. For both groups, the melatonin, cortisol, and cholesterol concentrations were lower on workday 5 than on workday 1. In the 84-hour group, most of the biomarkers were significantly lower in concentrations on workday 7 than on workday 1. Only testosterone showed a significant decrease between workdays 5 and 7. The concentrations of dehydroepiandrosterone and uric acid remained stable across all of the days, as did the melatonin concentrations between workdays 5 and 7. CONCLUSIONS: Working of one's own free will on an 84-hour regimen is not, in the short-term, necessarily more harmful for health than working on a 40-hour regimen with a similar type of heavy worktasks. However, working on an 84-hour schedule beyond the ordinary 40-hour week results in signs of a functional shift in hormonal regulation.

Adult↗
PubMed2006

Psychosocial stress and impaired sleep.

This review demonstrates that stress is closely related to impaired sleep in cross-sectional studies. In particular, the anticipation of high demands or effort the next day seems important. Sleep recordings show that stress is associated with shortened sleep, fragmentation, and possibly a reduction in sleep stages 3 and 4. Shortened or disturbed sleep causes increases in levels of traditional stress markers (eg, cortisol) and may thus exacerbate the effects of stress. Much knowledge is still lacking, however, particularly about the effects of real-life work stress. The latter requires longitudinal studies in real-life situations.

Animals↗
PubMed2005

Effort-reward imbalance, sleep disturbances and fatigue.

OBJECTIVES: The objective of this study was to investigate the validity of the effort-reward imbalance (ERI) model in relation to disturbed sleep and fatigue. METHODS: The study population derived from a subset of the WOLF (WOrk, Lipids, Fibrinogen) cohort study of cardiovascular risk in a working population who replied to the ERI-questionnaire comprising 789 men and 214 women. Cox regression analysis was used to calculate the prevalence ratio (PR) for sleep disorders and fatigue in relation to the components of ERI. RESULTS: As sleep disturbances and fatigue, based on literature, were defined to be represented by the uppermost quintile, 14% of the men and 23% of the women were affected by sleep disturbances while 14 and 26%, respectively, were affected by fatigue. Higher levels of exposure for the ERI components were associated with increased prevalence of sleep disturbances and fatigue. For men, the strongest association was seen between high overcommitment and fatigue (PR 5.77, 95% confidence interval 2.89-11.5). For women, high effort and sleep disturbances (PR 4.04, CI 1.53-10.7), high effort/reward ratio and sleep disturbances (PR 4.13, CI 1.62-10.5), and between low reward and fatigue (PR 4.36, CI 1.79-10.6) yielded the most obvious associations. CONCLUSIONS: The present study adds sleep disturbances and fatigue to the list of adverse consequences of effort-reward imbalance.

Adolescent↗
PubMed2005

Effects of acutely displaced sleep on testosterone.

CONTEXT: It is not yet clear whether the diurnal variation in testosterone is regulated by circadian or homeostatic (sleep) influences. OBJECTIVE: The present study tested whether testosterone is driven by a circadian-independent sleep effect by shifting sleep acutely to daytime in a 24-h sampling regiment. DESIGN, SETTING, AND PARTICIPANTS: In the sleep laboratory, seven healthy young men (age, 22-32 yr) participated in three conditions: habituation (sleep between 2300-0700 h), night sleep (2300-0700 h), and day sleep (0700-1500 h), the latter two in a balanced order. INTERVENTION AND MAIN OUTCOME MEASURE: Serum testosterone was, in all conditions, sampled by hourly blood drawing for 24 h during constant bed rest. RESULTS: Mean testosterone levels increased as a log-linear function of time (hours) across both sleep periods (b = 4.88; P < 0.001), from 15.3 +/- 2.1 to 25.3 +/- 2.2 nmol/liter during night sleep and from 17.3 +/- 2.1 to 26.4 +/- 2.9 nmol/liter during day sleep. Similarly, mean testosterone levels decreased with time (log-linear) awake (b = -1.80; P < 0.001). There was also evidence of a weak circadian component (acrophase ranging between 0651-0924 h) and an increase with time in the laboratory. Moreover, all these effects, except for the increase during sleep, differed significantly between individuals. CONCLUSION: In conclusion, testosterone increased during sleep and fell during waking, whereas circadian effects seemed marginal. Individual differences were pronounced.

Adult↗
PubMed2005

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.

Accidents, Traffic↗
PubMed2005

Less effective executive functioning after one night's sleep deprivation.

The prefrontal cortex (PFC) is affected negatively by sleep deprivation (SD) and executive functioning is largely dependent on activity in the PFC. Earlier studies have focused on subsystems of executive functioning, and tests of executive functioning have shown both low reliability and low validity. In the present study, 11 healthy volunteers were sleep deprived and compared with 11 healthy controls in a study on effects of one night's SD on integrative executive functioning. Following SD, the performance of subjects on an ecologically valid test, the modified Six Elements Test, was significantly impaired. There were no group differences on psychomotor vigilance, verbal or visuo-spatial working memory. This extends previous knowledge of performance effects of SD, and may be of special importance for individuals with cognitive work tasks.

Adult↗
PubMed2005

Comment on short-term variation in subjective sleepiness.

Subjective sleepiness at different times is often measured in studies on sleep loss, night work, or drug effects. However, the context at the time of rating may influence results. The present study examined sleepiness throughout the day at hourly intervals and during controlled activities [reading, writing, walking, social interaction (discussion), etc.] by 10-min. intervals for 3 hr. This was done on a normal working day preceded by a scheduled early rising (to invite sleepiness) for six subjects. Analysis showed a significant U-shaped pattern across the day with peaks in the early morning and late evening. A walk and social interaction were associated with low sleepiness, compared to sedentary and quiet office work. None of this was visible in the hourly ratings. There was also a pronounced afternoon increase in sleepiness, that was not observable with hourly ratings. It was concluded that there are large variations in sleepiness related to time of day and also to context and that sparse sampling of subjective sleepiness may miss much of this variation.

Adolescent↗
PubMed2005

The future of work hours--the European view.

In Europe the way work hours are handled varies between different countries. However, there are some issues that dominate the discussion in Europe and seem representative for what is happening. One such is the reduction of working hours--which was attempted in several countries but which now seems to be backfiring--probably related to the competition from countries outside Europe. Another area is compressed work hours--the drive towards maximizing the hours per work day in order to increase the number of days off. The health effects are debated--some find clear positive effects. A third area is company oriented flexible work hours, permitting the employer to make moderate changes in work hours when needed. The health impacts have not been evaluated but the loss of individual influence at work is obvious. In some parts of Europe self-determined work hours have been tried with very positive effects. The EU work hour directive is intended to provide uniformity but permits a counterproductive "opting out", creating problems of imbalance.

Choice Behavior↗
PubMed2005

Different levels of work-related stress and the effects on sleep, fatigue and cortisol.

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. CONCLUSIONS: 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.

Employment↗