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.     

Napping in shift work

Two hundred eighty-two three-shift workers on rotating schedules filled out a questionnaire on napping behavior. Fifty-one percent were habitual nappers, but these workers rarely napped when working the afternoon shift or on days off. Four patterns were seen: non-napping (49%), morning shift napping (18%), night shift napping (18%), and both night- and morning shift napping (15%). The napping behavior was closely related to the length of the major sleep episode, which depended on the shift worked and on diurnal type; for example, morning shift nappers rated lower on a morningness/eveningness scale and night shift nappers higher. A study repeated 1.5 years later revealed that non-napping was a very stable behavior, whereas napping in many cases had disappeared, particularly among those who had been transferred to day work. The results indicate that for most shift workers napping compensates for sleep loss caused by the temporal displacement of sleep and modified by diurnal type.     

A prospective study of fatal occupational accidents -- relationship to sleeping difficulties and occupational factors

Very little is known about the association between sleep and (fatal) occupational accidents. This study investigated this relationship using register data of self-rated sleep difficulties, together with occupational and demographic characteristics. The variables were related to subsequent occupational fatal accidents. A national sample of 47,860 individuals was selected at regular intervals over a period of 20 years, and interviewed over the phone on issues related to work and health. The responses were linked to the cause of death register (suicides excluded) and the data set was subjected to a (multivariate) Cox regression survival analysis. One hundred and sixty six fatal occupational accidents occurred, and the significant predictors were: male vs. female: relative risk (RR)=2.30 with a 95% confidence interval (CI) of 1.56-3.38; difficulties in sleeping (past 2 weeks): RR=1.89 with CI=1.22-2.94; and non-day work: RR=1.63 with CI=1.09-2.45. No significant effect was seen for age, socio-economic group, hectic work, overtime (>50 h per week), or physically strenuous work. It was concluded that self-reported disturbed sleep is a predictor of accidental death at work, in addition to non-day work and male gender.     

Sleep on the Night Shift: 24-Hour EEG Monitoring of Spontaneous Sleep/Wake Behavior

The present study sought to objectively describe the spontaneous sleep/wakefulness pattern of shift workers during a 24-hour period. Portable Medilog tape-recorders were used for ambulatory EEG monitoring of 25 male papermill workers (25-55 years) during days with night and afternoon work. The results showed that sleep after night work was two hours shorter than after afternoon work. The sleep reduction affected mainly Stage 2 and REM sleep while slow wave sleep was unchanged. In connection with night work 28% of the workers took a nap in the afternoon. These naps contained a large proportion of slow wave sleep and were, apparently, caused by the sleep deficit after the short main sleep period. The EEG recordings also revealed that 20% of the participants had sleep episodes during night work. These naps were as long as the afternoon naps, were experienced as "dozing offs" rather than naps, occurred at the time of the trough of the circadian wakefulness rhythm, and were concomitant with extreme subjective sleepiness and low rated work load. It was concluded that not only the sleep of shift workers was disturbed, but also the wakefulness--to the extent that sleepiness during night work sometimes reached a level where reasonable wakefulness could not be maintained. The latter observation is probably of special importance in work situations demanding a great responsibility for human lives or for great economic values.     

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.     

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.     

Snoring and progression of coronary artery disease: The Stockholm Female Coronary Angiography Study

STUDY OBJECTIVES: Snoring is associated with a significant increased risk for acute myocardial infarction and stroke. However, our knowledge of mechanisms is still incomplete. The aim of the study was to investigate the influence of snoring in combination with feelings of tiredness on the 3-year progression of atherosclerosis in women with cardiovascular disease. DESIGN: Repeated quantitative coronary angiograms were carried out with an average time interval of 3.25 years. SETTING: Department of Thoracic Radiology at Karolinska Hospital, Stockholm, Sweden. PARTICIPANTS: The study sample comprised 103 women cardiac patients with repeated, valid, and comparable measurement of quantitative coronary angiograms. MEASUREMENTS AND RESULTS: Absolute luminal diameter (in mm) was measured in 10 predefined coronary segments. Mean segment diameter was calculated as the mean of all diameters measured along a given segment. The change over time was calculated by subtracting the first from the second measurement. Snoring and feelings of tiredness were measured by a short version of the Karolinska Sleep Questionnaire. We found that snoring women, after adjusting for age, waist-hip ratio, smoking, event at hospitalization, education, hypertension and alcohol intake, had a statistically significantly larger progression of atherosclerosis than did nonsnoring women (0.18 mm vs 0.07 mm change; P = .0006). CONCLUSION: Snoring contributes to the atherosclerotic process and should be taken into consideration when treating patients with cardiac disease.     

Experimental exposure to toluene in combination with ethanol intake. Psychophysiological functions

Effects of experimental exposure to toluene (3.2 mmol/m3, ie, 300 mg/m3) for 4.5 h and ethanol ingestion (15 mmol/kg) on the results of four performance tests, symptoms, mood, and physiological indices of wakefulness were studied in 12 male volunteers. Toluene exposure produced symptoms like headache and local irritation, as well as a weak depression of heart rate during rest, but did not reduce performance capability. Ethanol ingestion impaired performance on two of the tests and also increased heart rate. Mood was likewise altered by ethanol, but no increase in subjective symptoms due to ethanol ingestion could be demonstrated. Physiological indices of wakefulness were not affected by toluene exposure or by ethanol intake. No interaction effects were found.     

Physicians during and following night call duty--41 hour ambulatory recording of sleep.

Six house officers at two Stockholm hospitals were subjected to 41 h of continuous ambulatory recording of EEG and EOG in connection with night call duty, and to 24 h in connection with normal day work. The results showed that night call duty greatly interfered with sleep, reducing its duration to 4 h. The reduction mainly affected sleep stages 2 and REM. SWS was not affected, whereas EEG spectral power density in the 0.5-7.9 Hz band was suppressed. During subsequent time off, napping and night sleep increased total sleep length above baseline levels. It was concluded that night call duty of the present type causes considerable sleep loss.     

Age and adjustment to night work.

OBJECTIVE--The study was designed to examine the effects of age on sleep and the circadian rhythms during consecutive night shifts. METHODS--Two groups of letter sorters (19-29 (n = 7) and 53-59 (n = 7) years of age were studied in a sleep laboratory under closely controlled conditions. After two baseline days, circadian adjustment to three night shifts was monitored by continuous measurement of rectal temperature, salivary melatonin, and sleep-wakefulness during the night shifts. RESULTS--Age was significantly related to the adjustment to night work of rectal temperature minimum and of self rated sleepiness. Young subjects delayed their temperature phase and decreased sleepiness more than the older subjects. Age was also significantly related to an increase of alertness and to the feeling of being refreshed after the day sleep. Although there were basic differences in sleep duration and structure between the age groups, the latter did not change across the night shifts. CONCLUSION--Aging decreases the ability to recover after several, but not after the first night shift.