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.     

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.     

Extreme sleepiness: quantification of EOG and spectral EEG parameters

Our earlier research has shown considerable increases of and intercorrelations between subjective sleepiness, alpha, theta, and delta power density of the EEG as well as slow rolling eye movements (SEM) during night-time, monotonous work tasks. The purpose of the present methodological study was to establish EEG-EOG criteria for extreme behavioral sleepiness. Medilog tape-recorders were used to record EEG and EOG on 5 males and 5 females during a 45 min visual vigilance test. Performance on the test was also recorded on the tape as well as experimenter-scored dozing off episodes (from TV supervision). The EEG was subjected to computerized spectral analysis in 7.5 s epochs, and the EOG was scored visually for slow eye movements in the same epochs. The epochs immediately preceding a hit, miss and dozing off differed significantly. There was most power density in the alpha, theta and delta bands and most SEM activity before dozing off episodes and least before hits. The power density and the SEM activity were significantly increased one whole minute before dozing off events and missed signals compared to hits. Just prior to the ultimate sleepiness, i.e., the dozing off, the SEM activity and the delta and theta power density were further increased, while alpha power density was at its maximum during the last three epochs before the dozing off. The response patterns of all subjects were rather homogeneous. In conclusion, behavioral sleepiness is systematically reflected in spectral EEG and EOG parameters and the results support attempts to use these variables to indicate sleepiness in active subjects in real life situations.     

Sleepiness on the job: continuously measured EEG changes in train drivers

Eleven train drivers participated in the study during 1 night and 1 day journey (4.5 h) over the same route. Their EEG, EOG and ECG were recorded on portable tape recorders. The EEG records were subjected to spectral analysis (FFT) and the EOG was scored visually for slow eye movements (SEMs). The results showed that rated sleepiness increased sharply during the night journey. A similar pattern was seen for spectral power density in the alpha band, SEM and, to a lesser extent, also for power in the theta and delta bands. Heart rate was low during the entire night drive. The day journey showed low values without any trend for all variables. The intra-individual correlations were very high between rated sleepiness and, particularly, alpha and theta power density, as well as SEM. Further analyses showed that most of the night time increases in EEG/EOG parameters were confined to the 6 most sleepy subjects. Among these, 4 admitted to dozing off during the night drive and 2 of these 4 subjects failed to act on signals while exhibiting large bursts of alpha activity. It was concluded that EEG and EOG parameters closely reflect variations in sleepiness on the job and that these parameters, together with self-ratings, demonstrate that severe sleepiness may occur in train drivers during night work.     

Effects on sleep stages and EEG power density of different degrees of exercise in fit subjects

In order to study the effects of exercise on sleep, 6 fit male subjects between 30 and 35 years of age were exposed to 4 conditions--sleep after a day with no running, sleep after a day with a moderate training run (15-20 km), the first night after an extremely exacting race (30 or 43 km), the second night after the race. All measurements were obtained in the respective homes of the subjects. The main effects of the race condition were a delay and decrease of REM sleep, an increase of stage 2 sleep and a weak decrease of SWS latency. Spectral analysis (FFT) of the EEG showed an increase of total power density as well as power in the delta band. The increase was significant also within SWS. By the second night all values had returned to baseline. The training run had virtually no effect on the sleep parameters although the values usually fell between baseline and race night values. Catecholamine excretion during the night and heart rate at bed-time and rising increased with increasing prior exertion. Subjective ratings showed no significant differences between the conditions. It was concluded that exercise effects mainly REM sleep, but although no SWS response was found in this age group, the increase of EEG power density after physical activity could lend some support to a hypothesized recovery theory.     

Disturbed sleep while being on-call: an EEG study of ships' engineers

In order to investigate the effects of on-call duty on sleep and wakefulness, five male ships' engineers were studied using electroencephalogram (EEG) and electrocardiogram (ECG) recordings and subjective ratings. Sleep during on-call nights (two alarms) was shortened and contained less slow wave sleep (SWS) and rapid eye movement (REM) sleep, lower spectral power density, and a higher heart rate. Many of the effects were observable before any alarms had occurred. Rated sleep quality was lower, and sleepiness was higher during the subsequent day. It was suggested that the effects were due to apprehension/uneasiness induced by the prospect of being awakened by an alarm.