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THE COMPETITION BETWEEN SWS AND REM SLEEP AS INDEX OF MALADAPTATION TO SHIFT WORK

V. S. Rotenberg

E-mail: vadir@post.tau.ac.il

Homeostasis, 33, 1991, No. 5-6

The competition between SWS and REM sleep as index of maladaptation to shift work - V. S.Rotenberg - Homeostasis 33,5 - 6, 1991 - Polysomnographic and questionnaire investigation was performed in 30 train dispatchers and in 15 employees of post transportation during one work-rest cycle. In the group of subjects well adapted to the shift work, the slow-wave-sleep reached its peak duration in the day sleep and in the first recovery night, while REM rebound took place only on the second night. In maladapted subjects, REM sleep prevailed in the day sleep as well as in the first recovery night. The alteration of sleep structure can be thus used as a sign of adaptation vs maladaptation to shift work. Sleep structure of the recovery day sleep after single night sleep deprivation may be used as a prediction of adaptation to the shift work.

The problem of adaptation to the shift work is very actual: 70 % of rotating and night workers complain on the quality of their sleep (Rutenfranz, Knauth, 1974). Shift workers display a higher level of neuroticism in comparsion with day workers (Tune, 1968). There are reports on increased rates of gastrointestinal and cardiovascular diseases among rotating and night workers compared to day workers (Alfredsson et al. 1982; Koller 1983; Knutsson et al. 1986). P. Lavie et al., 1989, established the association between subjective sleep disturbances in shift workers on the one hand, and their general psychophysiological adaptation to the shift system on the other hand: sleep disturbances were significantly associated with increased morbidity and increased blood pressure. According to this investigation, it is possible to suggest that there are some objective patterens of sleep structure which correlate with sleep disturbances and can be used to discriminate adapted vs. maladapted shift workers and to predict the capability of adaptation to shift work. It is also an interesting theoretical problem of the functional significance of different sleep stages in the process of adaptation to shift work.

SUBJECTS AND METHOD

A group of train dispatchers (22 men and 8 women, mean age 37, 30 to 50) was investigated during one work-rest cycle. The cycle included night work (20.00 - 8.00) with subsequent 48 hours of rest, and day work (8.00 - 20.00). Polysomnography was performed during the day sleep after the night work (9.00 - 15.00), during the night sleep after a night work (22.00 - 7.00), during night sleep after the day of rest (22.00 - 7.00) and during the night sleep after day work (22.00 - 7. 00). The duration of every shift was 12 hours. A group of 15 SS being involved in the post transportation was also investigated. Post transportation is characterized by an irregular regimen of work and rest during the trip. Subjects activity is distributed during the 24 hours very irregularly, they fall asleep 2-5 times during 24 hours, more often during the day. Their work schedule is: 7 day trip, and afterward 7 day rest. This group contained only men, age 26-43. All SS had complaints on sleep disturbances (difficulties in going to sleep and increased number of awakenings) and most of them presented also some somatic complaints. Polysomnography was performed after 7 day trip and after 7 day rest. Polysomnography was performed and analyzed according to Rechtschaffen and Kales (1968). Besides polysomnography, subjects were investigated by special questionnaires.

Questionnaire N1 was presented to the subject before the investigation and included questions which estimated the level of the general adaptation to the shift work: general satisfaction with sleep, average sleep latency, average number of awakenings, presence of neurotic and somatic complaints, the average level of mood, the general satisfaction with job, the level of social activity during rest (visiting and inviting friends, hobbies, etc.). The combination of the complaints on sleep disorders with neurotic and/or somatic complaints was suggested to be a sign of maladaptation to shift work. Questionnaire N 2 contained questions about the preceding wakefulness. The subject was asked to evaluate his emotional state, degree of fatigue and sleepiness, the number of naps during the day, the level of emotional tension and anxiety during the shift. Questionnaire N 3 was presented to the subject after the end of polysomnography and contained questions about sleep: the evalution of the total duration of sleep, the evaluation of the number of awakenings during sleep, the evaluation of sleep latency, the presence of dreams and evaluation of their quality (pleasant, unpleasant, active, passive), the general evaluation of sleep quality (from point 1 to point 5).

Student statistical method was used, as well as rank correlation between sleep structure and data of subjective evaluations.

RESULTS

1. A positive rank correlation (0.42) was found between the subjective evaluation of sleep quality and total delta sleep (Slow Wave Sleep, SWS) amount in night sleep but not in day sleep. SS estimated their sleep as excellent (point 5) only when SWS exceeded 70 min. and stage 4 exceeded 40 min. per night. It is in a good agreement with our previous data (Rotenberg, 1980). This correlation became stronger by taking into consideration the manifestation of fatigue and sleepiness was high, the correlation between SWS amount and self estimation of sleep was 0.61. It means that subjects who are not tired before sleep (for instance due to day naps during rest day, see Karacan et al. 1970) can be satisfied with their sleep quality even if SWS amount is decreased. There were no other significant correlations between objective sleep measurements and self evaluation of sleep.

According to this correlation we have picked out two extreme groups of dispatchers: subjects of group A (10 SS) exhibited more than 70 min. of SWS in every night. Subjects of group B (13 SS) exhibited SWS deficit in every night. Group A did not contain subjects who are suggested to be maladaptive according to the questionnaire N1, while most subjects in group B (11) were maladapted to shift work.

2. In group A SWS reached its maximum (105 min.) in the first night after night shift and is reduced to a minimum (85 min.) in the second night (which follows the day of rest). In group B there is no difference between SWS in the first (29 min.) and in the second night (28 min.), and SWS reached its peak (37 min.) after the day shift. In group A REM sleep has a nonreliable tendency to increase in the second night (90 min.) in comparison to the first (82 min.), but in 3 subjects REM sleep reached its peak in the 1st night, together with SWS. In 7 subjects of group B REM sleep was more prominent in the first night than in the second. In 5 SS of group B the sum of REM sleep amount in day sleep and in the 1st night sleep twice exceeded REM sleep after the day of rest. In group A there were no such cases (P 0.05). In group B there is a negative correlation between delta-sleep (SWS) and REM sleep in the first night (-0.45, p 0.05) and a positive correlation between REM sleep and sleep duration in the 3rd night after day shift (0.58, p 0.05).

3. REM latency after the high emotional tension during shift was 55 5, after a low emotional tension 717 min., p 0.05. Subjects of group B more often perceived their emotional tension during shift as high.

4. The mean day sleep duration after night shift in group A (162 min.) exceeded those in group B (134 min.), p 0.05. SWS was increased and REM sleep was reduced in day sleep in group A in comparison to group B.

5. Subjects occupied in post transportation displayed after the 7 day trip, in comparsion to 7 day rest, an increase of total sleep duration (429 21 vs. 351 29 min., p 0.05), a decrease of sleep latency (3.8 1.2 vs. 14.2 3.4 min., p 0.01), a decrease of waking time (30.1 6.9 vs. 63.9 8.7 min., p 0.01), and a decrease of the number of awakenings (0.710.24 vs. 2.540.52, p 0.01). At the same time REM sleep was increased in 30 % (107.013.6 vs 69.2 7.0 min., p 0.05). According to the questionnaire N1, all SS of this group are maladapted to the shift work. Thus, in this professional group maladaptation to the shift work also correlates with the primary REM rebound after shift work which cause sleep deprivation.

DISCUSSION

According to data of the present investigation, the sleep structure of day and night sleep after night shift and especially the alteration of sleep structure from night to night, reflect the adaptation to shift work. In the group of adapted SS this alteration of the sleep structure from night to night is the same as rebound effect in healthy SS with a normal work-rest regime after a single sleep deprivation: SWS reached its peak in the day sleep as well as in the first recovery night, while REM rebound took place only on the second recovery night (Agnewetal. 1967, Webb and Agnew, 1971; Nakazawaetal. 1978; Borbelyetal. 1981). The initial rebound effect of delta-sleep (SWS) in the day sleep after night shift seems to be a sign of a positive forecast of adaptation to the shift work; if so, a difficult and expensive night sleep investigation can be replaced by the day sleep registration to estimate the quality of adaptation to the shift work. It is important to take into consideration that the subjective estimation of day sleep, in contrast to the self estimation of night sleep, does not correlate with the representation of SWS. Such dissociation between subjective evaluation and objective data may be determined by the inversion of the sleep - wakefulness rhythm: sleep during the part of day being intended for activity may be underestimated.

In maladapted SS REM sleep exceeded SWS in the day sleep as well as in the 1st recovery night sleep, and REM rebound is most prominent in the 1st recovery night after night shift, in comparison to the 2nd night. It is possible to suggest that maladapted subjects are characterized by increased REM sleep requirement and that they need REM sleep for the psychological adaptation (Greenberg, Pearlman, 1974). In this aspect, the group of maladapted subjects is similar to subjects who demonstrate a long-lasting unproductive anxiety in a stressful situation (Rotenberg, Arshavsky, 1979). In these subjects the degree of sleep deprivation caused by shift work is related to the competition between SWS requirement which seems to be common for all SS irrespective of their psychological features and REM sleep requirement which depends on the peculiarities of defence mechanisms (Cartwright et al. 1967, Grieser et al. 1972), and on the type of waking behavior (Rotenberg, 1984) and may fluctuate in a very broad range. In healthy, well adapted and non-sensitive persons the competition between low REM requirement and high SWS requirement after sleep deprivation is easily resolved in favour of SWS (Brunner et al. 1990). For instance, short sleepers are characterized by low REM sleep requirement (Hartmann, 1973) and they are most resistent and adapted to shift work (Cherepanova, Putilov, 1992). On the contrary, persons with a low EGO-strength, who need REM sleep for EGO restoration, are especially sensitive to sleep deprivation (Lester et al. 1976). Increased REM sleep requirement, being not satisfied, can lead to the suppression of SWS and to sleep disturbances, as it happens in neurotics (Rotenberg, 1980).

The alteration of sleep structure can be thus used as a sign of adaptation vs. maladaptation to shift work. Sleep structure of the recovery day sleep after single night sleep deprivation may be used as a prediction of adaptation to the shift work.

Acknowledgement: Polysomnography in this investigation was performed by K. M. Shakhnarovich, A. M. Goncharenko, M. I. Kosilina, M. S. Tyurin, R. Arenalis-Garcia (Institute of Railway Hygiene, Moscow).

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