Sleep-Wake Disorders: Shift Work

Shift Work

Shift work problems occur when the circadian sleep–wake rhythm is in conflict with the rest–activity cycle imposed by the externally determined work schedule. Nearly a quarter of all American employees have jobs that require them to work outside the conventional 8 AM to 5 PM schedule. Different patterns in-clude rotating schedules and more or less permanent evening and night schedules. Rotating schedules, particularly rapidly shifting schedules, are difficult because constant readjustment of the en-dogenous circadian oscillator to the imposed sleep–wake cycle is necessary. In both rotating and shift work schedules, further dif-ficulties are encountered because the worker is usually expected to readjust to a normal sleep–wake cycle on weekends and holi-days. Even if the worker can adjust his or her circadian system to the work schedule, he or she is then out of synchrony with the rhythm of family and friends during off-duty hours. These indi-viduals, therefore, are constantly sleep deprived and constantly sleepy. They endure impaired performance and increased risk of accidents, somatic complaints and poor morale; hypnotics, stim-ulants and alcohol are used excessively in relationship to unu-sual or shifting work schedules. Shift work schedules may have played a role in human errors that contributed to the Three Mile Island and Chernobyl accidents and the Challenger disaster.

Treatment

No totally satisfactory methods currently exist for managing shift work problems. Because people vary in their ability to adjust to these schedules, self-selection or survival of the fittest may be involved for those who can find other employment or work sched-ules. Older individuals appear to be less flexible than younger persons in adjusting to shift work. Some experiments suggest that the principles of chronobiology may be useful in reducing the human costs of shift work. For example, because the endog-enous pacemaker has a cycle length (tau) longer than 24 hours, rotating shift workers do better when their schedules move in a clockwise direction (i.e., morning to evening to night) rather than in the other direction. Appropriate exposure to bright lights anddarkness may push the circadian pacemaker in the correct direc-tion and help stabilize its phase position, especially in associa-tion with the use of dark glasses outside and blackout curtains at home to maintain darkness at the appropriate times for promo-tion of sleep and shifting of the circadian pacemaker. Naps may also be useful in reducing sleep loss. Modest amounts of coffee may maintain alertness early in the shift but should be avoided near the end of the shift.

Jet Lag

Jet lag occurs when individuals travel across several time zones. Traveling east advances the sleep–wake cycle and is typically more difficult than traveling west (which delays the cycle). Jet lag may be associated with difficulty initiating or maintaining sleep or with daytime sleepiness, impaired performance and gastroin-testinal disturbance after rapid transmeridian flights. Individuals older than 50 years appear to be more vulnerable to jet lag than are younger persons.

Management

Considerable research and theorizing are under way better to prevent and manage the problems associated with jet lag. Some efforts before departure may be useful to prevent or ameliorate these problems. For persons who plan to readjust their circadian clock to the new location, it may be possible to move the sleep– wake and light–dark schedules appropriately before departure. In addition, good sleep hygiene principles should be respected be-fore, during and after the trip. For example, many people are sleep deprived or in alcohol withdrawal when they step on the plane because of last-minute preparations or farewell parties. Whereas adequate fluid intake on the plane is necessary to avoid dehydra-tion, alcohol consumption should be avoided or minimized be-cause it causes diuresis and may disrupt sleep maintenance.

On arriving at the destination, it may be preferable to try to maintain a schedule coinciding with actual home time if the trip is going to be short. For example, the individual should try to sleep at times that correspond to the usual bedtime or with the normal midafternoon dip in alertness. If, on the other hand, the trip will be longer and it is desirable to synchronize the biologi-cal clock with local time, exposure to appropriate schedules of bright light and darkness may be helpful, at least theoretically. Unfortunately, the exact protocols have not been established in all instances yet and require further research and experimenta-tion. In addition, some of these protocols require avoidance of bright light at certain times, necessitating wearing dark goggles, for example, when traveling.

In addition to synchronizing the clock with the new en-vironment, sleep and rest should be promoted by good sleep hy-giene principles, by avoidance of excessive caffeine and alcohol and, possibly, by administration of short-duration hypnotics. Care should be taken, however, to avoid hangover effects or am-nesia associated with hypnotics. Because individual responses to sleeping pills vary considerably from person to person, it is often helpful to develop experience with specific compounds and doses before departure.

Non-24-Hour-Day Syndrome

The non-24-hour-day (or “hypernyctohemeral”) syndrome is characterized by free-running in the natural environment, that is, the subject goes to bed and arises about 45 minutes later each day. The average duration of the sleep–wake cycle is about 24.5 to 25.0 hours. During the course of about 3 weeks, the subject’ssleep–wake cycle “goes around the clock” as the timing of the sleep period gradually delays. The lengthened sleep–wake cycle of these patients in the natural environment is similar to that of normal subjects living in a time-free environment. The disorder appears to be relatively common in patients with total blindness, because they no longer perceive visual Zeitgebers. In many cases, the cause is unknown, but it is sometimes observed in individu-als who are socially or linguistically isolated. Management may include bright light therapy in the morning to entrain the endog-enous oscillator. Administration of vitamin B₁₂ may be helpful, perhaps by enhancing the effectiveness of Zeitgebers.

The prevalence of circadian rhythm disturbances has not been established. Approximately two-thirds of shift workers have difficulty with their schedules. Circadian rhythm distur-bances must be differentiated from sleep-onset insomnia due to other causes (such as pain, caffeine consumption), early morning insomnia due to depression or alcohol use, and changes in sleep patterns due to lifestyle or lifestyle changes.