Читать книгу Counting Sheep: The Science and Pleasures of Sleep and Dreams - Paul Martin - Страница 18

My spirits grow dull, and fain I would beguile

The tedious day with sleep.

William Shakespeare, Hamlet (1601)

Fatigue and chronic sleep deprivation are obviously of crucial relevance to aviation safety. Tired pilots are bad pilots, for all the reasons that tired drivers are bad drivers. How big is the problem in practice?

Historically, severe fatigue among aircrews has sometimes been a major problem during crises where huge demands have been placed on precious personnel. Take, for example, the Berlin airlift of 1948–9. In June 1948 the forces of the former Soviet Union occupying eastern Germany began a blockade of road, rail and other communications between Berlin and the West. An international crisis ensued. The USA and UK mounted a huge airlift operation to supply West Berlin with food and other essential supplies. The airlift continued for 11 months until the Soviets eventually withdrew their blockade. During that time Allied planes delivered more than two million tons of food, fuel and other supplies to the beleaguered residents of West Berlin. To sustain this huge effort, the aircrews worked punishing schedules with grossly inadequate sleep. There were many accidents, some of them the result of fatigue. A special investigation during the crisis led to immediate improvements in the aircrews’ working conditions and sleeping quarters, which probably made a material contribution to the ultimate success of the whole operation.

Even in peacetime, tiredness is not unknown on the flight deck. Most airline flight crews experience some sleepiness and impairment in their performance, especially during long-haul and overnight flights. In one recent study, scientists from the British Defence Evaluation and Research Agency monitored 12 airline pilots during routine nine-hour flights between London and Miami. Recordings of their EEG brain-wave activity and eye movements revealed that 10 of the 12 pilots either slept or displayed signs of significant sleepiness during the flights. These episodes were often brief, lasting less than 20 seconds. Microsleeps of this brevity generally go unnoticed, and the pilots would probably have been unaware of drifting off.

Scientists from the NASA Ames Research Center in California also detected fatigue among flight crews on commercial long-haul flights. The crews on these flights, which crossed up to eight time zones, became measurably sleep-deprived. They felt more fatigued than normal, consumed more caffeine, ate more snacks and reported more minor health problems such as headaches, nasal congestion and back pain. Their sleep loss was made worse by the fact that their circadian rhythms did not have time to synchronise with local times. Their natural low points in alertness therefore often occurred while they were on duty, amplifying their sleepiness.

Jet lag is not just unpleasant and stressful – it also has physical effects on the brain. Researchers compared two groups of female flight attendants who had all been working on long-haul flights for at least five years. Half the women were in jobs that allowed them two weeks to recover between long-distance flights, while the other half usually had only a few days’ rest in between. The women who had little time between flights performed significantly worse on tests of learning and memory; their reactions were slower and they made more mistakes. More significantly, brain scans revealed distinct physical changes in their brains. A region of the brain known as the right temporal lobe had shrunk significantly. The women with the most shrunken right temporal lobes also had the highest levels of cortisol, a stress hormone that is known to affect the structure of the brain and the functioning of the immune system.

The implication of this research is that people who regularly fly long distances, crossing more than six or seven time zones, should ideally allow at least ten days to recover before doing it again. The research also raises questions about the policies of airlines that require their flight crews to fly long haul without adequate rest periods in between. The thought of sleepy, jet-lagged pilots with wizened right temporal lobes and impaired mental abilities slumped behind the controls of jumbo jets is mildly alarming.

Flying for a living can be tiring even when it does not involve crossing multiple time zones and becoming jet-lagged. Like workers in many other industries, flight crew are often required to start work early in the morning, and this alone can starve them of sleep. Researchers who monitored the sleep of female cabin crew found that when the women worked early mornings their sleep was reduced to an average of just over five hours. This is not enough sleep for the vast majority of people. Early-morning working was also unpleasant and mildly stressful for these women. They reported feeling apprehensive about having to rise early, they felt sleepy during the day and they complained more about their sleep being unrefreshing.

The only cure in situations like these is getting enough sleep, and at the right time of day. But that is not always possible on long-haul flights. Napping can provide a short-term palliative. If all else fails, a British firm has patented a technological aid to keep airline pilots awake. Worn like a wristwatch, it uses a motion sensor to monitor the pilot’s movements. A loud alarm sounds if there has been no movement for a few minutes. Personally, I would prefer not to find myself on a plane flown by a pilot who needs one of these devices. But if I do, I hope it works.

Space flight is even less conducive to sleep than air travel. Astronauts can and do sleep in space, but not very well. Space flight confuses the body’s internal clock and reduces both the quantity and quality of sleep. Astronauts on the Space Shuttle were typically getting only five or six hours of poor quality sleep a night, and often resorted to sleeping pills. More than 40 per cent of Space Shuttle astronauts took medication for sleep disturbances – about the same proportion as took drugs for motion sickness.

In recent years, NASA has been giving its astronauts doses of the ‘sleep hormone’ melatonin to help them sleep. (We shall see what melatonin does in chapter 6.) However, research by Charles Czeisler at Harvard Medical School found that melatonin actually had little beneficial effect on astronauts’ sleep. What did work, however, was covering the astronauts in electrodes to monitor their sleep. Czeisler discovered that Space Shuttle astronauts slept better when they were festooned with electrodes and physiological monitoring equipment. The most likely explanation is simple and psychological. The astronauts had probably been sleeping badly because they were so focused on performing their many duties. Swathing them in sleep-monitoring electrodes convinced them that sleep was also a legitimate and important part of their duties, and they consequently relaxed and slept better despite the marginal discomfort.