Understanding Sleep Disruption & Fatigue in Aviation


It is difficult to define fatigue in a human being. A simple defiinition would be "tiredness". One feels the lack of motivation or energy that can manifest itself physically, mentally or both. For most people, fatigue can be overcome by ceasing the particular activity they are involved in or by taking a nap. However, for someone operating a crane, commanding a large ship or performing a surgery, the onset of fatigue can be disastrous (FAA Civil Aerospace Medical Institute, n.d.). The causes of fatigue are extensive and can vary from boredom to circadian rhythm disruption and strenuous physical activities. According to medical experts, there are three types of fatigue: Pathological fatigue, which is the early stage of some serious ailments. Physiological fatigue, that is the hormonal changes in the blood that leaves the muscles of otherwise healthy people worn-out and psychological fatigue, which is a prolonged emotional clash, nervousness and monotony (Medical Recipe, 2010). Hence, it is important to note that ending a day filled with mental exhaustion such as analysing market data or studying for an examination can be just as tiring as performing manual labor. Ultimately, fatigue leaves the person in a state of diminished cognitive and physical functions, memory problems, reduced reaction times and decreased alertness.

Pilot fatigue is defined as “the state of tiredness that is associated with long hours of work, prolonged periods without sleep or the requirement to work at times that are out of synch with the body's biological or circadian rhythms" (Caldwell & Caldwell, 2003, p.15 2). Causes of pilot fatigue can be classified into sleep-related and non-sleep related. Examples of non-sleep related causes are poor nutrition, medication and alcohol, prolonged excessive physical activity, illness such as influenza, stress, depression or anxiety and even mental-boredom. Sleep-related causes range from poor sleeping habits, sleep disorders such as clinical insomnia, sleep restrictions related to short layovers, inadequate sleep due to an uncomfortable environment to circadian disruption due to shifting work schedules and sleeping through time zone transitions (Aviation Knowledge, 2011).

Our Body's Circadian Rhythm

A circadian rhythm is a roughly a 24 hour cycle in the physiological processes of plants and animals. In a nutshell, circadian rhythms are endogenously generated, although they can be modulated by external cues such as sunlight and temperature. Circadian rhythms is what determines the sleeping and feeding patterns of all animals, including human beings.
There are clear patterns of brain wave activity, hormone production, cell regeneration and other biological activities linked to this daily cycle. Most circadian rhythms are controlled by the body's biological "clock." This clock, called the suprachiasmatic nucleus or SCN is essentially a pair of pinhead-sized brain cell structures that contain about 20,000 neurons (National Institute of Neurological Disorders and Stroke: Brain Basics – Understanding Sleep, 2007). Circadian rhythms can be affected to a certain degree by almost any kind of external time cue, such as the beeping of alarm clocks, the clattering of a garbage cans, or meal timings. When travelers pass from one time zone to another, they suffer from disrupted circadian rhythms, an uncomfortable feeling known as jet lag. As an illustration, when traveling from California to New York, a person "loses" 3 hours according to the body's clock. Fatigue sets in when the alarm rings at 8 a.m. the next morning because according to the body's clock, it is still 5 a.m. It usually takes several days for the body's cycles to adjust to the new time.

Nature of Sleep

In the early days of medicine, sleep was regarded as a passive state where our body and mind was thought to be at rest to recover from the rigors of the day’s activities. Scientists have since discovered that the brain actually goes through a few stages of activities with specific brain wave characteristics at each stage. The brain remains very much active during sleep. This was accredited to the invention of the electroencephalograms (EEGs) in 1929, from which brainwaves could be recorded (Healthy Sleep: Natural Patterns of Sleep, 2007). Over time, other instruments were incorporated to study eye movements and muscle activity along with the use of EEGs and scientists today have managed to classify sleep into two types: rapid-eye-movement (REM) sleep and non-rapid-eye-movement (NREM) sleep. REM sleep is identifiable by its low-amplitude (small), high-frequency (fast) waves and alpha rhythm, accompanied by eye movements. NREM sleep can be categorized into three stages: N1, N2, and N3. In the progression from stage N1 to N3, brain waves become slower and more synchronized, with no eye movement. In stage N3, the deepest stage of NREM, EEGs show high-amplitude (large), low-frequency (slow) waves and spindles. This stage is referred to as "deep" sleep. NREM sleep and REM sleep continue to alternate throughout in a cyclical pattern. REM sleep episodes, the first of which may last only one to five minutes, generally become longer. The average length of the first NREM-REM sleep cycle is between 70 and 100 minutes; the average length of the second and later cycles is about 90 to 120 minutes. REM sleep comprises about 20 to 25 percent of total sleep in typical healthy adults (Healthy Sleep: Natural Patterns of Sleep, 2007).

Therefore the human body’s sleep patterns must synchronize with the circadian rhythm in order to achieve a healthy sleep quality.

Sleep Disruption

Traveling across time zones disrupts a person’s circadian rhythm. This wreaks havoc on the body and sets the path for the onset of fatigue and disorientation. This is known as jet lag. To reduce the effects of jet lag, doctors try to manipulate the biological clock with a technique called light therapy. They expose sufferers to special lights, much brighter than ordinary household lighting, for several hours near the time the subjects would want to wake up. This helps them reset their biological clocks and adjust to a new time zone (National Institute of Neurological Disorders and Stroke: Brain Basics – Understanding Sleep, 2007).

Another reason for sleep disruption is an active social lifestyle. For these group of people, staying up late on weekends and waking up late the next morning is routine. It seems innocent enough since they have no work on weekends and therefore can spend the whole day sleeping to regain “lost” sleep. However, studies have shown that our body cannot adjust to such abrupt changes in the circadian rhythm and paves the way for long-term sleep disorders and fatigue in the future or chronic fatigue.
Symptoms much like jet lag are also common in night or shift workers. Because these people's work schedules are in direct conflict with powerful sleep-regulating cues like sunlight, they often become uncontrollably drowsy during work, and they may suffer insomnia or other problems when they attempt to sleep. Shift workers also have an increased risk of heart problems, digestive disturbances, and emotional and mental problems, all of which may be related to their sleeping woes. The frequency and severity of workplace accidents also tend to increase during the night shifts. Major industrial accidents attributed partly to errors made by fatigued night-shift workers include the Exxon Valdez oil spill and the Three Mile Island and Chernobyl nuclear power plant accidents zone (National Institute of Neurological Disorders and Stroke: Brain Basics – Understanding Sleep, 2007).
One study also found that medical interns working on the night shift are twice as likely to misinterpret hospital test records, which could endanger their patients. Some solutions to reduce shift-related fatigue could be to possibly use bright lights at the workplace, therefore minimizing shift changes, and taking scheduled naps. These have shown promising results thanks to studies that were done on many people with total blindness. These few people experience life-long sleeping problems because their retinas are unable to detect light. They have a kind of permanent jet lag and periodic insomnia because their circadian rhythms follow their innate cycle rather than a 24-hour one.
Poor eating habits are also a major cause of sleep disruption. Having meals just prior to bedtime severely disrupts the circadian rhythm. It cues the body to be active as though it is daytime. This in turn leads to fatigue and diminished alertness during waking hours. Pilots have been trained to regularly exercise and maintain a strict regime of healthy lifestyle. This is why pilots are amongst the healthiest group of professionals and in general, we can also adopt the same lifestyles in order to preserve our sleeping quality.
For long haul flights, the FAA has also recently made some changes to its regulations for pilot rest and time off, raising the minimum time off between shifts to 10 hours from the previous 8-hour minimum. These regulations, although will not take effect until 2014 is viewed as a step in the right direction.


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