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1、3.1Fatigue:Definition of sleepPhysiology of sleepSleep disordersCircadian rhythm and circadian desynchronosis (including jet lag)Definition of fatigueCauses of fatiguePredisposing and contributing factors (individual, environmental, operational)Symptoms, signs, and performance effects of fatiguePrev
2、ention and countermeasuresINSTRUCTION“I departed from a parallel taxiway instead of the runway. I never thought I could ever do such a stupid, unsafe maneuver. Leading factor: fatigue; Second: “That will never happen to me” attitude; Third: complacency; Fourth: weather; Fifth: I was in a hurry to ge
3、t home. We had already been up more than 24 hours even though, technically, we were legal This event has cautioned me about two things: 1) fatigue is insidious, and 2) Im not as good as I thought I was, but Ill get better-for sure.”-Anonymous corporate pilot, quotation in Callback, NASAs Aviation Sa
4、fety Reporting System bulletin, Number 277, October 2002.INTRODUCTION Since World War II, flight operations have been increasingly performed over longer distances, longer intervals, and across multiple time zones. The biology governing the performance of men and women has not changed, however. The t
5、iming, quality and quantity of sleep needed may vary among individuals, but among all people, unalterable physiological needs and constraints exist. Efforts are being made within aerospace to design and employ behavioral and pharmacological interventions to overcome the effects of fatigue and sleepi
6、ness in personnel required to operate in a sleep deprived condition and at times when they would normally be sleeping. Complicating matters, however, is that ultra long haul aircraft that can fly 20 hours non-stop are in development, necessitating the need for more augmented or dual crews with appro
7、priate sleeping compartments. The development and implementation of automated flight systems may result in new opportunities for crew resource management (CRM), allowing for fewer pilots to be in the cockpit and more time for alternate pilots to get adequate sleep. Unfortunately, the more automated
8、systems may also promote complacency and inattention because there is not enough to keep the operators engaged with the aircraft.Aviation accidents are caused by human error 80% of the time. The role of fatigue and circadian rhythm disorders (desynchronoses) in these mishaps is probably underestimat
9、ed. The accident rate for long haul commercial flights is higher than for short and medium haul flights, leading to speculation that fatigue and sleepiness plays a more significant role with the larger transmeridian changes. It has been estimated that 15-20% of all transportation accidents are relat
10、ed to fatigue, which surpasses that of alcohol and drugs1. Recognition of the causes and signs of fatigue is central to safe and effective air operations. Every flight operation has its own tempo, time required to perform the major tasks, personnel structure, and number of personnel. There are a num
11、ber of different aerospace scenarios, ranging from ferrying operations to air rescue, combat and space flight. Prevailing cultural attitudes may pose a hindrance to adequate resting and napping. Our society now sleeps about an hour or two less on average than our ancestors a century ago. Sleep and t
12、he demand for productivity are at odds, and adult napping is virtually frowned upon. The sleep culture of modern society has fundamentally changed and as a result, fatigue-related problems have reached significant proportions in the population. Technological changes have led to sleep requirements be
13、ing pushed down on the needs scale. One-third of adults in a recent survey reported significant daytime sleepiness on the Epworth Sleepiness Scale, and 6% indicated they were severely sleepy2. Forty percent of adults indicated they were so sleepy during the day that it interfered with their daily ac
14、tivities, and 18% said they suffered from this type of problem several days a week. More than half the people surveyed also reported that chronic sleepiness adversely affected their mood, energy levels, concentration ability, and overall health, as well as their ability to pursue personal interests
15、and maintain quality relationships with their family and friends. Obviously, daytime sleepiness exerts a negative impact on mental and physical well-being and general productivity. A National Sleep Foundation (www.sleepfoundation.org) sponsored survey found that the U.S. workforce complains that on-
16、the-job concentration, problem-solving, interpersonal relationships, and performance suffer because of fatigue. Both personal and on-the-job safety is adversely affected by sleepiness. Improperly managed pilot and air traffic controller fatigue can become a significant problem in flight environments
17、 that require alertness, complex judgment, and quick reactions. Fatigue touches every aspect of life in modern society, including aviation sectors in which requirements for unpredictable and extended work episodes often occur at times when alertness tends to be most compromised.CAUSES AND EFFECTS OF
18、 SLEEP DEPRIVATION AND DESYNCHRONOSESThe Role of the Body Clock: The internal circadian clock, located in the suprachiasmatic nucleus of the hypothalamus, is one of two principal physiological determinants of waking alertness and performance4. The circadian clock controls the 24-hour rhythm for a wi
19、de range of functions, including performance, alertness, behavior, and mood. One prominent circadian pattern is exhibited by the sleep/wake cycle, with biological programming for a consolidated period of daytime wakefulness and nighttime sleep, recurring in a regular 24-hour pattern. Alertness and t
20、he ability to perform are related to two basic neurophysiological forces: the bodys circadian pacemaker (or biologic clock) and the drive or need for sleep (based on the length of previous wakefulness). Sleepiness cycles over a 24-hour period, and during this period, humans are programmed for two se
21、parate time frames of physiological sleepiness and two windows of alertness. For most, maximal sleepiness occurs at the lowest point of the circadian cycle, typically from about 3 to 5 AM, when the lowest levels in many functions are observed, such as temperature, mood, and performance. A second int
22、erval of sleepiness occurs at about 3 to 5 PM. The two windows of intrinsic alertness occur at approximately 9 to 11 AM and 9 to 11 PM. Several factors affect the specific timing of these episodes of alertness and sleepiness and the degree of change observed during these times. The ability to adapt
23、to a new time zone or shiftwork pattern takes up to 3 weeks, depending on individual differences, the frequency and magnitude of the time shifts. Environmental (light, activity) and social factors (sleep habits, social interactions, work schedule) may either assist or prevent the accommodation to a
24、new schedule. Constantly changing shifts are more disruptive because people rarely remain on the schedule long enough to adjust.Abruptly changing to a new schedule or time zone can result in both internal and external desynchronization. External desynchronization involves the internal clock being ou
25、t of synch with external time cues. Internal desynchronization involves the internal rhythms (e.g., temperature, sleep/wake, hormone secretion) being out of synch with one another. It can take from a few days to weeks for full circadian resynchronization. The adjustment time needed is dependent on f
26、actors such as direction flown, number of time zones crossed, and light exposure. Light is perhaps the most powerful cue that sets the circadian clock. Light exposure at times of clock sensitivity can be used to alter the clock and reset it to a new time zone or shift schedule. It can take 48 to 72
27、hours with expert application of light/dark cues to readjust the internal circadian clock. Therefore, there will not be significant circadian adjustment during trips of less than approximately 3 days; no matter what adaptation strategies are used. The Role of Acute and Chronic Sleep Loss: Human capa
28、bility and performance can be reduced with sleep loss5. Studies have shown that decision-making, reaction time, memory, communication skills, mood, vigilance, alertness, and more can be degraded by sleep loss and circadian disruption. Operationally, it is important to note that these reductions may
29、not occur as a smooth function. Performance becomes more variable when humans fatigue, and the onset of significant performance decrements can occur quickly. While performance may be at an acceptable and consistent level at one point, only moments later it can become irregular and significantly erod
30、ed. Falling asleep represents the absolute performance failure. However, performance can be reduced and can represent a safety risk well before or in the absence of an unplanned sleep episode. Sleepiness and fatigue cause reduced ability to function. Chronic sleep restriction to fewer than 6 hours p
31、er night has been shown to impair performance and increase the tendency to involuntarily fall asleep during normal wakefulness. Besides the chronic sleep deprivation, it is without doubt that many transportation workers are at serious risk for sleepiness while operating because of circadian disrupti
32、ons from rotating between day and night duty periods. Schedule rotation is a problem for aviation personnel as well. Studies have shown that irregular work schedules, compared with consistent daytime work schedules, are associated with an increase in vehicle accidents, more frequent complaints about
33、 inadequate daily sleep, a greater reliance on caffeine to boost performance, and an increase in the probability that alcohol will be used as a sleep aid. Lapses (the failure to respond to a situation) increase with increasing levels of fatigue. Lapses may be associated with microsleeps (episodes of
34、 sleep lasting 0.5 to 10 seconds), but can also occur without sleep onset. The four sleep-related factors involved in fatigue-induced performance impairments are the circadian phase of the biological clock, the presence of acute sleep loss, the presence of cumulative sleep loss and the presence of s
35、leep inertia. Lapses increase 2 to 10 times during night operations without pre-existing sleep loss. Acute sleep loss (following a single night of sleep loss) results in 4 to 10 times more lapses, while chronic sleep deprivation by reducing sleep 2-3 hours per night for 1 week may increase lapses by
36、 3 to 5 times normal. Sleep inertia is the difficulty awakening from a sleep episode. Sleep inertia results in increased lapses and is most likely to be present after abrupt awakenings and awakening from stages 3 and 4 NREM sleep. The potential for catastrophe due to lapses is enormous. An aircraft
37、going 250 kits on a glide path, for example, can travel over 400 feet during a 1-second lapse. Microsleeps have been shown to occur in aircrew during landing approaches in commercial carriers.The degree of resulting fatigue and risk of mishaps are dependent on the type of aircraft, mission, operatio
38、ns schedule, and environmental conditions. Increased workload, noise, temperature extremes and turbulence tend to exacerbate the effects of sleep loss and jet lag. Reaction times may be markedly slowed, which can be critical when rapid reactions are necessary. False responding also increases, i.e. t
39、he pilot may take action when no action is warranted, especially when aware of having missed signals. The resulting anticipation of another event and over attention on individual signals or problems further reduces situational awareness. Fatigue increases calculation errors, logical errors and ineff
40、ective problem solving. The member is less able to think of new solutions and repeatedly tries the same approach to a situational problem. Memory deficits progressively worsen with fatigue and sleep loss. The sleepy and tired crewmember reads or hears instructions repeatedly but cannot retain the in
41、formation, leading to critical errors and uncertainty about the status of the situation. Performance variability results from increased lapses and errors of omission. Although the member often becomes aware of the shortcomings in performance and responds by trying to increase self-motivation and eff
42、ort, performance improvement is short-lived. He/she may perceive the operation as more stressful and tiring as the effort continues. Ultimately, the crewmembers motivation to perform well and avoid risks erodes.No individual is immune to the effects of sleep loss and fatigue, although there are indi
43、vidual differences in the ability to tolerate sleep loss. After one night of sleep loss, half of healthy individuals perform reasonably well, but the remainder exhibit moderate to severe performance deficits. After 36 hours, there is little difference between individuals in their ability to perform-
44、all have severe performance deficits. The ability of a fatigued crewmember to self assess alertness is also limited6. In fatigued individuals, initial good performance early on may give a false sense of security. As time goes by, performance deteriorates. A crewmember is also more likely to overesti
45、mate his or her ability to perform if asked whether he or she is tired or able to perform. Relief from other crewmembers when signs of fatigue are observed (eyelids drooping, yawning, irritability, forgetfulness) is crucial.Although fatigue once was thought to be a minor concern that could be overco
46、me with sufficient motivation, training, or experience, it is now clear that the basis for this problem extends far beyond psychological factors. Sleep is a physiological need similar to hunger and thirst and adequate undisturbed sleep is the only remedy for sleepiness. When aircrews try to ignore t
47、he sleepiness, they become even sleepier and must expend greater and greater amounts of energy to stay awake and complete tasks. Fatigue from long work hours, sleep deprivation, and circadian disruption has been recognized as a substantial cause of serious human errors, and most recently, the effect
48、s of fatigue have received heightened consideration in the aviation sector.Research Studies in Real Aviation SettingsThe NASA Fatigue/Jetlag Program was initiated in 1980 in response to a Congressional inquiry about whether fatigue was a safety issue in flight operations. In 1990, the program evolve
49、d into the NASA Fatigue Countermeasures Program to emphasize strategies that would address the issue. Each branch of the Department of Defense and the FAA has also studied fatigue and its effects on safety and mission readiness. The NASA Program used a broad range of research methodologies and measures. Research projects included studies in controlled laboratory situations, high-fidel