David F. Neri

Fatigue Countermeasures in Aviation

Pilot fatigue is a significant problem in modern aviation operations, largely because of the unpredictable work hours, long duty periods, circadian disruptions, and insufficient sleep that are commonplace in both civilian and military flight operations. The full impact of fatigue is often underappreciated, but many of its deleterious effects have long been known. Compared to people who are well-rested, people who are sleep deprived think and move more slowly, make more mistakes, and have memory difficulties. These negative effects may and do lead to aviation errors and accidents. In the 1930s, flight time limitations, suggested layover durations, and aircrew sleep recommendations were developed in an attempt to mitigate aircrew fatigue. Unfortunately, there have been few changes to aircrew scheduling provisions and flight time limitations since the time they were first introduced, despite evidence that updates are needed. Although the scientific understanding of fatigue, sleep, shift work, and circadian physiology has advanced significantly over the past several decades, current regulations and industry practices have in large part failed to adequately incorporate the new knowledge. Thus, the problem of pilot fatigue has steadily increased along with fatigue-related concerns over air safety. Accident statistics, reports from pilots themselves, and operational flight studies all show that fatigue is a growing concern within aviation operations. This position paper reviews the relevant scientific literature, summarizes applicable U.S. civilian and military flight regulations, evaluates various in-flight and pre-/postflight fatigue countermeasures, and describes emerging technologies for detecting and countering fatigue. Following the discussion of each major issue, position statements address ways to deal with fatigue in specific contexts with the goal of using current scientific knowledge to update policy and provide tools and techniques for improving air safety.

Nonentrained circadian rhythms of melatonin in submariners scheduled to an 18-hour day.

The human circadian timing system has previously been shown to free run with a period slightly longer than 24 h in subjects living in the laboratory under conditions of forced desynchrony. In forced desynchrony, subjects are shielded from bright light and periodic time cues and are required to live on a day length outside the range of circadian entrainment. The work schedule used for most personnel aboard American submarines is6hon duty alternating with 12 h off duty. This imposed 18-h cycle is too short for human circadian synchronization, especially given that there is no bright-light exposure aboard submarines. However, crew members are exposed to 24-h stimuli that could mediate synchronization, such as clocks and social contacts with personnel who are living on a 24-h schedule. The authors investigated circadian rhythms of salivary melatonin in 20 crew members during a prolonged voyage on a Trident nuclear submarine. The authors found that in crew members living on the 18-h duty cycle, the endogenous rhythm of melatonin showed an average period of 24.35 h (n = 12, SD = 0.18 h). These data indicate that social contacts and knowledge of clock time are insufficient for entrainment to a 24-h period in personnel living by an 18-h rest-activity cycle aboard a submarine.

Chronopharmacokinetics and Chronopharmacodynamics of Dextromethamphetamine in Man

Stimulants, in particular the amphetamines, have been studied as countermeasures to fatigue induced by circadian desynchronosis and extended flight operations. To make recommendations concerning the use of dextromethamphetamine for operational tasks, its chronopharmacokinetic and chronopharmacodynamic profiles and influence on circadian rhythms as a countermeasure to performance deficits and fatigue were studied. Ten male volunteers, divided into two groups of five each, were given 30 mg/70 kg of oral dextromethamphetamine during two test sessions one week apart and were evaluated with cognitive (dichotic listening, pattern recognition, and compensatory tracking), subjective (fatigue scale), and physiologic (blood pressure) testing. Session order was counterbalanced with dextromethamphetamine administration at either 8:40 AM or 8:40 PM during session one and a crossover to the other time during session two. Subjective and cognitive testing was begun 1.5 hours before dextromethamphetamine administration and continued every half hour until 12.5 hours after administration. Blood pressure was measured immediately before behavioral testing. Serum and urine were collected at regular intervals for gas chromatography/mass spectrometer analysis of methamphetamine and one of its metabolites, amphetamine. No differences were found in the day‐versus‐night pharmacokinetic profile of dextromethamphetamine. Cognitive performance and subjective fatigue improved after daytime administration of dextromethamphetamine in comparison to performance before drug administration. This effect was suppressed during the circadian trough, which occurred approximately 8 hours into the night sessions (4:30 AM). No correlations were seen between serum concentration of methamphetamine and measured behavioral parameters.