Circadian rhythm desynchronosis in military deployments: a review of current strategies.

The combined problems of changing work schedules and work places are not uncommon in military operations. For example, during the Persian Gulf War, many military units underwent short notice transmeridian deployment with immediate commencement of 24-h operations upon arrival. Some of these individuals likely suffered from circadian desynchronosis, blunting their effectiveness. The United States Air Force approved limited use of one short acting hypnotic medication to assist aircrew sleep disorders in the operational theater and, until recently, one stimulant medication to enhance alertness. Multiple theoretical strategies for circadian rhythm management are available. However, many U.S. Air Force flight surgeons are not trained on how best to use medications in combination with other circadian rhythm strategies. We present a condensed review of current human circadian rhythm coping strategies pertinent to military operations.

Aircrew fatigue during Desert Shield C-5 transport operations.

The metrics used to define U.S. Air Force crew rest and flight duty limitations were not designed to manage surge operations such as Operation Desert Shield. Desert Shield provided an opportunity to obtain inflight data on acute and cumulative fatigue and the effect of other stressors during over-the-shoulder observations on 24 C-5 airlift crew members. Findings emphasize how sleep history, recent duty day cycles, subjective fatigue, scheduling patterns, nutrition, and billeting facilities contribute to fatigue and lower levels of alertness. The results of this fairly insignificant observational study attempt to preserve some of the aeromedical lessons of Desert Shield. The flight surgeon authors integrate their experience to outline development of a fatigue management and alertness enhancement doctrine.

Crew fatigue during simulated, long duration B-1B bomber missions.

Crew fatigue associated with successive and unaugmented 36 h missions was evaluated in B-1B simulators. Data were obtained from 32 operationally qualified crewmembers. All crew-members completed three consecutive, long duration missions, each preceded by 33 to 35 h of crew rest. Oral temperature, salivary melatonin and cortisol, as well as actigraph and subjective measures, were collected during all missions. Temperature and melatonin data indicate that crews maintained their local home base circadian cycles. Elevated cortisol and subjective fatigue during the first mission indicate that it was the most difficult of the three. Furthermore, quality and duration of sleep were lowest during the first mission. These findings emphasize the need for realistic training in long duration fatigue management to improve the safety and effectiveness of the first and subsequent missions.

Prevalence of decompression sickness among U-2 pilots.

BACKGROUND: Though it is rarely reported, decompression sickness (DCS) is an expected risk for U-2 aviators. The potential for chronic sequelae of untreated DCS in this population has never been addressed. METHODS: After conducting a preliminary survey at an active-duty U-2 squadron, a cohort of 416 U-2 pilots (active-duty and retired) were mailed two sequential anonymous surveys to assess demographic data, career prevalence of DCS symptoms, and overall health status with an emphasis on chronic musculoskeletal problems. RESULTS: The response rate for each mail-in survey was over 60%. During their career, 75.5% of pilots experienced DCS symptoms such as joint pain, skin manifestations, and/or various neurological problems. Symptoms generally started during flight and resolved upon descent. Many pilots voluntarily increased their oxygen prebreathing time, or inflated the pressure suit during flight to prevent or treat symptoms. At some point in their career 12.7% of those experiencing symptoms either altered the flight profile or aborted a mission as a result. The association of past DCS with current arthritic problems was not statistically significant. CONCLUSIONS: The career prevalence of DCS symptoms in U-2 pilots is higher than previously reported, and these symptoms sometimes affect mission completion. We found no evidence that chronic musculoskeletal sequelae (e.g., arthritis or dysbaric osteonecrosis) are causally associated with DCS in this population.

Prediction of maximal oxygen uptake from submaximal exercise testing in aerobically fit and nonfit men.

Aerobic physical fitness, as determined by the body's maximal capacity to utilize oxygen (VO2max) during demanding work, is an important determinant of a person's ability to perform many military tasks. The present 2.4 km (1.5 mi) run has not proven itself capable of accurately estimating this important factor on a periodic basis. This paper reviews prior studies of heart rate response to known workloads on a cycle ergometer to estimate VO2max. This submaximal test, as revised by scientists at the USAF Armstrong Laboratory at Brooks AFB, TX, was validated on 22 male subjects by comparing the test results with laboratory measurements of VO2max obtained by analysis of expired air during maximal treadmill exercise. Two groups of subjects were selected; one consisting of highly trained runners and the other of inactive subjects who did not perform regular aerobic exercise. The cycle ergometry prediction underestimated measured VO2max by 8.1 ml.kg-1 x min-1 (SEE = 4.25) in all subjects, but there was a correlation of 0.95 between the estimated and measured values. Both estimated and measured VO2max were significantly higher in the group of trained runners than in the inactive subjects.

Subjective fatigue of C-141 aircrews during Operation Desert Storm.

Airlift crews were exposed to extended work periods, reduced sleep periods, night work, and circadian dysrhythmia caused by shift work and time-zone crossings during Operations Desert Shield and Desert Storm. This research reveals the extent to which severe subjective fatigue was experienced by the crews during Operation Desert Storm. In addition, through the evaluation of long-term and short-term work and sleep histories, this research shows that recent sleep and flight histories are correlated with high fatigue levels. Furthermore, we found a tendency for fatigue to correspond with pilot error. We recommend that the training of personnel involved in long-duration operations include fatigue management strategies and, further, that work policies and environments be designed to take into account the importance of regular and restorative sleep when unusual duty hours are required.