Monk TH, Buysse DJ, Billy BD. Using daily 30-min phase advances to achieve a 6-hour advance: circadian rhythm, sleep, and alertness. Aviat Space Environ Med 2006; 77:677–686. Introduction: A ground-based study was undertaken to determine whether circadian and sleep dysfunction could be avoided by “trickling in” a 6-h phase advance in sleep/wake schedule by 12 consecutive 30-min phase advances as per NASA’s Appendix K. Methods: We simulated a 16-d (384 h) mission for each of 10 subjects. Temporal cues and light levels approximated those experienced in space. All sleep periods were exactly 8 h. Before the study, for 14 d, subjects were required to live on a schedule with a 23:00 bedtime and 07:00 wake time. Laboratory sessions then started with a 4-d baseline segment on that schedule. The fourth night and the day following it were then taken as baseline. Repeated 30-min phase advances in bedtime were then required on each of the next 12 successive nights, resulting in an eventual movement of bedtimes to a 6-h phase-advanced position (bedtime: 17:00, wake time: 01:00). Polysomnographic sleep, circadian rhythms in urinary free cortisol, urinary volume (every void), and core body temperature (once per minute), and ratings of performance, mood, and alertness (five per day) were measured. Results: While circadian dysfunction was largely avoided by trickling in the phase shift, there remained slight differences in phase between the endogenous circadian pacemaker and the imposed routine which disrupted sleep and daytime alertness. Conclusion: Though statistically significant, the disruption was less than we observed from repeated 2-h phase delays reported in a 2004 ASEM paper. Evidence would thus seem to favor repeated 30-min phase advances over repeated 2-h phase delays.

Wingo JE, Cureton KJ. Maximal oxygen uptake after attenuation of cardiovascular drift during heat stress. Aviat Space Environ Med 2006; 77:687–694. Introduction: Exercise intensity is often regulated in hot conditions by maintaining a constant target heart rate (HR) to counteract increased physiological strain and thereby avoid premature fatigue. It is unknown, however, whether the HR–percent maximal oxygen uptake (%[V-dot]O₂max) relationship is maintained during prolonged exercise in the heat when the rise in HR concomitant with cardiovascular drift (CV drift) is eliminated by lowering exercise intensity. The purpose of this study was to determine if [V-dot]O₂max is reduced when exercise intensity and absolute [V-dot]O₂ are lowered by a magnitude sufficient to reduce CV drift and maintain constant HR during prolonged exercise in the heat, and thereby examine if the HR–%[V-dot]O₂max relationship is preserved. Methods: Seven men cycled at 60% [V-dot]O₂max in 35°C for 15 min (one trial) and 45 min (two trials) while HR rose over time (HRvar) or remained constant (HRcon). [V-dot]O₂max was measured immediately after the 15 and 45 min trials to correspond with the same time interval in which CV drift occurred. Results: Power output decreased 37%, [V-dot]O₂ decreased 24%, and [V-dot]O₂max decreased 7.5% from 15 to 45 min in HRcon, while HR remained the same. In HRvar, HR increased 13%, SV decreased 10%, and [V-dot]O₂max decreased 15%. Discussion: %[V-dot]O₂max was decreased from ∼60% to 50% to hold HR constant in these conditions, so the HR–%[V-dot]O₂max relationship was not preserved in the absence of CV drift. Attenuating CV drift by lowering exercise intensity only partially eliminated the reduction in [V-dot]O₂max after prolonged exercise in the heat.

Tribukait A, Eiken O. Roll-tilt perception during gondola centrifugation: influence of steady-state acceleration (G) level. Aviat Space Environ Med 2006; 77:695703. Background: Spatial disorientation is an important problem in aviation. The significance of the G level for illusions elicited from the semicircular canals is not clear. The aim of the present investigation was to elucidate how a gravitoinertial force, acting in parallel with the subject’s long (z) axis, may influence the magnitude and persistence of canal-induced tilts of the subjective visual horizontal (SVH) present after acceleration in a gondola centrifuge. Methods: The SVH was measured by means of an adjustable luminous line in darkness. Two series of experiments were performed. In series 1, the SVH was measured in 13 subjects at 1.1 G, 1.7 G, and 2.5 G. In series 2, it was measured in 8 subjects at 2.5 G and 4.5 G. Results: After acceleration of the centrifuge the SVH was tilted relative to the gravitoinertial horizontal. The direction of tilt was compensatory to the gondola inclination. In series 1 the initial SVH tilt was: 16.2 ± 7.0° (1.1 G), 24.2 ± 10.2° (1.7 G), and 27.1 ± 13.9° (2.5 G). In series 2 it was: 27.6 ± 14.6° (2.5 G), and 31.2 ± 18.8° (4.5 G). The gain for this response, defined as the ratio between the initial tilt and the inclination of the gondola, was: 0.65 ± 0.28 (1.1 G), 0.45 ± 0.19 (1.7 G), 0.41 ± 0.21 (2.5 G) (series 1); and 0.42 ± 0.22 (2.5 G), and 0.40 ± 0.24 (4.5 G) (series 2). Thus, an increase from 1.1 G to 1.7 G caused a reduction in the gain, but at G levels beyond 1.7 G there was no further decrease. The time constant for exponential decay tended to increase with the G level. It was: 61 ± 31 s (1.1 G), 84 ± 36 s (1.7 G), 89 ± 42 s (2.5 G) (series 1); and 67 ± 49 s (2.5 G), and 101 ± 73 s (4.5 G) (series 2). Conclusion: It appears that otolithic stimulation via an increased gravitoinertial force vector, acting in parallel with the head and body long axis, does not substantially influence the magnitude of the canal-mediated sensation of roll-tilt after acceleration in a swing-out gondola centrifuge. Nor does it reduce the duration of this sensation.

Ersanli D, Yildiz S, Sonmez M, Akin A, Sen A, Uzun G. Intraocular pressure at a simulated altitude of 9000 m with and without 100% oxygen. Aviat Space Environ Med 2006; 77:704–706. Introduction: Exposure to high altitude may affect intraocular pressure (IOP). This study aimed to determine how IOP was altered by two different inspired oxygen tensions at altitude. Methods: There were 34 healthy male pilots, ages 26–39 yr (mean 31.9 yr), who were studied at the Air Health Examination and Physiological Training Centre in Eskisehir, Turkey. They were studied at ground level, which is 792 m (2414 ft), and during a training session in a hypobaric chamber at a simulated altitude of 9144 m (30,000 ft). IOP was measured with a Tone-pen XL tonometer before subjects entered the chamber, at altitude while breathing 100% oxygen by mask and after removing the mask, and again 30 min after leaving the chamber. Results: Ground level values for IOP (mean ± SD) were 12.31 ± 2.98 mmHg. Levels increased significantly at altitude on oxygen (16.75 ± 4.14 mmHg) and decreased slightly on breathing ambient air (14.37 ± 3.44 mmHg). In 30 min after leaving the chamber, IOP was 12.81 ± 1.74 mmHg, indistinguishable from pre-test values. Discussion: Healthy subjects whose baseline IOP is in the normal range experience only a small, temporary elevation of IOP during passive exposure to high altitude with either normoxia or acute hypoxia.

Caruso JF, Herron JC, Capps LB, Coday MA, Ramsey CA, Drummond JL. Blood lactate responses to leg presses performed against inertial resistance. Aviat Space Environ Med 2006; 77:707–712. Introduction: A flywheel ergometer has been devised which employs gravity-independent inertial resistance. Concentric and eccentric actions, which are integral to weight-bearing and ambulation activities, may be done on this ergometer. However, blood lactate responses to exercise on the ergometer by contractile mode and training volume are unknown. Methods: Workout order was balanced so that subjects performed each type of ergometer leg press workout twice in a non-sequential manner. Per workout, 10 repetitions were performed per set. Workouts were as follows: three sets with concentric and eccentric (CE3) actions, three sets with concentric-only (CO3) actions, and six sets with concentric-only (CO6) actions. Pre- and 5-min post-exercise lactate was measured from a fingertip blood drop. Lactate means were compared with a 2 × 3 (time × workout) ANOVA with repeated measures applied to both independent variables and Scheffe’s post hoc test. With body mass and performance measures as predictor variables, multivariate regression attempted to explain post-exercise and delta (post-pre) lactate variance. Results: Post-exercise blood lactate values (mmol · L⁻¹, mean ± SEM) were as follows: CE3, 8.08 ± 0.44; CO3, 7.57 ± 0.49; and CO6, 6.96 ± 0.43. CE3 and CO6 workouts produced comparable volumes of work. Though several CE3 performance measures were significantly correlated to post-exercise and delta lactate values, power indices had the strongest relationship. Discussion: Factors related to lactate production and clearance caused CE3 values to be highest. Power indices were most correlated to lactate as they denote a higher work rate and reliance on glycolysis.

Äng B, Harms-Ringdahl K. Neck pain and related disability in helicopter pilots: a survey of prevalence and risk factors. Aviat Space Environ Med 2006; 77:713–719. Introduction: Today’s demands on helicopter missions—often using helmet-mounted visual technology—place much physical stress on the cervical spine. The objective of the present analytical survey was to estimate the prevalence of, and associated risk factors for, helicopter pilots’ neck pain and related disability. Methods: There were 127 Swedish helicopter pilots consecutively enrolled for the study who completed a structured questionnaire during their regular medical health checkups. The questionnaire concerned flight-related and individual risk indicators, frequency of neck pain episodes, and disability. Multivariate regressions, with the potential to control for confounding factors, were used to estimate relative risks (RR). Results: The 3-mo prevalence of neck pain was 57%, with 32% reporting frequent pain. A history of previous neck pain (RR = 1.8, 95% CI = 1.2–2.7) and recent shoulder pain (RR = 1.6, 95% CI = 1.1–2.4) were significant risk factors, while the use of night-vision goggles and muscle strength-training showed a non-significant associated trend, the latter toward a decreased risk. In neck pain cases, 58% and 55% reported that their pain interfered with their flying and leisure, respectively, and those with frequent pain risked pain interfering with flying duty (RR = 1.6, 95% CI = 1.1–2.5). However, only 25% of the cases had ever been on sick leave due to neck pain. Conclusions: Neck pain is common among helicopter pilots, and certain factors are identified for use in risk reduction. The link between cases with frequent pain and reported interference with flying duty highlights the need for early prevention of neck pain when planning and implementing helicopter pilots’ health care. More clinical trials of good design are required.

Lyons TJ, Ercoline W, O’Toole K, Grayson K. Aircraft and related factors in crashes involving spatial disorientation: 15 years of U.S. Air Force data. Aviat Space Environ Med 2006; 77:720–723. Introduction: Previous studies have determined that spatial disorientation (SD) causes 0.5–23% of aircraft crashes, but SD-related crash and fatality rates in different aircraft types have not been systematically studied. Methods: SD crashes for the fiscal years 1990 to 2004 and aircraft sortie numbers for all U.S. Air Force (USAF) aircraft were obtained from the USAF Safety Center. Contingency table analysis and Chi-squared tests were used to evaluate differences in SD rates. Results: SD accounted for 11% of USAF crashes with an overall rate of 2.9 per million sorties and a crash fatality rate of 69%. The SD rate was higher in fighter/attack aircraft and helicopters than in training and transport aircraft. The risk of SD was increased at night with 23% of night crashes being caused by SD. But the SD rate and crash fatality rate were not higher in single-crewmember aircraft. Discussion: SD risk is significantly increased in helicopters and fighter/attack aircraft and at night. The data suggest that a second crewmember does not protect against SD. Further study of specific SD scenarios could lead to focused interventions for SD prevention.

Tvaryanas AP, Thompson WT, Constable SH. Human factors in remotely piloted aircraft operations: HFACS analysis of 221 mishaps over 10 years. Aviat Space Environ Med 2006; 77:724–732. Background : A primary tool for evaluating fielded systems is to review mishaps. This study is a 10-yr cross-sectional quantitative analysis of the distribution and determinants of operator error in remotely piloted aircraft (RPA) mishaps within the U.S. military services using a standardized human factors taxonomy and a hierarchical model of human error. Methods: Data on RPA mishaps during fiscal years 1994–2003 were obtained from the Air Force, Army, and Navy/Marines safety centers. Mishap reports were reviewed and human factors coded using the Department of Defense’s Human Factors Analysis and Classification System (HFACS). Binary logistic regression was used to create models predicting operator error. Results: A total of 221 mishaps were identified, of which 60.2% involved operations-related human causal factors. The frequency of human factors mishaps was 79.1%, 39.2%, and 62.2% for the Air Force, Army, and Navy/Marines, respectively. Latent failures at the organizational level were most prevalent and were associated with both operator error and mechanical failures. Predictors of operator error were technological environment and cognitive factors in the Air Force; organizational processes, psycho-behavioral factors, and crew resource management in the Army; and organizational processes, inadequate supervision, planned inappropriate operations, physical and technological environments, and cognitive and psycho-behavioral factors in the Navy. The frequency of specific types of errors differed between the services with skill-based errors more common in the Air Force and violations in the Army. Conclusion: Recurring human factors failure at the organizational, supervision, preconditions, and operator levels have contributed to more than half of RPA mishaps.

Rayman RB. Aircraft disinsection. Aviat Space Environ Med 2006; 77:733–736. Aircraft disinsection has been an international practice since the 1920s, the purpose of which is to protect public health, the environment, agriculture, and livestock by the eradication of disease vectors. Although most nations of the world have discontinued this practice, about 20 continue with this requirement. Aircraft disinsection is sanctioned by international law with the World Health Organization (WHO) publishing general procedural guidelines in the International Health Regulations (IHR). There are currently four acceptable procedures: blocks away, top of descent, on arrival, and residual. A 2% pyrethrum solution, a naturally occurring substance found in the chrysanthemum flower, or several synthetic pyrethroids, are the recommended agents because they are extremely effective insecticides which pose minimal health risks. Although the use of insecticides for aircraft disinsection is controversial, national policies compelling this requirement must be respected. This paper will explore the background of aircraft disinsection, the procedures, the types of agents, and the toxicity. If aircraft disinsection is regulatory policy, it should be done in accordance with WHO procedures. Residual application is probably the most efficacious method. The use of air curtains or plastic strips should be explored as an alternative to the use of chemicals.

Li G, Grabowski JG, Baker SP, Rebok GW. Pilot error in air carrier accidents: does age matter? Aviat Space Environ Med 2006; 77:737–741. Introduction: The relationship between pilot age and safety performance has been the subject of research and controversy since the “Age 60 Rule” became effective in 1960. This study aimed to examine age-related differences in the prevalence and patterns of pilot error in air carrier accidents. Methods: Investigation reports from the National Transportation Safety Board for accidents involving Part 121 operations in the United States between 1983 and 2002 were reviewed to identify pilot error and other contributing factors. Accident circumstances and the presence and type of pilot error were analyzed in relation to pilot age using Chi-square tests. Results: Of the 558 air carrier accidents studied, 25% resulted from turbulence, 21% from mechanical failure, 16% from taxiing events, 13% from loss of control at landing or takeoff, and 25% from other causes. Accidents involving older pilots were more likely to be caused by turbulence, whereas accidents involving younger pilots were more likely to be taxiing events. Pilot error was a contributing factor in 34%, 38%, 35%, and 34% of the accidents involving pilots ages 25–34 yr, 35–44 yr, 45–54 yr, and 55–59 yr, respectively (p = 0.87). The patterns of pilot error were similar across age groups. Overall, 26% of the pilot errors identified were inattentiveness, 22% flawed decisions, 22% mishandled aircraft kinetics, and 11% poor crew interactions. Conclusion: The prevalence and patterns of pilot error in air carrier accidents do not seem to change with pilot age. The lack of association between pilot age and error may be due to the “safe worker effect” resulting from the rigorous selection processes and certification standards for professional pilots.

Vardy J, Vardy J, Judge K. Acute mountain sickness and ascent rates in trekkers above 2500 m in the Nepali Himalaya. Aviat Space Environ Med 2006; 77:742–744. Introduction: The aim of this study was to ascertain the incidence of acute mountain sickness (AMS) at different altitudes in the Solu-Khumbu. This was a pilot to examine the feasibility of investigating demographic, behavioral, and physiological factors related to the etiology of AMS and to assess the region’s suitability for a future study. Methods: A convenience sample of 150 recreational trekkers staying in teahouses was interviewed at altitudes above 2500 m. Two interviews were performed, firstly in the evening and then the subsequent morning. Trekker’s age, gender, ascent profile, and use of acetazolamide were noted. A Lake Louise score was calculated to determine the presence of AMS. Results: The incidence of AMS was 0% at 2500–3000 m, 10% between 3000–4000 m, 15% between 4000–4500 m, 51% between 4500–5000 m, and 34% over 5000 m. There was no significant association between age or gender and the altitude studied or incidence of AMS. Subjects with AMS ascended significantly further in the preceding 72 h than subjects without AMS, with a mean altitude gained of 846 m vs. 722 m. Discussion: We concur with the literature that incidence of AMS increases with altitude. We found an abrupt increase in incidence over 4500 m. This appears to be a new finding. A future study examining factors predisposing to AMS would be most effectively performed above 4500 m. No association was found between age or gender and AMS. Mean vertical ascent gained in the previous 72 h was significantly higher among the trekkers with AMS but remained within recommended guidelines.

Stein TP, Schluter MD. Plasma protein synthesis after spaceflight. Aviat Space Environ Med 2006; 77:745–748. Introduction: Astronauts land in a protein-depleted state. An anabolic phase takes place during the postflight period as muscle regains the lost protein. Yet where dietary intake has been measured after spaceflight, there does not appear to be any significant increase in dietary protein intake relative to preflight to provide additional amino acids to support muscles as they regain protein. We hypothesized that protein synthesis in other tissues is sub-optimal after spaceflight because of substrate competition for amino acids occurring between the muscles needing protein and other tissues. Methods: We measured selected plasma protein synthesis rates before and after spaceflight on the Shuttle using the ¹⁵N glycine-hippuric acid method. The fractional protein synthesis rates (FSR) of four plasma proteins, fibrinogen, complement C-3, ceruloplasmin, and haptoglobin, were measured before and after a 16-d flight on the Space Shuttle. Data was obtained for four subjects. Preflight measurements of plasma protein synthesis rates were made 45 and 7 d before launch. Postflight measurements were done on the day of landing and 6 and 14 d later. Results: Compared with preflight, plasma protein synthesis rates were reduced 6 d after landing. Discussion: Plasma protein synthesis rates are depressed after spaceflight. The observations are consistent with amino acids being the limiting factor due to substrate competition between the muscles needing protein and other tissues.

Fitzsimons MG, Parrado C. ECG and thallium imaging abnormalities with normal coronary angiogram in a male flight surgeon. Aviat Space Environ Med 2006; 77:749–752. Coronary artery disease and cardiac anomalies have the potential to cause sudden incapacitation in the flight environment with potentially disastrous consequences. Flight surgeons are responsible for screening for these potential diseases. We report a case of a healthy, active, asymptomatic U.S. flight surgeon returning for duty who demonstrated an abnormal ECG, graded exercise test, and thallium imaging. He was ultimately referred for cardiac catheterization that revealed normal coronary arteries. We discuss the sensitivity of non-invasive screening studies in healthy young individuals and potential causes of “false-positive” thallium imaging.

Smart TL, Singh B. Excessive daytime sleepiness in a trainee military pilot. Aviat Space Environ Med 2006; 77:753–757. A 21-yr-old army trainee pilot was noted by his colleagues to be frequently falling asleep in his class and was reported to medical authorities. Despite a number of investigations and review by two sleep specialists, a formal diagnosis could not be made. During his medical review board three questions were posed: does the trainee have excessive daytime sleepiness (EDS), or is his sleepiness a variation of normal; if he is excessively sleepy, what is the most likely diagnosis; and should the trainee be allowed to continue to undertake pilot training based on most likely diagnosis and/or his history. The most likely diagnosis was considered to be idiopathic hypersomnia, a relatively uncommon condition which is a diagnosis of exclusion. The condition was considered incompatible with flight duties in a pilot under training due to the potential for compromise of performance, mission completion, and flight safety. Stimulant medications may control symptoms, but are incompatible with flying duties in the Australian Defense Force. This case illustrates the difficulties in determining aeromedical disposition in borderline cases of EDS where a clear diagnosis cannot be made.

Riley LK. Bacterial meningitis exposure during an international flight: lessons for communicable pathogens. Aviat Space Environ Med 2006; 77:758–760. Air transport of infectious patients presents challenges for screening, post-exposure follow-up of fellow passengers, and international coordination issues. This report illustrates how an index case may not receive a clear diagnosis until days after the flight of interest, complicating treatment and fellow passenger tracking. This patient was diagnosed with meningococcal meningitis after a transatlantic flight with over 200 other passengers. In such cases, prompt initiation of public health measures and rapid coordination between various agencies may be required to limit outbreaks. Similar concerns will likely complicate intentional pathogen exposures; however, there may also be additional challenges related to unfamiliar pathogens and legal or political limitations to information sharing. For meningococcal disease, published guidelines exist to assist in determining which passengers and health-care workers meet criteria for antimicrobial chemoprophylaxis.

Elliott JR. Polycythemia in the aviator. Aviat Space Environ Med 2006; 77:761–762. A potentially serious medical condition was identified by evaluation of an apparently benign elevation in red blood cell count. Although most cases of polycythemia are benign, a thorough evaluation of the cause and manifestations of the disorder is recommended before issuing a medical certificate to any airman with polycythemia.