Gaydos SJ, Harrigan MJ, Bushby AJR. Ten years of spatial disorientation in U.S. Army rotary-wing operations. Aviat Space Environ Med 2012; 83:739–45.Introduction: Spatial disorientation (SD) has plagued aviation since its inception, contributing to numerous lost lives, destroyed or damaged aircraft, and a reduction in operational mission effectiveness. Military rotary-wing (RW) operations are not immune. The U.S. Army has retired many “legacy aircraft” represented in older studies, developed new training regimens for aircrew, continued to expand its night vision capabilities, and has prosecuted combat operations for some 10 yr utilizing new tactics, techniques, and procedures. For these reasons, it is important and relevant to re-engage the subject of SD among accidents within the Army’s RW community. Methods: The U.S. Army’s Combat Readiness/Safety Center database at Fort Rucker, AL, was queried for the previous 10 yr RW mishaps from fiscal year (FY) 2002 through FY 2011 (FY11 current through 01 July). Accidents identified as having SD as a contributing factor were selected. Results: From FY 2002 to FY 2011, there were 100 Class A through C rotary-wing flight mishaps involving SD. This represents 11% of all Class A through C rotary-wing flight accidents for this period. Of the 100 SD-related accidents, 22% involved fatalities, and 39% involved fatalities and/or injuries. The total number of RW SD-related accidents with fatalities represents 31% of the total helicopter accidents with fatalities for the 10-yr period. Discussion: This review of accident data confirms that SD remains a substantial issue for the Army aviation community and reinforces the importance and relevance of SD awareness, research, education, and training in RW operations.

Færevik H, Reinertsen RE. Initial heat stress on subsequent responses to cold water immersion while wearing protective clothing. Aviat Space Environ Med 2012; 83:746–50.Introduction: In cold water emergency situations, helicopter aircrew will enter the water with a raised body temperature due to wearing immersion suits. Prewarming has been demonstrated to accelerate core cooling during subsequent cold water immersion (CWI) when wearing swimsuits. For this study we hypothesized that wearing an immersion suit would slow the rate of cooling in subjects who were prewarmed compared to those kept in a normothermic state. Methods: Two different groups of male subjects (age, 24.7 ± 4.2 yr; height, 183.1 ± 6.5 cm; weight, 86.7 ± 15.0 kg; body fat, 16.8 ± 3.3%) were used to gather data under two conditions: prewarming by exercise (Warm-CWI) and baseline (Base-CWI) when wearing a dry immersion suit (2.97 Clo). In Warm-CWI, seven subjects rested for 20 min and then cycled on an ergometer cycle for 20 min before immersion in water at 5°C for 140 min. In Base-CWI, six subjects were directly immersed in 5°C water after resting. Results: T_re and T_sk were significantly higher after Warm-CWI at start of CWI, resulting in faster core cooling rate, and a drop in T_re and T_sk during the first 10 min. In the long term, the overall core cooling did not differ between Warm-CWI (0.34 ± 0.11°C · h⁻¹) and Base-CWI (0.31 ± 0.05°C · h⁻¹). Discussion: Wearing a dry immersion suit eliminates long-term differences in core cooling between prewarmed subjects and those kept in a normothermic state. When entering cold water with a raised T_re and T_sk, different thermal responses during the first 10 min are expected, but this does not alter long-term core cooling.

Gelinas JC, Marsden KR, Tzeng YC, Smirl JD, Smith KJ, Willie CK, Lewis NC, Binsted G, Bailey DM, Bakker A, Day TA, Ainslie PN. Influence of posture on the regulation of cerebral perfusion. Aviat Space Environ Med 2012; 83:751–7.Background: Posture has a major influence on cerebral blood flow (CBF). Unlike head-up tilt (HUT), less is known about how CBF is regulated during head-down tilt (HDT). We hypothesized that CBF would be elevated during HDT and decreased during HUT. Methods: In 21 healthy young adults, while controlling for end-tidal Pco₂, we combined concurrent measurements of middle cerebral artery velocity and posterior cerebral artery velocity (MCAv and PCAv, respectively), blood pressure (BP), and heart rate (HR). Measures were made at rest and, in a randomized order, during −90° HDT and +90° HUT. Dynamic cerebral autoregulation was quantified using transfer function analysis. In a subgroup, volumetric blood flow recordings were obtained in the common carotid artery (CCA; N = 11), internal and external carotid arteries (ICA; N = 8 and ECA; N = 6), and vertebral artery (VA; N = 4). Results: End-tidal Pco₂, CCA, ICA, VA, MCAv_mean and PCAv_mean remained unchanged during −90° HDT and +90° HUT compared to supine. During −90° HDT, mean BP (+22 mmHg) and cerebral vascular resistance (CVR) in both the MCA and PCA were elevated relative to supine, whereas HR remained unchanged. During +90° HUT, when compared to supine, HR increased (+18 bpm), and mean arterial pressure (MAP) total power and low frequency (LF) power in the MCA and PCA increased. In both the very low frequency (VLF) and LF ranges, coherence during +90° HUT increased (P < 0.05 vs. supine) in both the MCA and PCA. In contrast, coherence was reduced during −90° HDT. Discussion: Despite marked changes in perfusion pressure with HUT or HDT, our findings indicate that cerebral perfusion is well maintained during acute severe changes in posture.

Wu B, Xue Y, Wu P, Gu Z, Wang Y, Jing X. Physiological responses of astronaut candidates to simulated +G_x orbital emergency re-entry. Aviat Space Environ Med 2012; 83:758–63.Introduction: We investigated astronaut candidates’ physiological and pathological responses to +G_x exposure during simulated emergency return from a running orbit to advance astronaut +G_x tolerance training and medical support in manned spaceflight. Methods: There were 13 male astronaut candidates who were exposed to a simulated high +G_x acceleration profile in a spacecraft during an emergency return lasting for 230 s. The peak value was 8.5 G. Subjective feelings and symptoms, cardiovascular and respiratory responses, and changes in urine component before, during, and after +G_x exposure were investigated. Results: Under high +G_x exposure, 15.4% of subjects exhibited arrhythmia. Heart rate (HR) increased significantly and four different types of HR response curves were distinguished. The ratio of QT to RR interval on the electrocardiograms was significantly increased. Arterial oxygen saturation (S_ao₂) declined with increasing G value and then returned gradually. S_ao₂ reached a minimum (87.7%) at 3 G during the decline phase of the +G_x curve. Respiratory rate increased significantly with increasing G value, while the amplitude and area of the respiratory waves were significantly reduced. The overshoot appeared immediately after +G_x exposure. A few subjects suffered from slight injuries, including positive urine protein (1/13), positive urinary occult blood (1/13), and a large area of petechiae on the back (1/13). Conclusions: Astronaut candidates have relatively good tolerance to the +G_x profile during a simulation of spacecraft emergent ballistic re-entry. However, a few subjects exhibited adverse physiological responses and slight reversible pathological injuries.

Canfield DV, Dubowski KM, Chaturvedi AK, Whinnery JE. Drugs and alcohol found in civil aviation accident pilot fatalities from 2004–2008. Aviat Space Environ Med 2012; 83:764–70.Introduction: The Federal Aviation Administration (FAA) Office of Aerospace Medicine sets medical standards needed to protect the public and pilots from death or injury due to incapacitation of the pilot. As a part of this process, toxicology testing is performed by the FAA on almost every pilot who is fatally injured in an aviation accident to determine the medical condition of the pilot, medications used by the pilot at the time of the accident, and the extent of impairment, if any. Method: The data were extracted from the FAA toxicology database for all pilots who died from 2004 to 2008 in aviation accidents. Results: The laboratory received and tested specimens from 1353 pilots who died in aviation accidents between 2004 and 2008; 507 of these pilots were found to be taking drugs and 92 had ethanol in excess of 0.04 g · dl⁻¹. Discussion: This study was conducted to determine the extent of drug use in pilots who have died in aviation accidents from 2004 to 2008 and to determine the types of drugs most commonly found. A comparison of previously published reports with this study’s report was made to determine trends in drug use by pilots who have died in aviation accidents over the past 20 yr. Factors were discussed that could influence drug trends. Diphenhydramine, an H1 antihistamine with impairing properties, is the most commonly found drug in pilots who died in an aviation accident.

Gempp E, Morin J, Louge P, Blatteau JE. Reliability of plasma D-dimers for predicting severe neurological decompression sickness in scuba divers. Aviat Space Environ Med 2012; 83:771–5.Background: A low-grade process of coagulation activation in association with severe neurological decompression sickness (DCS) in divers has been anecdotally observed. We aimed to investigate whether measurement of plasma D-dimers and other hemostatic parameters in injured scuba divers were effective as prognostic biomarkers of neurological DCS, and we compared the diagnostic accuracy of a combination of D-dimers test and initial clinical assessment with either one alone. Methods: Eligible for the study were 84 recreational divers (69 men, 46 ± 10 yr; 15 women, 44 ± 8 yr) referred for neurological DCS in 2007-2011 and treated with hyperbaric oxygen. Blood tests were collected for D-dimers, fibrinogen, and platelet count with a time interval less than 8 h upon admission. Presentation severity was rated numerically for the acute event with a validated scoring system and clinical outcome was assessed by a follow-up examination at 3 mo. Indices of accuracy for D-dimers test, initial clinical score, and combination were estimated. Results: Incomplete recovery was reported in 26% of patients with a definite relationship between elevated D-dimers and presence of sequelae after multivariate analysis. We did not find differences for other blood coagulation variables between outcome groups. Combination of positive D-dimers (cut-off value of 0.40 μg · ml⁻¹) with severe initial presentation attained a higher diagnostic accuracy than either method alone (post-test probabilities = 100%, 86%, and 57%, respectively). Conclusion: This study suggests that determination of plasma D-dimers, a marker of activation coagulation, improve the prognostication of neurological DCS affecting scuba divers when combined with presenting severity score.

Todd MA, Thomas MJW. Flight hours and flight crew performance in commercial aviation. Aviat Space Environ Med 2012; 83:776–82.Objective: To examine the relationship between a pilot’s flight hours and their performance. Background: There is current debate in the aviation industry on the minimum hours required for first officers to gain before they can fly for an airline. Despite years of pilot training and licensing, there are very little data available to determine whether or not pilot performance varies as a function of total hours within an airline environment. Method: Flight crew performance was measured during 287 sectors of normal operations against a set of technical and nontechnical measurements. Flightcrew were grouped into a categorical variable which defined low and high experience groups according to industry accepted thresholds. Results: There were no statistically significant differences between experience groups for First Officers or Captains against the set of technical measures; however, there were minor differences with regard to nontechnical measures as a function of crew composition. There was also a difference in automation use, with First Officers with less than 1500 h keeping the autopilot engaged until a significantly lower altitude. Discussion: Despite on-going debate that low-hour First Officers are not as capable as their more experienced colleagues, we found no evidence of this in our study.

Matsuo T, Ohkawara K, Seino S, Shimojo N, Yamada S, Ohshima H, Tanaka K, Mukai C. An exercise protocol designed to control energy expenditure for long-term space missions. Aviat Space Environ Med 2012; 83:783–9.Introduction: Astronauts experience weight loss during spaceflight. Future space missions require a more efficient exercise program not only to maintain work efficiency, but also to control increased energy expenditure (EE). When discussing issues concerning EE incurred through exercise, excess post-exercise energy expenditure (EPEE) must also be considered. The aim of this study was to compare the total EE, including EPEE, induced by two types of interval cycling protocols with the total EE of a traditional, continuous cycling protocol. Methods: There were 10 healthy men, ages 20 to 31 yr, who completed 3 exercise sessions: sprint interval training (SIT) consisting of 7 sets of 30-s cycling at 120% Vo_2max with a 15-s rest between each bout; high-intensity interval aerobic training (HIAT) consisting of 3 sets of 3-min cycling at 80-90% Vo_2max with a 2-min active rest at 50% Vo_2max; and continuous aerobic training (CAT) consisting of 40 min of cycling at 60-65% Vo_2max. During each session, resting metabolic rate, exercise EE, and a 180-min post-exercise EE were measured. Results: The EPEEs during the SIT, HIAT, and CAT averaged 32 ± 19, 21 ± 16, and 13 ± 13 kcal, and the total EE for an entire exercise/rest session averaged 109 ± 20, 182 ± 17, and 363 ± 45 kcal, respectively. While the EPEE after the CAT was significantly less than after the SIT, the total EE with the CAT was the greatest of the three. Discussion: The SIT and HIAT would be potential protocols to control energy expenditure for long space missions.

Kobayashi A, Kikukawa A, Kimura M, Inui T, Miyamoto Y. Cerebral near-infrared spectroscopy to evaluate anti-G straining maneuvers in centrifuge training. Aviat Space Environ Med 2012; 83:790–4.Introduction: Over the past decade, near-infrared spectroscopy (NIRS) has emerged as an easily manageable noninvasive method for the continuous monitoring of cerebral cortical oxygenation during +G_z exposure. NIRS is also used to evaluate pilot trainees’ ability to adequately perform anti-G straining maneuvers in the course of centrifuge training. This study aimed to determine the general patterns and individual differences in NIRS recordings during +G_z exposure. Methods: There were 22 healthy male cadets who participated in the study. The centrifuge training profiles included a gradual onset run (GOR, onset rate of 0.1 G_z · s⁻¹) and short-term repeated exposures, with G_z levels from 4 to 7 G_z at an onset rate of 1.0 G_z · s⁻¹ (rapid onset run, ROR). Cortical tissue hemoglobin saturation (tissue oxygenation index, TOI) and changes in the concentration of oxygenated hemoglobin (O₂Hb) were recorded from the right forehead during the period of G_z exposure. Results: Most of the subjects successfully performed an anti-G straining maneuver and maintained or increased the cerebral oxygenation level during G_z exposure. In four subjects, however, oxygenation decline was observed at levels over 4 G_z, even though their anti-G systems were functioning. In contrast to the O₂Hb response, TOI, which reflects intracranial oxygenation changes, was decreased during the anti-G straining maneuver at G_z onset or during the countdown to a ROR exposure. Conclusion: Although NIRS is an effective tool for monitoring anti-G straining maneuver performance, it should be carefully evaluated in terms of intracranial oxygenation results.

James JT, Zalesak SM. Prediction of crew health effects from air samples taken aboard the International Space Station. Aviat Space Environ Med 2012; 83:795–9.Introduction: Spaceflight aboard the International Space Station (ISS) involves stays of individual crewmembers for up to 6 mo during which they are exposed to a complex mixture of airborne pollutants. Methods to predict specific health effects from exposure to a mixture of air pollutants are not well developed. Herein, air monitoring data from the ISS are used to demonstrate a new method to estimate a threshold for possible health effects from exposure to mixtures. Methods: An empirical, additive approach was developed to transform monthly air pollutant data, which had been obtained primarily by gas chromatography-mass spectrometry from samples of ISS air, to threshold (T) values for 16 adverse health effect groups. Spacecraft maximum allowable concentrations (SMACs), available for most spacecraft air pollutants, were used to form target-organ/effect groups, from which group T values were estimated. If T > 1 for a group, then there is an unacceptable risk of the toxic effect. Results: Samples of air taken from the ISS in 2010 revealed that all 16 toxicological groups were within safe limits. Highest T values were as follows: mucosal irritants (0.53 ± 0.44), headache (0.52 ± 0.06), central nervous system depression (0.25 ± 0.06), and cardiac sensitization (0.13 ± 0.04). Discussion: The additive model is supported by limited inhalation data on rats in the literature. Our predictions of no adverse effect on crew health are useful as part of NASA’s Lifetime Surveillance of Astronaut Health (LSAH). If one of the 16 levels had exceeded T = 1, then standard surveillance could be supplemented to address this potential health risk.

Houston S, Dawson K, Butler S. Fatigue reporting among aircrew: incidence rate and primary causes. Aviat Space Environ Med 2012; 83:800–4.Introduction: In this study we describe our experience of voluntary fatigue reporting among pilots and cabin crew. Method: This was a prospective study to determine the crude incidence rate and primary cause of Fatigue Report Form submission among cabin crew and pilots within one airline. All crew duties had already undergone scrutiny at the ‘roster build’ stage to ensure compliance with fatigue control measures. Reports were investigated by the airline’s medical officer to determine the primary cause of fatigue and then allocated to one of five categories. The frequency and proportion of reports within each category was determined. Results: The crude incidence rate of fatigue report submission was 103 and 68 cases per 1000 persons per year for pilots and cabin crew, respectively. The primary cause for 27% of reports was attributed to the rostered duty pattern. Of the reports, 24% were primarily caused by roster disruption, 17% by problems with layover accommodation or transport, 23% by a domestic issue, and 9% had no obvious cause or were deemed invalid. A subanalysis of the ‘domestic’ category revealed that half had a primary cause attributable to commuting to or from the workplace. Conclusion: The number and trend of reports received per month can be used to detect otherwise unknown fatigue hazards and identify where improvements can be made. Fatigue reports allow individual crewmembers to give vital feedback on ‘whole-of-life’ fatigue risks, both inside and outside the workplace.

Garland MM, Gutierrez A, Barratt DM. Peripheral neuropathy of the extremity after hyperbaric exposure. Aviat Space Environ Med 2012; 83:805–8.Background: Neurological deficits occurring after diving or hyperbaric exposure are typically due to central nervous system decompression illness (DCI). However, consideration of alternate diagnoses is sometimes warranted. Case Report: A 47-yr-old female hyperbaric technician developed foot drop 2 d following her last hyperbaric exposure. She had worked in chamber once daily at 45 fsw for 90 min. The breathing gas was air until the last 15 min, during which she breathed oxygen. Her history was complicated by a gastric bypass and weight loss totaling 160 pounds within the preceding 9 mo. She was treated for presumed neurological DCI without improvement. The adherence to safe hyperbaric protocols, delayed presentation, ongoing medical issues, and lack of response to therapy brought the diagnosis into question. Extensive neurological evaluation, including nerve conduction studies, revealed a common peroneal mononeuropathy. We concluded that her neuropathy was more likely due to extreme weight loss and malnutrition than peripheral nervous system DCI. Discussion: There are rare reports of DCI affecting the peripheral nerves of the extremities. A literature search revealed only three such cases. Two further reports describe peripheral neuropathy in the extremities of divers that were attributed to other causes: compression by a weight belt and vasculitis. However, peroneal neuropathy is one of the most common focal mononeuropathies of the lower extremity and has been reported in association with extreme weight loss and malnutrition. We attributed our diver’s neuropathy to extreme weight loss and malnutrition rather than DCI.

Houston S, Graf J, Sharkey J. Commercial air travel after intraocular gas injection. Aviat Space Environ Med 2012; 83:809–10.Passengers with intraocular gas are at risk of profound visual loss when exposed to reduced absolute pressure within the cabin of a typical commercial airliner. Information provided on the websites of the world’s 10 largest airlines offer a considerable range of opinion as to when it might be safe to fly after gas injection. Physicians responsible for clearing passengers as ‘fit to fly’ should be aware modern retinal surgical techniques increasingly employ long-acting gases as vitreous substitutes. The kinetics of long-acting intraocular gases must be considered when deciding how long after surgery it is safe to travel. It is standard practice to advise passengers not to fly in aircraft until the gas is fully resorbed. To achieve this, it may be necessary to delay travel for approximately 2 wk after intraocular injection of sulfur hexafluoride (SF₆) and for 6 wk after injection of perfluoropropane (C₃F₈).

Craig-Grey RW. You’re the flight surgeon: cholera. Aviat Space Environ Med 2012; 83:814–6.

Restivo NL. You’re the flight surgeon: autoimmune polyglandular syndrome type 2. Aviat Space Environ Med 2012; 83:816–7.