Jersey SL, Jesinger RA, Palka P. Brain magnetic resonance imaging anomalies in U-2 pilots with neurological decompression sickness. Aviat Space Environ Med 2013; 84:3–11. Introduction: This was a retrospective observational study of imaging used to evaluate and treat 13 U-2 pilots with neurological decompression sickness (DCS). Magnetic resonance imaging (MRI) and computed tomography (CT) provided data for screening, diagnosis, and determinations of fitness to fly after recovery. While small series and case reports described the role of imaging in diving DCS, none addressed radiology’s role in aviation DCS. Methods: We performed a literature review of altitude DCS radiology studies. We then reviewed radiology images at our institution on U-2 pilots with neurological DCS between January 2002 and August 2010. We retrospectively analyzed MRI data for white matter hyper-intensities (WMHs), defined as hyperintense lesions ≥ 3 mm on T2 and FLAIR. All studies occurred after hyperbaric oxygen (HBO) treatment. Results: There were 17 pilots who reported 20 neurological DCS incidents. Of these 17 pilots, 13 underwent imaging. Two (15%) demonstrated acute subcortical lesions on MRI, seven (54%) had asymptomatic WMHs, and six (46%) were normal. The clinical significance of the lesions is unknown. Consistent with diving DCS, imaging played no role in acute diagnosis. However, imaging was vital for determining fitness for return to flying. Additionally, CT identified a potentially predisposing sinus condition in one pilot which may enable return to flying after treatment. Conclusions: Modern imaging has unique findings for altitude DCS patients. The high incidence of WMHs in this series is a matter of ongoing research to determine potential clinical consequences. Emerging techniques such as functional MRI may play important roles in future aeromedical decisions.
Flagg SY, Regis DP, Petersen K, Mahon RT. Interrupted oxygen pre-breathing and decompression outcomes in swine. Aviat Space Environ Med 2013; 84:12–6. Background: Rescue from a disabled submarine may result in substantial risk for severe decompression sickness (DCS) among survivors. Oxygen prebreathe (OPB) before rapid decompression has been shown to significantly reduce risk or delay onset for severe DCS in animals. However, the duration of this benefit remains unknown and might even be lost if a delay between the prebreathe period to initiation of recompression therapy allows for nitrogen reaccumulation. Methods: We hypothesized that the benefit of OPB would be lost following subsequent periods of air interruption in a 70-kg swine saturation model. Following OPB of 45 or 60 min with varying periods (30, 45, 60 min) of air interruption, 61 swine exposed to 2.7 ATA for 22 h were rapidly decompressed. Swine without OPB served as negative controls and swine treated with 45 min of OPB without air interruption served as positive controls. Results: Comparing experimental groups for Type II DCS incidence showed OPB120/60 being the only experimental group (11%) statistically different than the negative control group OPB0 (80%). Log rank tests comparing Type II DCS free survival only showed statistically significant differences for OPB45/60 compared to positive control group OPB45, while, more importantly, demonstrating a significant difference for OPB120/60 compared to that approximated for OPB45, indicating a significant reversal of the air interruption effects with longer OPB on Type II DCS disease free survival. Discussion: Based on these findings we concluded that the protective effects of OPB against severe DCS are reduced with increasing periods of air interruption.
Löfdahl P, Andersson D, Bennett M. Nitrogen narcosis and emotional processing during compressed air breathing. Aviat Space Environ Med 2013; 84:17–21. Background: Previous studies on nitrogen narcosis have focused on how it affects behavior, performance, and cognitive function. However, little is known about the effects of nitrogen narcosis on the emotional processing of external stimuli. Method: We presented 20 volunteers with images from the International Affective Picture System (IAPS) and categorized as unpleasant, neutral, or pleasant, while sitting in a hyperbaric chamber at the surface (101,3kPa) and at 39 m equivalent depth (496.4 kPa). The participants rated the images along three affective dimensions: valence (intrinsic attractiveness or aversiveness of a stimuli), arousal, and dominance. Results: In the valence dimension there was no significant effect of increased pressure or interaction between increased pressure and image category. There was a significant interaction between image category and the pressure at which the images were viewed in the arousal dimension. The mean arousal rating score for unpleasant stimuli was 0.5 point (on a 9-point scale) lower at hyperbaric conditions and equal arousal rating score for neutral stimuli in general. Discussion: The absence of any effect of pressure in the valence dimension suggests that divers have no impairment in their ability to determine the pleasantness or unpleasantness of different stimuli. Furthermore, this study suggests that the effects of nitrogen narcosis on the emotional processing of external stimuli are primarily evident in the arousal dimension. Although differences in arousal ratings were relatively small in magnitude, even a small alteration in emotional response to external stimuli might be important in the context of deep diving.
Wiseman RL, Kelly PT, Swanney MP, McNamara KP, Beckert L. Hypoxemia in healthy subjects at moderate altitude. Aviat Space Environ Med 2013; 84:22–6. Background: Healthy individuals are known to have significantly reduced oxygen saturations at rest when acutely exposed to moderate altitudes, such as during commercial flight. There is a paucity of data on the response of healthy individuals to exercise at these altitudes. The aim of this study was to establish the normal response to exercise during acute, moderate altitude exposure with regard to oxygen saturations. Secondary aims were to establish if this response can be predicted from pulmonary function measurements at sea level. Methods: At sea level, 20 subjects performed pulmonary function tests, including submaximal steady state exercise, followed by replication of submaximal steady state exercise during acute altitude exposure at 6844 ft (2086 m). Results: Mean resting oxygen saturation at 6844 ft (2086 m) was 96%, a significant reduction from the sea level value of 99%. Mean nadir oxygen saturation during steady state exercise at moderate altitude was 89%. There was a weak negative correlation between aerobic capacity and end exercise oxygen saturation at altitude. Modified BORG dyspnea scores were unchanged at rest at 6844 ft (2086 m) and higher post-exercise at 6844 ft (2086 m) when compared to sea level, although absolute values were low. Discussion: Healthy individuals desaturate at rest and upon exercise during acute altitude exposure at 6844 ft (2086 m). A quarter of participants experienced Spo2 ≤ 85% upon exercise at altitude, although this had no correlation with dyspnea scores or baseline pulmonary function measurements. The weak negative correlation between aerobic capacity and end exercise oxygen saturation is unexplained and merits further research.
Hampson NB, Kregenow DA, Mahoney AM, Kirtland SH, Horan KL, Holm JR, Gerbino AJ. Altitude exposures during commercial flight: a reappraisal. Aviat Space Environ Med 2013; 84:27–31. Background: Hypobaric hypoxia during commercial air travel has the potential to cause or worsen hypoxemia in individuals with pre-existing cardiopulmonary compromise. Knowledge of cabin altitude pressures aboard contemporary flights is essential to counseling patients accurately about flying safety. The objective of the study was to measure peak cabin altitudes during U.S. domestic commercial flights on a variety of aircraft. Methods: A handheld mountaineering altimeter was carried by the investigators in the plane cabin during commercial air travel and peak cabin altitude measured. The values were then compared between aircraft models, aircraft classes, and distances flown. Results: The average peak cabin altitude on 207 flights aboard 17 different aircraft was 6341 ± 1813 ft (1933 m ± 553 m), significantly higher than when measured in a similar fashion in 1988. Peak cabin altitude was significantly higher for flights longer than 750 mi (7085 ± 801 ft) compared to shorter flights (5160 ± 2290 ft/1573 ± 698 m). Cabin altitude increased linearly with flight distance for flights up to 750 mi in length, but was independent of flight distance for flights exceeding 750 mi. Peak cabin altitude was less than 5000 ft (1524 m) in 70% of flights shorter than 500 mi. Peak cabin altitudes greater than 8000 ft (2438 m) were measured on approximately 10% of the total flights. Conclusions: Peak cabin altitude on commercial aircraft flights has risen over time. Cabin altitude is lower with flights of shorter distance. Physicians should take these factors into account when determining an individual’s need for supplemental oxygen during commercial air travel.
Orsello CA, Phillips AS, Rice GM. Height and in-flight low back pain association among military helicopter pilots. Aviat Space Environ Med 2013; 84:32–7. Introduction: Low back pain (LBP) among helicopter pilots is a well-recognized problem, with prevalence ranging from 61 to over 80%. Studies indicate association with total flight hour (TFH) exposure and lack of association with height or body mass index (BMI); however, those that have excluded pilots with back injuries unrelated to flying are limited. Methods: Surveyed regarding LBP were 1028 U.S. Navy helicopter pilots. Of the 648 (63%) respondents, 83 pilots, or 12.9%, who reported nonflying related back injuries and those without necessary data were excluded, yielding N = 554. Case-control analysis was performed with logistic regression for height, BMI, and TFH on significant LBP (defined as > 30% of each flight) presence versus absence with Chi-square on the median split of each and ANOVA to include airframes. Results: Height was a positive predictor for significant LBP among all subjects (OR: 1.7), with the strongest association among male pilots (OR: 2.1). BMI, THF, and airframe (H-60, TH-57, H-53, and H-46) were not associated. Discussion: These results imply that ergonomic stressors that adversely impact lumbar symmetry may be a predominant factor in LBP during flight. Significant prevalence rates may persist in the absence of design enhancements that mitigate these stressors. Height was a significant predictor for in-flight LBP among U.S. Navy helicopter pilots studied and BMI, TFHs, and airframe were not. For every 1″ increase among male pilot height values, the odds of experiencing significant LBP in flight increased by 9.3%, with those equal/taller than median (71 in.) having over twice the odds compared with those shorter.
Weaver AS, Zakrajsek AD, Lewandowski BE, Brooker JE, Myers JG Jr. Predicting head injury risk during International Space Station increments. Aviat Space Environ Med 2013; 84:38–46. Introduction: NASA’s Human Research Program is using a probabilistic risk assessment approach to identify acute and chronic medical risks to manned spaceflight. The objective of this project was to estimate the likelihood of a neurological head injury to a crewmember severe enough to require medical assessment, treatment, or evacuation during a typical International Space Station (ISS) increment. Methods: A 2 degree-of-freedom analytical model of the human head was created to allow for analysis of the impact response. The output of the model is acceleration of the head, which was used to determine the probability that the simulated impact resulted in a head injury with an Abbreviated Injury Scale (AIS) score of 3 or greater. These data were then integrated into a probabilistic risk assessment, which outputs a likelihood of injury with a representative measure of the uncertainty. Results: A Monte Carlo simulation was performed to vary input parameters over their defined distributions. The mean probability of a moderate neurological injury (AIS 3 or greater) occurring due to a head impact by a crewmember translating through the ISS is 1.16 × 10−4 per 6-mo mission increment (2.32 × 10−4 per year). Discussion: Our head injury prediction model has shown that there is a low, yet not insignificant, probability of neurological head injury of AIS score 3 or greater. The results from this simulation will be input into the parent Integrated Medical Model, which incorporates the risks of over 80 different medical events in order to inform mission planning scenarios.
Carretta TR. Predictive validity of pilot selection instruments for remotely piloted aircraft training outcome. Aviat Space Environ Med 2013; 84:47–53. Introduction: Demand for remotely-piloted aircraft (RPA) support has increased dramatically over the last decade. Initial efforts to meet the demand focused on cross-training experienced manned aircraft pilots and funneling recent Specialized Undergraduate Pilot Training (SUPT) graduates to RPA pilot training. This approach reduced the number of personnel available for manned airframes and is no longer sustainable. In 2009, the USAF established an RPA career field and the Undergraduate RPA Training (URT) course to train officers with no prior flying experience to be RPA pilots. URT selection methods are very similar to those for SUPT. Some important factors for URT applicants are medical flight screening and aptitude tests [Air Force Officer Qualifying Test (AFOQT) and Pilot Candidate Selection Method (PCSM)]. The current study examined the predictive validity of the AFOQT pilot and PCSM composites for URT completion. Method: Subjects were 139 URT students with AFOQT and PCSM scores. The training criterion was URT pass/fail and the pass rate was 74.8%. Results: Both the AFOQT pilot (r = 0.378) and PCSM (r = 0.480) composites demonstrated good predictive validity. Discussion: No minimum qualifying PCSM score exists for URT. Had a minimum PCSM score of 25 been used, the pass rate would have been 80.2%; 12 more eliminees would have been screened out compared with the current AFOQT pilot minimum qualifying score of 25. Although current selection methods are effective, based on results of several RPA job/task analyses, the Air Force is examining the utility of other measures to supplement current methods.
Matthies AK, Tachikawa NJ. Alpha-1 adrenergic antagonists in aircrew for the treatment of benign prostatic hypertrophy. Aviat Space Environ Med 2013; 84:54–8.Benign prostatic hypertrophy (BPH) affects the majority of men later in life. Other than surgery, finasteride (Proscar®) is currently the only pharmacologic option available for U.S. Air Force (USAF) aircrew. This article will evaluate the current literature regarding the treatment of benign prostatic hypertrophy with FDA approved tamsulosin (Flomax®) and alfuzosin (Uroxatrol®), third-generation alpha-1 adrenergic antagonists. Current literature supports the fact that some third-generation alpha blockers limit the side effects of hypotension when compared to other alpha blockers as a result of the specificity of subtype binding of the receptors and the sustained release formulation. Alpha blockers are currently used almost universally for the treatment of BPH; however, they are currently not approved for USAF aircrew. This article will review the aeromedical implications of the side effects of alpha-1 adrenergic antagonists (alfuzosin, tamsulosin), which affect aircrew while performing aeronautical duties, and examine whether alpha-1 adrenergic antagonists should be acceptable medications in certain situations depending on airframe and aeronautical duties.
Blaber AP, Hinghofer-Szalkay H, Goswami N. Blood volume redistribution during hypovolemia. Aviat Space Environ Med 2013; 84:59–64. Background: The goal of this study was to investigate the contribution of splanchnic volume redistribution and lower limb vasoconstriction in the maintenance of blood pressure during progressive central hypovolemia induced by graded lower body negative pressure (LBNP). It was hypothesized that splanchnic blood volume loss during LBNP would buffer decreases in thoracic blood volume. Methods: There were 15 healthy subjects (8 men, 7 women) who participated in the study. We used LBNP of −10, −20, −30, and −40 mmHg with segmental impedance analysis to determine central and splanchnic volume changes, and near infrared spectroscopy (NIRS) to assess calf venous volume changes and vasoconstrictor tone. Results: In relation to baseline, LBNP to −40 mmHg resulted in a 57% increase in deoxygenated blood in the calf, indicating venous pooling in the lower limbs. These events led to a decrease in venous return and a 28% decline in cardiac output. Total upper body impedance increased by 6.6% with a 2.4% change in thoracic and a 13.1% increase in splanchnic impedance with progressive LBNP. Splanchnic blood volume contributed to more than 50% of the volume redistribution to the thoracic compartment during hypovolemia. Both men and women increased their heart rate, but only men vasoconstricted (4.4%) with increasing LBNP. The net result of these events was the maintenance of mean arterial blood pressure with no presyncopal symptoms in these subjects. Discussion: Our results suggest that splanchnic blood volume redistribution—rather than leg vasoconstriction—plays an important role in blood pressure regulation during central hypovolemia.
Smith TG, Chang RW, Robbins PA, Dorrington KL. Commercial air travel and in-flight pulmonary hypertension. Aviat Space Environ Med 2013; 84:65–7. Background: It has recently been shown that commercial air travel triggers hypoxic pulmonary vasoconstriction and modestly increases pulmonary artery pressure in healthy passengers. There is large interindividual variation in hypoxic pulmonary vasoreactivity, and some passengers may be at risk of developing flight-induced pulmonary hypertension, with potentially dangerous consequences. This study sought to determine whether it is possible for a susceptible passenger to develop pulmonary hypertension in response to a routine commercial flight. Case Report: Using in-flight echocardiography, a passenger was studied during a 6-h commercial flight from London to Dubai. The passenger was generally well and frequently traveled by air, but had been diagnosed with Chuvash polycythemia, a genetic condition that is associated with increased hypoxic pulmonary vasoreactivity. Hematocrit had been normalized with regular venesection. During the flight, arterial oxygen saturation fell to a minimum of 96% and systolic pulmonary artery pressure (sPAP) rapidly increased into the pulmonary hypertensive range. The in-flight increase in sPAP was 50%, reaching a peak of 45 mmHg. Discussion: This study has established that an asymptomatic but susceptible passenger can rapidly develop in-flight pulmonary hypertension even during a medium-haul flight. Prospective passengers at risk from such responses, including those who have cardiopulmonary disease or increased hypoxic pulmonary vasoreactivity, could benefit from preflight evaluation with a hypoxia altitude simulation test combined with simultaneous echocardiography (HAST-echo). The use of in-flight supplementary oxygen should be considered for susceptible individuals, including all patients diagnosed with Chuvash polycythemia.
Law J, Mathers CH, Fondy SRE, Vanderploeg JM, Kerstman EL. NASA’s human system risk management approach and its applicability to commercial spaceflight. Aviat Space Environ Med 2013; 84:68–73.As planning continues for commercial spaceflight, attention is turned to NASA to assess whether its human system risk management approach can be applied to mitigate the risks associated with commercial suborbital and orbital flights. NASA uses a variety of methods to assess the risks to the human system based on their likelihood and consequences. In this article, we review these methods and categorize the risks in the system as “definite,” “possible,” or “least” concern for commercial spaceflight. As with career astronauts, these risks will be primarily mitigated by screening and environmental control. Despite its focus on long-duration exploration missions, NASA’s human system risk management approach can serve as a preliminary knowledge base to help medical planners prepare for commercial spaceflights.
Frey MA. Research Progress Reports from the NASA Human Research Program: updates for establishing astronaut radiation limits. Aviat Space Environ Med 2013; 84:75–6.
Tingey J. You’re the flight surgeon: marital counseling. Aviat Space Environ Med 2013; 84:80–1.
Reaume J. You’re the flight surgeon: nutritional supplements. Aviat Space Environ Med 2013; 84:81–3.
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