INTRODUCTION: A review of decompression sickness (DCS) cases associated with the NASA altitude physiological training (APT) program at the Johnson Space Center (JSC) motivated us to place our findings into the larger context of DCS prevalence from other APT centers.METHODS: We reviewed JSC records from 1999 to 2016 and 14 publications from 1968 to 2004 about DCS prevalence in other APT programs. We performed a meta-analysis of 15 APT profiles (488 cases / 385,116 exposures). We used meta-regression to evaluate the relation between estimated exposures and probability of DCS in a test group, accounting for the heterogeneity between studies.RESULTS: Our in-house review identified 6 Type I DCS (1 from an inside observer) and 1 Type II DCS. There were 6 cases in 9560 student hypobaric exposures from 3 NASA training flights; a student pooled prevalence rate of 0.44 cases / 1000 exposures compared to 1.44 cases / 1000 from 12 published APT profiles. The overall pooled DCS prevalence rate was 1.16 cases / 1000 exposures. There was substantial heterogeneity in DCS prevalence across studies. Denitrogenation time, exposure pressure, and exposure time were associated with probability of DCS in the meta-regression model.CONCLUSIONS: While the overall DCS prevalence rate is relatively low, there is marked heterogeneity among profiles. The pooled DCS prevalence rate estimate for the NASA profiles was lower than the overall rate. Variability in APT profile DCS prevalence could be further explained given student level and additional test-level covariates.Conkin J, Sanders RW, Koslovsky MD, Wear ML, Kozminski AG, Abercromby AFJ. A systematic review and meta-analysis of decompression sickness in altitude physiological training. Aerosp Med Hum Perform. 2018; 89(11):941–951.

BACKGROUND: While respiratory muscle fatigue is present following load carriage activity at sea level, the effect of environmental conditions on respiratory strength while undertaking load carriage is unknown.METHODS: The effect of thoracic load carriage during walks (5.5 km) in four environments [(thermo-neutral sea level (SL), −10°C (C), 4300 m (H) and 4300 m at −10°C (HC)] was evaluated on respiratory muscle fatigue. Ten subjects completed eight self-paced randomized treadmill walks comprising a variety of gradients, unloaded and loaded (18.2 kg), across the four environments. Respiratory muscle strength was measured via maximal inspiratory pressure (P_Imax) and expiratory pressure (P_Emax) assessments.RESULTS: Submaximal walking in HC elicited respiratory muscle fatigue when compared to SL. Inspiratory muscle fatigue was independent of load. The relative change in P_Imax from baseline was significantly greater in HC compared to SL (9.6% vs. 1.3%). P_Emax showed a significant reduction during HC (−22.3 cmH₂O, −14.4%) when compared to the other three environments.CONCLUSION: These results highlight the need to focus on respiratory muscle strength in preparation for exercise in cold hypoxic conditions.Hinde K, Low C, Lloyd R, Cooke C. Interaction between ambient temperature, hypoxia, and load carriage on respiratory muscle fatigue. Aerosp Med Hum Perform. 2018; 89(11):952–960.

BACKGROUND: Postural control is adversely affected by mental and physical fatigue, but its validity in fatigue assessment has not been investigated systemically among pilots. We explored the correlations of posturographic balance with physiological and psychological signals among cadet pilots.METHODS: In experiment 1, 37 cadet pilots performed a posturographic balance test, heart rate variability (HRV), and profile of mood states (POMS) during 40 h of sleep deprivation. For experiment 2, physiological signals of 60 subjects, including breathing rate (BR), systolic blood pressure (SBP), and heart rate (HR) were measured under the effects of physical fatigue. Then correlations with a mental and physical fatigue index based on effective posturographic parameters with those subjective and objective methods were analyzed by linear regression.RESULTS: The mental fatigue index correlated linearly with the depression score of the POMS (r = 0.212), standard deviation of normal to normal beats (r = 0.286), and square root of the mean differences of successive beat intervals (r = 0.207). Meanwhile, linear correlations with frequency-domain parameters of HRV such as total power, low frequency power, and high frequency power were also statistically significant. With the increase in the physical fatigue index, physiological signals such as SBP (r = 0.300), HR (r = 0.349), and BR (r = 0.266) increased linearly.CONCLUSIONS: Impairment of postural stability can reflect the aggravation of mental and physical fatigue among cadet pilots, which provides a potential method for assessing fatigue level before flight tasks and preventing errors by pilots.Cheng S, Sun J, Ma J, Dang W, Tang M, Hui D, Zhang L, Hu W. Posturographic balance’s validity in mental and physical fatigue assessment among cadet pilots. Aerosp Med Hum Perform. 2018; 89(11):961–966.

INTRODUCTION: Different aspects of the aviation system, such as pilot’s fitness, supervision, and working conditions, interact to produce or protect against flight safety hazards. Machine learning methods such as Random Forests may help identify system characteristics with the potential to affect flight safety from the large number of candidate predictors that results when multiple system levels are considered simultaneously.METHODS: There were 54 pilot-related and occupational candidate predictors of simulator flight performance in 2 malfunction scenarios completed by 51 male European helicopter emergency medical services pilots derived from pilots’ self-report questionnaires and aeromedical examination records. In a cross-sectional explorative analysis, the Random Forest method was used to screen for informative predictors. Predictors scoring above the critical threshold for the conditional permutation variable importance (VI) statistic were selected.RESULTS: In five predictors, the VI statistic averaged across 2000 Random Forest runs exceeded the selection threshold: higher perceived rewards (VI = 0.0691) and predictability (VI = 0.0501) at work were associated with higher performance scores, and higher physiological dysregulation (VI = 0.0495) and alanine aminotransferase (VI = 0.0224) with lower scores. Performance also differed between the simulators at the two training sites (VI = 0.0298).DISCUSSION: Random Forests may usefully complement previously applied methods for the identification of human factors safety hazards. The identified performance predictors suggest further areas with potential for safety improvements.Bauer H, Nowak D, Herbig B. Helicopter simulator performance prediction using the Random Forest method. Aerosp Med Hum Perform. 2018; 89(11):967–975.

INTRODUCTION: The auditory system is not as heavily involved in the pilot’s spatial orientation as the visual and vestibular systems; however, it plays a significant role in the cockpit for communication and warning information. The aim of this research was to investigate the combined effect of selective auditory attention and simulator-induced spatial disorientation (SD) cues on pilots’ flight performance. We hypothesized that the flight performance in both disoriented and oriented flight profiles would be impaired by selective auditory attention.METHODS: Using an SD simulator, 40 male military pilots (M = 31.9; SD = 7.41) were exposed to 12 flight sequences, where 6 contained a SD-conflict, 3 with motion illusions and 3 with visual illusions. The pilots performed a duration discrimination task (DDT) involving sound stimuli while completing these profiles under SD-conflict and nonconflict conditions.RESULTS: In five flight profiles tested, the DDT and SD cues increased the pilots’ cognitive workload, adversely affecting their flight performance. In the approach and landing profiles involving visual illusions, significant differences between the control and DDT groups were found for both nonconflict and SD-conflict flight sequences, whereas differences were only significant between nonconflict and SD-conflict flights for the two vestibular SD profiles.DISCUSSION: The results obtained partially support our hypothesis that performing the DDT, even in the absence of SD-conflict, significantly affects pilots’ flight performance. In some cases, despite the large increase in cognitive workload, pilots did not activate the “posture first” principle. Pilots should be trained not to respond to auditory stimuli until they have recovered their spatial orientation.Lewkowicz R, Stróżak P, Bałaj B, Francuz P, Augustynowicz P. Selective auditory attention and spatial disorientation cues effect on flight performance. Aerosp Med Hum Perform. 2018; 89(11):976–984.

INTRODUCTION: Human-spacesuit fit is not well understood, especially in relation to operational performance and injury risk. Current fit decisions use subjective feedback. This work developed and evaluated new metrics for quantifying fit and assessed metric sensitivity to changes in padding between the human and hip brief assembly (HBA).METHODS: Three subjects donned the Mark III (MKIII) spacesuit with three padding thicknesses between the lower body and HBA. Subjects performed a walking task with inertial measurement units on the thigh and shin of both the human and suit. For each step, cadence, human knee task range of motion (tRoM), difference in human and suit tROM (ΔtRoM), and the relative coordination metric (ρ) between the human-suit femur and tibia were computed.RESULTS: The MKIII significantly reduced user cadence by 20.4% and reduced tRoM by 16.5% during walking with subject-dependent changes due to added padding. In general, the addition of padding significantly altered ΔtRoM; however, variability did exist between subjects. Mixed-effect regressions of dynamic fit (ρ) reflect distinct positive spikes in ρ around heel strike (human-dominated motion) and negative dips following toe off (suit-dominated motion).DISCUSSION: There were mixed effects of padding on gait performance and dynamic fit measures. Differences in dynamic fit between subjects may be more reliant on alternate aspects of fit, such as suit component sizes and designs, than padding level. Subjective feedback supported quantitative observations, highlighting metric utility. Future work will explore the effects of suit sizing components on measures of fit and performance.Fineman RA, McGrath TM, Kelty-Stephen DG, Abercromby AFJ, Stirling LA. Objective metrics quantifying fit and performance in spacesuit assemblies. Aerosp Med Hum Perform. 2018; 89(11):985–995.

INTRODUCTION: Performing at high altitude and scuba diving impose functional limitations to the respiratory system and impair exercise performance compared to normobaria. At altitude, the partial pressure of oxygen is reduced, which decreases arterial oxygen saturation and exercise performance. Falling arterial oxygen saturation results in hyperventilation and increased pulmonary ventilation. Diving poses unique effects on the respiratory system. The work of breathing is increased from marked increased airway resistance, static lung load, and hydrostatic pressure from the water on the thoracic wall. Both altitude and diving increase the work and energy cost of breathing, resulting in respiratory muscle fatigue. Respiratory muscle training (RMT) has been employed to target the deleterious effects on the respiratory system and exercise capacity. Although the literature is sparse, RMT has been reported to decrease the work and energy cost of breathing and improve pulmonary ventilation, respiratory muscle strength, pulmonary function, and exercise capacity. This narrative review summarizes what is currently known about RMT for exercise performance at altitude and in diving, including potential mechanisms and outlines gaps in the literature.Hess H, Hostler D. Respiratory muscle training effects on performance in hypo- and hyperbaria. Aerosp Med Hum Perform. 2018; 89(11):996–1001.

BACKGROUND: In September 2004 a new pilot certificate, sport pilot, was established, which enabled pilots to fly with a valid driver’s license in lieu of a valid third-class medical certificate. In 2016 Mills and DeJohn published a paper in which they demonstrated that sport pilots had a higher accident rate than private pilots with Class 3 medical certificates. They concluded that this privilege should not be extended to a broader range of pilots due to the higher accident rate. They failed to investigate why these pilots crashed. This short communication aims to fill that gap.METHODS: The NTSB database was reviewed for the entire period that sport pilot has been available, and reasons for the accidents were determined, both for sport pilots and private pilots with Class 3 medicals.RESULTS: Sport pilot accidents were caused by medical incapacitation 3.7% of the time. Private pilots with Class 3 medicals had accidents that cited medical incapacitation 2.5% of the time.DISCUSSION: Medical incapacitation represents either a probable cause or contributing factor in aviation accidents less than 5% of the time. There is a slightly higher rate of this incapacitation among pilots not receiving regular aeromedical evaluations, but the difference was not statistically significant.Mulvey JR. Aviation accident causes among sport pilots as compared to Class 3 private pilots from 2004–2017. Aerosp Med Hum Perform. 2018; 89(11):1002–1004.

BACKGROUND: Non-arteritic anterior ischemic optic neuropathy (NAION) is a common cause of optic neuropathy with the exact pathophysiology unknown. Risk factors include advanced age, small optic nerve head, hypertension, diabetes mellitus, and sleep apnea.⁶ High altitude is considered another risk factor, although only few cases have been reported. No cases of NAION have been reported to occur during flight.CASE REPORT: A 41-yr-old male pilot presented with vision change while performing high G-force maneuvers in an A10 fighter jet. He developed a paracentral visual field defect superiorly in the left eye. Contrasted MRI was within normal limits. The left optic nerve showed blurred margins while the right was sharp, but cupless. The left eye had similar episodes 16 mo before and 8 mo after, but not during flight.DISCUSSION: Our case may be the first reported NAION during flight in an airplane pilot. Our patient was an active U.S. Air Force pilot whose second episode of NAION occurred while performing maneuvers in a fighter jet. The patient is younger than expected for NAION and he did not have any of the commonly associated risk factors. His nonflight episodes suggest he was predisposed to NAION. G-force maneuvers, which restrict blood flow and force blood to the extremities away from the optic nerve head, were the precipitant of his second NAION. With a single case, whether high G maneuvers in general are a risk factor for NAION is unknown.Distefano AG, Lam BL. Non-arteritic anterior ischemic optic neuropathy in pilots. Aerosp Med Hum Perform. 2018; 89(11):1005–1007.

BACKGROUND: Spontaneous pneumothorax (PTX) is a diagnostic challenge in aviators given the common occurrence of musculoskeletal pain after flight and notorious underreporting of symptoms of other diseases in this group.CASE REPORT: A 24-yr-old active duty F/A-18 Weapon Systems Officer performed an anti-G straining maneuver (AGSM) in response to a 6.5-g warm-up turn during a training flight at 16,000 ft (4876.8 m) above sea level. He immediately developed right-sided thoracic back pain. The flight was terminated, he landed, and the pain improved. Over the next 5 d, he noticed the insidious development of pleuritic chest pain and dyspnea. His symptoms prompted presentation to an aviation medicine clinic where a large right sided PTX was identified. After transfer to a local emergency department, a large bore chest tube was placed. A CT scan showed bilateral apical blebs requiring right and subsequently left video assisted thoracoscopy (VATS) with chemical/mechanical pleurodesis and apical wedge resection. Pulmonary function testing (PFT) showed a mild restriction defect 2-1/2 mo after surgery. The patient also completed cardiopulmonary exercise testing (CPET), performing better than his predicted reference range. After a high resolution CT showed no remaining signs of bleb or cyst disease and another month of healing he was returned to flight.DISCUSSION: PTX should be considered in aviators with perithoracic pain after flight as several aspects of flight in high performance aircraft may increase the risk for PTX. These include positive pressure breathing through a facemask, repeated use of the AGSM, and the possibility of bleb expansion at altitude.DeYoung H, Ahmed Y, Buckley J. F/A-18 aviator successfully returned to flight after an in-flight spontaneous pneumothorax. Aerosp Med Hum Perform. 2018; 89(11):1008–1012.

Elliott T. You’re the flight surgeon: rapid onset of weakness. Aerosp Med Hum Perform. 2018; 89(11):1013–1015.