BACKGROUND: Virtual reality (VR) is an effective technique to reduce cost and increase fidelity in training programs. In VR, visual and vestibular cues are often in conflict, which may result in simulator-induced motion sickness. The purpose of this study is to investigate the integration of Galvanic Vestibular Stimulation (GVS) with a VR flight training simulator by assessing flight performance, secondary task performance, simulator sickness and presence.

METHODS: There were 20 participants who performed 2 separate VR flight simulation sessions, with and without GVS (control). Flight performance, secondary task performance, and electrogastrogram were measured during VR flight simulation. The standardized simulator sickness and presence questionnaires were administered.

RESULTS: Electrogastrogram measures such as dominant power instability coefficient (DPIC) and percentages of bradygastric waves (%B) were lower in the GVS session than the control session in the flight simulation (DPIC: 0.44 vs. 0.54; %B: 21.2% vs. 30.5%) and postflight (DPIC: 0.38 vs. 0.53; %B: 22.8% vs. 31.4%) periods. Flight performance (#hit-gates) was improved in the GVS session compared to the control (GVS: 17, Control: 15.5). Secondary task performance (%hits) was improved with GVS for the Easy task (GVS: 55.5%, Control: 43.1%).

DISCUSSION: This study demonstrates the potential of synchronizing GVS with visual stimuli in VR flight training to reduce visual-vestibular sensory conflict to improve fidelity and performance. These results provide initial evidence, but continued research is warranted to further understand the benefits and applications of GVS in VR simulator training.

Pradhan GN, Galvan-Garza RC, Perez AM, Stepanek J, Cevette MJ. Visual vestibular conflict mitigation in virtual reality using galvanic vestibular stimulation. Aerosp Med Hum Perform. 2022; 93(5):406–414.

INTRODUCTION: Obstructive sleep apnea (OSA) is a condition characterized by disrupted sleep and excessive daytime fatigue. Associated cognitive and psychomotor decrements pose a threat to aviators’ performance and flight safety. Additionally, the longer term health effects associated with the disease can jeopardize an aviator’s career and negatively impact operational outputs. This study reviews OSA prevalence, related comorbid conditions in Army aviators, and analyzes the aeromedical dispositions of affected individuals.

METHODS: The U.S. Army Aeromedical Electronic Resource Office (AERO) database was interrogated for all cases of OSA from June 2005 through June 2015 using ICD-9 code 327.23. Prevalence rates for OSA and other comorbid conditions were then calculated using the total number of aviators in the AERO database.

RESULTS: A total of 663 unique instances of OSA were found among the aviator population (N = 24,568), giving a point prevalence of 2.69%. Four cases affected women. Mean age of initial presentation was 42.62 yr and mean Body Mass Index was 28.69. The top five most prevalent comorbid conditions were hypertension, lumbago, degeneration of a lumbar or lumbosacral intervertebral disc, PTSD, and testicular hypofunction.

DISCUSSION: Prevalence of OSA among aviators is lower than the general population but is not uncommon. A positive diagnosis requires a waiver or can result in suspension if not managed effectively, potentially leading to a reduction in aviator numbers. Aggressive health promotion and robust medical surveillance and aeromedical disposition management by the aeromedical community is essential to reduce OSA numbers, maintain aviator health, and maximize flight safety.

Goldie C, Stork B, Bernhardt K, Gaydos SJ, Kelley AM. Obstructive sleep apnea among army aircrew. Aerosp Med Hum Perform. 2022; 93(5):415–420.

BACKGROUND: This study evaluated the executive functions of air traffic controllers (ATCs) in relation to demographic and occupational characteristics such as length of service, technical qualifications, and work shifts.

METHODS: This was a cross-sectional study based on a convenience sample with sequential selection of 52 Brazilian ATCs using the Wisconsin Card Sorting Test (WCST), questionnaire applied to the ATCs, Student’s t-test, and one-way analysis of variance with post hoc Tukey multiple comparisons of WCST with functional characteristics.

RESULTS: ATCs with 0 to 5 yr of service presented scores significantly above the cohort average in the WCST [0-5 yr: 0.54 ± 0.01 vs. 6-15 yr: 0.31 ± 0.52 vs. 151 yr: -0.02 ± 0.80]. ATCs working a 3-shift pattern presented an efficient performance and fewer perseverative errors in the WCST (3-shift: −0.63 ± 0.38 vs. 4-shift: −0.45 ± 0.43), that did not rise to significance. In a comparison between executive brain functions and technical qualifications, the controllers who worked in the TWR (Aerodrome Control Tower) only, and those who worked in both the TWR and APP (Approach Control Service) showed no differences in the number of completed categories and in perseverative errors.

DISCUSSION:The executive brain functioning of the ATCs, such as mental flexibility, strategic planning and inhibitory control, were identified as being above average when compared to the general population. While alterations in work shifts appear to have a negative (but nonsignificant) impact, newer ATCs showed stronger scores than more experienced ATCs on the WCST. Successful performance as an ATC has complex foundations, such as understanding the context of air navigation and having strong executive function capabilities.

de Freitas AM, Portuguez MW, Russomano, T, da Costa JC. Air traffic controllers and executive brain function. Aerosp Med Hum Perform. 2022; 93(5):426–432.

INTRODUCTION: COVID-19 has had a significant impact on the aviation industry. While reduced flying capacity may intuitively translate to reduced fatigue risk by way of fewer flights and duty hours, the actual impact of the pandemic on pilot fatigue is unknown.

METHODS: We surveyed U.S. commercial airline pilots in late 2020 (N = 669) and early 2021 (N = 156) to assess the impact of COVID-19 on schedules and fatigue during the pandemic.

RESULTS: Overall, pilots reported reduced flight and duty hours compared to prepandemic. Average sleep on workdays was slightly shorter in late 2020 (6.87 ± 1.14 h) and recovered to prepandemic levels in early 2021 (6.95 ± 1.11 h). Similarly, the frequency of sleepiness on days off and in-flight increased in late 2020, with 54% of pilots reporting an increase in in-flight sleepiness, then returned to prepandemic levels in early 2021. The use of in-flight sleepiness countermeasures remained the same across assessed time points. Pilots highlighted several factors which impacted their sleep and job performance, including limited access to nutritional food during duty days and layovers, reduced access to exercise facilities during layovers, increased stress due to job insecurity and health concerns, increased distractions and workload, and changes to scheduling.

DISCUSSION: Despite a reduction in flights and duty days, COVID-19 led to increased sleepiness on days off and in flight, potentially due to the negative impact of lack of access to essential needs and heightened stress on sleep. Operators need to monitor the change in these COVID-19 related risks as the industry returns to full service.

Hilditch CJ, Flynn-Evans EE. Fatigue, schedules, sleep, and sleepiness in U.S. commercial pilots during COVID-19. Aerosp Med Hum Perform. 2022; 93(5):433–441.

BACKGROUND: There is a paucity of research on general aviation accidents in Germany. The authorities investigate only a fraction of all national accidents. The current study analyzes existing accident reports and aims to identify injury severity in regard to concomitant risk factors.

METHODS: Data of flight accidents was analyzed for aircraft of <5700 kg maximum takeoff weight (MTOW) over a 20-yr period. Besides descriptive data, concomitant factors (type and category of aircraft, date, occupants and outcome, flight phase, etc.) were analyzed. Statistical analysis was performed using the Chi-squared test.

RESULTS: The authorities list 1595 aircraft accidents between 2000 and 2019, but only 17.9% of these were analyzed in detail. Accidents of aircraft of <2000 kg MTOW were over-represented between May and September and between Friday and Sunday. The fraction of fatal accidents was highest during cruise. During landing, significantly more mishaps of larger aircraft occurred. The number of seriously injured or deceased occupants was significantly higher for accidents involving private pilots. An occupancy rate of more than three persons on board correlated significantly with fewer number of deaths.

CONCLUSIONS: The annual count of aircraft accidents has almost halved during the previous 20 yr. Unfortunately, only a small number of mishaps were further investigated by authorities, which leads to a lack of evaluable data needed for in-depth investigations. The accumulation of larger aircraft mishaps in winter and the superior outcome of professional pilots in terms of safety, as well as the fewer number of mishaps in larger aircraft, should be further investigated.

Liebold F, Hippler C, Schmitz J, Yücetepe S, Rothschild M, Hinkelbein J. Fixed-wing motorized aircraft accidents: analysis of injury severity and concomitant factors (2000–2019). Aerosp Med Hum Perform. 2022; 93(5):442–449.

INTRODUCTION: With improved imaging technology, the number of incidental findings detected in cerebral MRI is increasing. This is a challenge that the German Air Force has to deal with in the context of standardized MRI examinations of young pilot candidates and pilots.

METHODS: The German Air Force Centre of Aerospace Medicine hosted a 2-d conference to develop recommendations and procedures for the handling of some of the most frequently encountered cerebral incidental findings.

RESULTS: Radiological MRI findings from a total of 2724 routine examinations of the skull of pilots and pilot applicants (26.8 ± 10.6 yr old; range from 16 to 62; over 80% range from 17 to 33; 96% men) revealed that in 28.1% of the examinations, one or more incidental findings were discovered. For seven of the following categories of incidental findings, decision guidelines could be established: white matter hyperintensities (N = 393; prevalence 14.4%; 95% CI 13.11–15.75), pinealis cysts (317; 11.6%; 10.43–12.84), developmental venous anomalies (64; 2.3%; 1.78–2.92), cavernomas (15; 0.6%; 0.27–0.83), aneurysms (14; 0.5%; 0.25–0.78), cholesterol granulomas (22; 0.8%; 0.47–1.14), and heterotopias of the gray matter (6; 0.2%; 0.04–0.4).

CONCLUSION: Considering pilots health and aviation safety, a waiver decision is often possible after thorough discussion, depending on the specific criteria of the incidental finding and of the type of license.

Kühn S, Sönksen S-E, Noble H-J, Knopf H, Frischmuth J, Waldeck S, Müller-Forell W, Weber F, Bressem L. Incidental findings in head and brain MRI of military pilots and applicants: consequences for medical flight fitness. Aerosp Med Hum Perform. 2022; 93(5):450–457.

INTRODUCTION: Between 43 and 97% of helicopter pilots in the Canadian Armed Forces report neck pain. Potential contributing factors include the weight of their helmet, night vision goggles (NVG), and counterweight (CW) combined with deviated neck postures. Therefore, the purpose of this investigation was to quantify changes in neck loads associated with posture, helmet, NVG, and CW.

METHODS: Eight male subjects volunteered. They undertook one of five deviated neck postures (flexion, extension, lateral bending, axial rotation) times four configurations (no helmet, helmet only, helmet and NVG, and helmet, NVG, and CW). 3D kinematics and EMG from 10 muscles (5 bilaterally) drove a 3D inverse dynamics, EMG-driven model of the cervical spine which calculated joint compression and shear at C5-C6.

RESULTS: The compression in the neutral posture was 116.5 (5.7) N, which increased to 143.7 (11.4) N due to a 12.7 N helmet. NVGs, weighing 7.9 N, also generated this disproportionate increase, where the compression was 164.2 (3.7) N. In flexion or extension, the compression increased with increasing head-supported mass, with a maximum of 315.8 (67.5) N with the CW in flexion. Anteroposterior shear was highest in the lateral bending [34.0 (6.2) N] condition, but was generally low (< 30 N). Mediolateral shear was less than 5 N for all conditions.

DISCUSSION: Repositioning the center of gravity of the helmet with either NVGs or CW resulted in posture-specific changes to loading. Posture demonstrated a greater potential to reposition the head segment’s center of gravity compared to the helmet design. Therefore, helmet designs which consider repositioning the center of gravity may reduce loads in one posture, but likely exacerbate loading in other postures.

Barrett JM, McKinnon CD, Dickerson CR, Laing AC, Callaghan JP. Posture and helmet configuration effects on joint reaction loads in the middle cervical spine. Aerosp Med Hum Perform. 2022; 93(5):458–466.

INTRODUCTION: The previous Spacecraft Maximal Allowable Concentrations (SMACs) for propylene glycol were established based on a study of rodents exposed to propylene glycol (PG) aerosol for 6 h/d, 5 d/wk for 90 d. This study has been used as the basis for the few existing limits, but all exposure concentrations were well above the saturated vapor concentration of ∼100 ppm for pure propylene glycol at room temperature. For this reason, the Environmental Protection Agency and the Agency for Toxic Substances and Disease Registry noted that the method used to generate the aerosols for the two published studies of animal exposures are not relevant to exposure conditions for the general public, and most regulatory agencies have not established inhalation limits for propylene glycol, citing lack of data. Since publication of the PG SMACs in 2008, an acute inhalation study was conducted in healthy human subjects which allows us to revise our assessment. This manuscript provides the rationale for increasing the prior limits for PG in spacecraft air from 32 and 17 ppm to 64 and 32 ppm for off-nominal scenarios/releases (1-h and 24-h limits) and from 9, 3, and 1.5 ppm to 32 ppm for all nominal timeframes (7, 30, and 180 d). Due to a lack of longer-term exposure data, NASA has elected to eliminate the 1000-d SMAC limit at this time.

Ryder VE, Williams ES. Revisions to limits for propylene glycol in spacecraft air. Aerosp Med Hum Perform. 2022; 93(5):467–469.

BACKGROUND: Physiological episodes are a top safety concern for aviators across the United States military. While many cases and a variety of causes for physiological episodes have been described, few cases, if any, have been reported of hyperventilation-induced hypocapnia and transient loss of consciousness.

CASE REPORT: Here we describe a case of an aviator who experienced tingling extremities, confusion, and loss of consciousness during a flight. The aviator incorrectly believed he was experiencing hypoxia and continued to take multiple steps to troubleshoot the wrong underlying problem for his symptoms. Evaluation after landing suggested this was instead a stress-induced hyperventilation that resulted in symptomatic hypocapnia.

DISCUSSION: We report this case to add to the body of literature in understanding this phenomenon as well as to provide aviators, physiologists, and flight surgeons with practical suggestions for recognizing hyperventilation-induced hypocapnia and awareness of how to remedy this situation when they recognize it.

Kramer KEP, Anderson EE. Hyperventilation-induced hypocapnia in an aviator. Aerosp Med Hum Perform. 2022; 93(5):470–471.