INTRODUCTION: Hypobaric decompression has been associated with brain white matter injury. Relevant exposure limits are unknown, raising ethical concerns over safety of volunteers for altitude chamber research. To inform this, a prospective study of white matter status using brain Magnetic Resonance Imaging (MRI) was conducted before and after a 9-mo program of hypobaric research.METHODS: Volunteers underwent 3-D, volumetric, fluid attenuated inversion recovery (FLAIR) MRI at the University of Nottingham, UK, on study entry and again after their final exposure. MRI data were analyzed and reported independently at the University of Maryland, Baltimore, MD, USA. Entry criteria were 5 subcortical white matter hyperintensities (WMH) of total volume 0.08 mL.RESULTS: One volunteer failed screening with 63 WMH (total volume 2.38 mL). Eleven individuals completed 160 short-duration (< 1h) exposures (range 3 to 26) to 18,000 ft pressure altitude (maximum 40,000 ft), no more often than twice weekly. The cohort exhibited eight total WMH on study entry (total volume 0.166 mL) and five (mostly different) total WMH on exit (0.184 mL). Just one WMH (frontal lobe) was present on both entry and exit scans. Excess background WMH on MRI screening were associated with past mild traumatic brain injury (MTBI).CONCLUSIONS: One hypoxia familiarization plus multiple, brief, infrequent, nonhypoxic hypobaric exposures (with denitrogenation) have not promoted WMH in this small cohort. Less intensive programs of decompression stress do not warrant MRI screening. A negative past history of MTBI has strong negative predictive value for excess WMH in young healthy subjects (N 33).Connolly DM, Lupa HT. Prospective study of white matter health for an altitude chamber research program. Aerosp Med Hum Perform. 2021; 92(4):215222.

INTRODUCTION: In fighter aircraft, long-duration high-altitude sorties are typically interrupted by refueling excursions to lower altitude. In normoxia, excursions to moderate cabin altitude may increase the occurrence of venous gas emboli (VGE) at high cabin altitude. The aim was to investigate the effect of hyperoxia on VGE and decompression sickness (DCS) during alternating high and moderate altitude exposure.METHODS: In an altitude chamber, 13 healthy men were exposed to three different conditions: A) 90 min at 24,000 ft (7315 m) breathing normoxic gas (54% O₂; H-NOR); B) 90 min at 24,000 ft breathing hyperoxic gas (90% O₂; H-HYP); and C) three 30-min exposures to 24,000 ft interspersed by two 30-min exposures to 18,000 ft (5486 m) breathing 90% O₂ (ALT-HYP). VGE occurrence was evaluated from cardiac ultrasound imaging. DCS symptoms were rated using a scale.RESULTS: DCS occurred in all conditions and altogether in 6 of the 39 exposures. The prevalence of VGE was similar in H-NOR and H-HYP throughout the exposures. During the initial 30 min at 24,000 ft, the prevalence of VGE was similar in ALT-HYP as in the other two conditions, whereas, after the first excursion to 18,000 ft, the VGE score was lower in ALT-HYP than in H-NOR and H-HYP.DISCUSSION: Hyperoxic excursions from 24,000 to 18,000 ft reduces VGE occurrence, presumably by facilitating diffusive gas exchange across the bubble surfaces, increasing the share of bubble content contributed by oxygen. Still, the excursions did not abolish the DCS risk.Ånell R, Grönkvist M, Gennser M, Eiken O. Hyperoxic effects on decompression strain during alternating high and moderate altitude exposures. Aerosp Med Hum Perform. 2021; 92(4):223230.

INTRODUCTION: Research has shown that astronauts performing extravehicular activities may be exposed, under certain conditions, to undesired electrical hazards. This study used computer models to determine whether these undesired induced electrical currents could be responsible for involuntary neuromuscular activity caused by either large diameter peripheral nerve activation or reflex activity from cutaneous afferent stimulation.METHODS: A multiresolution variant of the admittance method along with a magnetic resonance image millimeter resolution model of a male human body were used to calculate the following: 1) induced electric fields; 2) resistance between contact areas in a Extravehicular Mobility Unit spacesuit; 3) currents induced in the human body; 4) the physiological effects of these electrical exposures; and 5) the risk to the crew during extravehicular activities.RESULTS: Using typical EMU shock exposure conditions, with a 15V source, the current density magnitudes and total current injected are well above previously reported startle reaction thresholds. This indicates that, under the considered conditions during a spacewalk in the charged ionospheric plasma of space, astronauts could experience possibly harmful involuntary motor response and sensory pain nerve activation.Hamilton DR. Electrical shock hazard severity estimation during extravehicular activity for the International Space Station. Aerosp Med Hum Perform. 2021; 92(4):231239.

INTRODUCTION: U.S. Air Force Special Operations Command (AFSOC) female aircrew represent a small group of military personnel in challenging high-risk, high-demand professions. Personality characteristics may play a key role in distinguishing those women who pursue a career as a special operations aircrew member and succeed in this pursuit. Having access to normative personality data can potentially support psychologists in assessing AFSOC female aircrew and subsequently making informed recommendations to leadership.METHODS: A total of 586 AFSOC aircrew trainees58 (9.9%) women and 528 (90.1%) mencompleted a series of computer-based psychological tests to assess cognitive ability and personality traits.RESULTS: Results indicated significant differences between female AFSOC aircrew and female civilians on four of the five NEO Personality Inventory domains: Neuroticism (M 74.9 vs. M 87.1), Extraversion (M 123.7 vs. M 112.8), Openness to Experience (M 122.6 vs. M 111.0), and Conscientiousness (M 136.0 vs. M 120.6), respectively. The comparison between female AFSOC aircrew and male AFSOC aircrew revealed significant differences across three of the five domains: Neuroticism (M 74.9 vs. M 65.1), Openness to Experience (M 122.6 vs. M 115.0), and Agreeableness (M 119.6 vs. M 112.7), respectively.DISCUSSION: Implications for assessment and interpretation of psychological testing are discussed. This paper provides a unique perspective and insight into those who pursue and excel in this career field. Identifying specific personality traits in our AFSOC female aircrew allows for tailored care and support when evaluating readiness in special operations aircrew for optimizing performance.Chappelle W, Shadle AH, Martinez RN, Reardon LE, Goodman T, Spencer H, Thompson W. Personality traits that distinguish special operations female aircrew. Aerosp Med Hum Perform. 2021; 92(4):240247.

BACKGROUND: The study investigated the heat strain of personnel operating in the rear cabin of a helicopter during desert-climate missions, and to what extent the strain can be mitigated by use of battery-driven ventilation vests.METHODS: Eight men undertook 3-h simulated flight missions in desert conditions (45C, 10% humidity, solar radiation). Each subject participated in three conditions wearing helicopter flight equipment, including body armor, and either: a ventilation vest with a 3-dimensional mesh (Vent-1), a ventilation vest with a foam sheet incorporating channels to direct the air flow (Vent-2), or a T-shirt (NoVent); each mission comprised a 10-min walk, followed by sitting for 30 min, kneeling on a vibration platform for 2 h, and finally 30 min of sitting. Core temperature, heart rate, skin temperatures and heat flux, oxygen uptake, sweating rate, and subjective ratings were recorded. Evaporative capacity and thermal resistance of the garments were determined using a thermal manikin.RESULTS: All subjects completed the NoVent and Vent-1 conditions, whereas in the Vent-2 condition, one subject finished prematurely due to heat exhaustion. The increase in core temperature was significantly (P 0.01) greater in Novent (0.93C) and Vent-2 (0.88C) than in Vent-1 (0.61C). Evaporative capacity was significantly higher for Vent-1 (7.8 g min¹) than for NoVent (4.1 g min¹) and Vent-2 (4.4 g min¹).DISCUSSION: Helicopter personnel may be at risk of heat exhaustion during desert missions. The risk can be reduced by use of a ventilation vest. However, the cooling efficacy of ventilation vests differs substantially depending on their design and ventilation concept.Grönkvist M, Mekjavic I, Ciuha U, Eiken O. Heat strain with two different ventilation vests during a simulated 3-hour helicopter desert mission. Aerosp Med Hum Perform. 2021; 92(4):248256.

INTRODUCTION: Recent reports of in-flight, hypoxia-like events have prompted concern that aircraft life support systems (LSS) may not always provide effective altitude protection. An analysis was undertaken of hypoxia-like incidents reported in a UK front-line combat aircraft.METHODS: A search of the UK Aviation Safety Information Management System database identified all Typhoon Defense Air Safety Occurrence Reports (DASORs) notifying in-flight symptoms over the decade 20082017. Qualitative analysis focused on the event narrative, altitude profile, timeline, symptom description, sortie characteristics, LSS function, postflight engineering investigation, and training implications. The plausibility and likelihood of hypobaric hypoxia were assessed, and the probable cause of symptoms ascribed.RESULTS: There were 18 DASORs with notified symptoms of suspected in-flight hypoxia, 13 in solo pilots and 5 reports of symptoms affecting 7 of 10 aircrew in 2-seat aircraft. Two cases of probable hypoxia comprised one oxygen bottle failure and one mask-off cabin depressurization. In one report, hypoxia was assessed as plausible but unlikely, following birdstrike with failure of cabin pressurization during climb. Symptoms were explained by hyperventilation in 13 cases (65%) and twice by minor constitutional upset. Suspected hypoxia was managed by immediate selection of emergency oxygen and expedited descent in 10 of 18 occurrences (56%).CONCLUSIONS: Only 2 cases of probable hypoxia have been reported in over 150,000 Typhoon flying hours. The Typhoon LSS has provided effective altitude protection including during cases of cabin depressurization. Symptom occurrences in Typhoon are idiosyncratic and unrelated; hyperventilation probably accounts for two-thirds of reports.Connolly DM, Lee VM, McGown AS, Green NDC. Hypoxia-like events in UK Typhoon aircraft from 2008 to 2017. Aerosp Med Hum Perform. 2021; 92(4):257264.

INTRODUCTION: A topic in aviation medicine that attracts much attention from the scientific community as well as from the media concerns medical incidents on board commercial airline flights. It was noticed that many papers on the subject were written by authors whose specialization was outside that of aviation medicine and that they sometimes made basic errors concerning the application of scientific principles of the subject. A review was undertaken to determine if there were any patterns to the observed errors and, if so, to consider whether recommendations might be provided that could reduce their frequency.METHOD: A literature search was undertaken of MEDLINE using PubMed for English-only articles published between January 1, 1974, and February 1, 2019, employing the following search terms: air emergency, air emergencies, air passenger, air travel, aircraft, airline, aviation, commercial air, flight, and fitness to fly. In addition, other relevant papers held in the personal collection of the authors were reviewed.RESULTS: Many cases of misinterpretation or misunderstanding of aviation medicine were found, which could be classified into eight main categories: references; cabin altitude; pressure/volume relationship; other technical aspects of aircraft operations; regulations; medical events; in-flight deaths; and automated external defibrillator.CONCLUSION: Papers were identified as having questionable statements of fact or of emphasis. Such instances often appeared to result from authors being unfamiliar with the subject of aviation medicine and/or the commercial aviation environment. Simple steps could be taken by authors to reduce the future rate of such instances and recommendations are provided.Thibeault C, Evans AD. Medical events on board aircraft: reducing confusion and misinterpretation in the scientific literature. Aerosp Med Hum Perform. 2021; 92(4):265273.

INTRODUCTION: In response to the urgent need for safe aircrew respiratory protection due to the COVID-19 pandemic, three small descriptive evaluations were conducted with aircrew and air traffic controllers (ATC) that assessed the impact of mask use on safety and performance onboard rotary wing aircraft.METHODS: A series of evaluations assessed aircrew performance using the 3M^TM Model 1860 N95 respiratory protection mask, two aviation-specific cloth mask prototypes, and a commercial off-the-shelf aviation-specific cloth mask. The series of evaluations included different sets of subjects consisting of up to five Black Hawk helicopter aircrew members, air traffic control (ATC), and 12 CH-47 aircrew members. The Modified Rhyme Test was used to measure speech intelligibility and was administered in the UH-60 among crewmembers of the same aircraft, between pilots of different aircraft, and between the pilots and ATC. Measures of workload, usability, comfort, and pulse oximetry were also administered.RESULTS: Results from the Modified Rhyme Test indicated that all subjects scored greater than 80% accuracy given the proper microphone positioning relative to the mask. With respect to workload, NASA-TLX total scores for the perform radio communications task was 50.83.DISCUSSION: Despite an elevated perceived degree of workload on the communications flight task, results from the speech intelligibility test indicated that performance was maintained within the acceptable range as defined by MIL-STD-1474E, Design Criteria Standard Noise Limit. This abbreviated evaluation suggests that the face masks tested are safe for use by helicopter aircrew under the conditions tested.Cave KM, Kelley AM, Feltman KA, Gerstner JA, Stewart JL, Crowley JS. Aircrew performance and safety while using protective masks in response to coronavirus disease. Aerosp Med Hum Perform. 2021; 92(4):274280.

BACKGROUND: Swyer-James-MacLeod syndrome (SJMS) is a specific form of bronchiolitis obliterans that occurs rarely, but represents recognized sequelae of common pediatric respiratory illness, and presents as unilateral hyperlucency on chest imaging. This case study describes such an incidental radiographic finding identified during the assessment of chest wall discomfort in a military pilot.CASE REPORT: A 35-yr-old military pilot presented to his flight surgeon with vague intermittent chest discomfort. Initial evaluation revealed an abnormal chest radiograph with unilateral hyperlucency and mild expiratory airflow limitation on pulmonary function testing. The evaluation also included computed tomography imaging with contrast infusion and echocardiography, though the presenting complaint had resolved. The airman was referred to our clinic for further evaluation and aeromedical recommendations regarding returning to flight duties. He was diagnosed with SJMS and recommended to be returned to flight duties.DISCUSSION: SJMS can be challenging to recognize to the untrained eye. An inflammatory response from viral or bacterial infection in childhood results in dysfunctional growth of the affected region of the lung, causing radiographic asymmetry. Although destruction of the alveoli and emphysema may occur, for most cases, there are minimal clinical sequelae. SJMS is not known to be progressive and is not associated with systemic conditions. The pilot likely had the abnormal chest radiograph at the time of commission and had not experienced any in-flight complications. His chest pain had resolved without intervention and SJMS was determined to be unlikely to impact his flight performance (such as response to supplemental oxygen) or life expectancy.Harrison MF, Cowl CT. Incidental diagnosis of Swyer-James-MacLeod syndrome in a military pilot. Aerosp Med Hum Perform. 2021; 92(4):281285.