INTRODUCTION: Exploration beyond low Earth orbit requires innovative solutions to support the crew medically, especially as the opportunity for timely evacuation to Earth diminishes. This includes assessing the risks and benefits that a complicated medical evacuation (MEDEVAC) poses to the injured crewmember, the crew, and the mission. This qualitative study identifies common MEDEVAC risk assessment principles used in spaceflight and other extreme environments to better inform future risk assessment tools and exploration mission concepts.

METHODS: Semistructured interviews were conducted with subject matter experts in spaceflight and analog domains, including polar operations, undersea operations, combat medicine, and mountaineering. Transcripts were analyzed using the qualitative method of Thematic Analysis with the technique of consensus, co-occurrence, and comparison.

RESULTS: Subject matter experts described 18 themes divided into two main categories: Primary Risk Considerations (e.g., crew, mission, resources, time) and Contributing Factors (e.g., psychological considerations, medical preparation, politics).

DISCUSSION: Primary Risk Considerations can assess MEDEVAC risk across mission phases, with Contributing Factors acting as premission tools to adjust those risks. Inter- and intracategory connections identified medical support considerations, MEDEVAC support considerations, and philosophy as the most impactful Contributing Factors. Medical support considerations, psychological considerations, and political considerations were found to have unique aspects given the distances and societal impact of exploration vs. low Earth orbit spaceflight. The Contributing Factor theme of decision making was determined to be unique due to its impacts across both categories. These findings expand current considerations and are important inputs for exploration mission MEDEVAC Concepts of Operations.

Almand A, Ko SY, Anderson A, Keller RJ, Zero M, Anderson AP, Laws JM, Lehnhardt K, Easter BD. A qualitative investigation of space exploration medical evacuation risks. Aerosp Med Hum Perform. 2023; 94(12):875–886.

INTRODUCTION: High-altitude [>2400 m (7874 ft)] acclimatization has been well studied with physiological adaptations like reductions in body weight and exercise capacity. However, despite the significance of moderate altitude [MA, 1524–2438 m (5000–8000 ft)], acclimatization at this elevation is not well described. We aimed to investigate differences in mice reared at MA compared to sea level (SL). We hypothesized that MA mice would be smaller and leaner and voluntarily run less than SL mice.

METHODS: C57BL/6 mice reared for at least three generations in Laramie, WY [2194 m (7198 ft), MA], were compared to C57BL/6J mice from Bar Harbor, ME [20 m (66 ft), SL]. We quantified body composition and exercise outputs as well as cardiopulmonary morphometrics. Subsets of MA and SL mice were analyzed to determine differences in neuronal activation after exercise.

RESULTS: When body weight was normalized to tibia length, SL animals weighed 1.30 g ⋅ mm^-1 while MA mice weighed 1.13 g · mm^-1. Total fat % and trunk fat % were higher in MA mice with values of 41% and 39%, respectively, compared to SL mice with values of 28% and 26%, respectively. However, no differences were noted in leg fat %. MA animals had higher heart mass (119 mg) and lower lung mass (160 mg) compared to SL mice heart mass (100 mg) and lung mass (177 mg). MA mice engaged in about 40% less voluntary wheel-running activity than SL animals.

DISCUSSION: Physiological differences are apparent between MA and SL mice, prompting a need to further understand larger scale implications of residence at moderate altitude.

O’Connor AE, Hatzenbiler DM, Flom LT, Bobadilla A-C, Bruns DR, Schmitt EE. Physiological and morphometric differences in resident moderate-altitude vs. sea-level mice. Aerosp Med Hum Perform. 2023; 94(12):887–893.

INTRODUCTION: G tolerance has been widely assessed using Peripheral Light Loss (PLL), but this approach has several limitations and may lack sensitivity. The aim of this study was to investigate the use of a foveal visual endpoint for centrifuge research (Grating Loss; GL) and assess its repeatability, reliability, and usability with PLL as a reference.

METHODS: A total of 11 subjects undertook centrifuge assessment. Gradual onset sessions (GOR; 0.1 G · s⁻¹) measured both endpoints simultaneously and were performed twice, consisting of six determinations with anti-G suits activated (GOR-On) and six without (GOR-Off). Four determinations of each endpoint were also taken during rapid onset runs (ROR; 3 G · s⁻¹). Usability was scored subjectively.

RESULTS: The GL endpoint was reached 0.3–0.5 G_z lower than PLL with each endpoint correlating strongly in GOR-Off (r = 0.93), GOR-On (r = 0.95), and ROR (r = 0.86). The GL had excellent test–retest repeatability (intraclass correlation coefficient: GOR-Off/On = 0.99, ROR = 0.92) and low within-subject variability. Between-subject variance equaled PLL in all conditions. Subjective usability endpoint ratings were equal for all conditions.

DISCUSSION: For the 11 individuals tested, the GL was a reliable, repeatable, and usable endpoint, with similar performance to PLL. GL may prove useful as a supplementary endpoint for human centrifuge research as a secondary data point or to reduce fatigue in repeated measurements. The foveal GL stimulus was lost before PLL, contrary to popular models of visual changes under +G_z.

Britton J, Connolly DM, Hawarden DE, Stevenson AT, Harridge SDR, Green NDC, Pollock RD. Initial investigation of a grating stimulus as a visual endpoint for human centrifuge research. Aerosp Med Hum Perform. 2023; 94(12):894–901.

INTRODUCTION: The present study examined long-term retention and transfer of knowledge and skills, as well as the effect of cognitive load on retention and transfer, using a sample of astronaut candidates and two comparison groups. The first comparison group, recruited from Johnson Space Center, was similar in age, education, and general health to the astronaut candidate group; the second comparison group included university undergraduate students.

METHODS:This study employed two different tasks—a simple perceptual-motor task involving data entry and a complex memory updating task requiring both prospective and retrospective memory. Subjects completed multiple sessions involving both tasks over a 500-d period, with test sessions involving transfer and/or a cognitive load manipulation. For the perceptual-motor task, transfer involved changes to the stimuli that increased intrinsic cognitive load or changes to the required motoric procedures. For the memory updating task, extraneous cognitive load was increased by the addition of a concurrent secondary task.

RESULTS:For both the perceptual-motor and memory updating tasks, astronaut candidates and candidate-like subjects performed more accurately, with greater speed, and were less impacted by increased cognitive load than undergraduate students. Despite the generally superior performance of astronaut candidates and candidate-like subjects, they were more likely to experience negative transfer on the perceptual-motor task, whereas undergraduate students demonstrated positive transfer.

DISCUSSION:Candidate-like subjects provided a more accurate approximation of astronaut candidate performance than did undergraduate students, especially with regard to negative transfer effects and cognitive load.

Kole JA, Barshi I, Healy AF, Schneider VI. Astronaut candidate, candidate-like, and undergraduate subjects compared on retention and transfer. Aerosp Med Hum Perform. 2023; 94(12):902–910.

INTRODUCTION: There is no consensus on whether cardiopulmonary reserve affects the risk of gravity-induced loss of consciousness (G-LOC) or almost loss of consciousness (A-LOC). Few previous studies have used cardiopulmonary exercise testing (CPET) to assess cardiopulmonary reserve function (CPRF) of fighter aviators. We compared CPET-related parameters in G-LOC/A-LOC and non-G-LOC/A-LOC fighter aviators to explore the effect of cardiopulmonary reserve function on G tolerance.

METHODS: A total of 264 male fighter aviators with more than 500 h of flight experience participated in the study, all of whom underwent CPET and human centrifuge testing. We divided the aviators into two groups based on whether they experienced G-LOC/A-LOC during the human centrifuge test and compared the CPET parameters between the two groups.

RESULTS: A total of 37 aviators (14%) experienced G-LOC/A-LOC. There were no significant differences in age (26.65 ± 4.30 vs. 26.01 ± 4.95), height (173.68 ± 4.21 vs. 173.55 ± 3.37), weight (69.51 ± 6.22 vs. 69.63 ± 6.01), or body mass index (23.06 ± 2.11 vs. 23.11 ± 1.82) between the two groups. Forced vital capacity (FVC) (4.95 ± 0.87 vs. 4.65 ± 0.79) and forced expiratory volume in 1 s (FEV₁) divided by FVC (FEV₁/FVC) (79.88 ± 7.24 vs. 83.72 ± 9.24) of pulmonary function of the G-LOC/A-LOC group was significantly lower than that of the non-G-LOC/A-LOC group. There was no significant difference in CPET-related parameters between the two groups.

DISCUSSION: In conclusion, FEV₁/FVC may be a factor affecting aviators’ G-LOC/A-LOC, meaning aviators with slightly lower ventilation are more likely to experience G-LOC/A-LOC. However, oxygen uptake and exercise blood pressure, oxygen pulse, etc., may not be the main factors influencing G-LOC/A-LOC.

Lan X, Zhu W, Du J, Wang J, Yang M, Xu Y, Cao Y. High G tolerance and cardiopulmonary reserve function in healthy air force aviators. Aerosp Med Hum Perform. 2023; 94(12):911–916.

INTRODUCTION: Coronary artery disease (CAD) is the leading cause of denial or withdrawal of flying privileges for aircrew. Screening for CAD is therefore crucial. The present study analyzed German military aircrew with diagnosed CAD and/or acute coronary syndrome despite close medical monitoring with the intention to further optimize individual outcomes and aeromedical disposition.

METHODS: The digital information systems of the German Air Force Centre of Aerospace Medicine were searched for pilots and nonpilot aircrew with CAD and/or myocardial infarction (MI). They were retrospectively analyzed for age at initial diagnosis, body mass index, cardiovascular risk factors, diagnostic procedures, treatment, and aeromedical disposition.

RESULTS: Between February 1987 and March 2023, 126 aircrew, 55% pilots and 45% nonpilot aircrew, were identified with CAD and/or MI. An accumulation of two to six risk factors was found in 77% of both groups. Most pilots (54%) received conservative treatment, 44% underwent percutaneous coronary intervention, and 3% coronary artery bypass grafting. In the group of nonpilot aircrew, conservative treatment was performed in 47%, coronary intervention in 37%, and bypass grafting in 16%. A total of 45 pilots (65%) returned to flying duties, albeit 39 (57%) with restrictions. In the group of nonpilot aircrew, 31 (54%) returned to flying duties.

DISCUSSION: A small group of aircrew developed CAD over the years, some with severe coronary artery stenoses and MI. Further optimization of individual prognosis and aeromedical disposition should aim at appropriate CAD screening and risk factor elimination. CAD management needs a comprehensive approach regarding military aviation requirements and clinical guidance.

Guettler N, Sammito S. Coronary artery disease management in military aircrew. Aerosp Med Hum Perform. 2023; 94(12):917–922.

BACKGROUND: Bone mineral density (BMD) is a measure of skeletal health that may foretell disorders like osteoporosis.

METHODS: To reduce bone losses on Earth, treatments include exercise, diet, and drugs. Each impact osteoblast and osteoclast activity dictates skeletal remodeling and subsequent BMD changes. BMD loss is a concern during spaceflight. For astronauts, low BMD undermines in-flight tasks and compromises their postflight health.

RESULTS: While bisphosphonates exhibited promise as an in-flight bone loss treatment, study results are mixed, and this class of drugs has numerous side-effects. While the role antiresorptive agents play in reducing BMD loss is discussed, this review focuses on exercise-induced strains and nutrition, two in-flight treatments without bisphosphonates’ side-effects.

DISCUSSION: Evidence supports in-flight exercise and a healthy diet with vitamin D and Ca⁺² supplementation to limit BMD loss. This review suggests how exercise and nutrition may limit BMD loss during spaceflight. Also discussed is an in-flight version of the inertial exercise trainer (IET; Impulse Technologies, Knoxville TN). By imparting high bone-strain magnitudes, rates, and frequencies with less mass, footprint, and power needs than other forms of in-flight resistance exercise hardware, the IET warrants inquiry for use aboard future long-term spaceflights.

Caruso J, Patel N, Wellwood J, Bollinger L. Impact of exercise-induced strains and nutrition on bone mineral density in spaceflight and on the ground. Aerosp Med Hum Perform. 2023; 94(12):923–933.

INTRODUCTION: Motion sickness affecting military pilots and aircrew can impact flight safety and, if severe, can lead to disqualification from flight status. However, due to the common adverse effects of motion sickness pharmaceuticals (e.g., drowsiness), medication options are severely limited. The purpose of this study was to explore the potential utility of a nonpharmaceutical method for motion sickness prevention, specifically an osteopathic manipulative technique (OMT).

METHODS:A novel OMT protocol for the reduction of motion sickness symptoms and severity was evaluated using a sham-controlled, counterbalanced, between-subjects study design. The independent variable was OMT treatment administered prior to the motion sickness-inducing procedure (rotating chair). The primary dependent measures were total and subscale scores from the Motion Sickness Assessment Questionnaire.

RESULTS:The OMT treatment group experienced significantly fewer gastrointestinal (mean scores postprocedure, treatment M = 20.42, sham M = 41.67) and sopite-related (mean scores postprocedure, treatment M = 12.81, sham M = 20.68) symptoms than the sham group while controlling for motion sickness susceptibility. There were no differences between groups with respect to peripheral and central symptoms.

DISCUSSION:The results suggest that the treatment may prevent gastrointestinal (nausea) and sopite-related symptoms (sleepiness). These preliminary findings support further exploration of OMT for the prevention of motion sickness. A more precise evaluation of the mechanism of action is needed. Additionally, the duration of the effects needs to be investigated to determine the usefulness of this technique in training and operational settings.

Thomas VA, Kelley AM, Lee A, Fotopoulos T, Boggs J, Campbell J. Preliminary evaluation of an osteopathic manipulative treatment to prevent motion sickness. Aerosp Med Hum Perform. 2023; 94(12):934–938.

INTRODUCTION: Management of aeromedical risk is essential for flight safety. Given the many operator stressors for pilots, militaries maintain a vested interest in selecting aircrew applicants who meet rigorous initial medical standards. Very little published literature exists regarding the extent of medical disqualifications or precluding conditions for initial candidates.

METHODS: For the British Army, pilot selection is a phased, multistep process that includes Phase I medical screening followed by a comprehensive Phase II medical exam. De-identified summary data were retrospectively reviewed for medical fitness and disqualifying categories for the 5-yr period of 2018–2022, inclusive. For those ultimately deemed unfit for aviation service, etiology was grouped into general categories.

RESULTS: Approximately one-third (30.2%) of candidates were disqualified at Phase I initial medical screening with leading categories of attrition due to respiratory etiology, especially a history of asthma or reactive airway disease, followed by ophthalmology. For the Phase II medical exam cohort, 21.0% were medically disqualified with most attrition from anthropometry and ophthalmology. There were no statistical differences in disqualifications for gender or pathway of entry (civilian vs. serving personnel).

DISCUSSION: Major categories of medical attrition were similar to that of other nations, yet the published literature in this area is surprisingly tenuous. Given the desire for evidence-based medical selection standards, it is important for regular review of processes and standards such that the risks of known physiological challenges are judiciously weighed with the benefits of a large, diverse pool of selection as well as force structure and recruitment demand.

Adams MS, Goldie CE, Gaydos SJ. Retrospective analysis of medical attrition for pilot applicants to the British Army Air Corps. Aerosp Med Hum Perform. 2023; 94(12):939–943.