INTRODUCTION: Following a transition from microgravity to a gravity-rich environment (e.g., Earth, Moon, or Mars), astronauts experience sensorimotor impairment, primarily from a reinterpretation of vestibular cues, which can impact their ability to perform mission-critical tasks. To enable future exploration-class missions, the development of lightweight, space-conscious assessments for astronauts transitioning between gravity environments without expert assistance is needed.

METHODS: We examined differences in performance during a two-dimensional (2D) hand–eye multidirectional tapping task, implemented in augmented reality in subjects (N = 20) with and without the presence of a vestibular-dominated sensorimotor impairment paradigm: the binaural bipolar application of a pseudorandom galvanic vestibular stimulation (GVS) signal. Metrics associated with both the impairment paradigm and task performance were assessed.

RESULTS: Medial-lateral sway during balance on an anterior-posterior sway-referenced platform with eyes closed was most affected by GVS (effect size: 1.2), in addition to anterior-posterior sway (effect size: 0.63) and the vestibular index (effect size: 0.65). During the augmented reality task, an increase in time to completion (effect size: 0.63), number of misses (effect size: 0.52), and head linear accelerations (effect size: 0.30) were found in the presence of the selected GVS waveform.

DISCUSSION: Findings indicate that this multidirectional tapping task may detect emergent vestibular-dominated impairment (near landing day performance) in astronauts. Decrements in speed and accuracy indicate this impairment may hinder crews’ ability to acquire known target locations while in a static standing posture. The ability to track these decrements can support mission operations decisions.

Allred AR, Weiss H, Clark TK, Stirling L. An augmented reality hand–eye sensorimotor impairment assessment for spaceflight operations. Aerosp Med Hum Perform. 2024; 95(2):69–78.

INTRODUCTION: Health-related factors can impact aviation safety. This study investigated the published, historical aviation accidents that have been investigated by the U.S. National Transportation Safety Board (NTSB) to understand medical conditions and medication use that have been determined to be causal to mishaps.

METHODS: A two-part approach was adopted for this study: 1) a scoping review was conducted to provide an overview of the current medical literature addressing medical factors and flight safety; and 2) a comprehensive review of aviation accident reports from the NTSB database from January 2013 to October 2022.

RESULTS: The literature review demonstrated that psychiatric, cardiovascular, and neurological medications were the major categories of medications reported in fatal aircraft accidents. Age was not found to be a risk factor. Review of the NTSB database demonstrated that, among 15,654 mishaps, medical factors were associated in 703 (4.5%) accidents. NTSB data showed that cardiovascular (1.3%), psychiatric (0.23%), and endocrine diseases (0.17%) were the most commonly reported diseases among pilots. In accident reports, cardiovascular medications (1.49%), sedating antihistamines (0.91%), and alcohol (0.70%) were the most commonly used medications at the time of the accidents.

DISCUSSION: Health-related factors were a small yet likely underestimated proportion of the factors associated with accidents. Cardiovascular diseases and treatment were the most important factors. It is important to continue to investigate the association between health-related factors and the commission of mishaps.

Zhu Y, Wolf ME, Alsibai RA, Abbas AS, Alsawaf Y, Saadi S, Farah MH, Wang Z, Murad MH. Health-related factors among pilots in aviation accidents. Aerosp Med Hum Perform. 2024; 95(2):79–83.

INTRODUCTION: The illusions of head motion induced by galvanic vestibular stimulation (GVS) can be used to compromise flight performance of pilots in fixed-base simulators. However, the stimuli used in the majority of studies fail to mimic disorientation in realistic flight because they are independent from the simulated aircraft motion. This study investigated the potential of bilateral-bipolar GVS coupled to aircraft roll in a fixed-base simulator to mimic vestibular spatial disorientation illusions, specifically the “post-roll illusion” observed during flight.

METHODS: There were 14 nonpilot subjects exposed to roll stimuli in a flight simulator operating in a fixed-base mode. GVS was delivered via carbon rubber electrodes on the mastoid processes. The electrical stimulus was driven by the high-pass filtered aircraft roll rate to mimic the semicircular canals’ physiological response. The post-roll test scenarios excluded outside visual cues or instruments and required subjects to actively maintain a constant bank angle after an abrupt stop following a passive prolonged roll maneuver. The anticipated outcome was an overshot in roll elicited by the GVS signal.

RESULTS: The responses across subjects showed large variability, with less than a third aligning with the post-roll illusion. Subjective ratings suggest that the high-pass filtered GVS stimuli were mild and did not induce a clear sense of roll direction. However, uncontrolled head movements during stimulation might have obscured the intended effects of GVS-evoked illusory head movements.

CONCLUSION: The mild and transient GVS stimuli used in this study, together with the uncontrolled head movements, did not convincingly mimic the post-roll illusion.

Houben MMJ, Stuldreher IV, Forbes PA, Groen EL. Using galvanic vestibular stimulation to induce post-roll illusion in a fixed-base flight simulator. Aerosp Med Hum Perform. 2024; 95(2):84–92.

INTRODUCTION: Preselection of pilot candidates in the military is critical and determines the quality of subsequent selection. The Aero Medical Institute in Belgrade uses the following centrifuge endpoints: peripheral vision loss, heart rate above 180 bpm, cardiac arrhythmias, and G-induced loss of consciousness to assess relaxed +G_z tolerance. The aim of this study was to evaluate heart rate variability (HRV) associated with cardiovascular adaptability to different types of stress as a predictor of +G_z tolerance.

METHODS: Thirty-six candidates were exposed to centrifuge runs, consisting of the following +G_z-acceleration phases: a 2-G plateau followed by an increase to 5.5 G, a decrease to 2 G, and ending with a plateau. Time-domain HRV indices were calculated for candidates, for a 60-s 2-G plateau, and for the entire test. The correlation was made between the groups that did (Group 1) and did not meet the criteria (Group 2).

RESULTS: The results show significantly lower values in all time domain HRV indices, namely standard deviation of the normal-to-normal interval (SDNN) and root mean square of successive differences, in Group 2. Mean SDNN values were 45.98 ± 24.80 ms (2-G plateau) and 109.99 ± 39.64 ms (entire test) in Group 1, while the SDNN were 22.99 ± 12.04 ms and 69.70 ± 33.45 ms in Group 2. Root mean square of successive differences was higher in Group 1 for the 2-G plateau and for the entire test.

DISCUSSION: The results suggest that HRV is positively correlated with +G_z-tolerance and can be used as an additional selection tool for military aircrew.

Bacevic N, Ninkovic M, Drvendzija M, Vidakovic J, Bacevic M, Stepanic P. Heart rate variability as a predictor of +G_z tolerance during the high-G selective test. Aerosp Med Hum Perform. 2024; 95(2):93–100.

INTRODUCTION: Migraine is a common condition that can carry considerable risk to aeromedical duties. Because randomized controlled trials are not an appropriate method to evaluate flight safety risk for medical conditions that may cause subtle or sudden incapacitation, the determination of fitness-to-fly must be based on risk assessments informed by extrapolated evidence. Therefore, we conducted a review of current literature to provide background information to inform the aeromedical risk assessment of migraine using a risk matrix approach.

METHODS: We identified studies on topics pertinent to conducting an aeromedical risk assessment of migraine. We generated an overview of the literature synthesizing the findings of articles retrieved from searches of Scopus, Ovid, PubMed, and the Cochrane Library published in English from all years, in both general and aircrew populations. International headache and neurology guidelines, as well as headache policies from the U.S. Air Force, were also reviewed.

RESULTS: This review includes information on the following topics relevant to conducting an evidence-based risk assessment of migraine: diagnosis, prevalence, incidence, natural course, clinical presentation, triggers, comorbidities, neuroimaging, implications of family history, and efficacy of pharmacological and nonpharmacological therapies.

DISCUSSION: This review summarizes current literature on migraine for use in a risk matrix approach to the aeromedical assessment of migraine in prospective and current aircrew. Awareness of the most current epidemiological data related to a variety of migraine parameters facilitates an evidence-based risk assessment of migraine in aircrew and requires iterative updates as new information becomes available.

Mainland RL, Skinner CR, Saary J. Aeromedical risk of migraine. Aerosp Med Hum Perform. 2024; 95(2):101–112.

INTRODUCTION: Current guidelines regarding the time to flight after an acquired pneumothorax have been generally accepted and in place for years. The majority of these typically advise holding off on air travel until the complete resolution of a pneumothorax. Over the past decade, however, there has been an increase in the amount of literature focusing on this subject and challenging this well-held dogma. A review of these studies has shown that recent evidence contradicts the historical guidelines that many practitioners follow about the safety and timing of flying after pneumothoraces. Based on these studies, air travel with a known pneumothorax is likely safe and can be undertaken much sooner than current guidelines advise.

Kashtan HW, Schulte SN, Connelly KS. Pneumothorax and timing to safe air travel. Aerosp Med Hum Perform. 2024; 95(2):113–117.

INTRODUCTION: Aircraft are manufactured according to design parameters that must account for the size and physical characteristics of the pilot. While cockpit dimensions, seats, restraints, and related components do not change substantially over the airframe lifecycle, it is conceivable that the occupant may, even if initially well-suited. This investigation focused on longitudinal body mass index (BMI) changes within a cohort of British Army Air Corps pilots.

METHODS: The study was a retrospective examination of electronic medical record data to assess longitudinal change within a representative cohort of Army pilots. Voluntary subjects were assigned unique subject numbers matched with individual electronic medical record data. Subject’s age, service length, height, weight, and BMI were extracted from routine historical aviation medical exams.

RESULTS: Among 106 British Army Air Corps pilots, the mean age was 35.3 yr (SD = 7.4) with average length of service as a pilot of 9.0 yr (SD = 5.2). Within the observed cohort, the mean change in individual weight over time was an increase of 4.6 kg (SD = 7.3). Height remained relatively stable with a mean increase of 0.6 cm (SD = 1.9). Given the increase in weight, BMI was noted to increase longitudinally with a mean of 1.3 kg · m⁻² (SD = 2.4).

DISCUSSION: British Army pilots experience increases in BMI over time much like the general population. Results of this study serve to inform future policy related to the body composition of aviation applicants, the retention of previously qualified pilots, and the safety concerns of crashworthiness design specifications.

Porter WD, Wilde GD, Jeffery NP, Walters PL, Eke AJ, Bushby AJR, Adams MS, Gaydos SJ. Longitudinal changes in the body mass index of British Army pilots. Aerosp Med Hum Perform. 2024; 95(2):118–122.

INTRODUCTION: Human access to space is expanding rapidly in the commercial environment, with various private companies offering commercial flights to spaceflight participants (SFPs). SFPs are more likely than career astronauts to have medical conditions novel to spaceflight and may not have undergone as rigorous a medical screening process as that used for career astronauts, representing new and unstudied risks in the spaceflight environment. We report participation of a subject with recent median sternotomy for aortic valve replacement and atrial septal defect closure in centrifuge-simulated dynamic phases of orbital and suborbital spaceflight.

CASE REPORT: A 40-yr-old man with a history of congenital bicuspid aortic valve and atrial septal defect with successful repair 8 mo prior participated in an ongoing human centrifuge research study. The subject had the opportunity to participate in up to five centrifuge runs in an 8-h period, with profiles simulating commercial spaceflight. Maximum exposures included +4.0 G_z, +4.5 G_x, 6.1 G resultant, and maximum onset rate < 0.5 G_z · s⁻¹ and +1 G_x · s⁻¹. Physiological data acquisition included hemodynamics, electrocardiogram, neurovestibular exams, and postrun questionnaires covering motion sickness, disorientation, and similar. The subject tolerated the physiological aspects of hypergravity well, noting progressive sternal pain with increasing +G_x, ultimately leading him to opt out of the final profile.

DISCUSSION: Postcardiothoracic surgery risks to SFPs are largely unknown, especially within 12 mo of a significant surgical procedure. This case provides an approach for risk stratification, preparticipation evaluation, and medical management of a postsurgical patient with significant cardiac history in spaceflight and analog environments.

Fernandez WL, Blue RS, Harrison MF, Powers W, Shah R, Auñón-Chancellor S. Centrifuge-simulated spaceflight after aortic valve replacement and atrial septal defect repair. Aerosp Med Hum Perform. 2024; 95(2):123–131.