INTRODUCTION: The pathophysiological basis of neurological decompression sickness and the association between cerebral subcortical white matter (WM) change and nonhypoxic hypobaria remain poorly understood. Recent study of altitude decompression sickness risk evaluated acute WM responses to intensive hypobaric exposure using brain magnetic resonance imaging.

METHODS: Six healthy men (20 to 50 yr) completed 6 h of hyperoxic hypobaria during three same-day altitude chamber decompressions to pressure altitudes ≥ 22,000 ft (6706 m). Research magnetic resonance imaging sequences, conducted on the days preceding and following decompression, evaluated subcortical WM integrity, cerebral blood flow, neuronal integrity (fractional anisotropy), and neurometabolite concentrations.

RESULTS: No subcortical lesions were evident on diffusion weighted imaging and WM fractional anisotropy was unaffected. Mean WM blood flow was upregulated by 20% to over 25 mL · 100 g⁻¹ · min⁻¹. Gray matter flow was unchanged. There were no changes in gray matter or cerebellar neurometabolites. In parietal subcortical WM, levels of γ-aminobutyric acid (GABA) fell from (mean ± SD) 1.68 ± 0.2 to 1.35 ± 0.3 institutional units while glutathione (GSH) fell from 1.71 ± 0.4 to 1.25 ± 0.3 institutional units. Lactate increased postexposure in five subjects.

CONCLUSIONS: Postexposure decrements in GABA and GSH imply WM insult with loss of neuroprotection and oxidative stress. An association between decrements in GABA and GSH support a common origin, while GSH decrements also correlate with WM blood flow responses. WM lactate increments are prone to error but suggest dysregulation of subcortical microvascular flow. WM neurometabolite and blood flow indices did not normalize by 24 h postexposure.

Connolly D, Davagnanam I, Wylezinska-Arridge M, Mallon D, Wastling S, Lee VM. Brain magnetic resonance imaging responses to nonhypoxic hypobaric decompression. Aerosp Med Hum Perform. 2024; 95(10):733–740.

INTRODUCTION: Habituation to motion has therapeutic applications for motion sickness desensitization and rehabilitation of patients with vestibular disease. Less attention has been devoted to the opposite process: sensitization.

METHODS: Subjects (N = 50) were randomly allocated to four sequences: Baseline visual stimulus; then 15 min of time gap; cross-coupled motion (C-C) or a Control condition; then a time gap of 15 min or 2 h; then a retest visual stimulus. Motion exposures were for 10 min or until moderate nausea, whichever was sooner. The visual stimulus was a scene rotating in yaw at 0.2 Hz with superimposed "wobble". C-C was whole-body rotation on a turntable with eight 45° head tilts during each 30-s period. Control was head tilt without rotation. Rotational velocity was incremented in staircase steps of 3° · s⁻¹ every 30 s.

RESULTS: Groups were equivalent for Total Motion Sickness Symptom scores elicited by the first visual stimulus (combined: mean ± SD 10.8 ± 8.4). C-C produced greater Total Symptoms (20.3 ± 6.8) than Control (3.1 ± 3.7). Subjects recovered subjectively from C-C before retest of visual stimulus. For the retest visual stimulus, Total Symptoms were higher following C-C (15.1 ± 9.0) than following Control (8.3 ± 7.1) for both the 15 min and 2 h retests. Sickness ratings (SR) mirrored these effects of C-C.

DISCUSSION: C-C motion sensitized subsequent responses to visual stimulation up to 2 h later. Sensitization of visual stimulation crossed modalities and appeared subconscious since it occurred despite subjective recovery from C-C. For some individuals, a previously relatively innocuous visual stimulus became nauseogenic on retest. The results have implications for the use of visual technologies within hours of exposure to provocative motion.

Golding JF, Alund D, Gresty MA, Flynn MB. Sensitization of visually induced motion sickness by prior provocative physical motion. Aerosp Med Hum Perform. 2024; 95(10):741–748.

INTRODUCTION: One of the most important factors affecting visual performance during vision aided by night vision goggles (NVGs) is image quality, which depends mainly on the image-intensifier technology used. Although NVGs with green image color (P43 phosphor) are only accepted in military aviation, white image (P45 phosphor) seems to be equally well-regarded by aviators. The aim of our study was to determine if the experience of using NVGs with the green screen affects image preference for that color, and if the screen color preference is related to luminance level.

METHODS: Subjects (127 military pilots, 26–56 yr, M = 37.2; 62 pilots with flight experience with NVG use) were asked to observe a model terrain board at two different luminance levels (corresponding roughly to ambient conditions during starlight and one-half moonlight) while using two types of NVGs (green P43 and white P45 phosphor screens). The pilots were asked to answer a questionnaire about their preference for NVG display color.

RESULTS: The findings showed a significant difference between screen color preference and pilots’ experience with the green-phosphor-based NVGs (43.5% vs. 23.1% for white screens). However, there was no relationship between screen color preference and luminance level.

DISCUSSION: Previous NVG experience seems to play an important role in shaping a user’s individual preference for a certain phosphor screen color, although green and white phosphor screens both provide satisfactory visibility. Nevertheless, when deciding, it is advisable to experiment with both colors and select the one that suits the user’s preferences and needs.

Lewkowicz R, Dereń-Szumełda J. Phosphor screens color preferences depending on night vision experience and luminance level. Aerosp Med Hum Perform. 2024; 95(10):749–757.

INTRODUCTION: Hypoxia training is mandatory for military pilots, but variability in hypoxia symptoms challenges the training. In a previous study we showed that 64% of pilots recognized hypoxia faster in their second normobaric hypoxia session conducted 2.4 yr after the first. Our aim here was to evaluate whether a third session conducted 5.0 yr after the first would provide further benefit.

METHODS: This study was conducted under normobaric conditions in a tactical F/A-18C Hornet simulator in three sessions in which the pilots performed visual identification missions and breathed 21% oxygen in nitrogen. The breathing gas was changed to a hypoxic mixture containing either 8%, 7%, or 6% oxygen in nitrogen without the pilot’s knowledge. Data were collected from 102 military pilots. The primary outcome was the time taken for initial identification of hypoxia symptoms.

RESULTS: Hypoxia symptoms were recognized on average in the first session in 8% oxygen in 100 s, 7% oxygen in 90 s, and 6% oxygen in 78 s; in the second in 87 s, 80 s, and 71 s, respectively; and in the third in 79 s, 67 s, and 64 s, respectively. In 2 sessions 20 pilots and in each 3 training sessions 3 pilots had slow recognition times.

DISCUSSION: Hypoxia symptom recognition improved the further the repeated normobaric hypoxia training went. More emphasis should be put on the 23% group of slow hypoxia symptom recognizers and more customized hypoxia training for them should be offered.

Leinonen AM, Varis NO, Kokki HJ, Leino TK. Normobaric hypoxia symptom recognition in three training sessions. Aerosp Med Hum Perform. 2024; 95(10):758–764.

INTRODUCTION: The global rise in aesthetic surgery has led to an increase in aesthetic medical tourism (AMT). As patients pursue surgical interventions abroad, concerns about the elevated complication rates in AMT have emerged. This study explores the complexities of AMT, emphasizing the intersection of plastic surgery and aerospace medicine, to elucidate the incidence of complications, identify associated variables, and introduce aeromedical considerations to proactively enhance patient safety.

METHODS: A comprehensive retrospective observational cohort study was conducted using data spanning 2004 to 2023 from a private plastic surgery practice in Bogota, Colombia. The study included 3367 patients, of whom 26% were international patients. Sociodemographic and clinical variables, flight details, and surgical complications were analyzed. Statistical analyses involved descriptive statistics, odds ratios, and multiple regression analyses.

RESULTS: Of the 865 AMT patients, 75 exhibited complications. Infection and wound dehiscence were the most prevalent; no severe complications or mortality was reported. The study revealed that AMT patients have a higher risk of complications compared to those locally treated (adjusted odds ratio = 4.6; 95% confidence interval = 2.6–8.2). Flight time exceeding 4 h was a factor associated with nonaesthetic complications.

DISCUSSION: This study reveals that AMT is linked to a higher risk of nonaesthetic complications, with flight duration being a significant contributing factor. Despite the increased risk, complication rates for AMT patients did not surpass thresholds reported in the literature; this may be attributed to the safety protocols implemented. Aeromedical considerations played a crucial role in mitigating physiological stress associated with air travel.

Hoyos AE, Ramirez B, Benavides J, Perez Pachon ME, Varela A. Aeromedical considerations for patient safety in aesthetic medical tourism. Aerosp Med Hum Perform. 2024; 95(10):765–770.

INTRODUCTION: Acute calculous cholecystitis is a common surgical emergency and cholecystectomy is the gold-standard treatment. However, alternative drainage modalities such as percutaneous cholecystostomy tube (PCT) placement have been proposed for poor surgical candidates or in remote environments, such as space. We reviewed the literature to assess the theoretical utility of PCT to treat acute cholecystitis during long-duration spaceflight or on the Moon or Mars.

METHODS: A systematic review of 16 peer-reviewed articles published since 2018 was completed to describe the terrestrial efficacy of PCT placement for acute calculous cholecystitis.

RESULTS: The mean initial clinical success rate after PCT was 89.9% (range 82.2–100.0%). Duration of indwelling PCT ranged from median 6 to 58 d. Mean rate of recurrent cholecystitis was 15.8% (range 5.0–36.4%). A mean 35.6% of patients (range 18.0–61.0%) required interval cholecystectomy. Mean 30-d mortality was 9.6% (range 5.8–14.0%). A mean 18.6% of patients (range 7.2–30.0%) required repeat percutaneous intervention due to PCT placement complications.

DISCUSSION: While PCT achieves high rates of early resolution of cholecystitis, the long-term outcomes after PCT are relatively poor, with risk of recurrent cholecystitis, need for cholecystectomy, and frequent postprocedural complications requiring repeat procedural interventions. In cislunar space, the return to Earth for cholecystectomy following PCT may be achieved, eliminating some of these concerns. However, with long-duration space travel such as a mission to Mars, PCT is likely inadequate for the long-term treatment of cholecystitis. Prophylactic cholecystectomy, developing surgical capabilities in space, or preflight screening ultrasound for cholelithiasis should be seriously considered for long-duration spaceflight.

Lazow SP, Siu M, Brown L, Kamine TH. Percutaneous cholecystostomy for acute cholecystitis during spaceflight. Aerosp Med Hum Perform. 2024; 95(10):771–776.

INTRODUCTION: With increased access to commercial spaceflight and space tourism, plus a push for longer duration spaceflights, it is especially important to understand the impact of spaceflight on musculoskeletal health. Upper extremity injuries are the most common musculoskeletal injuries in spaceflight. It is, therefore, vital to determine the changes to the upper extremities during spaceflight. The purpose of this study was to examine the state of knowledge on the impact of spaceflight on upper extremity orthopedic health, and to identify knowledge gaps and future areas of research.

METHODS: A literature review was performed and studies and reports that amassed data on shoulder, elbow, wrist, and hand health were included.

RESULTS: Spaceflight decreases bone mineral density in the upper extremities and increases risk of fracture, especially upon return to gravitational environments. Spaceflight does not uniformly affect all muscles; in the shoulder, the various muscles crossing the joint appear to be variably affected: the deltoid experiences a greater degree of atrophy than the rotator cuff muscles. Spaceflight additionally affects the peripheral nervous system, with astronauts experiencing hand numbness and loss of manual dexterity but cause of these symptoms is undetermined. Spacesuits have also been implicated in causing upper extremity injury, especially while training for or performing extravehicular activities.

DISCUSSION: While upper extremity orthopedic health in spaceflight is incompletely understood, known adaptations increase risk for weakening and injury. Existing research provides valuable information for best practices, but there is still much to be discovered to optimize upper extremity health in spaceflight.

Fiedler B, Jami M, Rakauskas T, Ahmed AS. Impact of spaceflight on upper extremity orthopedic health. Aerosp Med Hum Perform. 2024; 95(10):777–783.

BACKGROUND: Stroke in young patients is frequently associated with a patent foramen ovale (PFO). Controversy exists over whether the PFO is a cause, a risk factor, or an incidental finding. Estimating the individualized risk of stroke recurrence has been difficult to ascertain. This has implications for aeromedical certification for pilots following stroke recovery.

CASE REPORT: A 28-yr-old male flight instructor presented with sudden onset unilateral facial paresthesia, hand weakness, and blurred vision, accompanied by gradual onset bilateral headache. While the cranial symptoms resolved, left hand weakness persisted for 3 d. MRI revealed two punctate ischemic foci in the right precentral gyrus and superior parietal lobe. A transesophageal echocardiogram revealed a PFO with a small bidirectional shunt. His cardiologist and neurologist advised the PFO was unlikely to have caused his stroke and estimated an annual recurrence rate of < 1.8%. He was treated medically and declined PFO closure. He was able to return to flying light-sport aircraft. However, an enduring copilot restriction for general aviation activities was placed on his Class 1 and 2 medical certificates.

DISCUSSION: This case highlights the difficulty in determining individualized recurrence risks for pilots recovering from a stroke associated with a PFO. While medical treatment does reduce the risk of recurrence, PFO closure provides marginal additional benefit in certain patients with a risk of side effects. Contemporary evidence-based risk scoring systems combined with echocardiography findings may be used together to better risk stratify patients and suitability for medical aviation recertification.

Rengel AC, Gericke C. Embolic ischemic cortical stroke in a young flight instructor with a small patent foramen ovale. Aerosp Med Hum Perform. 2024; 95(10):784–787.

INTRODUCTION: Strong neck muscles may decrease the risk of flight-induced neck pain and possible disability among fast jet pilots. The purpose of this study was to examine the intra- and interrater reliability of a commercial force gauge attached to a pilot’s helmet for measuring isometric force production of the neck muscles.

METHODS: A total of 41 subjects performed maximal isometric cervical flexion, extension, and lateral flexion in two measurement sessions for intrarater reliability, and 31 of these subjects participated in a third session for measuring interrater reliability. Delayed muscle soreness and neck pain were assessed using the Visual Analog Scale before and after each measurement session. The intraclass correlation coefficient (ICC) was used to compare values between the test and retest assessments.

RESULTS: The overall interrater reliability was good (ICC 0.79–0.90), whereas the intrarater reliability varied from moderate to good (ICC 0.58–0.84). In both intra- and interrater reliability, the flexion test had good (ICC 0.84–0.89) reliability, while the lateral flexion test results had moderate to good (ICC 0.73–0.90) reliability. The extension test had the lowest reliability in both intra- (ICC 0.58) and interrater (ICC 0.79) tests. The average visual analog scale score (from 1–100 scale) prior to the second measurement session was 16 ± 18 in delayed muscle soreness and 0 ± 0 in neck pain.

DISCUSSION: The present study demonstrated that the helmet-attached force gauge is a reliable, safe, and clinically applicable method to evaluate isometric neck strength in the flexion and lateral flexion directions.

Honkanen T, Mattila V, Kinnunen O, Janhunen M, Sovelius R, Vaara JP, Kyröläinen H. Reliability of a flight helmet-attached force gauge in measuring isometric neck muscle strength. Aerosp Med Hum Perform. 2024; 95(10):788–793.

INTRODUCTION: Emergency medical kits (EMK) are provided to clinicians who volunteer on commercial aircraft during a medical emergency. The contents of the EMKs are mandated by the Federal Aviation Administration in the United States and, internationally, by the International Civil Aviation Organization and the country of airline origin. The mandatory contents of the kits have not been updated by the Federal Aviation Administration since 2006, and the EMKs continue to lack key equipment such as automated blood pressure cuffs, glucometers, pulse oximeters, and epinephrine autoinjectors. Of further concern is a lack of standardized and centralized reporting for in-flight medical events that, if it existed, could better inform the contents of the kits. This commentary is intended to advocate for an update to the EMKs in the United States given the authors’ experiences with in-flight medical events.

Rajagopal AB, Pissaris A, Clark K, Merrill A, Glatter R, Ho A, Towle DC, Yanuck J, Lahham S, Ulin L, Fischetti C, Apisa L. Recommendations for updates to emergency medical kits for commercial aviation. Aerosp Med Hum Perform. 2024; 95(10):794–796.

INTRODUCTION: From the very beginning of America’s human spaceflight program, space medicine has been at the forefront. There has been a variety of diverse individuals, over six decades, whose contributions helped shape what space medicine is within NASA today.

METHODS: An extensive review of historical documents (including reports, manuscripts, advisory committee reports, and oral histories of key individuals) related to space medicine, aerospace medicine, and life sciences at NASA Headquarters was performed.

RESULTS: Early in NASA’s history, oral histories from individuals in key leadership positions were obtained. In addition, repeated searches of the archives provided a plethora of material on space medicine and life sciences from the first two decades or so, but it is somewhat sparse over the most recent four decades. Each of these sources helped develop a historical narrative of those key individuals who were in senior leadership positions at NASA Headquarters beginning in 1958 through the present time.

DISCUSSION: A review of the archived material tells a compelling story of how and why space medicine developed in the way it did at the agency level. The inspiration and the individual personalities, concomitant with the early influence from the U.S. Air Force, laid the groundwork for this discipline as it relates to human spaceflight.

Doarn CR. Evolution of space medicine at NASA. Aerosp Med Hum Perform. 2024; 95(10):797–805.