INTRODUCTION: Consistent blood biomarkers of hypobaric (altitude) decompression stress remain elusive. Recent laboratory investigation of decompression sickness risk at 25,000 ft (7620 m) enabled evaluation of early pathophysiological responses to exertional decompression stress.METHODS: In this study, 15 healthy men, aged 20–50 yr, undertook 2 consecutive (same-day) ascents to 25,000 ft (7620 m) for 60 and 90 min, breathing 100% oxygen, each following 1 h of prior denitrogenation. Venous blood was sampled at baseline (T0), immediately after the second ascent (T8), and next morning (T24). Analyses encompassed whole blood hematology, endothelial microparticles, and soluble markers of cytokine response, endothelial function, inflammation, coagulopathy, oxidative stress, and brain insult, plus cortisol and creatine kinase.RESULTS: Acute hematological effects on neutrophils (mean 72% increase), eosinophils (40% decrease), monocytes (37% increase), and platelets (7% increase) normalized by T24. Consistent elevation (mean five-fold) of the cytokine interleukin-6 (IL-6) at T8 was proinflammatory and associated with venous gas emboli (microbubble) load. Levels of C-reactive protein and complement peptide C5a were persistently elevated at T24, the former by 100% over baseline. Additionally, glial fibrillary acidic protein, a sensitive marker of traumatic brain injury, increased by a mean 10% at T24.CONCLUSIONS: This complex composite environmental stress, comprising the triad of hyperoxia, decompression, and moderate exertion at altitude, provoked pathophysiological changes consistent with an IL-6 cytokine-mediated inflammatory response. Multiple persistent biomarker disturbances at T24 imply incomplete recovery the day after exposure. The elevation of glial fibrillary acidic protein similarly implies incomplete resolution following recent neurological insult.Connolly DM, Madden LA, Edwards VC, D’Oyly TJ, Harridge SDR, Smith TG, Lee VM. Early human pathophysiological responses to exertional hypobaric decompression stress. Aerosp Med Hum Perform. 2023; 94(10):738–749.

INTRODUCTION: Fatigue is a major contributor to aviation accidents. Sufficient sleep may be difficult to achieve under operational conditions in military aviation. Countermeasures include caffeine, however, studies evaluating its effects often do not represent daily practice with regular caffeine consumption. This study aims to establish the effect of caffeine on psychomotor performance in a realistic scenario (i.e., after a limited period of extended wakefulness).METHODS: This randomized, double-blind, crossover, placebo-controlled trial included 30 aeromedically fit subjects. On trial days, subjects followed their normal routine till 17:00, after which caffeine intake was stopped. At midnight, subjects were given 300 mg of caffeine or placebo and performed the Psychomotor Vigilance Test, Vigilance and Tracking Test, and the Stanford Sleepiness Scale hourly up to 04:00 and again at 06:00 and 08:00. Four blood samples were collected. Statistical analyses included repeated-measures ANOVA or Friedman tests, marginal models, and Wilcoxon Signed Rank tests.RESULTS: Median time awake at midnight was 17 h (IQR 16.5–17.5 h). Performance decreased significantly less during the night in the caffeine condition versus placebo. Neither habitual intake nor daytime caffeine consumption affected this. No statistically significant correlation was identified between blood concentrations of caffeine and performance.DISCUSSION: A single dose of 300 mg of caffeine has beneficial effects on performance during the night in a realistic scenario for military aviation. Daytime caffeine consumption does not affect the effects of caffeine at night. These findings could be relevant for all industries in which optimal performance is required during nighttime after a limited period of extended wakefulness.Wingelaar-Jagt YQ, Wingelaar TT, de Vrijer L, Riedel WJ, Ramaekers JG. Daily caffeine intake and the effect of caffeine on pilots’ performance after extended wakefulness. Aerosp Med Hum Perform. 2023; 94(10):750–760.

INTRODUCTION: The chronic effects of regular exposure to high acceleration levels (G-force) on the neuro-cardiovascular system are unclear. We compared the mean arterial pressure (MAP) and cardiac autonomic modulation between nonpilots (NP) vs. military fighter (FP) and transport (TP) pilots. Additionally, we correlated the cardiac autonomic indices with the cardiorespiratory fitness and flight experience of FP.METHODS: A total of 21 FP, 8 TP, and 20 NP performed a tilt test (TT), during which beat-to-beat blood pressure and heart rate were recorded.RESULTS: No difference was detected between groups for changes in MAP and heart rate variability indices during the TT. However, the analysis of areas under the curves showed a greater increase in MAP in FP vs. TP and NP. Conversely, there was a greater decrease in indices reflecting vagal modulation in TP vs. FP and NP (rMSSD, pNN50, and SDNN), and a greater increase in heart rate and sympathovagal balance in TP vs. other groups (LF/HF). The maximal oxygen uptake was strongly correlated with the vagal reserve in FP (r = −0.74). Moreover, the total flying hours of FP were positively correlated with resting HFnu (r = 0.47) and inversely correlated with resting LFnu (r = −0.55) and LF/HF (r = −0.46).CONCLUSION: FP had a higher pressor response to TT than TP and NP. Vagal withdrawal and sympathovagal increase induced by TT in FP were similar vs. NP and attenuated vs. TP. Greater cardiorespiratory fitness and accumulated flying hours in FP seemed to favor lower sympathetic and greater vagal modulation at rest.dos Santos Rangel MV, de Sá GB, Farinatti P, Borges JP. Neuro-cardiovascular responses to sympathetic stimulation in fighter pilots. Aerosp Med Hum Perform. 2023; 94(10):761–769.

INTRODUCTION: Adding noise to a system to improve a weak signal’s detectability is known as stochastic resonance (SR). SR has been shown to improve sensory perception and cognitive performance in certain individuals, but it is unknown whether this performance improvement can translate to meaningful macrocognitive enhancements in performance for complex, operational tasks.OBJECTIVE: We investigated human operator performance in a lunar landing simulation while applying auditory white noise and/or noisy galvanic vestibular stimulation.METHODS: We measured performance (N = 16 subjects) while completing simulation trials in our Aerospace Research Simulator. Trials were completed with and without the influence of auditory white noise, noisy galvanic vestibular stimulation, and both simultaneously in a multimodal fashion. Performance was observed holistically and across subdimensions of the task, which included flight skill and perception. Subjective mental workload was collected after completing four trials in each treatment.RESULTS: We did not find broad operator improvement under the influence of noise, but a significant interaction was identified between subject and noise treatment, indicating that some subjects were impacted by additive noise. We also found significant interactions between subject and noise treatment in performance subdimensions of flight skill and perception. We found no significant main effects on mental workload.CONCLUSIONS: This study investigated the utility of using additive sensory noise to induce SR for complex tasks. While SR has been shown to improve aspects of performance, our results suggest additive noise does not yield operational performance changes for a broad population, but specific individuals may be affected.Sherman SO, Shen Y-Y, Gutierrez-Mendoza D, Schlittenhart M, Watson C, Clark TK, Anderson AP. Additive sensory noise effects on operator performance in a lunar landing simulation. Aerosp Med Hum Perform. 2023; 94(10):770–779.

INTRODUCTION: +G_z tolerance is an important aspect for the success of fighter aircrew as it reflects the ability of the neuro-cardiovascular response to compensate and prevent adverse manifestations such as gray-out, black-out, and G-induced loss of consciousness (G-LOC) under high-G stress.METHODS: The data for aircrew taking the Operational Training in Aerospace Medicine for Fighters course at the Institute of Aerospace Medicine Indian Air Force (IAF) from January 2017 to December 2020 were analyzed to assess the effectiveness of the existing training goal to recommend a G-tolerance standard for fighter aircrew.RESULTS: During the study period, 334 aircrew took the Operational Training in Aerospace Medicine for Fighter course. Only three aircrew failed to achieve the training goal of the course (failure rate <1%). There was a significant difference in the relaxed gradual onset rate tolerance of aircrew experiencing G-LOC and not experiencing G-LOC during the training. The odds of experiencing G-LOC at 9 G after clearing the 7-G and 8-G profiles were 4.4 and 4.7, respectively.DISCUSSION: It is generally accepted that aircrew having higher G tolerance have less chance of G-LOC in the air. There is a need to have an operational definition of G tolerance for fighter aircrew that aligns with the operational training goal of the organization. The G tolerance of IAF aircrew is as per the institutional definition of the IAF Institute of Aerospace Medicine. The high-G training has stood the test of time and has served well for the IAF.Kumar A. +Gz standards for the Indian Air Force. Aerosp Med Hum Perform. 2023; 94(10):780–785.

INTRODUCTION: The advancement of human spaceflight has made urgent the need to develop medical imaging technology to ensure a high level of in-flight care. To date, only ultrasound has been used in spaceflight. Radiography has multiple advantages over ultrasound, including lower operator dependence, more rapid acquisition, typically higher spatial resolution, and characterization of tissue with acoustic impedance precluding ultrasound. This proof-of-concept work demonstrates for the first time the feasibility of performing human radiographs in microgravity.METHODS: Radiographs of a phantom and human subject’s hand, knee, chest, cervical spine, and pelvis were obtained aboard a parabolic flight in microgravity and simulated lunar gravity with various subject and operator positions. Control radiographs were acquired with the same system on the ground. These radiographs were performed with a Food and Drug Administration-approved ultra-portable, wireless, battery-powered, digital x-ray system.RESULTS: The radiographs of the phantom acquired in reduced gravity were qualitatively and quantitatively compared to the ground controls and found to exhibit similar diagnostic adequacy. There was no statistically significant difference in contrast resolution or spatial resolution with a spatial resolution across all imaging environments up to the Nyquist frequency of 3.6 line-pairs/mm and an average contrast-to-noise ratio of 2.44.DISCUSSION: As mass, power, and volume limitations lessen over the coming decades and the miniaturization of imaging equipment continues, in-flight implementation of nonsonographic modalities will become practical. Given the demonstrated ease of use and satisfactory image quality, portable radiography is ready to be the new frontier of space medical imaging.Lerner D, Pohlen M, Wang A, Walter J, Cairnie M, Gifford S. X-ray imaging in the simulated microgravity environment of parabolic flight. Aerosp Med Hum Perform. 2023; 94(10):786–791.

BACKGROUND: Many current cell phone (mobile phone, smartphone) batteries are lithium-ion. These batteries can overheat and catch fire under certain conditions. If it happens during a flight or air activity, this might compromise aviation safety. We report a case of a man whose phone caught fire during a parachute jump.CASE REPORT: The individual, a member of Police Special Forces, is required to regularly perform parachute jumps. During the incident flight, the man had a cell phone in a pocket that ignited during the jump. He was able to land and then extract the phone with burns requiring acute medical care and later a skin graft.DISCUSSION: This is a cautionary tale of lithium-ion batteries in flight. Many other situations could also occur with these batteries. There is little medical documentation of the risk of fire with lithium-ion batteries causing injuries during flight operations. To reduce the risk of fire, the devices should be powered down and phones should not be worn directly touching the skin. Damaged devices are more prone to overheating.des Robert V, Saint-Jean L, Corcostegui S-P, Romary E, and Derkenne C. Burnt by his cellphone during a parachute jump. Aerosp Med Hum Perform. 2023; 94(10):792–795.