INTRODUCTION: Transcranial direct current stimulation (tDCS) is a promising method for maintaining cognitive performance. Anticipated changes in rotary-wing aircraft are expected to alter aviator performance.

METHODS: A single-blind, randomized, sham-controlled study evaluated effects of 2-mA anodal tDCS to the right posterior parietal cortex on aviator performance within a Black Hawk simulator. A mixed design with one between-subjects factor was assessed: stimulation prior to flight (20 constant min) and during flight (two timepoints for 10 min each). The within-subjects factor included active vs. sham stimulation. Randomly assigned to each stimulation group were 22 aviators. Aircraft state metrics derived from the simulator were used to evaluate performance. Subjects completed two flights (active stimulation and sham stimulation) with an in-flight emergency introduced at the end to assess whether the timing of tDCS application (prior or during flight) affected the ability to maintain attention and respond to an unexpected event.

RESULTS: Results found active stimulation during flight produced statistically significant improvements in performance during the approach following the in-flight emergency. Subjects maintained a more precise approach path with glideslope values closer to zero (M = 0.05) compared to the prior-to-flight group (M = 0.15). The same was found for localizer values (during flight, M = 0.07; prior to flight, M = 0.17). There were no statistically significant differences between groups on secondary outcome measures.

DISCUSSION: These findings suggest stimulation during flight may assist in maintaining cognitive resources necessary to respond to an unexpected in-flight emergency. Moreover, blinding efficacy was supported with 32% of subjects correctly guessing when active stimulation was being delivered (52% correctly guessed the sham condition).

Feltman KA, Kelley AM. Transcranial direct current stimulation and aviator performance during simulated flight. Aerosp Med Hum Perform. 2024; 95(1):5–15.

BACKGROUND: In this study, we investigated the impact of a loss of horizon due to atmospheric conditions on flight performance and workload of helicopter pilots during a low-altitude, dynamic flight task in windy conditions at sea. We also examined the potential benefits of a helmet-mounted display (HMD) for this specific task.

METHODS: In a fixed-based helicopter simulator, 16 military helicopter pilots were asked to follow a maneuvering go-fast vessel in a good visual environment (GVE) and in a degraded visual environment (DVE). DVE was simulated by fog, obscuring the horizon and reducing contrast. Both visual conditions were performed once with and once without an HMD, which was simulated by projecting head-slaved symbology in the outside visuals. Objective measures included flight performance, control inputs, gaze direction, and relative positioning. Subjective measures included self-ratings on performance, situation awareness, and workload.

RESULTS: The results showed that in DVE the pilots perceived higher workload and were flying closer to the go-fast vessel than in GVE. Consequently, they responded with larger control inputs to maneuvers of the vessel. The availability of an HMD hardly improved flight performance but did allow the pilots to focus their attention more outside, significantly improving their situation awareness and reducing workload. These benefits were found in DVE as well as GVE conditions.

DISCUSSION: DVE negatively affects workload and flight performance of helicopter pilots in a dynamic, low-altitude following task. An HMD can help improve situation awareness and lower the workload during such a task, irrespective of the visual conditions.

Ledegang WD, van der Burg E, Valk PJL, Houben MMJ, Groen EL. Helicopter pilot performance and workload in a following task in a degraded visual environment. Aerosp Med Hum Perform. 2024; 95(1):16–24.

BACKGROUND: Research has shown that excessive sugar-sweetened beverage (SSB) consumption has been associated with being overweight and obese and the military is not immune to this disorder. Being overweight/obese is one of the characteristics that comprise a condition known as Metabolic Syndrome (MetS). The global prevalence of MetS in the military population is estimated to be 21%, which varies depending upon the armed forces type and specialty. The purpose of this study is to identify the subset of the aviation population that may develop MetS at some future point and to put forth suggestions on how best to combat this and maintain operational readiness.

METHODS: Data were collected by means of an anonymous 44-item survey administered and completed by 302 students enrolled in Aviation Preflight Indoctrination at the Naval Air Station Base in Pensacola, FL.

RESULTS: Results indicated that 70.86% of students reported SSB consumption, with 95.3% preferring caffeinated to decaffeinated SSBs. 11.7% of personnel met the “at risk criteria” of consuming SSBs four times per week or greater (four 12-oz cans or more per week).

DISCUSSION: Findings from this study indicate that approximately 11.7% of aviation pilots or flight officers are “at risk” of developing MetS. Given that it takes up to 4 yr to train a new fighter pilot, this could become a significant readiness issue on par with the impact seen with pilots leaving the services through natural attrition.

Sather TE. Sugar-sweetened beverage consumption and implications for aviation preflight indoctrination students. Aerosp Med Hum Perform. 2024; 95(1):25–28.

INTRODUCTION: Gravity-induced loss of consciousness (G-LOC) is a major threat to fighter pilots and may result in fatal accidents. The brain has a period of 5–6 s from the onset of high +G_z exposure, called the functional buffer period, during which transient ischemia is tolerated without loss of consciousness. We tried to establish a method for predicting G-LOC within the functional buffer period by using machine learning. We used a support vector machine (SVM), which is a popular classification algorithm in machine learning.

METHODS: The subjects were 124 flight course students. We used a linear soft-margin SVM, a nonlinear SVM Gaussian kernel function (GSVM), and a polynomial kernel function, for each of which 10 classifiers were built every 0.5 s from the onset of high +G_z exposure (Classifiers 0.5–5.0) to predict G-LOC. Explanatory variables used for each SVM were age, height, weight, with/without anti-G suit, +G_z level, cerebral oxyhemoglobin concentration, and deoxyhemoglobin concentration.

RESULTS: The performance of GSVM was better than that of other SVMs. The accuracy of each classifier of GSVM was as follows: Classifier 0.5, 58.1%; 1.0, 54.8%; 1.5, 57.3%; 2.0, 58.1%; 2.5, 64.5%; 3.0, 63.7%; 3.5, 65.3%; 4.0, 64.5%; 4.5, 64.5%; and 5.0, 64.5%.

CONCLUSION: We could predict G-LOC with an accuracy rate of approximately 65% from 2.5 s after the onset of high +G_z exposure by using GSVM. Analysis of a larger number of cases and factors to enhance accuracy may be needed to apply those classifiers in centrifuge training and actual flight.

Ohrui N, Iino Y, Kuramoto K, Kikukawa A, Okano K, Takada K, Tsujimoto T. G-induced loss of consciousness prediction using a support vector machine. Aerosp Med Hum Perform. 2024; 95(1):29–36.

INTRODUCTION: Sleep is an indispensable physiological phenomenon. The complexity of sleep and the time it occupies in human life determine that its quality is positively correlated with human health. Since polysomnography was used in spaceflight in 1967, the sleep problem during astronaut flight has been studied in depth for more than 50 yr, and many solutions have been proposed, but astronauts have always had sleep problems during orbital flight. Insufficient sleep and changes in the rhythm of human sleep-wake activity will lead to disturbance of the human body’s internal rhythm indicators, which will lead to psychological and emotional fluctuations and reduced cognitive ability, decision-making ability, teamwork, and work performance. NASA has identified operational errors due to sleep deprivation and altered circadian rhythms as an important risk factor in the key biomedical roadmap for long-term flight, so the importance of sleep monitoring in spaceflight is self-evident. On-orbit sleep-monitoring methods include both subjective and objective aspects. We review objective sleep-monitoring technology based on its application, main monitoring physiological indicators, intrusive advantages, and limitations. This paper reviews the subjective and objective sleep evaluation methods for on-orbit applications, summarizes the progress, advantages, and disadvantages of current ground sleep-monitoring technologies and equipment, and looks forward to the application prospects of new sleep-monitoring technologies in spaceflight.

Zhang C, Chen Y, Fan Z, Xin B, Wu B, Lv K. Sleep-monitoring technology progress and its application in space. Aerosp Med Hum Perform. 2024; 95(1):37–44.

INTRODUCTION: A recent finding of a deep venous thrombosis during spaceflight has prompted the need to clarify mechanisms and risks of venous thromboembolism (VTE). In turn, mitigation countermeasures, diagnostic modalities, and treatment options must be explored. The objective of this review was to synthesize current evidence on VTE in spaceflight.

METHODS: A literature review was performed from inception to April 2023 pertaining to VTE in the context of spaceflight or ground-based analogs with human participants. PubMed was searched for papers written in English using the terms “spaceflight” or “weightlessness” and “thrombotic” or “embolism” or “thromboembolism” in “venous” or “veins”. Papers using cellular or animal models were excluded.

RESULTS: There were 63 papers captured; 7 original scientific studies, 3 narrative reviews, 2 systematic reviews, and 3 commentaries discussed VTE in spaceflight. Reference lists were screened. Important themes included: altered venous hemodynamics, increased fibrinogen and coagulation markers, hypoalbuminemia, and immune dysfunction. Additional risk factors may be seen in women, such as the use of oral contraceptives.

DISCUSSION: Venous stasis and decreased shear stress secondary to fluid shifts may induce inflammatory changes in the venous system, resulting in endothelial damage and upregulation of the coagulation cascade. Additionally, women in space are subject to physiological factors increasing their VTE risk, such as the use of oral contraceptives, inducing increased blood viscosity and hypoalbuminemia. Efforts should also be placed in optimizing sensitivity and specificity of imaging markers, payload, and training ability, notably the use of vector flow imaging, and improving point-of-testing biomarkers, such as albumin and p-selectin.

Levasseur S, Purvis N, Trozzo S, Chung SH, Ades M, Drudi LM. Venous thromboembolism in exploration class human spaceflight. Aerosp Med Hum Perform. 2024; 95(1):45–53.

INTRODUCTION: Exposure to high ambient altitudes above 10,000 ft (3048 m) over sea level during aviation can present the risk of hypobaric hypoxia. Hypoxia can impair sensory and cognitive functions, degrading performance and leading to mishaps. Military aircrew undergo regular hypoxia familiarization training to recognize their symptoms and understand the consequences of hypoxia. However, over the years, aviators have come to believe that individuals have a “personal hypoxia signature.” The idea is that intraindividual variability in symptom experience during repeated exposure is low. In other words, individuals will experience the same symptoms during hypoxia from day to day, year to year.

METHODS: We critically reviewed the existing literature on this hypothesis. Most studies that claim to support the notion of a signature only examine group-level data, which do not inform individual-level consistency. Other studies use inappropriate statistical methods, while still others do not control for accuracy of recall over the period of years. To combat these shortcomings, we present a dataset of 91 individuals who completed nearly identical mask-off, normobaric hypoxia exposures days apart.

RESULTS: We found that for every symptom on the Hypoxia Symptom Questionnaire, at least half of the subjects reported the symptom inconsistently across repeated exposure. This means that, at best, 50% of subjects did not report the same symptom across exposures.

DISCUSSION: These data provide compelling evidence against the existence of hypoxia signatures. We urge that hypoxia familiarization training incorporate these findings and encourage individuals to expect a wide range of hypoxia symptoms upon repeated exposure.

Cox BD, McHail DG, Blacker KJ. Personal hypoxia symptoms vary widely within individuals. Aerosp Med Hum Perform. 2024; 95(1):54–58.

INTRODUCTION: High quality cardiopulmonary resuscitation and medical care in an emergency can save lives, especially when resources are limited, as when in flight on a commercial airplane. A medical student or resident may be the most qualified person to offer assistance during an in-flight cardiac arrest; however, he/she may not yet have experience acting as a sole provider on the ground. Moreover, physicians-in-training may feel an ethical obligation to help a fellow passenger in need, but later worry that their help is subject to questions of tort liability action. This commentary will discuss who should volunteer to help in flight, considering the capability, ethics, and legal consequences of medical students and residents providing medical assistance on an airplane. It will also discuss how changes in medical curriculum due to the COVID-19 pandemic may aid medical trainees’ ability to help during an in-flight emergency as well as propose further opportunities for training.

Edelson J, Ruskin K. Considerations for medical students’ and residents’ response to an in-flight call for help. Aerosp Med Hum Perform. 2024; 95(1):59–60.