Background Aircrew members are required to attend hypoxia awareness training regularly to strengthen their memory of their personal hypoxia symptoms by undergoing training inside a hypobaric chamber. The aim of this study was to examine the association between hypoxia symptoms experienced during two training sessions that were 4 years apart. Methods This was a crossover study to compare hypoxia symptoms and self-reported physiological effects of trapped gas between a previous training session and a current training session in an altitude chamber. The subjects were military crew members who undertook a 25,000feet refresher training course in 2018. We used a structured questionnaire to obtain the target information before and during hypoxia exposure. Data were analyzed using SPSS software. Results A total of 341 trainees participated in this survey and completely filled out the questionnaire. Gastrointestinal tract discomfort caused by the expansion of trapped gas was the main physiological reaction during the previous and current training sessions. Frequently reported symptoms were poor concentration (30.5%), impaired cognitive function (20.5%), visual disturbances (16.4%), hot flashes (15.8%), and paresthesia (12.6%) during both exposures. However, the proportions of participants reporting poor concentration (P = 0.378) and visual disturbances (P = 0.594) were not significantly different between the recalled and current training sessions. The five most common symptoms among the subjects with less than 1,000 flight hours were poor concentration (29.8%), visual disturbance (27.3%), impaired

Gravity in the head-to-toe direction, known as +Gz (G force), forces blood to pool in the lower body. Fighter pilots experience decreases in blood pressure when exposed to hypergravity in flight. Human centrifuge has been used to examine the G tolerance and anti-G straining maneuver (AGSM) techniques of military pilots. Some factors that may affect G tolerance have been reported but are still debated. The aim of this study was to investigate the physiological responses and anthropometric factors correlated with G tolerance. We retrospectively reviewed the training records of student pilots who underwent high G training. Variables were collected to examine their correlations with the outcome of 7.5G sustained for 15 s (7.5G profile). There were 873 trainees who underwent 7.5G profile training, 44 trainees (5.04%) could not sustain the test for 15 s. The group with a small heart rate (HR) increase (less than 10%) during the first 1–5 s of the 7.5G profile had a nearly ten-fold higher failing chance compared with the large HR increase group (adjusted odds ratio: 9.91; 95% confidence interval: 4.11–23.88). The chances of failure were inversely related to the HR increase percentage (p for trend <0.001). Factors, including body mass index, relaxed and straining G tolerance, and AGSM, were found to be negatively correlated with the outcome.

Hypoxia remains a flight-safety issue in terms of aviation medicine. Hypoxia-awareness training has been used to help aircrew members recognize personal hypoxia symptoms. There is still no study, as yet, to establish the association of within-subject data between inflight hypoxia events and the altitude chamber. The main purpose of our study was to use paired subjects’ data on inflight hypoxia symptoms compared with those experienced during training. A questionnaire was developed to obtain information on military aircrew members in 2018. Among 341 subjects, 46 (13.49%) suffered from inflight hypoxia. The majority of the subjects detected ongoing inflight hypoxia on the basis of their previous experience with personal hypoxia symptoms or sensations in previous chamber flights. Of the top five hypoxia symptoms, the data revealed that hot flashes, poor concentration, and impaired cognitive function appeared both during the inflight events and during the hypoxia-awareness training. The occurrence rate of hypoxia symptoms was found to not be significantly different between the in-flight events and the past chamber flights through an analysis of within-subject data. Because the individual memory had faded away over time, fresher hypoxia awareness training is still mandatory and valuable to recall personal hypoxia experience for military aircrew members.

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