Military aircrew are occupationally exposed to a high-G environment. A tolerance test and surveillance is necessary for military aircrew before flight training. A cardiac force index (CFI) has been developed to assess long-distance running by health technology. We added the parameter CFI to the G tolerance test and elucidated the relationship between the CFI and G tolerance. A noninvasive device, BioHarness 3.0, was used to measure heart rate (HR) and activity while resting and walking on the ground. The formula for calculating cardiac function was CFI = weight × activity/HR. Cardiac force ratio (CFR) was calculated by walking CFI (WCFI)/resting CFI (RCFI). G tolerance included relaxed G tolerance (RGT) and straining G tolerance (SGT) tested in the centrifuge. Among 92 male participants, the average of RCFI, WCFI, and CFR were 0.02 ± 0.04, 0.15 ± 0.04, and 10.77 ± 4.11, respectively. Each 100-unit increase in the WCFI increased the RGT by 0.14 G and the SGT by 0.17 G. There was an increased chance of RGT values higher than 5 G and SGT values higher than 8 G according to the WCFI increase. Results suggested that WCFI is positively correlated with G tolerance and has the potential for G tolerance surveillance and programs of G tolerance improvement among male military aircrew.

BACKGROUND Military aircrew are occupationally exposed to a high-G environment. G force causes blood to flow to the lower body region and challenges their cardiac function and anti-G straining maneuver effectiveness. A tolerance test is necessary for every military aircrew member before undergoing flight training. A novel cardiac force index (CFI) has been developed and used to assess long-distance running by mobile health (mHealth) technology. There is still no study to monitor the CFI by wearable devices during the G tolerance test. OBJECTIVE We added the cardiac function parameter CFI to the G tolerance test and elucidated the relationship between cardiac function and G tolerance among military aircrew. METHODS A noninvasive device, BioHarness 3.0, was used to measure heart rate (HR) and activity while resting and walking on the ground. The mathematical formula for cardiac function calculation is CFI = weight × activity/HR. The cardiac force ratio (CFR) is calculated by walking CFI (WCFI)/resting CFI (RCFI). G tolerance includes relaxed G tolerance (RGT) and straining G tolerance (SGT) tested by a human centrifuge under the gradual-onset-rate profile. RESULTS In total, 92 male participants voluntarily completed this study. The average values of RCFI, WCFI, and CFR were 0.02 [SD 0.04], 0.15 [SD 0.04], and 10.77 [SD 4.11], respectively. The mean RGT and SGT were 5.1G [SD 0.9] and 7.8G [SD 1.1], respectively, in the centrifuge. The percentages of participants with RGT greater than 5G or SGT greater than 8G were equally noted as 54.3%. Each 100-unit increase in WCFI increased RGT by 0.14G [SE 0.02, 95% CI 0.09 to 0.19] and by 0.17G [SE 0.03, 95% CI 0.11 to 0.22], corresponding to SGT. In addition, there was an increased chance of RGT values higher than 5G and SGT values higher than 8G according to the increase in WCFI. CONCLUSIONS Our results suggested that WCFI is positively correlated with G tolerance in the centrifuge and has the potential to be used for military aircrew selection.

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Background: In-flight spatial disorientation (SD) is a predominant threat to flight safety in aviation. This study was conducted to understand the prevalence, severity, and frequency of in-flight SD among military pilots in Taiwan. Methods: A survey was conducted to collect tri-service pilots' experiences of SD during flight. Participants completed anonymous SD questionnaires during refresher physiology training. There were 486 questionnaires delivered to trainees and the completion rate was 97.1% (n = 472). All data were processed using SPSS version 24 software (IBM, Armonk, NY, USA). Results: Of the 472 participants, the average age of the pilots was 36.7 so 7.3 years and 97.7% were male. About 80% of participants experienced in-flight SD events. There was a significant difference between prevalence of SD in fighter (87.0%), trainer (89.8%), transporter (70.6%), and helicopter (66.7%) pilots (P < 0.001). Less than 10% of the events were severe, and there was no obvious variation between aircraft types (P = 0.126). Pilots were sensitive to SD in clouds and under low visibility. Over 70% of pilots experienced visual illusions, especially loss of horizon during bad weather (45.1%), followed by leans (44.5%), false horizon (44.1%), false sense in clouds (39.6%), Coriolis illusion (25.0%), and confusion on entry to instrument meteorological conditions (25.0%). Conclusions: Our survey showed that SD is a common physiological problem among military pilots, who were easily disoriented by in-flight SD without visual cues. Visual illusion was relatively more frequent, especially for trainer and fighter pilots.