INTRODUCTION: There is no consensus on whether cardiopulmonary reserve affects the risk of gravity-induced loss of consciousness (G-LOC) or almost loss of consciousness (A-LOC). Few previous studies have used cardiopulmonary exercise testing (CPET) to assess cardiopulmonary reserve function (CPRF) of fighter aviators. We compared CPET-related parameters in G-LOC/A-LOC and non-G-LOC/A-LOC fighter aviators to explore the effect of cardiopulmonary reserve function on G tolerance.

METHODS: A total of 264 male fighter aviators with more than 500 h of flight experience participated in the study, all of whom underwent CPET and human centrifuge testing. We divided the aviators into two groups based on whether they experienced G-LOC/A-LOC during the human centrifuge test and compared the CPET parameters between the two groups.

RESULTS: A total of 37 aviators (14%) experienced G-LOC/A-LOC. There were no significant differences in age (26.65 ± 4.30 vs. 26.01 ± 4.95), height (173.68 ± 4.21 vs. 173.55 ± 3.37), weight (69.51 ± 6.22 vs. 69.63 ± 6.01), or body mass index (23.06 ± 2.11 vs. 23.11 ± 1.82) between the two groups. Forced vital capacity (FVC) (4.95 ± 0.87 vs. 4.65 ± 0.79) and forced expiratory volume in 1 s (FEV₁) divided by FVC (FEV₁/FVC) (79.88 ± 7.24 vs. 83.72 ± 9.24) of pulmonary function of the G-LOC/A-LOC group was significantly lower than that of the non-G-LOC/A-LOC group. There was no significant difference in CPET-related parameters between the two groups.

DISCUSSION: In conclusion, FEV₁/FVC may be a factor affecting aviators’ G-LOC/A-LOC, meaning aviators with slightly lower ventilation are more likely to experience G-LOC/A-LOC. However, oxygen uptake and exercise blood pressure, oxygen pulse, etc., may not be the main factors influencing G-LOC/A-LOC.

Lan X, Zhu W, Du J, Wang J, Yang M, Xu Y, Cao Y. High G tolerance and cardiopulmonary reserve function in healthy air force aviators. Aerosp Med Hum Perform. 2023; 94(12):911–916.