Relationship of fatigue, physical fitness and cardiovascular endurance to the hypoxic response of military pilots in Indonesia

Even with pressurized aircraft cabins, hypoxic conditions present a continual threat for pilots. The purpose of this study was to determine the risk factors associated with hypoxia for Indonesian military pilots. This cross-sectional study consecutively recruited 120 military pilots who carried out education and aerophysiology exercises during June 2017 at Saryanto Institute for Medical and Health Aviation and Aerospace, Jakarta, Indonesia. The subjects exercised in a hypobaric chamber simulating an altitude of 25,000 ft (7600 m), and their response to hypoxia were characterized by time of useful consciousness (TUC). Multivariate logistic regression was used to analyze relationships between TUC with a cutoff of <4 min and parameters of fatigue, physical fitness, cardiovascular endurance (VO_2max), and characteristics of the pilots. Fatigue, physical fitness, and VO_2max max did not show a statistically significant relationship with TUC (p > 0.05). Total flight hours and smoking habits were found to be the main factors affecting TUC. The subjects with more than 1000 flight hours were at 2.6 times higher risk to have TUC <4 min (odds ratio 2.65; 95% confidence interval 1.21-5.78; p = 0.014). Compared with the non-smokers, the smokers showed a 63% lower risk of TUC <4 min (odds ratio 0.37; 95% confidence interval 0.14-0.95; p = 0.039). In summary, fatigue, physical fitness, and cardiovascular endurance were not associated with a hypoxic response characterized by TUC <4 min, but total flight hours ≥1000 increased the risk of TUC <4 min and being a smoker reduced the risk.