Effects of training flights of combat jet pilots on parameters of airway function, diffusing capacity and systemic oxidative stress, and their association with flight parameters

Background: Fighter aircraft pilots are regularly exposed to physiological challenges from high acceleration (G z ) forces, as well as increased breathing pressure and oxygen supply in the support systems. We studied, whether effects on the lung and systemic oxidative stress were detectable after real training flights comprising a wide variety of exposure conditions and their combinations. Methods: Thirty-five pilots of the German Air Force performed 145 flights with the Eurofighter Typhoon. Before and after flights, lung diffusing capacity for carbon monoxide (DL CO ) and nitric oxide (DL NO ), alveolar volume (V A ), and diffusing capacities per volume (K CO , K NO ) were assessed. Additionally, the fractional concentration of exhaled nitric oxide (FeNO) was determined, and urine samples for the analysis of molecular species related to 8-hydroxy-2’-deoxyguanosine (8-OHdG) were taken. For statistical analysis, mixed ANOVA models were used. Results: DL NO , DL CO , K NO , K CO and V A were reduced (p<0.001) after flights, mean±SD changes being 2.9±5.0, 3.2±5.2, 1.5±3.7, 1.9±3.7 and 1.4±3.1%, respectively, while FeNO decreased by 11.1% and the ratio of 8-OHdG to creatinine increased by 15.7±37.8%. The reductions of DL NO (DL CO ) were smaller (p<0.001) than those of K NO (K CO ). In repeated flights on different days, baseline values were restored. Among various flight parameters comprising G z -forces and/or being indicative of positive pressure breathing and oxygenation support, the combination of long flight duration and high altitude appeared to be linked to greater changes in DL NO and DL CO . Conclusions: The pattern of reductions in diffusing capacities suggests effects arising from atelectasis and increased diffusion barrier, without changes in capillary blood volume. The decrease in exhaled endogenous NO suggests bronchial mucosal irritation and/or local oxidative stress, and the increase in urinary oxidized guanosine species suggests systemic oxidative stress. Although changes were small and not clinically relevant, their presence demonstrated physiological effects of real training flights in a modern 4 th generation fighter jet.