Oxidative Stress Reaction to Hypobaric-Hyperoxic Civilian Flight Conditions

Background: In military flight operations fighter pilots work during flights constantly under hyperoxic breathing conditions with supplemental oxygen in varying hypobaric environments. These conditions are suspected to cause oxidative stress to neuronal organ tissues. For civilian flight operations the Federal Aviation Administration (FAA) also recommends supplemental oxygen for flying under hypobaric conditions equivalent to higher than 3048m altitude and makes it mandatory for conditions equivalent of more than 3657m altitude. Aim: We hypothesized that hypobaric-hyperoxic civilian commercial and private flight conditions with supplemental oxygen in a flight simulation in a hypobaric chamber at 2500m and 4500m equivalent altitude would cause significant oxidative stress in healthy individuals. Methods: 12 healthy subjects (6m, 6f, mean age 35,7yrs) from a larger cohort were selected to perform a 3hrs flight simulation in a hypobaric chamber with increasing supplemental oxygen levels (35%,50%,60% and 100% FiO2 via venturi valve equipped face mask) switching back and force between simulated altitudes of 2500m and 4500m. Arterial blood pressure and oxygen saturation were constantly measured via radial catheter and blood samples for blood gases taken from the catheter at each altitude and oxygen level. Additional blood samples from the arterial catheter at baseline and 60% oxygen at both different altitudes were centrifuged inside the chamber and the serum frozen instantly at minus 21°Celsius for later analysis of the oxidative stress markers malondialdehyde low density lipoprotein (M-LDL) and glutathione-peroxidase (GLP) via elisa test. Results: 11 subjects finished the study without adverse events. Whereas PO2 levels increased in the mean with increasing oxygen levels from baseline 96.2 mmHg to 160.9 mmHg at 2500m altitude and 60% FiO2 and 113.2 mmHg at 4500m altitude and 60% FiO2, there was no significant increase in both oxidative markers from baseline to 60% FiO2 at these simulated altitudes. Some individuals had a slight increase, some not at all or even a slight decrease. A moderate correlation (Pearson correlation coefficient 0,55) existed between subject age and glutathione peroxidase levels at 60% FiO2 at 4500m altitude. Conclusion: Supplemental oxygen of 60% FiO2 in a flight simulation comparing to flying in cabin pressure levels equivalent to 2500m-4500m altitude does not lead to a significant increase or decrease in the oxidative stress markers M-LDL and GLP in serum of arterial blood.