Hyperoxia

The goal of this trial is to investigate whether adding a small fraction of hydrogen gas to an oxygen-enriched breathing mixture can reduce pulmonary oxygen toxicity (POT) in healthy and active divers from the Swedish Armed Forces. The main questions it aims to answer are: * Does hydrogen gas reduce oxidative stress and changes in pulmonary function associated with prolonged hyperbaric oxygen exposure? * What are the underlying pathophysiological mechanisms of pulmonary oxygen toxicity? Researchers will compare oxygen-enriched breathing gas with 1-2% hydrogen to oxygen-enriched gas with 1-2% nitrogen (control) to see if hydrogen provides protective effects against POT during hyperbaric exposure. Participants will: * Complete two hyperbaric exposure sessions (hydrogen vs. nitrogen), each lasting 240 minutes at 1.75 ATA * Undergo pulmonary function tests and sampling of blod and urin before and after each session * Serve as their own controls in a double-blind, randomized, crossover study design

The aim of this study is to identify and determine the levels of oxidized lipids and lipid mediators following exposure to oxygen supplementation during mechanical ventilation by oxidative lipidomics. The investigators will include patients with mechanical ventilation and have received FiO2=\>0.5 atleast 90 minutes and collected two sequential mini bronchoalveolar lavage on them 24 hours apart. Mass Spectrometry Lipid chromatography will be conducted and clinical data will be analyzed.