Oxidative stress during oxygen tolerance test

Reactive oxygen species, including oxygen free radicals are normally generated in human cells during aerobic metabolism. Their production may increase during breathing of hyperoxic mixtures. The 'oxidative stress' has been postulated to be an important contributor to CNS oxygen toxicity. One of the highest partial pressure of oxygen used in healthy humans is 280 kPa(a) during 30 min of 'oxygen tolerance tests' (OTT). This test is conducted in order to detect some individuals with an increased sensitivity to high partial pressures of oxygen leading them to develop CNS oxygen toxicity earlier than others. The purpose of this study was to investigate whether the OTT (30 min of breathing pure oxygen at 280 kPa(a)) would significantly induce oxidative stress in healthy population. The first group consisted of 52 subjects, in whom total antioxidant status (TAS) was measured. The second group consisted of 44 subjects, in whom protein carbonyls (PC), total thiol (t-SH) and heat shock proteins (HSP70) were measured. All measurements were done just before and immediately after the OTT. There was no statistically significant change of TAS. We observed a small, however statistically significant increase of PC and decrease of t-SH. A significant decrease of HSP70 was detected, however false positives of initial measurements are suspected. In summary, in young healthy subjects 30 min of breathing oxygen under pressure of 280 kPa(a) induces oxidative stress which can be detected by increase of protein carbonyls and by decrease of total thiol. In our study this stress was not reflected in measurement of total oxidative status and heat shock proteins.