Pulmonary function in men after repeated sessions of oxygen breathing at 0.25 MPa for 90 min

Hypothesis: We wanted to evaluate the pulmonary effects of discontinuous ox ygen breathing (15 min O-2, 2 min air breaks, 15:2), at 0.25 MPa once a day for 90 min O-2 (6 sequences) over 10 d. This sequence, which has never bee n evaluated, is currently used in our hyperbaric therapy center. Methods: C linical and functional pulmonary status (questionnaire, spirometry, flow/vo lume loop, pulmonary diffusing capacity for carbon monoxide) was assessed i n 10 non-smoking healthy volunteers after one exposure at 0.25 MPa consisti ng of 90 min of discontinuous oxygen breathing (15:2) and in 10 non-smoking patients who received a hyperbaric treatment consisting of 90 min of the s ame discontinuous O-2 breathing (15:2) once a day over 10 d. The patients r eceived daily intravenous methylprednisolone (1 mg.kg(-1)) and nicergoline (60 mg). Results: There were no respiratory symptoms in either group. As ex pected, for a single exposure of that duration, lung function did not chang e in volunteers; however, a significant decrease in maximal expiratory flow s (MEF) at 50 (-15%) and 25% (-33%) of forced vital capacity (p < 0.05) wit hout change in forced vital capacity (FVC) appeared in patients treated ove r 10 d. Conclusion: Repetition of the 15:2 oxygen breathing sequence for 90 min once a day over 10 d led to greater flow limitation in peripheral airw ays than reported after continuous oxygen breathing of 210 min at 0.3 MPa w hich showed a 7% decrement in MEF50 and a 12% decrement in MEF25. No studie s reporting these indexes were found in the 0.2-0.25 MPa range. Similar dec rements in MEF50 and MEF25 with steady FVC have been reported after 14 d of daily hyperbaric therapy (0.24 MPa) with 30:5 sequence (-9% and -13%, resp ectively), 80% of the patients were symptom free. Similarity, our patients were all symptom free and remained so 1 yr after the study, hence, this tox icity is of weak clinical significance in subjects free of inflammatory lun g diseases. HBO therapy, though safe, is not totally without effect on the lung.