Effects of a standard hyperbaric oxygen treatment protocol on pulmonary function

The prescription of hyperbaric oxygen (HBO) therapy for disorders not related to diving is increasing. Pulmonary oxygen toxicity is well known, but the effect of the cumulative oxygen exposure corresponding to a standard HBO treatment protocol has not been quantified before. Twenty patients (10 male) had 21 HBO treatments at a partial pressure of oxygen of 240 kPa for 90 min daily. None had any previous lung disease and all had normal chest radiography and lung function at the start of the study. Dynamic lung volumes, forced expiratory flows and the transfer factor of the lung for carbon monoxide (TL,CO) were measured before the HBO treatment, on days 7, 14 and 21 during treatment and then 3-4 weeks after treatment. Four patients (one male) reported nonproductive coughing during the last week of treatment. There was a progressive reduction in forced expiratory volume in one second (FEV1) (p<0.001), mean forced mid-expiratory flow rate (FEF25-75%) (p<0.001) and forced expiratory flows at 50 and 75% of forced vital capacity (FVC) expired during HBO treatment. The reduction in FEV1 on day 21 was 4.4+/-1.7% and in FEF25-75% 10.3+/-6.1%. Four weeks after treatment there was a partial normalization. There were no changes in FVC or peak expiratory flow (PEF). TL,CO was slightly reduced on day 21 of treatment only (p<0.01) and fully normalized 1 month later. A reduction in small airways conductance is consistent with other studies where total oxygen exposures have been below the limit causing toxic pulmonary effects traditionally measured as a reduction in vital capacity. This effect is not considered to be of any clinical significance for patients treated with hyperbaric oxygen unless repeated treatment series are to be given.