Respiration Physiology 108 (1997) 241 – 246 Effects on pulmonary function of daily exposure to dry or humidified hyperbaric oxygen A. Shupak *, A. Abramovich, Y. Adir, I. Goldenberg, Y. Ramon, P. Halpern, A. Ariel Israel Naal Medical Institute, IDF Medical Corps, P.O. Box 8040, Haifa 31080, Israel Accepted 10 March 1997 Abstract The purpose of this study was to examine the effects of breathing dry or humidified hyperbaric oxygen on pulmonary function. Pulmonary function tests were performed before and after each of 10 hyperbaric oxygen exposures at 2.5 atmospheres absolute (ATA) for 95 min in a group of 13 patients treated daily by hyperbaric oxygen for problem wounds. Patients breathed dry oxygen during five successive sessions and humidified oxygen during the remaining five. No differences were found between forced vital capacities (FVC) and maximal expiratory flows before and after hyperbaric oxygen exposure while breathing dry or humidified oxygen. Significant differences were found for the changes in the percentage of FVC expired in 1 s (FEV 1% ) and mean forced mid-expiratory flow rate during the middle half of the FVC (FEF 25–75% ) on day 1 alone: decrements of 1.42 and 2.96%, respectively, under dry oxygen, vs. increments of 3.93 and 34.4%, respectively, for humidified oxygen. Day-to-day decrements in the percent changes in FEV 1% and FEF 25–75% were observed while breathing humidified hyperbaric oxygen. These results demonstrate that repeated daily exposure to humidified hyperbaric oxygen abolishes the initial beneficial effect of humidification on peripheral airways flow characteristics. © 1997 Elsevier Science B.V. Keywords: Function test; Dry vs. humidified hyperbaric oxygen; Humidification; Hyperbaric oxygen; Lung 1. Introduction Repeated daily exposure to hyperbaric oxygen (HBO) at 2.5 atmospheres absolute (ATA) for 90–120 min is widely employed in the combined treatment of problem wounds (Thom, 1992). The oxygen delivered to the patients is kept dry to prevent corrosion and icing in the gas storage and supply system. To reduce the risk of bronchocon- striction due to the airway hyper-reactivity, air- way epithelial damage and inflammation that may * Corresponding author. Tel.: +972 4 8693040; fax: +972 4 8693240. 0034-5687/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S00 4-5687(97)00022-4