Protection against the Toxic Effects of Hyperbaric Oxygen by Intermittent Exposure to Reduced Oxygen Pressures

Abstract

Summary exposures to normoxic gas may be inappropriately long, resulting in severe hypoxemia. The urinary of the was wed to 'Ompare In the present study using the isolated urinary bladder of the the effects on 0, toxicity of 1-min and 5-min intermittent toad, the effects on O2 toxicity of I-min and 5-min intermittent nOrmOxic during a prolonged period h~~erOxic normoxic exposures were compared during a prolonged period (OHP). Various exposure were of hyperoxic exposure, Continuous exposure of the toad bladder tested at atmospheres (ATA) 4-1 (4 loo% O2 to 0, at pressures of 2 ATA or greater reversibly inhibits active fouOwed by 4% 02) 6-19 9-1, 15-59 and 20-5' With sodium transport (short circuit current) across the bladder (2, 3, all schedules tested, intermittent normoxic exposure significantly 6). OHP exposure of the toad bladder was regularly interprotected the SCC (active sodium transport) against the inhibi- rupted by or 5-min exposures to reduced 02 pressures. tion ATA O2' Two intermittent (4-1 and Various schedules of intermittent exposure were tested at 5 and were tested at lo ATA using 4% O2 for the reduced O2 pressure 10 ATA. In all cases, intermittent exposure of the toad bladder exposure. A significant decrease in the rate of SCC inhibition to reduced O2 pressures delayed the onset and reduced the was observed using both intermittent exposure schedules. The extent of sodium transport inhibition by OHP, One intermittent observed SCC protection by intermittent exposure (at 5 and 10 schedule actually caused a significant of sodium ATA) was not entirely a result of the decreased time of exposure transport across the bladder when with continuous to OHP. Four intermittent schedules were tested at 5 ATA, and normoxic exposure. It was concluded that I-min intermittent the effects On the SCC were 'Om* normoxic exposures were highly effective in protecting the toad pared with the effects of continuous normoxic exposure. During bladder sodium transport system from the inhibitory effects of a 5-hr exposure period, no significant SCC stimulation occurred OHP. using a 2-1, 4-1, or 9-1 intermittent schedule. Using a 5-5 intermittent schedule, however, a significant stimulation of SCC was observed at 4 and 5 hr. It was concluded that intermittent