EFFECTS OF SINGLE AND REPEATED EXPOSURES TO OXYGEN AT HIGH PRESSURE ON NORMAL RATS

Abstract

Unanesthetized rats were exposed to oxygen at high pressure (OHP)—60 lb/sq. inch gauge pressure (60 p.s.i.g.)—and kept at this pressure until three convulsions had occurred (average time 3.3 minutes). Electroencephalographic (EEG) frequency decreased and amplitude increased just before and after a convulsion; heart rate decreased and respiratory rate increased. After stage-decompression the EEG pattern became similar to that observed during the precompression stage in about 11 minutes; heart rate returned within 32 minutes, but the respiratory rate fell below precompression levels and did not recover for some 79 minutes. With exposure to 2% carbon dioxide in oxygen (CO₂–OHP) at 60 p.s.i.g. the convulsion time was significantly shorter than with pure oxygen. Convulsions did not occur with exposure to air or oxygen at atmospheric pressure nor to air at 60 p.s.i.g. On prolonged exposure to OHP the rats survived an average of 48.4 convulsions, the survival time being 104.45 minutes; rats exposed to CO₂–OHP experienced an average of 20.7 convulsions and survived only 38.50 minutes. In both groups the respiration was the first to fail, followed by the heart. Postmortem examination revealed severe pulmonary congestion in these rats.Repeated exposures to OHP at weekly intervals led to a decrease in the time to the first convulsion in one series of experiments but these rats were found to have elevated respiratory rates, marked pulmonary damage, and increased Hb and erythrocytes. In a second series no change in convulsion time was noted over six weekly exposures; these animals had minimal lung pathology and showed no change in the blood picture. An increase in time to the first convulsion was noted in the group exposed repeatedly to CO₂–OHP.