Experimental animals were used to anticipate and/or delineate more clearly factors that may either facilitate or complicate long-term oxygen therapy. Gradual adaptation, ie, increasing the oxygen concentration in steps (40% and 70%) prolonged survival of adult Sprague-Dawley rats when they were finally exposed to 95 or 100 per cent oxygen. The adaptation had to start at 40 or 70 per cent. Nearly all rats lost weight during their exposure to high oxygen until they died. The partial adaptation or prolonged survival was accompanied by a third (chronic) phase of pulmonary oxygen toxicity, which was characterized by pulmonary scarring, honeycombing, and emphysematous blebs. The variability in individual susceptibility to oxygen toxicity during the adaptation regimen was less pronounced among Colony I animals than among Colony II animals. Because a significant number of animals were very sensitive to 70 and 80 per cent oxygen, one should consider the possibility in clinical oxygen therapy that some human patients may also be excessively sensitive to relatively brief exposures to 70 or 80 per cent oxygen. Some patients may be liable to a chronic phase of oxygen toxicity with prolonged exposure to elevated inspired oxygen tensions.
Paegle et al. (Wed,) studied this question.