The influence of hyperbaric oxygen on the clinical course of experimental allergic encephalomyelitis

Abstract

Studies were conducted to investigate clinical levels of hyperbaric oxygen (HBO) on experimental allergic encephalomyelitis (EAE). These investigations evaluated oxygen exposures of 1.0, 1.5, 2.0, 2.5, and 3.0 atmospheres absolute (ATA). Initial investigations focused on the generation of a chronic-relapsing and an acute form of EAE. Attempts were made to establish a dose/response relationship by varying the ratios of the purified myelin basic protein, Mycobacterium tuberculosis, and Freunds' adjuvant. In attempts to induce the chronic-relapsing form of the disease, this relationship could not be established in either adult or juvenile strain 13 guinea pigs. However, acute EAE was sucessfully induced in adult strain 13 guinea pigs. Studies were conducted to evaluate the effect of hyperbaric oxygen (HBO) in three areas related to acute EAE. Firstly, to evaluate hyperoxic exposures on the clinical progression of EAE, treatments were initiated when definitive clinical symptoms of the disease appeared. The results of this study indicated that HBO treatments initiated at this time were unable to alter the clinical course or outcome of EAE. Secondly, HBO was evaluated on the induction phase of the disease,by initiating therapy within 24 hours o f sensitization. Results indicated that hyperoxic exposures of 2.0 ATA significantly increased the mean time to clinical symptom onset and the mean survival time (P < 0.005), when compared to the controls. However, the mean survival time was significantly decreased when animals were treated at 1.0 ATA (6 hours per day). A similar decrease was noted in mean time to clinical symptom onset in animals exposed at 2.5 ATA oxygen. Once clinical symptoms appeared, however, the clinical pattern or outcome was not altered. Thirdly, residual effects of hyperoxic exposures were evaluated. Experimental animals were subjected to a pre-sensitization treatment protocol of HBO (20-40 treatments). Within 24 hours of treatment termination, the animals were sensitized with the appropriate immunogen. Although preliminary in nature, these studies indicate that the induction time for the disease and animal survival may be significantly lengthened by pretreatment with HBO. These findings indicate a possible residual effect of hyperoxia on the delayed-type hypersensitivity responses.