Comparative Effects of Hyperoxia and Hyperbaric Pressure in Treatment of Primary Blast Injury

Abstract : Guinea pigs and rabbits were exposed to lethal reflected pressures in an air-driven shock tube and were subsequently treated in a hyperbaric chamber in which the oxygen tension (PO2) and chamber pressure were independently varied. Treatments involving increases in PO2 resulted in increased survival times of guinea pigs whereas pressurization for 30 minutes at 36 or 72 p.s.i.g. with the PO2 retained at the normal ambient level by use of an N2-air mixture had no detectable effect on survival times of the animals. To study the effects of prolonged hyperbaric oxygenation in treatment of blast injury, guinea pigs and rabbits were treated on a 29-hour schedule having an initial 3-hour hold- time at the pressure-treatment level followed by 26 hours for decompression. In rabbits, an initial PO2 of 17.5 p.s.i.a., achieved either by air pressure at 72 p.s.i.g. or by pressurization to 15 p.s.i.g. with 65-percent O2, 35-percent N2, resulted in full survival and recovery of all treated animals. In guinea pigs, treatment with 100-percent O2 at 5.5 p.s.i.g. (PO2 = 17.5 p.s.i.a.) or at 12 p. s.i.g. (PO2 = 24 p.s.i.a.) resulted in increased survival times with no increase in overall survival and recovery in the first case and significantly increased survival and recovery compared to that of untreated controls in the second case. The pathophysiology of primary blast injury is discussed with special reference to the roles of air embolism and cardiopulmonary pathology in the etiology of death.