Repeated effect of hyperbaria on rat blood system

Abstract

The reactions of the blood system in male Wistar rats to repeated effects of nitrogenoxygen hyperbaria (pressure 0.5 MPa, density of gas medium 6 g/l, pO2 = 0.02–0.03 MPa) were studied. Rats were placed into a pressure chamber for 5 h-in 24, 72, and 120 h after first exposure (ambient air pressure control). The red blood cell parameters were analyzed and the general condition of animals was estimated. It was established that after first exposure the stress reaction developed in rats with all objective stress markers (corticosteroid and adrenal ascorbic acid levels). On repeated exposure after 24 h, almost complete normalization of all stress markers occurred except for the increased plasma hemoglobin level as a result of impaired erythrocyte membrane permeability. After repeated exposures in 72 and 120 h, the stress markers recurred. After exposure in 120 h, the general condition of animals sharply deteriorated: they did not move in the “open” field, could not hold themselves on a horizontal bar and were mainly lying. The immobilization stress control showed that after the initial stress reaction rats recovered completely with no changes in the blood system and general condition of animals occurred on repeated exposures. We believe that the hyperbaria-induced stress is associated with breathing difficulty under pressure. Thus, the repeated effect of hyperbaria is a harmful factor which causes no habituation.