Effects of continuous compression at different compressing rates on the survival time of rats exposed to hyperbaric air

Abstract

Objective To observe the effects of continuous compression at different compressing rates on the survival time of rats exposed to hyperbaric air, and also to explore the possible time remained for the rescue of the diver following hard shell leakage of the atmospheric diving suit(ADS). Methods Twenty-four male healthy SD rats were divided into 3 subgroups: the high compressing rate group, the moderate compressing rate group and the low compressing rate group. All the animals groups were compressed to a pressure of 120 m at a compression rate of 1 m/min. Then, the high compressing rate group was further compressed to a pressure of 300 m at a compression rate of 1 m/min, the moderate compressing rate group was first further compressed to a pressure of 200 m at a compression rate of 0.44 m/min and was finally compressed to a pressure of 300 m at a compression rate of 0. 21 m/min, and the low compressing rate group was first further compressed to a pressure of 200 m at a compression rate of 0.44 m/min and was finally compressed to a pressure of 300 m at a compression rate of 0. 1 m/min. Clinical manifestations, pressure tolerance limit, convulsion latency(CL)and survival time(ST)of the animals were closely observed. Results The pressure tolerance limit of the high compressing rate group, when the animals died, was the highest(242.50±26.77)m, the convulsion latency was(178.00 ±1.93)min and the survival time was the shortest(247.75 ± 14.86)min. As compared with that of the high compressing rate group, the pressure tolerance limits of the moderate compressing rate group and the low compressing rate group significantly decreased, convulsion latency and survival time were obviously prolonged, and statistical significance could be noted, when comparisons were made between them(P 0.05), however, convulsion latency was prolonged(P<0.05). With the decrease in compressing rate, oxygen partial pressure limits also decreased, when the animals died. And statistical significance could be seen, when comparisons were made between the low compressing rate group and the high compressing rate group(P=0.001). The value of unit pulmonary toxic dose(UPTD)increased with the decrease in compressing rate. As compared with the high compressing rate group, statistical significance could be found in the moderate compressing rate group and the low compressing rate group(P<0.05 or P<0.01). However, the UPTD values of the 3 groups were still within maximum human tolerance limits. Conclusions At the compressing rate lower than 1 m/min, the air pressure tolerance limit of the rat was about 200 m, the tolerance time was within 200-320 min. The human pressure tolerance limit was lower than that of the animal. For this reason, in case of relatively low leakage of the ADS, rescue should be implemented immediately. When the increase in pressure(200 m)was still within the survival time, the survival probability was still relatively high. With the increase in the rate of pressure leakage, the time left for rescue would be obviously shortened. Key words: Air compression; Pulmonary oxygen toxicity; Survival time; Compressing rate