EVALUATION OF SAFETY OF HYPOBARIC DECOMPRESSION AND EVA FROM POSITIONS OF PROBABILISTIC THEORY

Formation and subsequent evolution of gas bubbles in blood and tissues of subjects exposed to decompression are casual processes in their na ture. Such character of bubbling processes in a body predetermines pro babilistic character of decompression sickness.(DCS) incidence in dive rs, aviators and astronauts. Our original probabilistic theory of deco mpression safety is based on stochastic models of these processes and on the concept of critical volume of a free gas phase in body tissues. From positions of this theory, the probability of DCS incidence durin g single-stage decompressions and during hypobaric decompressions unde r EVA in particular, is defined by the distribution of possible values of nucleation efficiency in ''pain'' tissues and by its critical sign ificance depended on the parameters of a concrete decompression. In th e present study the following is shown: 1) the dimensionless index of critical nucleation efficiency for ''pain'' body tissues is a more ade quate index of decompression stress in comparison with Tissue Ratio, T R; 2) a priory the decompression under EVA performed according to the Russian protocol is more safe than decompression under EVA performed i n accordance with the U.S. protocol; 3) the Russian space suit operate d at a higher pressure and having a higher ''rigidity'' induces a stro nger inhibition of mechanisms of cavitation and gas bubbles formation in tissues of a subject located in it, and by that provides a more con siderable reduction of the DCS risk during real EVA performance. (C) 1 998 Published by Elsevier Science Ltd. All rights reserved.