THE COMPENSATORY ROLE OF CARDIOVASCULAR SYSTEM UNDER ACUTE HYPOXIC HYPOXIA IN HUMAN

Abstract

Interinstitute Laboratory of Comparative Ecological Physiological Research, I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry of Russian Academy of Sciences, Scientific Research Centre “Arktika", Far East Branch of Russian Academy of Sciences, St-Petersburg, Russia The compensatory role of the cardiovascular system during hypoxic hypoxia has been considered in the paper. It has been shown that cardiac output during acute hypoxic hypoxia (FiO 2 = 0.14 - 0.08) increased relatively little - not more than 20 % compared to the background level. Tissue oxygen delivery (DO 2) decreased under the background level already at small degrees of hypoxia. This DO 2 deficit increased as hypoxia intensified. On the basis of the analysis of mechanisms of oxygen delivery to tissues - delivery in capillaries, division of oxygen flows between tissues and the venous bed, formation of intracapillary and tissue oxygen tension, we have made a conclusion that the compensatory role of the cardiovascular system during hypoxia was not in support of DO 2, but in limitation of capillary hypoxemia and tissue hypoxia. This mechanism during hypoxic hypoxia did not restore capillary oxygen tension, and for this reason it was only supplementary to the tissue mechanism, which compensated hypoxia. It has been suggested that the term “tissue oxygen delivery speed (DO 2)” should be substituted by a more accurate one - “capillary oxygen delivery speed”.