Physiological Adaptation to Environmental Changes

Abstract

Abstract : Dogs with varying hematocrit ratios were subjected to cardiovascular and respiratory insults designed to determine what cell to plasma ratio was most effective in carrying oxygen to the tissues of the body. It was found that dogs with initial hematocrit ratios of from 35 to 39 were able to carry more oxygen to their tissues after a massive hemorrhage than those dogs with hematocrit ratios outside this range. Furthermore, since the hematocrit ratio tends to increase during hemorrhage, the optimal value for the hematocrit ratio is 40. Normal dogs with this optimal value were subjected to high altitude studies and it was found that these dogs could survive and be active at altitudes lethal to animals with hematocrit ratios outside the optimal range. The optimal range is indicated by the dual nature of the hematocrit ratio as it affects both oxygen carrying capacity and blood viscosity. With low cell content, the viscosity is low but the oxygen carrying capacity is also low. As the cell content of the blood increases, so does both oxygen carrying capacity and viscosity. The inflection of the curve has been at 40 for all types of experiments of this nature. Acclimatized dogs show an optimum at 46, indicating that high altitude polycythemia is detrimental. A mathematical analysis, and a discussion of these facts are included.