Influence of hematocrit ratio on survival of unacclimatized dogs at simulated high altitude

Abstract

Eighty-six dogs were subjected to acutely induced, simulated high altitudes to determine the optimum hematocrit ratio for survival. High altitudes were simulated by diluting atmospheric air with nitrogen. Dogs with various hematocrit ratios were obtained by natural selection, hemorrhage, transfusion, and pretreatment with phenylhydrazine. Fifty-one dogs, in groups of 5–15, were placed in a closed chamber, and a 40,000-ft altitude was simulated by proper adjustment of the oxygen-to-nitrogen ratio. This altitude was maintained for a period of 6 hr. Most dogs with hematocrits less than 24 or greater than 66 died before the simulated altitude of 40,000 ft was attained; those with hematocrits of 24–30 survived from 1/2 to 5 hr. Some dogs with hematocrits of 30–65 survived the entire 7-hr period. However, no dogs with hematocrits from 37 to 54 died. The same procedures were repeated at a simulated altitude of 50,000 ft with a group of 38 dogs. The survival group was composed of dogs with hematocrits of 36–46. Dogs with hematocrits of 40–41 were conscious and active while those with hematocrits on either side of this value were comatose. These data indicate that the optimum hematocrit for survival of the unacclimatized dog at acutely induced high altitude is about 40. Deaths occurring on both sides of the optimum value may be explained by a simultaneous consideration of the curves depicting oxygen-carrying capacity of the blood, and blood viscosity, at all ranges of hematocrit.