Effect of cold exposure on resistance to hemorrhage in dogs

¹ Physiology Department, U. S. Army Medical Research Laboratory, Fort Knox, Kentucky

Effects of progressive hemorrhage during severe cold exposure were studied in 17 unanesthetized dogs. The amount of blood required to be withdrawn to reduce the mean arterial blood pressure to 50 mm Hg by a standardized bleeding procedure was determined in the same animals at air temperatures of +25°C and –25°C. Cold-exposed dogs showed a statistically significant increased ‘resistance’ to hemorrhage in that an average withdrawal of 20% more blood was required to reduce mean arterial blood pressure to shock levels in the cold than in the same dogs at comfortable temperature. In six animals it was necessary to draw a minor, but measurably greater, amount of blood from a given dog to produce hypotension during cold exposure than when the procedure was performed at a comfortable temperature and, in two animals, a minor, but measurably less, amount of blood was withdrawn during cold exposure. In seven animals a significantly greater amount of blood was drawn in the cold than in a neutral environment, but in some of these animals the control bleeding was apparently substandard. In two animals the control bleedings were in the normal range and bleedings were substandard in the cold. Cortisone administration did not alter resistance to hemorrhage during cold exposure.