Some physiological changes were studied in 42 hypothermic dogs. Hypothermia was achieved by means of body surface cooling with ice water and rewarming with hot water (45-48?). The range of esophageal temperatures was from 21 to 23?. Results were as follows:
1. Heart rate, blood pressure were decreased as hypothermia progressed. Heart rate decreased from normal mean value of 169 per minute to 62 per minute at 22?1? and it returned to normal when animal was rewarmed. Upon cooling, there was a transient elevation of blood pressure and then it fell from normal value of 143 mmHg down to 81mm Hg at an esophageal temperature of 22?1? and came up to normal during rewarming.
2. Pulse pressure decreased with cooling.
3. During rewarming, all the circulatory signs to within normal limits at 37? level.
4. Formed elements of blood showed various changes.Hemoglobin, hematocrit and red blood cell count increased significantly with cooling and further increase was noted with rewarming, hemoglobin from a normal meanof 11.2gm% te 13.1gm%; hematocrit from 42.7% to 47.7% and red blood cell count from 661?10 4/mm3{ to 754?10 4/mm{. White blood cell count decreased significantly from 14,300/mm{ to 1,800/mm, with cooling and it returned to 42% of the normal count at an esophageal temperature of 37? Polymorphonuclear neutrophil played an important role in changing the white blood cell count. platelets count also decreased by cooling but recovered by rewarming.
5. The ratio between cooling time and body weight during cooling was less than that of rewarming in this experiment.
6. Mean pH value of control as well as that of at 22?1? was 7.37, while the control value was 7.46. Ventilation with room air(700-800cc/kg/min) was done throughout the experiments. Carbon dioxide content fell from 33.5 vol.% to 21.71 vol.% at 22?.
7. Mean value of O?content of arterial blood changed during hypothermia. Oxygen content increased with cooling.8. The incidence of ventricular fibrillation was 17.2%. 9. Cooling was continued on 3 dogs untination of the experiment by death. The animals died at the esophageal temperature ranging from 12 to 19?.
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