Blood Acid-Base Status and Oxygen Binding During Stress-Induced Hyperthermia in Pigs

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Abstract
Three groups of eight Dutch Landrace pigs were fitted with permanent arterial and venous catheters and subjected to (1) exercise for three 10-min. intervals on a treadmill at 35 C, (2) exercise as in group 1 at 25 C or (3) exposure to 35 C. The pigs were also grouped on the basis of susceptibility to stress as indicated by post-treatment rectal temperatures of (A)2 and pO2 were measured after each treatment interval and subsequent determinations were made of actual and standard bicarbonate and percent oxygen saturation. Comparison of the treatment groups revealed that the exercise and excitement elicited by the treadmill were more severe stresses than heat stress alone (measured by body temperature elevation). In general, the heat and exercise resulted in a respiratory alkalosis followed by metabolic acidosis, whereas, the heat alone produced only a respiratory alkalosis. At the end of the stress period, the stress susceptible pigs (group B) had low pH and reduced actual and standard bicarbonate in both arterial and venous blood as compared to the pigs of group A. Adequate levels of arterial oxygen were maintained in both groups of pigs but stress susceptible pigs had lower venous oxygen saturation and greater A-V differences in oxygen saturation at the end of stress than pigs with more stress resistance. It is likely that the low pH resulting from lactic acid production caused a dissociation of oxygen from its carrier. Evidence cited supports the hypothesis that the body temperature rise and acidosis experienced by stress susceptible pigs are largely the result of the heat and lactate produced by muscle anaerobic glycolysis in the presence of adequate arterial oxygen pressure. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.

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