Physiological responses of dogs on exposure to hot, arid conditions

Acid-base parameters were determined in chronically cannulated dogs exposed to ambient temperatures increasing from 25–47° C (with relative humidity below 30%). pH increased from 7.409±0.004 (S.E.M.) to 7.538±0.017, \(Pa_{CO_2 } \) decreased from 33.0±0.5 to 20.9±1.2 torr, and [HCO ₃ ⁻ ] decreased from 20.9±0.3 to 17.2±0.4 mEq/l. Minimal base excess change, together with a rapid return to normal parameters upon recooling to 25° C, suggests that the stress is almost exclusively respiratory, with little metabolic involvement. Analysis of serial exposures shows no acclimatization effect in acid-base status. This suggests the possible existence of natural acclimation to heat in dogs maintained in a warm climate, permitting excellent tolerance of hot, arid conditions with limited acid-base disturbance.