Physiological responses of dogs on exposure to hot, arid conditions. Acid-base status

Acid-base parameters were determined in chronically cannulated dogs exposed to ambient temperatures increasing from 25-47 degrees C (with relative humidity below 30%). pH increased from 7.409 +/- 0.004 (S.E.M.) to 7.538 +/- 0.017, PaCO2 decreased from 33.0 +/- 0.5 to 20.9 +/- 1.2 torr, and [HCO3-] 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 degrees 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.