AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 3 369-R374, Copyright © 1984 by American Physiological Society
Cardiovascular and respiratory responses to heat in dehydrated dogs
M. A. Baker
The effect of dehydration on rectal temperature, respiratory frequency,
upper respiratory evaporation, cardiac output, and common carotid blood
flow was studied in large mongrel dogs at rest at ambient temperatures
between 25 and 45 degrees C. Measurements were made in animals hydrated ad
libitum and when they had been dehydrated by removal of drinking water. In
hydrated animals, mean body weight was 31.6 +/- 1.7 (SE) kg and plasma
osmolality was 296 +/- 2 mosmol/kg H2O. Dehydration decreased body weight
to 28.2 +/- 1.5 kg and increased osmolality to 328 +/- 5 mosmol/kg H2O. At
all ambient temperatures, every dehydrated animal had a higher rectal
temperature, lower respiratory frequency, lower upper respiratory
evaporation, lower cardiac output, and lower common carotid blood flow.
Rectal temperature, measured in seven animals, was constant as ambient
temperature was raised from 25 to 45 degrees C in both the hydrated and
dehydrated state, but was elevated by 0.72 degrees C in dehydrated animals.
Hypothalamic temperature, measured in two animals, was elevated less than
rectal temperature when they were dehydrated. Upper respiratory evaporation
and respiratory frequency, measured in seven animals, increased with
increasing ambient temperature in both the hydrated and the dehydrated
dogs, but were lower at every ambient temperature in dehydrated animals.
Cardiac output, measured in five animals, was lower in dehydrated animals
at every ambient temperature.(ABSTRACT TRUNCATED AT 250 WORDS)
