Journal of Applied Physiology, Vol 55, Issue 2 300-306, Copyright © 1983 by American Physiological Society
Canine blood volume and cardiovascular function during hyperthermia
K. Miki, T. Morimoto, H. Nose, T. Itoh and S. Yamada
The effect of acute hyperthermia on hemodynamic functions and blood volume
regulation was examined on eight splenectomized dogs. Elevation of core
body temperature by 2 degrees C over 90 min caused significant increase in
cardiac output (11.2 +/- 12.5 ml X min-1 X kg-1 or about 10%) and
significant decrease in total peripheral resistance (TPR; -1.3 +/- 1.0 mmHg
X s X ml-1 or about 20%), whereas blood volume (BV), plasma oncotic
pressure, and intravascular protein mass remained unchanged. Thus the
raised core temperature caused peripheral vasodilation with decreased TPR
and compensatory increase in cardiac output. Because BV remained unchanged
during warming, mobilization of extravascular fluid did not occur; only the
redistribution of blood to the vasodilated cutaneous circulation took
place. To assess the effects of heat stress on transvascular fluid
equilibrium, Ringer solution (10.7 ml X kg-1 X 10 min-1) was infused under
normothermic and hyperthermic conditions. The volume of fluid retained
within the intravascular space under equilibrium state was 33.5% in
hyperthermia and 9.4% in normothermia. In hyperthermia, the transvascular
fluid shift and urinary output were decreased both during and after
infusion. The role of preferential fluid retention within the intravascular
space observed during hyperthermia was discussed in relation to the
mechanism to maintain cardiovascular function and BV under heat stress.
