AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 2 254-R263, Copyright © 1987 by American Physiological Society
Regional circulatory responses to head-out water immersion in conscious dogs
G. Hajduczok, K. Miki, J. R. Claybaugh, S. K. Hong and J. A. Krasney
We determined the regional blood flow responses to head-out water immersion
(WI) in intact (INT) and cardiac-denervated (CD) conscious dogs. Immersing
dogs in thermoneutral water (37 degrees C) in the quadruped position for
100 min resulted in significant increases in cardiac output (Qco) above
control values by 38.7% in the INT dogs and 39.2% in the CD dogs (P less
than 0.01). Arterial pressure increased by 32 and 34.7% in the INT and CD
groups, respectively, during WI, with no significant changes occurring in
the calculated total peripheral resistance. Regional blood flow responses
were measured with 15-microns radiolabeled microspheres. Flows in the INT
and CD groups increased significantly to the heart (40, 38%), skin (93,
96%), fat (79, 83%), diaphragm (44, 48%), and intercostal muscles (58,
55%), whereas there were no changes in renal cortical blood flows during
WI. Total brain blood flows did not change significantly on immersion;
however, blood flows in both INT and CD animals were increased to the
cerebellum (19, 22%), but a significant decrease in pituitary flow (52%)
was observed only in the CD group during WI. Gastrointestinal tissue flows
increased only during early WI in both INT (45%) and CD (47%) animals.
However, blood flows to the skeletal muscles increased only during late WI
in the INT (53%) and CD (47%) groups. There were no significant differences
between the INT and CD groups. Rectal temperatures and systemic O2
consumption (VO2) were unchanged during WI in both groups of animals. These
observations indicate that WI leads to a sustained elevation of Qco
accompanied by selective increases in regional tissue perfusion that may be
accounted for in some tissues by an increase in metabolic demand or by
local heating responses and produces a time-dependent redistribution of
blood flow away from the gastrointestinal tissues toward skeletal muscle
tissues, which may be due to a partial uncoupling of the normal Q/VO2
relationship. This may be caused by thermal or central neurohumoral
mechanisms. These regional circulatory responses are not dependent on the
presence of the cardiac nerves.
