AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 4 595-R601, Copyright © 1988 by American Physiological Society
Altered heart rate-arterial pressure relation during head-out water immersion in conscious dog
H. Yoshino, D. C. Curran-Everett, S. K. Hong and J. A. Krasney
Department of Physiology, School of Medicine, State University of New York at Buffalo 14214.
The influence of head-out water immersion (WI) (37 degrees C) on baroreflex
control of heart rate was studied in five trained, instrumented, conscious
dogs. Arterial pressure was raised and lowered using occluder cuffs
implanted around the aorta and inferior vena cava. Function curves relating
transmural systolic arterial pressure (TSAP = systolic arterial
pressure-pleural pressure) to heart rate (HR) were constructed to compare
responses in air and during WI. The resting TSAP in air [142 +/- 8 mmHg
(mean +/- SE) at 78 +/- 6 beats/min] increased significantly during WI (161
+/- 9 mmHg at 109 +/- 9 beats/min). During WI, the saturation TSAP at the
bradycardia plateau of the relation increased significantly, by 19 mmHg,
whereas the average gain (slope) of the relation decreased significantly,
from -1.426 to -0.752 beats.min-1.mmHg-1. Therefore, WI elicits both a
resetting and a decrease of the average gain of the TSAP-HR relation. The
heart rate range increased during WI as well. After cholinergic blockade
with atropine, WI did not elicit a resetting of the relation and the change
in average gain was abolished. However, after beta 1-blockade with
metoprolol, the resting TSAP increased significantly during WI and
resetting persisted, but the decrease of average gain was abolished.
Therefore, the alteration of the TSAP-HR relation in WI is achieved via a
modulation of both adrenergic and cholinergic regulation of HR.
