AJP - Heart and Circulatory Physiology, Vol 256, Issue 2 361-H367, Copyright © 1989 by American Physiological Society
Effects of steps in cardiac output and arterial pressure in awake dogs with AV block
D. S. O'Leary, A. M. Scher and J. E. Bassett
Department of Physiology and Biophysics/SJ-40, University of Washington School of Medicine, Seattle 98195.
In awake dogs with atrioventricular block, we examined the responses in
total peripheral resistance and atrial rate to square-wave changes in mean
arterial pressure or cardiac output. We compared the responses 2-3 min
after a step change with the responses 19-20 min after a step. With
resetting of arterial pressure control, the compensatory responses should
decrease as the baroreceptors reset to the prevailing pressure. With step
changes in mean arterial pressure or cardiac output, the responses in both
peripheral resistance and atrial rate increased from minutes 2-3 to minutes
19-20. The responses in peripheral resistance also increased in animals
studied after bilateral vagal block. All of the above changes were
significant in the majority of cases. In another experiment, the animals
were "conditioned" by 20 min at imposed high or low pressure. When control
was returned to the animal after conditioning at high pressure, arterial
pressure was not significantly different (P greater than 0.05) from the
initial control levels. When control was returned after conditioning at low
pressure, arterial pressure was significantly greater (P less than 0.05)
than during the initial control period. These results indicate an absence
of resetting of the entire arterial pressure control system.
