AJP - Regulatory, Integrative and Comparative Physiology, Vol 237, Issue 3 197-R202, Copyright © 1979 by American Physiological Society
Regulation of cardiac output during rapid volume loading
G. E. Barnes, B. C. Chevis and H. J. Granger
Interactions between heart rate (HR) and the Frank-Starling mechanism in
augmenting cardiac output (CO) during acute volume loading were studied in
dogs under varying conditions. In normal conscious dogs with low HRs of
70--90 beats/min, end-diastolic diameter (EDD) was maximal and CO was
increased reflexly by cardioacceleration. By contrast, anesthetized
open-chest dogs with high HRs ranging from 140 to 160 beats/min, responded
with bradycardia and CO was adjusted solely by increasing stroke volume
(SV). In anesthetized open-chest dogs with low HRs, EDD was less than
maximal and increases in both HR and SV contributed to augment CO. These
data show that both the cardioacceleration reflex and the Frank-Starling
mechanism are important determinants of the cardiac response to elevated
preload. Although the relative contribution of each control mechanism
varies with initial conditions, their interplay extends the range of
cardioregulation beyond that attainable by either loop operating alone.
