Capacitive function of the heart: influence of acute changes in
heart volume on mean right atrial pressure.
Sheriff, Don D., and Zhengyu Luo.
Division of Cardiovascular Research, St. Elizabeth's Medical
Center, Boston, Massachusetts 02135
APStracts 3:0338H, 1996.
Net transfer of blood volume into or out of the cardiac chambers
should have the same effect on central venous pressure as does
transfer of an equal volume of blood to or from peripheral organs
(e.g. spleen or liver). We studied 5 pentobarbital anesthetized, open
chest pigs (20-23 kg) to determine whether a reduction in the time
-averaged volume of blood contained in the heart, induced by rapid
atrial pacing, can raise right atrial pressure. A central premise of
our study is that the mean value of right atrial pressure is acutely
governed by the volume of blood that distends the central veins, and
that atrial contractions primarily determine how atrial pressure
varies about its mean value. To prevent changes in cardiac output
from altering central blood volume and pressure, cardiac output
during rapid pacing (2.36 +/-0.18 l.min-1) was made to equal the
resting output (2.35 +/-0.16 l.min-1). This was achieved by selecting
a rate of pacing at which the tendency for more frequent cardiac
contractions to raise cardiac output was counterbalanced by the
decrease in stroke volume induced by rapid pacing. Autonomic reflex
mechanisms were attenuated by pharmacological blockade. Mean arterial
pressure was minimally affected in the transition from a normal sinus
rhythm (89 +/-6 beats.min-1) to rapid atrial pacing (165 +/-7
beats.min-1) in 4 pigs. Mean right atrial pressure rose abruptly from
2.8 +/-0.5 mmHg during normal sinus rhythm to 3.5 +/-0.5 mmHg (p
=0.015) at the onset of rapid pacing in these 4 pigs, presumably
owing to decreased cardiac blood volume and a reciprocal expansion of
central venous volume. In the fifth pig, a reduction in CO induced by
tachycardia led to a larger rise in mean right atrial pressure than
did a reduction in CO induced by bradycardia, presumably because
tachycardia reduces cardiac blood volume whereas bradycardia raises
cardiac volume. We conclude that the heart may play an important role
in maintaining or raising its own filling pressure when heart rate
rises.
Received 10 January 1996; accepted in final form 2 August 1996.
APS Manuscript Number H8-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996