Journal of Applied Physiology, Vol 54, Issue 5 1261-1268, Copyright © 1983 by American Physiological Society
Effect of diaphragm contraction on canine heart and pericardium
T. C. Lloyd Jr and J. A. Cooper
Pericardiophrenic attachments transmit diaphragm contraction to the
pericardium. We investigated this in two ways. 1) We replaced the hearts of
externally perfused dogs with a balloon from which we measured pressure
changes. Diaphragm contraction increased pressure from 4.6 to 5.5 Torr,
equivalent to an isobaric volume decrease of 1.5%, and decreased volumetric
compliance by 3%. 2) We selectively servo controlled right atrial pressure,
left atrial pressure, or cardiac output in open-chest dogs and monitored
the effect of diaphragm contraction on cardiovascular and abdominal
pressures, cardiac output, and the volume of blood added to or withdrawn
from the circulation to achieve servo control. Diaphragm contraction
decreased left atrial pressure 0.4 Torr when right atrial pressure was
controlled and right atrial pressure increased 0.2 Torr while controlling
left atrial pressure, but there were no significant changes in cardiac
output. Atrial pressure did not change significantly when output was
controlled. Servo control required removal of approximately 50 ml of blood,
presumably reflecting a decreased splanchnic vascular capacity at the
higher abdominal pressure. We conclude that the diaphragm may slightly
tense the pericardium, but this has no important primary effect on the
heart.
