Journal of Applied Physiology, Vol 65, Issue 4 1662-1675, Copyright © 1988 by American Physiological Society
Effects of changes in left ventricular loading and pleural pressure on mitral flow
J. L. Robotham, R. S. Stuart, A. M. Borkon, K. Doherty and W. Baumgartner
Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Hospital, Baltimore, Maryland 21205.
The cause of the fall in left ventricular (LV) stroke volume (SV) during a
fall in pleural pressure (Pp1) has been in dispute for over a century. We
have defined the changes in the temporal relationship between LV inflow
(Qm) and outflow (Qa) in a canine preparation to test the mutually
exclusive hypotheses that the fall in LVSV is caused only by changes during
diastole (e.g., ventricular interdependence) or only by changes during
systole (e.g., afterload). The ability of the experimental preparation to
measure the results of acute changes in right heart volume or output and
acute changes in LV afterload was validated in open-chest studies with and
without pericardial constraint. In closed-chest studies, with a fall in Pp1
during a Mueller maneuver Qm reached both its inspiratory minimum and
expiratory maximum before Qa in 80% of the Mueller maneuvers, invalidating
both hypotheses, which each required that one flow lead the other in 100%
of the Mueller maneuvers. Review of individual records suggested that if
the rapid changes in Pp1 occurred during systole, Qa could vary in a manner
independent of the preceding Qm. These studies suggest that both diastolic
and systolic events may contribute to the fall in SV, while causing
opposite changes in LV volumes.
