Mechanisms of venous return and ventricular filling in elasmobranch
fishes.
Lai, N. Chin, Jeffrey B. Graham, Valmik Bhargava, and Ralph Shabetai.
Cardiology Section, Veterans Administration Medical Center, San
Diego, CA, Center for Marine Biotechnology and Biomedicine and Marine
Biology Research Division, Scripps Institution of Oceanography,
University of California, San Diego, La Jolla, CA 92093-204,
Department of Medicine, University of California, San Diego, San
Diego, CA
APStracts 2:0484H, 1995.
The current concept of ventricular filling in the elasmobranch fishes
(sharks and rays) is that a subambient pericardial pressure
establishes a negative diastolic pressure gradient for the atrium and
that ventricular end-diastolic volume is exclusively determined by
atrial systole. In contrast, recent findings using echo-Doppler and
digital imaging techniques have demonstrated two filling phases in
the elasmobranch ventricle. In this study, simultaneous atrial and
ventricular pressure measurements made on sharks with either an open
or intact pericardium establish that atrial pressure is above
ventricular diastolic pressure until the onset of ventricular
systole. A positive biphasic atrio-ventricular pressure gradient thus
assures ventricular filling during early diastole, as a result of
ventricular relaxation, as well as during atrial systole. Although a
reduction in pericardial pressure resulted in a decline in both the
atrial and ventricular pressure, a positive atrio-ventricular
pressure gradient is conserved. The finding that atrial diastolic
pressure is not lower than ventricular diastolic pressure, when
combined with previous results showing that pericardial pressure is
generally at or above ambient and that ventricular filling is
biphasic, constitute a strong body of evidence favoring the operation
of a direct venous inflow as the mechanism by which the elasmobranch
heart fills.
Received 18 July 1994; accepted in final form 9 October 1995.
APS Manuscript Number H632-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95