AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 1 174-R180, Copyright © 1986 by American Physiological Society
Pressure-volume characteristics of aortas of harbor and Weddell seals
E. A. Rhode, R. Elsner, T. M. Peterson, K. B. Campbell and W. Spangler
The mechanical properties of the radially enlarged proximal segment of the
aorta of diving marine mammals was studied on 15 excised aortas of harbor
seals and five aortas of Weddell seals. This was done by recording static
pressure-volume relationships for the whole thoracic aorta, the aortic
bulb, and the descending thoracic aorta and passive length-tension
measurements of aortic strips. Aortic bulb volume distensibility was found
to be much greater than that of the descending thoracic aorta or of an
equivalent aortic segment of terrestrial mammals. The consequences were
that the total potential energy and volume that may be stored within the
aortic bulb is very large, with a capacity for storage of the stroke work
of more than two normal heart beats and a volume of more than three times
normal stroke volume. The aortic bulb has an average radius and wall
thickness twice that of the descending aorta, but at any level of
distension the wall stress (g/cm2) is the same throughout. The static
mechanical properties of aortic strips from the bulb and descending
thoracic aortas were not markedly different, so that the differences in the
pressure-volume relationships are explained by differences in geometry of
the two sections. The expanded aortic bulb functions through energy and
volume storage actions and through uncoupling actions to maintain arterial
pressures and stroke volume at near predive levels during a dive.
