AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 3 805-R818, Copyright © 1994 by American Physiological Society
Arterial mechanics in the fin whale suggest a unique hemodynamic design
R. E. Shadwick and J. M. Gosline
Department of Biology, University of Calgary, Alberta, Canada.
An analysis of the dimensions of the aortic tree and the mechanical
properties of arterial wall tissues in the fin whale (Balaenoptera
physalus) is presented. The aortic arch is greatly expanded, having an
internal radius at an estimated mean blood pressure (13 kPa) that is 2.5
times greater than that of the descending thoracic aorta. At this pressure,
the elastic modulus of the arch wall (0.4 MPa) is 30 times less than that
of the descending aorta (12 MPa). Consequently, even though some
capacitance is provided anteriorly by the relatively compliant innominate
and carotid arteries, > 90% of the arterial capacitance resides in the
arch. The characteristic pressure wave velocity (C0) and impedance (Z0)
were calculated from vessel dimensions and elasticity. A predicted 20-fold
increase in Z0 between the arch and thoracic aorta should provide a major
reflecting site, effectively uncoupling the arch from the remainder of the
arterial tree. The dimensions of the arch relative to the likely pressure
wavelengths within it suggest that it acts like a compliant windkessel that
greatly reduces the pulsatility of the inflow to the descending aorta,
which itself likely acts as a rigid, tapered manifold. It is suggested that
the presence of both a highly compliant arch and a relatively rigid
descending aorta is an adaptation for diving.
