Dynamics of blood circulation during diving in the bottlenose dolphin (Tursiops truncatus): the role of the retia mirabilia.
, Paola Bagnoli, Cinzia Centelleghe, Mike Maric, Ginevra Brocca, Sandro Mazzariol, Bruno Cozzi.
Abstract: The retia mirabilia are vascular nets composed of small vessels
dispersed among numerous veins, allowing blood storage, regulation of
flow and pressure damping effects. Here, we investigated their potential
role during the diving phase of the bottlenose dolphin (Tursiops truncatus).
To this effect, the whole vertebral retia mirabilia of a series of
dolphins were removed during post-mortem analysis and examined to assess
vessel diameters, and estimate vascular volume and flow rate. We
formulated a new hemodynamic model to help clarify vascular dynamics
throughout the diving phase, based on the total blood volume of a
bottlenose dolphin, and using data available about the perfusion of the
main organs and body systems. We computed the minimum blood perfusion
necessary to the internal organs, and the stroke volume and cardiac
output during the surface state. We then simulated breath-holding
conditions and perfusion of the internal organs under the diving-induced
bradycardia and reduction of stroke volume and cardiac output, using
10 beats min-1 as the limit for the heart rate for an
extended dive of over 3 min. Within these simulated conditions, the
retia mirabilia play a vital role as reservoirs of oxygenated blood that
permit functional performances and survival of the heart and brain. Our
theoretical model, based on the actual blood capacity of the retia
mirabilia and available data on organ perfusion, considers the dynamic
trend of vasoconstriction during the diving phase and may represent a
baseline for future studies on the diving physiology of dolphins and
especially for the blood supply to their brain.
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