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In situ cardiac perfusion reveals interspecific variation of intraventricular flow separation in reptiles

Journal article
Authors W. Joyce
Michael Axelsson
J. Altimiras
T. Wang
Published in Journal of Experimental Biology
Volume 219
Issue 14
Pages 2220-2227
ISSN 0022-0949
Publication year 2016
Published at Department of Biological and Environmental Sciences
Pages 2220-2227
Language en
Links dx.doi.org/10.1242/jeb.139543
Keywords Cardiovascular, Cardiac shunting, Reptile, Blood flow, Perfused heart, pulmonary blood-flow, lizard varanus-exanthematicus, south-american, rattlesnake, turtles trachemys-scripta, fresh-water turtle, cardiovascular-system, python-molurus, ventricular hemodynamics, chrysemys-scripta, crotalus-durissus, xon g. e. h., 1956, proc zool soc london, v126, p145, xon geh, 1955, biological reviews of the cambridge philosophical society, v30, p196
Subject categories Biological Sciences

Abstract

The ventricles of non-crocodilian reptiles are incompletely divided and provide an opportunity for mixing of oxygen-poor blood and oxygen-rich blood (intracardiac shunting). However, both cardiac morphology and in vivo shunting patterns exhibit considerable interspecific variation within reptiles. In the present study, we develop an in situ double-perfused heart approach to characterise the propensity and capacity for shunting in five reptile species: the turtle Trachemys scripta, the rock python Python sebae, the yellow anaconda Eunectes notaeus, the varanid lizard Varanus exanthematicus and the bearded dragon Pogona vitticeps. To simulate changes in vascular bed resistance, pulmonary and systemic afterloads were independently manipulated and changes in blood flow distribution amongst the central outflow tracts were monitored. As previously demonstrated in Burmese pythons, rock pythons and varanid lizards exhibited pronounced intraventricular flow separation. As pulmonary or systemic afterload was raised, flow in the respective circulation decreased. However, flow in the other circulation, where afterload was constant, remained stable. This correlates with the convergent evolution of intraventricular pressure separation and the large intraventricular muscular ridge, which compartmentalises the ventricle, in these species. Conversely, in the three other species, the pulmonary and systemic flows were strongly mutually dependent, such that the decrease in pulmonary flow in response to elevated pulmonary afterload resulted in redistribution of perfusate to the systemic circuit (and vice versa). Thus, in these species, the muscular ridge appeared labile and blood could readily transverse the intraventricular cava. We conclude that relatively minor structural differences between non-crocodilian reptiles result in the fundamental changes in cardiac function. Further, our study emphasises that functionally similar intracardiac flow separation evolved independently in lizards (varanids) and snakes (pythons) from an ancestor endowed with the capacity for large intracardiac shunts.

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