FUNCTIONAL-ROLE OF CARDIAC SHUNTS IN REPTILES

Cardiac shunting normally occurs in chelonians (turtles), squamates (l izards and snakes) and crocodilians (alligators, caimans, crocodiles). The magnitude of these shunts is affected by the ventilatory state an d provides these animals with a flexibility in blood flow that cannot be achieved in mammals or birds. The differential distribution of bloo d flow into the pulmonary and systemic circulations has prompted physi ologists to postulate the functional significance of such a circulator y design. Most authors agree that cardiac shunts are not atavistic rel ies, but represent an important cardiovascular adaptation in extant re ptiles. Nevertheless, while these hypotheses may be intuitively appeal ing, experimental evidence attesting the advantageous role of cardiac shunts in pulmonary gas exchange is lacking. The purpose of this paper is to review, in detail, the various hypotheses that explain the func tional significance of cardiac shunts in pulmonary gas exchange in int ermittently breathing reptiles. (C) 1996 Wiley-Liss, Inc.