Circulatory changes during experimental diving in the turtle.

WHITE, FRED N., AND GORDON Ross. Circulatory changes during experimental diving in the turtle. Am. J. Physiol. 2 I I ( I) : I 518. I g66.-Blood flow (electromagnetic flowmeters) and pressures in pulmonary and systemic circuits were studied in intact, unanesthetized turtles (Pseudemys scripta) in both nondiving and diving states. Cardiac output (combined pulmonary, left and right arch flows) in the predive state was in the order of 50-60 ml/kg per min with 60% distributed to the pulmonary circuit (left-to right shunt). During diving, bradycardia and a reduction and redistribution of cardiac output (right-to-left shunt) occurred after an interval varying from 8 to 180 min. The development of the shunt was accompanied by a decrease in the systemic and increase in the pulmonary resistances. These changes were rapidly reversed on surfacing into air or nitrogen, but persisted when the turtles surfaced into carbon dioxide, suggesting that hypercarbia is involved in their maintenance.