Cardiovascular responses to diving in the turtle, Pseudemys scripta

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Ware, Stuart
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The cardiovascular responses to diving in the freshwater turtle, Pseudemys scripta, were determined by using the classical techniques of electrocardiography, impedance pneumography and direct blood pressure recording. The radioactive microsphere method was used to measure cardiac output and regional blood flows as well as to quantitate the intracardiac shunting of blood;Following a forced dive (with the animal being firmly attached to an adjustable diving platform) the heart rate gradually decreased by as much as 98%. Voluntarily diving animals, however, usually showed an immediate bradycardia of about 28%. A heart rate reduction similar to that obtained in voluntarily diving animals was occasionally observed during apnea in aerial turtles;Mean systemic and pulmonary arterial blood pressures did not change during diving, but pulse pressures increased about 2-fold. Central venous pressure remained constant;Total heart output was reduced by one-half in forcibly submerged animals. Since the pulmonary and systemic circuits are in parallel rather than in series, blood flow through the 2 systems need not be equal. In the submerged turtles, blood flow to the lungs decreased by 70%, while systemic flow decreased 39%. Stroke volume increased by 146% to the 2 systemic arteries, while increasing only 19% to the pulmonary trunk. Most of the parameters measured showed a large variation between animals;Pulmonary vascular resistance was elevated 235% after forced submergence while the systemic impedance increased 62%. The impedance of the 2 circuits was similar in aerial animals;Above water, animals showed a 25% net right-to-left intracardiac shunt (25% of the right atrial blood being ejected directly into the systemic arches) and this increased to 60% in submerged animals. Therefore, in relative terms, blood flow is being shifted away from the lungs and towards the systemic tissues during a forced dive;Microsphere data indicated that right-to-left shunted blood is directed primarily to the left aorta in turtles. Furthermore, the right atrial blood which did enter the brachiocephalic artery was, in large measure, kept away from the carotid arteries. Since the shunted and unshunted blood which enter the systemic arteries remains separated, viscera received more of the shunted blood, whereas the kidneys and posterior skeletal muscles received less;The vasoconstriction which allows blood pressure to be well maintained during diving appears to be a selective process. During a forced dive, blood was primarily distributed to the brain (537% increase), heart and skeletal muscles. Flow was drastically reduced to most other tissues;Due to methodological considerations, blood flow data could not be obtained in voluntarily diving animals. However, in forcibly submerged turtles, there occurred a cardiovascular response similar to that which is known to occur in birds and mammals.

Tue Jan 01 00:00:00 UTC 1980