Functional anatomy of the heart of reptiles.

Abstract

Intravascular pressures, distributions of blood oxygen, dye-dilution curves, cineradiography, and electromagnetic flowmeters in major vessels suggest a highly directional flow oE systemic and pulmonary venous blood through reptilian hearts. The lacertilian right aortic arch contains blood from the pulmonary, and the left from the pulmonary or sometimes both pulmonary and systemic veins. Traces made of the pressure and blood flow show that the lacertilian and chelonian cava venosum and pulmonale are functionally distinct. Atrioventricular valves probably prevent regurgitation during ventricular systole and form an obstruction between the cava arteriosum and venosum during ventricular filling. The muscular ridge approaches the ventral ventricular wall at systole forming a functional ventricular septum. Low pulmonary vascular resistance favors pulmonary ejection before systemic. In Pseudemys the balance between pulmonary and systemic resistance causes a left-to-right shunt during respiration and a right-to-left shunt during diving; the latter probably reduces the expenditure of cardiac energy during hypoxia. Pressure traces and cineradiography indicate separation of systemic and pulmonary venous returns in alligators. The left ventricle perfuses both aortic arches and the right the pulmonary arch. Right ventricular pressure may exceed pulmonary pressure during ejection suggesting an impedance in the pulmonary outflow tract. Pulmonary resistance in crocodilians may increase during diving, instituting a right-to-left shunt.