The Functioning of the Frog’s Single Ventricle

Abstract

African clawed frog (Xenopus laevis) has double-inlet and single-outlet single ventricle supporting both systemic and pulmonary circulations, with normal lifespan of 25-30 years. The relationship between pulmonary and systemic blood flows was investigated using echocardiography. Twelve female African clawed frogs, age 18-24 months, mean weight 173±19 grams were studied. Heart rate, percutaneous oxygen saturation, echocardiography derived 2D and blood flow in all cardiovascular structures were measured in two temperature setting, 17◦C (normal environment for frogs) and 22 C. In eight frogs cerebral Near-Infra-Red Spectroscopy (NIRS) was measured. Mean oxygen saturation was 66±9% with temperature of 22◦C and 85±6% with 17◦C (P<0.001), while there was no statistical difference between mean heart rates, respectively 48 13 and 42±7 beats/min. Doppler echocardiography showed a mean total pulmonary blood flow (QP) =173.0 ml/min and mean total systemic blood flow (QS) = 99.3ml/min, with mean QP/QS of 1.74:1.00. The only statistical correlation between size of the cardiovascular structures and body weight was found for the pulmonary veins, with correlation coefficient = 0.71 (P=0.02). NIRS measurements showed a reverse correlation (coefficient = -0.21) with oxygen saturation. The frog’s heart has peculiar morphologic and functional characteristics allowing normal quality of life for many years despite the presence of single ventricle. Baseline QP/QS under general anesthesia was significant for increased total pulmonary blood flow. Exposure to environmental temperature 5◦C higher than normal caused peripheral vasodilatation, with subsequent decrease of QP/QS and reduced oxygenation.