How the python heart separates pulmonary and systemic blood pressures and blood flows

Abstract

SummaryThe multiple convergent evolution of high systemic blood pressure among terrestrial vertebrates has always been accompanied by lowered pulmonary pressure. In mammals, birds and crocodilians, this cardiac separation of pressures relies on the complete division of the right and left ventricles by a complete ventricular septum. However, the anatomy of the ventricle of most reptiles does not allow for complete anatomical division, but the hearts of pythons and varanid lizards can produce high systemic blood pressure while keeping the pulmonary blood pressure low. It is also known that these two groups of reptiles are characterised by low magnitudes of cardiac shunts. Little, however, is known about the mechanisms that allow for this pressure separation. Here we provide a description of cardiac structures and intracardiac events that have been revealed by ultrasonic measurements and angioscopy. Echocardiography revealed that the atrioventricular valves descend deep into the ventricle during ventricular filling and thereby greatly reduce the communication between the systemic (cavum arteriosum) and pulmonary (cavum pulmonale) ventricular chambers during diastole. Angioscopy and echocardiography showed how the two incomplete septa, the muscular ridge and the bulbuslamelle -ventricular structures common to all squamates -contract against each other in systole and provide functional division of the anatomically subdivided ventricle. Washout shunts are inevitable in the subdivided snake ventricle, but we show that the site of shunting, the cavum venosum, is very small throughout the cardiac cycle. It is concluded that the python ventricle is incapable of the pronounced and variable shunts of other snakes, because of its architecture and valvular mechanics. Supplementary material available online at

In situcardiac perfusion reveals interspecific variation of intraventricular flow separation in reptiles

“…Clamping of the right atrial filling line almost abolished pulmonary flow, suggesting that the right atrium exclusively fills the cavum pulmonale, guided by the large atrioventricular valves (Jensen et al, 2010). In both species, occluding left atrial filling led to a lesser (but still significant) decrease in systemic flow.…”

“…These species are also functionally exceptional, as pressure in the cavum arteriosum may exceed that in the cavum pulmonale several fold (Burggren and Johansen, 1982;Wang et al, 2003), whereas intraventricular pressures are homogenous in other non-crocodilian reptiles (Johansen, 1959;Shelton and Burggren, 1976;Jensen et al, 2014). Recent echocardiographic and angioscopic investigations demonstrate that the pressure separation is facilitated by the MR forming a pressure-tight seal with the adjacent bulbuslamelle during systole (Jensen et al, 2010. In agreement, our study suggests that blood has little, or no, capacity to cross the muscular ridge during systole in both species.…”

“…In the vast majority of species, the cavum arteriosum and cavum pulmonale generate identical systolic pressures (Johansen, 1959;Shelton and Burggren, 1976;Jensen et al, 2014). However, outstanding amongst reptiles are varanid lizards (Burggren and Johansen, 1982) and pythons (Wang et al, , 2003Jensen et al, 2010), in which the anatomically undivided ventricle becomes 'functionally divided' during systole (Jensen et al, 2010. This functional division requires that the MR and an opposing septum, the bulbuslamelle, adjoin during ventricular contraction, forming a pressure-tight seal between the cavum pulmonale and the rest of the ventricle (Jensen et al, 2010.…”

“…However, outstanding amongst reptiles are varanid lizards (Burggren and Johansen, 1982) and pythons (Wang et al, , 2003Jensen et al, 2010), in which the anatomically undivided ventricle becomes 'functionally divided' during systole (Jensen et al, 2010. This functional division requires that the MR and an opposing septum, the bulbuslamelle, adjoin during ventricular contraction, forming a pressure-tight seal between the cavum pulmonale and the rest of the ventricle (Jensen et al, 2010. This ability correlates with a conspicuously large MR, small cavum venosum and relatively thick cavum arteriosum wall (Farrell et al, 1998;Jensen et al, 2014), and allowed for a convergent evolution of systemic pressures in vast excess of pressures in the pulmonary circuit (Millard and Johansen, 1974;Burggren and Johansen, 1982;Wang et al, 2003;Zaar et al, 2007).…”

Ablation of the ability to control the right-to-left cardiac shunt does not affect oxygen consumption, specific dynamic action or growth in rattlesnakes,Crotalus durissus

“…Jensen et al, 2010b). While numerous studies show that both the magnitude and net direction of these cardiac shunts vary consistently with pulmonary ventilation and metabolic state (e.g.…”