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

Area of Science:

• Comparative Cardiology
• Vertebrate Physiology
• Reptilian Anatomy

Background:

• High systemic blood pressure in terrestrial vertebrates typically requires lowered pulmonary pressure.
• Mammals, birds, and crocodilians achieve this with a complete ventricular septum.
• Most reptiles lack complete ventricular division, yet pythons and varanid lizards maintain pressure separation with minimal cardiac shunts.

Purpose of the Study:

• To elucidate the cardiac mechanisms enabling pressure separation in python hearts.
• To describe the specific cardiac structures and intracardiac events responsible for this physiological feat.

Main Methods:

• Utilized ultrasonic measurements (echocardiography) to visualize cardiac structures and blood flow.
• Employed angioscopy to observe intracardiac events during the cardiac cycle.
• Investigated the roles of atrioventricular valves and ventricular septa in pressure regulation.

Main Results:

• Echocardiography showed atrioventricular valves descending into the ventricle during diastole, reducing chamber communication.
• Angioscopy and echocardiography revealed that the muscular ridge and bulbuslamelle contract during systole, functionally dividing the ventricle.
• The cavum venosum, the site of shunting, was observed to be very small throughout the cardiac cycle in pythons.

Conclusions:

• The python ventricle's architecture and valvular mechanics prevent pronounced and variable shunts seen in other snakes.
• These features allow pythons to achieve high systemic blood pressure while maintaining low pulmonary blood pressure.
• This study reveals the specialized cardiac adaptations for pressure separation in pythons.