THE ROLE OF CARDIAC SHUNTS IN THE REGULATION OF ARTERIAL BLOOD-GASES

The pulmonary and systemic circulations are not completely separated i n reptiles and amphibians, so oxygen-rich blood returning from the lun gs can mix with oxygen-poor blood returning from the systemic circuit (cardiac shunts), In these animals, the arterial blood gas composition is determined by both lung ventilation and the cardiac shunt, Therefo re, changes in cardiac shunting patterns may participate actively in t he regulation of arterial blood gases, In turtles the cardiac shunt pa ttern changes independently of ventilation and the cardiac R-L shunt ( pulmonary bypass of systemic venous blood) is reduced under circumstan ces where the demands on efficient gas exchange are high (hypoxia, hyp oxemia or exercise), We propose, therefore, that the size of cardiac s hunts is regulated independently of ventilation and hypothesize that t here exist at least two groups of peripheral chemoreceptors with diffe rent reflex roles.