THE EFFECT OF CARDIAC SYMPATHETIC BLOCKADE ON THE RELATIONSHIP BETWEEN CARDIAC OUTPUT AND CARBON DIOXIDE TENSION IN THE ANAESTHETIZED DOG

In dogs anaesthetized with either halothane or chloralose cardiac output was measured at three levels of arterial carbon dioxide tension. As the carbon dioxide tension was raised there were significant increases in cardiac output. After the administration of a selective cardiac beta-receptor blocking agent (practolol) there were no significant changes in cardiac output as the carbon dioxide tension was increased. It was concluded that the increased cardiac output seen with a raised arterial carbon dioxide tension was brought about by an increased activity in the sympathetic nervous system.