Alterations in Central Blood Volume and Cardiac Output Induced by Positive Pressure Breathing and Counteracted by Metaraminol (Aramine)

High levels of positive pressure breathing in the dog resulted in substantial depression of central blood volume as well as cardiac output and arterial pressure. The administration of metaraminol elevated these lowered values while positive pressure breathing was maintained. The beneficial effects observed are thought to be attributable to this drug's influence on venous and arteriolar tone and myocardial contractility. The mechanism of the circulatory depression produced by positive pressure breathing is discussed.