THE REGULATION OF CIRCULATION

Abstract

Using methods previously described, the authors have studied the mechanism responsible for the increase in cardiac output with anoxemia. Brief and severe anoxemia caused an increased cardiac output in mor-phinized and trained unnarcotized dogs and studies of mild anoxemia placed the "anoxemic threshold" at about 75% O saturation. After adrenalectomy anoxemia caused an increase in the output, indicating that the adrenals were not necessary for the response. After cardiac denervation by removing the stellate ganglia and thoracic sympathetic trunks and sectioning the vagi, anoxemia still caused an increased output. Anoxemia caused a similar response in sympathecto-mized dogs, vagotomized dogs and atropinized dogs. The results suggested that deficient oxygenation of the coronary blood caused an increase in cardiac output by a direct effect on the myocardium. Ligation of the thoracic aorta and thoracic vena cava caused a diminution in the output but there was in these cases an increase following anoxemia. Anoxemia also caused an increased cardiac output after ligation of the carotid and subclavian arteries.