The physiologic action of oxygen and carbon dioxide on the coronary circulation, as shown by blood gas and electrocardiographic studies

Abstract By means of blood gas and electrocardiographic observations, the physiologic action of oxygen and carbon dioxide on the coronary circulation was studied. When a deficiency of oxygen has been produced in the arterial blood by decreasing the oxygen concentration of inspired air, certain compensating mechanisms become manifest, such as an increase in pulmonary ventilation and circulation velocity. In cases of coronary sclerosis, the narrowed lumina of the coronary arteries impose a variable degree of obstruction to an increase in the flow of blood. The induction of oxygen want in the presence of this relative ischemia results in severe anoxia of the heart muscle, the consequences of which are (1) coronary insufficiency, with precordial pain and cardiac or peripheral circulatory failure, and (2) electrocardiographic changes, particularly lowering of the T wave or depression of the S-T segment. The increased pulmonary ventilation produced by acute anoxia engenders a disproportionate loss of dissolved carbon dioxide, with a shift in blood pH toward the alkaline side. Since alkalosis produced by hyperventilation has been shown to cause constriction of capillaries in other parts of the body, the possibility that it may have the same effect on the coronary circulation was investigated. The addition of small amounts of carbon dioxide, such as 2 to 3 per cent, to a low-oxygen mixture prevented the clinical and electrocardiographic signs of coronary insufficiency which have been described above. Although the inhalation of a low-oxygen carbon dioxide mixture in eight out of ten cases of coronary disease resulted in a higher arterial oxygen saturation than the inhalation of a comparable low-oxygen mixture, there were four cases in which the symptoms or electrocardiographic signs of coronary insufficiency either did not occur, or were diminished, in the presence of a comparable, severe arterial anoxemia, when carbon dioxide loss was prevented. The inhalation of high-oxygen concentrations is known to improve the function of the coronary circulation when it has been previously impaired. The electrocardiographic effects of the inhalation of approximately pure oxygen in thirty-two cases of coronary disease were studied. In twenty-seven cases, the T wave was rendered more upright. The addition of carbon dioxide to high-oxygen concentrations either had no effect, or, in six cases, diminished slightly the T-wave elevation produced by inhaling high-oxygen mixtures. Accepting Macleod's thesis that one of the factors influencing the height of the T wave is the speed of recovery of cardiac muscle, we tentatively conclude that the evidence obtained in these studies suggests that the inhalation of low-oxygen mixtures prolongs the recovery period of heart muscle in patients with coronary disease, and that the inhalation of high-oxygen mixtures shortens the recovery period. In the presence of acute anoxia, the inhalation of small amounts of carbon dioxide shortens the recovery period of cardiac muscle, in part by increasing the arterial oxygen tension, and in part by preventing constriction of capillaries in the coronary circulation. The administration of carbon dioxide in the absence of alkalosis may in some cases delay the recovery period of heart muscle.