Increases in coronary vascular resistance related to high arterial oxygen tension in dogs

It is known that oxygen inhalation induces coronary vessel constriction as well as brings about a reduction in myocarial oxygen consumption. The present study was performed to clarify whether or not this constriction of the coronary vessels resulting from oxygen is secondary to the reduction in myocardial oxygen consumption. The regional myocardium in 12 mongrel dogs was perfused with femoral arterial blood at a constant rate of flow. While maintaining myocardial oxygen consumption equal by adjusting heart rate, coronary vascular resistance was compared under the two following conditions: 1) perfusion of the coronary artery with the dog's own femoral arterial blood (pO2 : 95 +/- 14 mmHg) and 2) perfusion with blood with a high level of oxygen tension (pO2 : 497 +/- 56 mmHg). Coronary vascular resistance was increased (p < 0.001) from 3.00 +/- 1.25 to 3.36 +/- 1.28 mmHg/ml/min by incresing the pO2 in the perfusing blood, even though myocardial oxygen consumption was kept at the same level. This increase in coronary vascular resistance resulting from the increase in oxygen tension was independent of the coronary perfusion rate as well as independent of the presence or absence of myocardial ischemia. This suggests that coronary vasoconstriction due to oxygen is not secondary to decreases in myocardial oxygen demand.