The effect of chronic cardiac volume overload on regional myocardial blood flow in the dog

Regional myocardial blood flow was studied in the anaesthetized, open-chest dog with a large chronic aorto-caval fistula, using carbonized microspheres of 7-10 mum diameter. The results from fourteen dogs with fistulae of 4-84 days duration were compared to those from nine normal animals. 2. Myocardial blood flow to all areas of both ventricles was increased to between 180 and 250% of the normal despite lower aortic diastolic (coronary diastolic) pressure. Myocardial blood flow in the right ventricle was lower than in the left in both groups of dogs although the increase above normal in dogs with fistulae was relatively greater in the right ventricle. Increased myocardial blood flow is attributed to coronary autoregulation resulting from increased myocardial oxygen consumption due to increase in myocardial tension development. 3. Although absolute blood flow to the inner left ventricular wall was markedly increased in all dogs with fistulae, in those with aortic diastolic pressure below 55 mmHg the ratio of flow in the inner to that in the outer free left ventricular wall was significantly less than in those with aortic diastolic pressure above 55 mmHg (P less than 0 with 02). Low aortic diastolic pressurere and diastolic coronary perfusion pressure probably resulted in relative ischaemia of the inner left ventricular wall.