The Influence of Combined Intra-aortic Balloon Counterpulsation and Hyperosmotic Mannitol on Regional Myocardial Blood Flow in Ischemic Myocardium in the Dog

We investigated the combined effectiveness of intraaortic ballooon counterpulsation and hyperosmotic mannitol (25%) on regional myocardial blood flow during acute coronary insufficiency. Cardiac output and paced heart rate were held constant in chloraloseanesthetized dogs during right heart bypass. Acute coronary insufficiency was produced by ligation of the proximal left anterior descending coronary artery (LAD). Regional myocardial blood flow was measured using radioactive microspheres. Left ventricular end-diastolic pressure, mean aortic pressure, maximum left ventricular dp/dt, and hematocrit were unchanged by combined mannitol infusion and balloon pumping. Studies of combined treatment with balloon pumping and mannitol immediately after the second of two 13-minute consecutive reversible ligations of the LAD demonstrated that (1) collateral coronary blood flow increased 46% (P < 0.02) in ischemic myocardium compared with mannitol infusion alone during the first LAD ligation, and (2) collateral coronary blood flow increased 27% (P < 0.05) in ischemic myocardium compared with balloon pumping along during the first LAD ligation. Studies in which combined treatment was delayed until 20 minutes after LAD ligation demonstrated that collateral coronary blood flow was elevated by 33% (P < 0.05) in ischemic myocardium compared to control studies in which balloon pumping alone had no effect. The results suggest that the increase in collateral coronary blood flow was in part a result of an increased transmural pressure gradient produced by balloon diastolic augmentation and the ability of mannitol to reduce coronary vascular resistance in ischemic myocardium.