Arteriovenous shunts in dilated or reperfused canine coronary vasculature.

Abstract Arteriovenous shunts in the coronary circulation were investigated by measuring the passage of microspheres, 7–10 μm in diameter, through the coronary vascular bed of anesthetized open-chest dogs. In Group I (12 dogs), the left common coronary artery was cannulated and perfused with arterial blood at aortic pressure. Venous blood was collected from the coronary sinus. In Group IA (six dogs), the following measurements of percentage shunt flow were made: control, 2.0 ± 0.2%; reactive hyperemia following 20-sec coronary artery occlusion, 1.8 ± 0.2%; coronary dilation with adenosine, 2.0 ± 0.1%. In Group IB (six dogs), the following observations were made: control, 1.8 ± 0.7%; coronary dilation with adenosine and perfusion pressure elevated to 170 mm Hg, 2.4 ± 0.5%; systemic hypoxia due to inhalation of nitrogen and perfusion pressure elevated to 170 mm Hg, 4.2 ± 0.9%. Only under the hypoxic condition was the percentage shunt flow significantly elevated above the control condition. In Group II (six dogs), the left anterior descending coronary artery (LAD) was cannulated and perfused, and the ascending coronary vein was cannulated for collection of venous blood. For 2 hr, the LAD perfusion line was clamped. Upon reperfusion of the LAD vasculature, the following observations of shunt flow were made: at 5 min, 2.2 ± 0.7%; at 1 hr, 2.5 ± 0.8%; at 2 hr, 2.8 ± 2.0%. These values did not significantly differ among themselves or from the control observations in Group I.