Pressure trap created by vein valve closure and its role in graft stenosis.

Saphenous vein graft stenosis has become the leading cause of reoperation in coronary bypass operations. We investigated the role of vein valves in vein graft stenosis by studying 14 human saphenous veins placed in a simulator of the left side of the heart in parallel with the arterial system. The vein had a variable resistance and a capacitance simulating the distal vascular bed. The pressures at the proximal and distal ends of the vein and the venous flow were measured while the following were changed: venous flow 200 to 0 ml/min, aortic pressure 150/120 to 80/60 mm Hg, cardiac output 3 to 5 L/min, and compliance of distal vascular bed 0 to 1 ml of air. The pressures at both ends of the vein were the same when venous flow rate was greater than 60 ml/min and the vein valve remained open. As the venous flow decreased the valve began to open and close in each cardiac cycle. The flow rate at which the valve began to close ranged from 30 to 10 ml/min. When the valve closed, it trapped the pressure in the segment distal to the valve. Because the segmental hypertension is expected to accelerate atherosclerotic changes, the pressure trap created by closure of the vein valve could be an important cause of vein graft stenosis.