Influence of blood flow and the effect of protamine on the thromboresistant properties of a covalently bonded heparin surface

Polyethylene tubings, 2-mm inner diameter and the length of 1 m, untreated or furnished with a covalently bonded heparin surface layer, were inserted as arteriovenous shunts bilaterally in dogs. By compressing the middle part, the initial blood flow was adjusted to 10 or 40 mL/min. The thrombogenicity of the tubings was assessed by the patency of the shunts and by assaying the generation of fibrinopeptide A (FPA) in arterial blood and in blood after its passage through the shunts. In untreated shunts clotting rapidly occurred preceded by high FPA generation in blood passing through the shunts. The blood flow in heparinized shunts remained unchanged throughout the test period. At the low flow rate a certain degree of FPA generation in the shunts occurred. At the high flow rate no changes in FPA levels occurred. The function of the heparin surface is thus flow rate dependent. Systematic heparinization and subsequent neutralization with protamine or administration of protamine alone did not interfere with the function of the heparin surface.