The significance of graft diameter

To study the influence of diameter on graft patency, an 8 mm aortoiiliac Dacron graft was implanted in on leg of 25 dogs that had liac arteries 3 to 5 mm in diameter and a 5 mm graft was placed in the other leg. In six dogs both grafts clotted within 3 months, in 10 dogs both grafts remained patient until the dogs were killed between 7 and 66 months, and in nine dogs one graft became occluded before the other. In eight of these nine animals the 8 mm graft became occluded before the 5 mm graft; only in one dog did the 5 mm graft become occluded first. When the 10 dogs with two patient grafts were killed, the 8 mm graft was found to be lined with thick, organized fibrin, whereas the 5 mm graft had a thin, smooth, glistening lining. Histologic examination confirmed that healing was more complete in the 5 mm graft. In vivo blood flow measurements in the dogs were used to compare flow rates and graft resistance in 4, 6, 8, 10, and 12 mm grafts. A given sized graft carried the same flow capacity as larger grafts until the flow rate was reached when graft resistance developed. Once resistance appeared, the graft could still triple or quadruple its flow capacity but it could not deliver the same rate of flow under the same pressure head as larger grafts. In 4 mm grafts, resistance first appeared at approximately 150 cc/min and capacity was 450 cc. In 6 mm grafts, resistance developed at 400 cc/min and capacity exceeded 1,200 cc. In 8 and 10 mm grafts, resistance was first noted at 800 and 1.400 cc/min, respectively. These studies suggest that 6 mm diameter grafts can carry the 200 cc/min or less that is measured in the human superficial femoral artery at rest, as well as the four-to sixfold increase that accompanies vigorous exercise.