Changes in the manufacture of expanded microporous polytetrafluoroethylene: effects on patency and histological behavior when used to replace the superior vena cava.

Polytetrafluoroethylene (PTFE) has been used clinically and experimentally as a vein substitute. Since its introduction, changes have been made in the manufacture of the material. This study was designed to evaluate the effects of pore size (fibril length), PTFE cover, and spiral tube support on long-term patency and histological behavior when this material is used as a replacement for the precava in the dog. A graft of 30-mu pore size has adequate fibroblastic ingrowth, a neointima of 200 mu or less, and the best long-term patency. The PTFE cover results in less fibroblastic involvement of the prosthetic graft and prevents late occlusion caused by transmural fibrosis in the 90-mu graft. The spiral support does not affect patency and may be indicated when external pressure on the tube must be avoided.

Coronary flow distribution and dynamics during continuous and pulsatile extracorporeal circulation in the pig.

Four extracorporeal perfusion conditions (continuous beating, continuous fibrillating, pulsatile beating, and pulsatile fibrillating) were tested for 15 minutes each in pigs. Coronary flow, endocardial-epicardial flow ratio, phasic coronary flow, myocardial oxygen consumption, and myocardial lactate extraction were measured. No significant differences in any of these variables were found between pulsatile and continuous flow states in either fibrillating or beating hearts (p greater than 0.05). In both fibrillating conditions, significant elevations of myocardial oxygen consumption and decreases in endocardial-epicardial flow ratios were found (p less than 0.05). Lactate extraction occurred in all conditions, and phasic coronary flows were similar in both beating conditions. These data suggest caution in the expectation that pulsatile perfusion will reverse the coronary flow and myocardial oxygen consumption changes seen with fibrillation.