Validity of some methods of estimating circumferential elastance of vascular prostheses

The two methods for tensile testing of vascular prostheses, cited in a Draft International Standard, have been compared on normal aorta, autologous vein, two knitted Dacron, expanded PTFE and elastomeric composite prostheses before and after implantation as an aorto-femoral bypass in the dog. With the exception of Gore-Tex expanded PTFE, tensiometric stressing and balloon distension are not equivalent techniques in 'as supplied' prostheses or in normal vessels, owing to the basic anisotropic properties of the different materials. The tensiometric method gave much lower estimates of circumferential elastance, ranging from 44.6% for CCV elastomeric to 80.4% for normal canine aorta of the elastance estimate using balloon distension. The differences between the two methods were much less marked on explant samples of synthetic prostheses, but remained for autologous vein. It is concluded that although the methods are equally valid for quality assurance purposes they are inappropriate to compare probable clinical performance, unless carried out on explant samples. The preferred method to cover all the prostheses studied, including autologous vein, should employ omnidirectional stressing. Manufacturers' specifications are, therefore, not necessarily related to clinical performance.