Vascular implants for peripheral arterial bypass and aortic aneurysm repair - Biomaterials and Devices for the Circulatory System - page 220

which this response is induced are multifactorial and complex. Studies into
distal anastomotic IH after arterial bypass have elucidated some of the
important causes.

8.4.1 Trauma

The arteriotomy and anastomosis of a graft to the native vessel during a
bypass procedure elicit a healing response. Re-growth of endothelium and
development of underlying hyperplasia is an integral part of this; however,
once intimal integrity has been restored there appears to be the potential
for continued thickening. Only relatively subtle trauma is required
to provoke such a response and studies have shown that simple endothelial
denudation through desiccation or balloon angioplasty induces re-
endothelialisation and IH (Zollikofer et al. , 1984; Davies et al. , 1993, 1996;
More et al. , 1994).

8.4.2 Compliance mismatch

The term compliance mismatch describes the discrepancy in physical prop-
erties between autologous tissue and prosthetic materials and has gener-
ated much interest as a cause of IH and subsequent graft occlusion (Walden
et al. , 1980). Expanded PTFE and Dacron, the two most commonly used
prosthetic bypass conduits, may be considered to be almost non-compliant
when perfused with a pulsatile waveform (Table 8.3).
In creating an anastomosis between such a graft and the inherently
elastic artery one generates a compliance mismatch which infl uences some
of the haemodynamic forces in the juxta-anastomotic regions. Stewart and
Lyman (1992) and Miyawaki et al. (1990) described fl ow disturbances at
regions of compliance mismatch in straight tube models, with microscopic
zones of fl ow separation and stagnation at the wall. They speculated that

￿ ￿ ￿ ￿ ￿

Table 8.3 Compliance measurements of bypass graft conduit
materials (Walden et al. , 1980)

Compliance (% radial
change/mmHg Conduit material × 10 − 2 )

Human femoral artery 5.9 ± 0.5

Saphenous vein 4.4 ± 0.8

Human umbilical vein 3.7 ± 0.5

Bovine heterograft 2.6 ± 0.3

Dacron 1.9 ± 0.3

ePTFE 1.6 ± 0.3