A common surgical procedure is bypass graft implantation, in which a natural or synthetic arterial substitute ("the graft") is used to carry blood around an obstructed portion of an artery (Fig. 4.36). Data suggest that these grafts perform best if their compliance matches that of the native artery that they are attached to. Compliance is a measure of the elasticity of the vessel walls; here it is defined as C=(Ds / Dd-1) /(Ps-Pd) where Ds and Dd are systolic and diastolic diameter, and Ps and P