The saphenous vein as a bypass conduit: the potential role of vascular nerves in graft performance.

The saphenous vein is the most commonly used conduit in patients undergoing coronary artery bypass surgery. However, a high proportion of vein grafts occlude within the first year and over 50% patients require further grafting within 10 years. Using conventional harvesting techniques the saphenous vein is damaged due to considerable surgical and mechanical trauma, a situation that affects graft patency. As a superficial vessel located in the leg, the saphenous vein in man is subjected to variations in orthostatic pressure associated with exercise and alterations in posture. These conditions require the vein's calibre to be regulated predominantly by the autonomic nervous system. While posture-induced changes occur in man, and other bipeds, such alterations in pressure may not occur or be more subtle in other species, conditions that may limit the usefulness of various experimental models. The neural control of the saphenous vein is under the influence of a plethora of neurotransmitters and neuropeptides which, apart from affecting vascular tone, possess mitogenic properties that may contribute to morphological changes caused by vascular injury. In addition to their neurotransmitter role a number of factors have a direct action on vascular smooth muscle cells that affects neural blood flow with subsequent influence on peripheral nerve conduction. Such neurovascular actions may potentially play a role in the altered vein reactivity and structure involved in graft failure. In this review we discuss the pressure changes experienced by the saphenous vein, its innervation and use as a bypass graft for revascularization of ischaemic tissue, in particular the myocardium. Also, we consider the value of various common experimental techniques for studying vasoactive and mitogenic factors and their potential role in vein graft performance.