Altered small artery morphology and reactivity in critical limb ischaemia

Although the pathophysiology of critical limb ischaemia is poorly understood, there is evidence that the condition of the small arteries may determine the outcome of revascularization procedures. This study was designed to investigate the effects of critical limb ischaemia on the structure and function of the small arteries in the leg. Small arteries (< 500 μm) from proximal (non-ischaemic) and distal (ischaemic) sites were obtained from patients undergoing bypass surgery for critical limb ischaemia and mounted in a myograph. Reactivity and morphological measurements were carried out and compared with controls. Control vessels from the thigh and calf showed no difference in media to lumen ratio. However, a comparison of ischaemic and non-ischaemic vessels from the patients with critical limb ischaemia showed significant thinning of the ischaemic vessel wall. Contraction studies using noradrenaline and angiotensin II revealed a significant decrease in the response of ischaemic vessels compared with the non-ischaemic vessels from the same patient. Moreover, these differences in reactivity were still apparent after the responses were corrected for wall thickness. Endothelial function assessed using the endothelium-dependent agonists acetylcholine and bradykinin showed a significantly impaired relaxation response to acetylcholine but not to bradykinin in the ischaemic vessels, and acetylcholine-induced relaxation was not improved after incubation with indomethacin. There was no change in the response to the endothelium-independent cAMP-mediated vasodilator iloprost but a significant impairment to sodium nitroprusside which acts via cGMP. These results suggest that small arteries in critical limb ischaemia are altered in both structure and function, with vessel wall thinning and impaired responses to acetylcholine and sodium nitroprusside.