Small-artery changes in hypertension

OBJECTIVETo summarize the arguments challenging the pathological significance of the structural changes observed in small arteries in hypertension in maintaining peripheral vascular resistance or in serving as amplifiers in the development of the disease. SETTINGWhile the existence of a change in vascular wall architecture in small arteries exposed to prolonged hypertension is not in dispute, a number of issues remain contentious. These focus first on the nature of the change in morphology observed, second on whether the small arteries (150–300 μm) make a significant contribution to peripheral resistance, third on whether such changes are a cause of raised blood pressure or merely a consequence, and finally on whether they can serve as amplifiers of a pressor stimulus. CONCLUSIONSA careful review of the literature suggests that the techniques used to investigate these issues can give discrepant results, and that given the heterogeneity of functions performed by specialized tissues, the variations recognized in receptor populations and the differences in innervation found in the arterial wall, to extrapolate findings from one vascular bed to all of them might be inappropriate. The evidence suggests that in small arteries the structural changes observed are adaptive, and that enhanced reactivity may not be seen in whole-animal studies. In the absence of a primary effect at this level of the circulation, a pathogenetic mechanism for hypertension must be sought elsewhere. We suggest that this may reside in the haemodynamically important arterioles where derangement of the myogenic response may have a crucial effect.