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Retinal microcirculation and early mechanisms of hypertension.

The microcirculation plays a critical role in the pathophysiology of hypertension.1,2 The increase in peripheral resistance underlying the raised blood pressure is localized primarily in small arteries (diameter 150 to 300 μm) and arterioles (diameter 10 to 150 μm). The rise in blood pressure causes a further narrowing of small arteries and rarefaction of capillaries and precapillary arterioles, thus creating a vicious cycle. This cycle has been well documented in several animal models of hypertension. However, it has been more difficult to grasp the complete picture in humans, because of technical difficulties to evaluate the microcirculation in vivo. The study of small arteries in humans is based on biopsies usually taken from subcutaneous fat tissue. Using this approach Rizzoni et al3,4 were able to show that small artery narrowing predicts the prevalence of cardiovascular complications in both normotensive and hypertensive individuals. Capillary rarefaction has been assessed in humans using in vivo capillaroscopy of the nailfold microvasculature. The majority of these studies support the hypothesis of capillary rarefaction as an early hallmark of …