[The importance of microcirculation and tissue perfusion in hypertension]

The importance of abnormalities observed in the microcirculation of hypertensive subjects is being increasingly recognised. These microvascular changes may be central to the development of end-organ damage brought about by hypertension, including ischaemic heart disease. The primary function of the microcirculation is to supply oxygen and nutrients to myocardial tissue, and it also has an important role in regulating coronary blood flow. Some 70-90% of the overall peripheral resistance of the circulatory system arises at the level of the microcirculation. In hypertension, thickening of the microvascular walls occur, with narrowing of the lumen, so that eventually the vessel is functionally occluded. The result is a reduction in the number of arterioles or capillaries in a given vascular bed. Such changes have been seen in the structure and density of the microvasculature of heart muscle, the conjunctiva and retina, and in the kidneys. In hypertension a vicious circle occurs, with an increase in blood pressure producing a rise in resistance in the microcirculation, leading to further elevation of blood pressure. New techniques for exploring the coronary microcirculation have shown that microvascular damage results in reductions of coronary vasodilator reserve, an important predictor of clinical deterioration and death. With studies showing that impairment of microcirculation occurs early in patients with hypertension, there would seem to be a need for new therapeutic perspectives in hypertension, concentrating on preventing or reversing changes to the microvasculature of affected organs.