The pathogenesis of hypertensive emergency and urgency is complex and not completely elucidated. Our current understanding is based on animal studies and sparse human trials. In order to maintain adequate organ perfusion, arteries dilate or constrict in response to changes in blood flow and pressure. Unfortunately, this ability is only possible within a range of physiologic values (mean arterial pressure between 50 and 150 mm Hg, usually). At extremes of blood pressure values, vessels are not able to adequately ensure constant blood flow. A blood pressure value around 150 to 160 mm Hg represents a breaking point for the capacity of human vessels. Beyond this value, protection cannot be ensured, and the pressure induces direct organ damage.
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