Chronic hypertension and autoregulation of blood flow
The mechanism by which acute reduction of blood pressure leads to harm is related to autoregulation of blood flow. It must be remembered that in patients who have elevated blood pressure, even severely elevated blood pressure, these pressures often have been present for many months to years. Any attempt to lower blood pressure acutely may lead to harm by offsetting the patient’s adaptive autoregulatory control.
Cerebral autoregulation of blood flow ensures that brain perfusion is unchanged within a wide range of systemic blood pressures. This flow is maintained by a dynamic interplay of vasoconstriction and vasodilatation . In patients who have chronic hypertension, the lower limit of autoregulation is often much higher, as high as 130 mm Hg. In addition, many changes in the vessel wall, such as smooth muscle hyperplasia, change the patient’s inherent autoregulatory curve  and .
The clinical bottom line is quite simple: patients who have asymptomatic, chronic hypertension should not have their blood pressure acutely lowered because of the risk of precipitating adverse events, such as stroke.
Epidemiology and cardiovascular events
Hypertension is evaluated frequently in primary care medicine practices. It is estimated to affect approximately 1 million persons annually in the United States and as many as 1 billion persons worldwide. In addition, it is estimated that as many as 35 million office visits in the United States are made annually for the evaluation and management of hypertension .
Primary care physicians are on the front lines of evaluating and treating hypertension, so it is important to understand the impact that chronic hypertension can have. According to data from the JNC-7, the health risks of chronic, untreated hypertension are potentially serious. For individuals between 40 and 70 years of age, each increment of 20 mm Hg in the systolic blood pressure or 10 mm Hg in diastolic blood pressure doubles the risk of a cardiovascular event. Important events include myocardial infarction, stroke, and renal failure.
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Robert L. Rogers MD, FAAEM, FACEP, FACP and Robert S. Anderson, Jr. MD
Department of Emergency Medicine, The University of Maryland School of Medicine, 110 South Paca Street, Suite 200, 6th floor, Baltimore, MD 21201, USA
Department of Medicine, The University of Maryland School of Medicine, 22 South Greene Street, Baltimore, MD 21201, USA