Definition
In populations, blood pressures fit a normal distribution, but the attendant risks of heart disease and stroke increase curvilinearly with increasing levels of blood pressure, without any obvious breakpoint (Fig. 63-1). Thus, the separation of normal from high blood pressure is arbitrary, and the definition of hypertension has been a moving target. The first estimate was that systolic blood pressure should be 100 plus a person's age and that only higher values needed to be treated. This formula was predicated on the incorrect notion that the progressive increase in blood pressure with advancing age is essential to maintain blood flow through atherosclerotic arteries, hence the term essential hypertension . Later, hypertension in adults was redefined as a blood pressure of 160/95 mm Hg or greater, regardless of age, because this is the value above which the risk of stroke or myocardial infarction roughly doubles compared with the risk associated with pressures below 120/80 mm Hg. Now, however, based on the results of randomized clinical drug trials, hypertension is defined as a blood pressure of 140/90 mm Hg or greater because this is the value above which the benefits of treatment appear to outweigh the risks. Prehypertension is now defined as a blood pressure of 130–139/80–89 mm Hg. Individuals with blood pressure in this range are twice as likely to progress to hypertension compared with individuals with lower blood pressures.
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