Blood pressure is measured by two numbers taken when the heart contracts (systolic pressure) and when it rests between beats (diastolic pressure). Both are expressed in millimeters of mercury. Pressures below 120 systolic and 80 diastolic are considered normal.
Under the new guidelines, prehypertension is defined as having a blood pressure reading of 120 to 139 for systolic blood pressure and a diastolic blood pressure of 80 to 89 millimeters. The previous guidelines called this level "high normal" and did not suggest any special treatment. But studies show that the risk of death from heart disease and stroke begin to rise at blood pressure levels as low as 115 over 75.
Sally Squires, "New Guidelines Issued for High Blood Pressure," Washington Post, May 14, 2003
Sat Sharma, "Hypertension," eMedicine Journal, January 17, 2003
Olli Sallinen, "Re: hypertension," alt.meditation.transcendental, March 15, 1999
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