The guidelines released today establish a new category of "prehypertension" and merge other categories of high blood pressure included in the 1997 guidelines.

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.

After a long invariable asymptomatic period, persistent hypertension develops into complicated hypertension, in which target organ damage to the aorta and small arteries, heart, kidneys, retina, and central nervous system is evident. The progression begins with prehypertension in persons aged 10-30 years (by increased cardiac output) to early hypertension in persons aged 20-40 years (in which increased peripheral resistance is prominent) to established hypertension in persons aged 30-50 years, and, finally, to complicated hypertension in persons aged 40-60 years.

Early hypertension (prehypertension) can still be cured, if one has the motivation for it, without drugs.