For a variety of reasons medical science has had difficulties in establishing a standard norm. First of all, there is the natural daily fluctuation mentioned earlier. The blood pressure of a normal person at rest can range from 95/65 mm Hg at night to 135/80 in the morning to 150/90 in the evening. Moreover, the blood pressure of many, though by no means all, people goes up with age but they do not suffer fr^m hypertension. Also, blood pressure levels like other biological norms can be established only after taking the measurements many times in healthy individuals. But since the pressure levels of such persons vary enormously it is difficult to establish a rigid dividing line between normal (normotension) and high blood pressure (hypertension).
On the other hand, it is vital to establish firm upper normal limits, for without them we cannot detect high blood pressure nor evaluate the effectiveness of treatment. After much debate one has arrived at a rule of thumb to determine a valid norm:
To determine the acceptable upper norm of systolic pressure
age plus 100 (maximum 160 mm Hg)
To determine the acceptable upper norm of diastolic pressure
90 mm Hg, regardless of age.
Thus, if you are forty years of age, your blood pressure should not exceed 140/90. If it is between 140/90 and 160/90, you should have your pressure checked every three to six months to make sure that there is no upward trend. A reading of 160/95 would certainly seem to indicate that you have high blood pressure.
Moderate divergences from the systolic standard values—from 20 to 30 mm Hg lower, and, if sixty years and older, of 10 to 20 mm Hg higher are not unusual and compatible with good health.
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