Your blood pressure is the force exerted by your heart, against the resistance created by the arteries, to keep blood flowing through your body. Your blood pressure is high (hypertension) when the force is excessive.
A blood pressure measurement is made up of two parts: systolic and diastolic. Systolic pressure occurs in arteries during heart contraction, and diastolic pressure during the period of heart relaxation between beats. This is why a blood pressure measurement is expressed as one figure "over" another, for example 140/90 mm Hg. The measurement unit, millimetre mercury (symbol Hg), is derived from the distance that a column of mercury in the measurement instrument is pressed upward.
The following table shows the normal ranges of blood pressure and the stages of hypertension for South Africans. High normal blood pressure requires more regular monitoring. Stage 1 is less severe than Stage 3.
Blood Pressure
Systolic (mm Hg)
Diastolic (mm Hg)
NORMAL RANGE
Optimal
120 or less
80 or less
Normal
Less than 130
Less than 85
High normal
130 -139
85 - 89
HYPERTENSION
Stage 1
140 - 159
90 - 99
Stage 2
160 - 179
100 - 109
Stage 3
180 or higher
110 or higher
This represents an arbitrary decided upon level of blood pressure above which the advantages of treatment is more than the disadvantages.
Hypertension is diagnosed when blood pressure measurements are above either of these normal levels on two or more separate occasions.
Elevated blood pressure readings may not always indicate that a person has hypertension, as in the case of White coat hypertension – high readings caused by a natural alerting response during blood pressure measurement (the emotional stress of having a clinician take your blood pressure).
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