Blood pressure (BP) varies with age (it increases as we get older).
120/80, is the often quoted (on TV) 'normal' blood pressure (and it's
about right for 30 year olds). It doesn't matter whether you're
standing, sitting, or lying down, your blood pressure will tend to be
maintained at the level.
What the question is getting at is the CHANGE of position, causing a change in BP.
When someone moves from lying flat to sitting up, (or from sitting to
standing) blood pools in veins in their legs. This decreases the
amount of blood that gets back into the right atrium of the heart,
which means less blood is pumped with the next beat. This means a drop
in blood pressure.
In most healthy people, this momentary low blood pressure will cause a
contraction of the veins, causing them to hold less blood. And the
problem will be minimised. The heart will also beat faster and more
powerfully, keeping blood pressure steady.
Blood pressure measurement (in my eyes) is such an inexact science
that it's difficult to have clear cutoff values.
Generally, if the drop is greater than 20/10 mmHg, one minute
following a change in postition, this is classified as postural (or
orthostatic) hypotension.
So in a normal, healthy individual, sitting, standing and lying,
should have less than a 20/10 mmHg change. |
