High Blood Pressure  Understanding Blood Pressure  Blood
pressure is a measurement of the force exerted upon blood vessel
walls by blood as it flows through the arteries. High blood
pressure occurs when there is an increase of force against the
arterial wall, with potentially damaging consequences. Since the
heart has distinct “beats”, the pressure of oxygenated blood in
the arteries is not continuous, but varies between two values,
one when the heart is contracting, and one when the heart is
relaxing. As the heart contracts, blood is expelled from the
left ventricle under the greatest force; this upper pressure
limit is the systolic blood pressure.  Following contraction of
the heart, the aortic valve closes, which prevents blood from
flowing backward into the heart, and helps maintain pressure in
the arteries. This allows the heart muscle to relax and fill
with blood. Unlike all other organs, which receive blood flow
when the heart “beats” or contracts, the heart itself is unique
in that it receives blood s