Your heart is an amazing fluid pump. It works reliably for
decades, and it safely pumps blood -- one of the trickiest liquids
around. In the same way, your blood vessels are pipes. They take the
output from the pump and distribute it throughout the body. A blood pressure gauge is simply a way
to measure the performance of the pump and the pipes. There are two
numbers in a blood pressure reading: systolic
and diastolic. For example, a
typical reading might be 120/80. When
the doctor puts the cuff around your arm and pumps it up, what
he/she is doing is cutting off the blood flow with the pressure
exerted by the cuff. As the pressure in the cuff is released, blood
starts flowing again and the doctor can hear the flow in the
stethoscope. The number at which blood starts flowing (120) is the
measure of the maximum output pressure of the heart (systolic
reading). The doctor continues releasing the pressure on the cuff
and listens until there is no sound. That number (80) indicates the
pressure in the system when the heart is relaxed (diastolic
reading).
If the numbers are too high, it means that the
heart is having to work too hard because of restrictions in the
pipes. Certain hormones, like adrenaline (which is released when
you are under stress) cause certain blood vessels to constrict,
and this raises your blood pressure -- if you are under constant
stress, your blood pressure goes up, and it means that your heart
has to work too hard. Other things that can increase the blood
pressure include deposits in the pipes and a loss of elasticity as
the blood vessels age.
Q: What is the unit of (120,
80)? Pascal or mmHg?
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