Blood pressure is really just that- the pressure at which blood moves around the body in your arteries. The easiest and least invasive way to test the pressure is to momentarily stop the flow of blood and then slowly allow it to begin again. The pressure at which it begins to flow is the highest pressure the blood exerts on your artery walls.
Medical professionals do this by using a blood pressure meter known
as a Sphygmomanometer. They encircle a limb, usually an arm, with a
balloon-like device known as a blood pressure cuff. While pumping
the cuff up, they use a stethoscope to listen for a heart beat past
where the cuff is cutting off blood flow. When they no longer hear
the heart beating, they slowly release the pressure while watching
the pressure gauge.
When they start to hear the heart beat again, this is the top number
of blood pressure, known as systolic pressure. They continue to
release the pressure until they once again, no longer hear the heart
beating, this is the bottom number of blood pressure, known as
diastolic pressure. Together these numbers tell them two things: the
pressure that is inside arteries between heartbeats (the
bottom number) and the pressure inside arteries when the heart
squeezes (the top number).
Different disease processes like coronary artery disease can cause
higher than normal blood pressure. Lower than normal blood pressures
can be a sign of other disease processes, like shock caused by
infection. The difference between top and bottom numbers, or a
change in that difference, can also point to specific problems like
too much fluid around the heart, not allowing it to work properly.
Combining this information with a person’s heart rate can also tell
numerous other things that could be happening. If you have been in a
car accident and have a lower than normal blood pressure and higher
than normal heart rate, you could be bleeding internally. If you
were in another car accident and have an extremely high blood
pressure and a low heart rate, you could be bleeding in your brain.
High blood pressure is not a disease or illness in and of itself.
It is merely a symptom for other problems.