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Blood pressure is the pressure inside your blood vessels, both as your heart is pumping blood through them and while the heart is relaxed. If too high, the condition can cause health problems, so keeping your blood pressure at a proper level is essential. While 120/80 is considered normal, it usually varies within a certain range, so it's best to use more than one reading to determine your average.
Blood pressure is the amount of force (pressure) that blood exerts on the walls of the vessels as it passes through them.
As blood is pumped from your heart into your blood vessels, enough pressure is created to send it to all other parts of your body. As blood vessels travel away from the heart, they branch off and gradually get smaller, just like the branches of a tree. One branch may go to the brain, while another may go to your kidneys. Blood pressure keeps the blood flowing through all these branches so your body's cells get the oxygen and nutrients they need.
When measuring blood pressure, a fabric cuff is wrapped around your arm and then slightly inflated. The blood pressure shows up on a gauge attached to the cuff. The healthcare provider reads the numbers from the gauge as air is released from the cuff. This device used is called a sphygmomanometer. Blood pressure can also be measured with a special machine.
The two numbers that measure your blood pressure are written like a fraction: one number on top and one on the bottom. For example, what many people consider normal blood pressure is read as 120/80. The number on top is called the systolic pressure. It measures the pressure inside your blood vessels at the moment your heart beats. The number on the bottom is your diastolic pressure. It measures the pressure in your blood vessels between heartbeats, when your heart is resting.