Blood Pressure Home > Systolic and Diastolic Blood Pressure

Systolic blood pressure (the top number) measures the amount of pressure that blood exerts on vessels while the heart is beating. Diastolic blood pressure (the bottom number) measures the pressure in your vessels between heartbeats. If systolic and diastolic blood pressures are too high, you have hypertension. Your doctor will probably use a sphygmomanometer to measure diastolic and systolic blood pressure.

What Are Systolic and Diastolic Blood Pressures?

Blood pressure is the amount of force (pressure) that blood exerts on the walls of the blood vessels as it passes through them. Two pressures are measured for a blood pressure reading:
  • Systolic blood pressure is a measure of blood pressure while the heart is beating
  • Diastolic pressure is a measure of blood pressure while the heart is relaxed, between heartbeats.

How Are Diastolic and Systolic Blood Pressures Measured?

When measuring these blood pressures, your doctor will likely use a sphygmomanometer. This familiar device with a long name contains a cuff, valve, gauge, and dial. The cuff is wrapped around your arm and then inflated slightly. The systolic and diastolic blood pressures are measured on a gauge attached to the cuff. Your doctor reads the numbers that appear on the gauge as air is released from the cuff.
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.

Why Are These Numbers Important?

As blood is pumped from your heart into your blood vessels, enough systolic blood 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 a tree's branches. One branch may go to the brain while another may go to your kidneys.
Systolic blood pressure keeps blood flowing through the branches so that your body's cells get the oxygen and nutrients they need and waste matter can be removed.
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Last reviewed by: Arthur Schoenstadt, MD
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