Blood pressure is measured as systolic (sis-TOL-ik) and diastolic (di-a-STOL-ik) pressures. Systolic blood pressure is the pressure when the heart beats while pumping blood. Diastolic blood pressure is the pressure when the heart is at rest between beats.
[Read: Causes of Hypotension]
You will most often see blood pressure numbers written with the systolic number above or before the diastolic, such as 120/80 mmHg. (The mmHg is millimeters of mercury-the units used to measure blood pressure.)
Normal blood pressure in adults is lower than 120/80 mmHg. Hypotension is blood pressure that's lower than 90/60 mmHg.
Blood pressure changes during the day. It lowers as you sleep and rises when you wake up. It also can rise when you're excited, nervous, or active.
Your body is very sensitive to changes in blood pressure. Special cells in the arteries can sense if your blood pressure begins to rise or fall. When this happens, the cells trigger your body to try to bring blood pressure back to normal.
For example, if you stand up quickly, your blood pressure may drop. The cells will sense the drop and will quickly take action to make sure that blood continues to flow to your brain, kidneys, and other important organs.
Most forms of hypotension happen because your body can't bring blood pressure back to normal or can't do it fast enough.
[Read: Treatment of Hypotension]
Some people have low blood pressure all of the time. They have no signs or symptoms, and their low blood pressure is normal for them. In other people, certain conditions or factors cause blood pressure to drop below normal.
Hypotension is a medical concern only if it causes signs or symptoms, such as dizziness, fainting, or, in extreme cases, shock.
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