What Is Hypotension?

Hypotension (HI-po-TEN-shun) is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood.

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.

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.

Overview

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.

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.

Outlook

In a healthy person, low blood pressure without signs or symptoms usually isn't a problem and needs no treatment. If low blood pressure causes signs or symptoms, your doctor will try to find and treat the underlying condition that's causing it.

Hypotension can be dangerous. It can make a person fall because of dizziness or fainting. Shock, a severe form of hypotension, is a condition that's often fatal if not treated right away. With prompt and proper treatment, shock can be successfully treated.

September 2008