The classic OH is defined as a decrease in the blood pressure (BP) when the person stands up.¹ The BP goes down in the first 3 minutes after the person stands up.

To be "classic OH", the systolic blood pressure (top number) has to go down by at least 20 mm Hg or the diastolic (bottom number) drops by at least 10 mm Hg. The person gets orthostatic symptoms, like dizziness or lightheaded feeling, vision change, and feeling of weakness.

Example: The person's BP lying down is 120/80 mmHg. Pulse is 74. After standing up for 3 minutes, the blood pressure is 90/64 mm Hg. The pulse is still 74. The person feels dizzy, has vision change, & weakness. This would be "orthostatic hypotension".

The drop in blood pressure (BP) and symptoms can come at different times. Then, it has a different name. If the BP drops:
    •  Within 15 seconds of standing up - it's called "initial orthostatic hypotension"¹
    •  In the first 3 minutes - it's called "orthostatic hypotension", the classic condition.¹
    •  After 3 minutes of standing - it's called "delayed orthostatic hypotension".¹

To see a comparison of the symptoms, the time symptoms develop the BP and pulse changes, and the diagnosis, go to Symptoms and Type of OI.

Orthostatic hypotension (OH) that is caused by a problem with the autonomic nervous system is also called neurogenic orthostatic hypotension and neurally-mediated hypotension (NMH).

It is a chronic condition that is debilitating; it interferes with a person's ability to live a normal life^2,3. It affects a person's ability to work, to go to school, do normal everyday life things (like have fun, go out to church, shop), and take care of themselves.

What is causing it:   It is called ANS "failure" because something in the ANS is not working as it is supposed to: there has been damage to the nerves or the way they handle chemicals and hormones and send messages to the rest of the body organs. It is sometimes called autonomic dysfunction or dysautonomia.

The decrease in blood pressure with standing up is due to failure of the blood vessels to constrict (get narrower) when chemical messages are sent. (medical language - sympathetic vasoconstrictor failure).

With the decrease in blood pressure, there is a decrease in blood going to the brain and other organs starting at the top of the body. The person gets orthostatic intolerance symptoms: dizziness, lightheadedness, vision changes like black spots or tunnel vision, weakness.

Fainting with OH:  If the pulse (heart rate) goes down also, the person will usually faint. When there is dizziness or fainting with the OH, the person may go to the emergency room the first time (or other times if there is injury). OH may be the cause of the symptoms in about 20% of the people with these symptoms in the ER. (If 100 people with these symptoms went to the ER, 20 of them would have OH)⁶

About 20% of people over 65 have been reported to have their systolic blood pressure go down more than 20 mm Hg when they stood up. In another study, 18% of people over age 60 had symptoms of dizziness that was severe enough to interfere with their activities of daily lives.⁶

Difference in symptoms with OH⁶:   In addition to the usual orthostatic symptoms (dizziness, lightheadedness, vision changes, weakness), people with OH do not report that they have the pallor, nausea/vomiting or clamminess (sweating).

Other findings:   In OH due to dysautonomia, other findings include; mild anemia, decrease sweating, sleep apnea, hoarseness, nasal stuffiness, constipation or diarrhea, Pakrinsonian-like syndrome, recurrent urinary tract infections and/or bladder dysfunction, and impotence in men.

NMH is the most common cause of recurrent fainting. (fainting more often)

Who gets NMH depends on what group of people are being studied. In some reports, OH is more common in very old people². It is related the types of medical problems a person has and the medications they take to manage them. With the older people, the blood pressure lying down is often high.

There is a group of younger people who develop NMH, especially women². It is common in people with low normal blood pressure. It is also more common following infection. It is more common in those with Chronic Fatigue Syndrome (CFS). Family members are often affected. In this group, the blood pressure lying down is often low.

The hypotension may not be detected unless orthostatic stress is prolonged (delayed OH).

POTS vs. NMH - Numbers in Children:   In a review of children referred for autonomic testing, Sukul and colleagues found that POTS was the most common - found in in 71% of the chilcren.⁹ (If 100 children were tested, 71 would have POTS. If only 4 were tested, 3 would have POTS). Orthostatic hypotension (NMH) was only present in 5%. (That would be 5 children out of 100 tested.)

For another perspective on the overlap between OH and POTS, check out Types of OI under the Causes - Dysautonomia.

Syncope (fainting) or orthostatic symptoms from orthostatic hypotension can occur with these also:

• Prolonged bedrest - If a person has been on prolonged bedrest, they might have orthostatic symptoms when they stand up⁷. If the bedrest has been shorter than 4 weeks, the symptoms should get better as the person gets back to normal activities. It is taught that for every 1 day of bedrest, it takes 5 days to recover. For more about bedrest and orthostatic symptoms, go to Bedrest, Bedrest and OI or Bedrest: Space flight and ICU-stays.
• Drug related: side effect of drug. This is a very common cause of orthostatic hypotension especially in older people.
• Pregnancy
• Addison’s disease (usually volume depletion)⁸
• Atherosclerosis – It changes the arteries and makes it difficult for them to adapt quickly to changing position.