Question:
My 17-year-old son was told he has "neurally mediated hypotension." What is this, and how is it treated? Are there medications for this condition?
Answer:
Neurally mediated hypotension (NMH) is a condition of the autonomic nervous system. This system includes centers in the brain plus nerves that carry signals between the brain and the body. The autonomic nervous system controls what are called "vital functions" of the body. For example, it controls your body temperature, how fast your heart beats, your blood pressure, and the contractions of your intestines.
When a person who has been lying or sitting down suddenly stands up, gravity pulls blood down into the legs and away from the heart. This causes the blood pressure to drop. However, the autonomic nervous system senses this happening, and reacts to make the drop in blood pressure both small and brief. In NMH, however, the system fails to make this correction, and the blood pressure falls to an unusual and prolonged degree. That can make a person feel lightheaded, or even faint, because the brain needs a good blood pressure to function normally.
Sometimes, blood pressure falls sharply on standing because a person is dehydrated, or is on a medicine that causes blood pressure to fall on standing. When there is no such clear cause, a person is said to have NMH. The cause of NMH is not known. It comes and goes, for no clear reason.
There are a number of different treatments. Drinking extra fluid and taking extra salt can help, but your doctor needs to check that your blood pressure does not go too high as a result. A medicine called fludrocortisone holds extra salt in your body. It can help treat NMH, but your doctor needs to check your blood pressure for that, too.
A relatively new drug called midodrine, and an old group of drugs called beta blockers, work very well for some people — but, again, your doctor needs to check that they do not cause unacceptable side effects. Midodrine can cause high blood pressure and a heart rate that is too rapid, and jitteriness. Beta blockers can cause the heart to beat too slowly and can provoke asthma attacks in some people.
Despite the possibility of side effects, however, most people with NMH respond very well to treatment.
