Dizzy When I Stand Up: Postural Hypotension

Dear Dr. Dave and Dr. Dee,

I read your discussion of vertigo and wonder if that is what I'm experiencing. When I get up, say from a chair, I feel dizzy, start seeing black or black dots, and my legs sometimes feel like they are going to give out. Sometimes I have to lean up against something to keep from falling down. I do have trouble with my balance, although there is no spinning. Is this vertigo?

Signed,

Having dizzy days

Dear Having dizzy days,

Although vertigo can be triggered by standing, it's less likely to be vertigo if there's no sensation of the body, or surroundings, moving or spinning.

There is another type of dizziness upon standing that's caused by postural hypotension. This type of dizziness, faintness or light-headedness results from a decrease in blood flow to the brain, due to a drop in blood pressure upon standing up.

At one time or another, we've probably all experienced mild postural hypotension from standing up too quickly. As long as it occurs only occasionally, there's little cause for alarm.

But chronic postural hypotension can be a debilitating condition, associated with increased risk of injury from accidents and falls, and obviously is a cause for concern. Persistent light-headedness or faintness upon standing may be a symptom of a serious underlying disorder. Anyone with this problem should be seen by his or her physician.

POSTURAL HYPOTENSION

In order to understand postural hypotension, imagine the body as a column of fluid. When we've been lying down for a while, the column is horizontal, so the fluid pressure is equally distributed from head to toe.

When we stand up, the fluid column becomes vertical, causing the fluid pressure to increase at the bottom of the column, and fall dramatically at the top. This pressure drop must be corrected, otherwise blood flow to the brain will drop, and we'll get light-headed or pass out.

HOW DOES THE BODY COMPENSATE FOR VERTICAL POSTURE?

Credit the body's highly effective reflex mechanisms for keeping blood pressure and flow to the brain constant when we stand up. Special pressure sensors in blood vessels act, via the involuntary nervous system, to trigger important responses that maintain normal blood pressure and flow to the brain:

1) The heart is stimulated to increase its output by increasing the number of heart beats per minute, the volume of blood pumped per beat, and the force with which the heart squeezes. We can actually feel this happening, from time to time, when we stand up.

2) When we stand, blood vessels throughout the body undergo dynamic changes. The muscular walls of arteries constrict, and veins of the lower body contract increasing blood pressure and, in effect pushing blood upward toward the heart and brain.

The net effect is that, if all components of the circulatory reflexes are working properly, the move from lying to standing usually proceeds without symptoms.

WHAT ARE SOME CAUSES OF POSTURAL HYPOTENSION?

Dizziness upon standing, from postural hypotension, usually means that either something has gone awry with the circulatory reflexes, or for some reason, the body's fluid volume is depleted:

1) Blockade of the normal heart or blood vessel response: Some medications impair the circulatory reflexes by blocking transmission of the message from the involuntary nervous system to the heart and blood vessels. This is the mechanism of action of some blood pressure medications such as beta blockers and alpha blockers, and a number of other medications. Postural hypotension is one of the more common side effects associated with these types of drugs.

2) Involuntary nervous system dysfunction: Postural hypotension can be caused by a number of conditions and diseases which affect the involuntary nerves, such as diabetes, alcoholism, nutritional deficiencies, and other nervous system disorders.

3) Inadequate blood volume: If there isn't enough fluid volume in the blood vessels, then the circulatory reflexes can't restore normal blood pressure. This can happen in any condition which causes dehydration, which may be due to inadequate oral intake, vomiting, diarrhea, or other causes of excessive fluid loss, such as overuse of diuretics, failure of the adrenal glands, and blood loss.

Sometimes the cause of postural hypotension is unknown (idiopathic, Shy-Drager syndrome).

HOW DOES YOUR DOCTOR DIAGNOSE POSTURAL HYPOTENSION?

Your doctor or nurse checks your blood pressure and pulse in the lying, sitting and standing positions. A postural blood pressure drop below the acceptable range makes the diagnosis. Often a diligent history and physical exam are all that's required to identify the cause. Sometimes more advanced testing is needed.

WHAT CAN BE DONE ABOUT POSTURAL HYPOTENSION?

If the cause turns out to be a medication, then your doctor may attempt to decrease the dose, discontinue the offending agent, or switch over to another class of drug that doesn't have that side effect.

If the cause is volume depletion, then your doctor will institute measures to restore circulating volume to a normal level. If indicated, further work-up may be needed to determine the cause of volume depletion.

Depending on the type of problem, other approaches have been tried, including lower extremity support hose, support garments that compress the lower trunk, adrenal gland medications with salt and fluid loading (in cases of failure of the adrenal glands), and in some cases, blood vessel constricting medications.

Anyone who experiences persistent dizziness upon standing deserves a thorough history and physical examination by a physician, and other tests as needed, to determine the diagnosis and institute appropriate treatment.

Remember, if you have trouble accessing a physician, your local emergency department is open 24 hours a day, to see and treat people regardless of economic status.