The most common name for a medical condition describing a dysfunction of the autonomic nervous system that causes patients' blood pressures to drop abnormally low when they are in a sitting or standing position. Also known as Neurally Mediated Hypotension, Postural Hypotension and Orthostatic Hypotension.

Patients with dysautonomia often feel fine when lying in a reclined position, but when they stand up or sit for a very long period of time, they start to feel fatigued, drained, and dizzy. This disorder is believed to be caused by a miscommunication between the brain and the autonomic nervous system, resulting in an ineffective regulation of the patient's blood pressure.

In many cases, dysautonomia appears to be associated (or at least closely correlated) to a minor heart condition known as Mitral Valve Prolapse, which affects about 10% of the population. The connection between dysautonomia and MVP is controversial, however, and many doctors doubt there is a real correlation. Regardless, many sufferers of dysautonomia happen to have MVP, lending credence to the belief that MVP is the cause of (or a symptom of) dysautonomia.

While the true nature of the brain's miscommunication with the nervous system in the dysautonomic patient is not totally understood, it is believed that when the patient stands or sits up, rather than increase blood pressure to compensate, the heart misinterprets signals from the brain and instead lowers blood pressure, allowing less blood to reach the brain. This may explain why dysautonomic patients often feel light-headed, dizzy, or even sleepy when standing.

A diagnosis of dysautonomia is confirmed via a test known as a tilt table exam. In this examination, a patient lies on a specially-designed table and is slowly rotated from a lying-down position to a near-standing position. The patient's blood pressure is measured throughout the exercise to see how s/he reacts to the change in table incline; if a drop of more than 20 mmHg drop in blood pressure is detected, then the patient is considered to have "failed the tilt test" and is diagnosed with dysautonomia.

There are several treatments for dysautonomia, the first of which being a steady exercise regimen. Studies have shown that symptoms of dysautonomia are far less prevalent in patients who exercise regularly than in those who live a sedentary lifestyle. It is believed that cardiovascular exercise lowers the heart's resting rate, thus "training" it not to react as inappropriately to the sitting and standing of normal day life.

Dysautonomic patients are also generally instructed to increase water and sodium intake for the purposes of building blood volume. Some theorize that dysautonomia is caused by the body's failure to recognize when it has stored enough water; thus the dysautonomic patient is always "running a quart low." Patients are advised to drink at least 64oz of water a day. And since sodium helps the body absorb and hold onto water for longer periods of time, increased sodium intake is advised to help the patient avoid losing all that water in urine output.

Unfortunately, exercise, water, and sodium rarely are enough to fully treat the dysautonomic patient. There are several medications that work hand-in-hand with these treatments. Beta blockers (such as Toprol or Tenormin) are used to inhibit the adrenal response, as this response is often misinterpreted in the dysautonomic patient as an instruction to decrease, rather than increase, base blood pressure. Additionally, a steroid called Florinef Acetate (fludrocortisone) is often prescribed; Florinef helps the kidneys retain more sodium, thus assisting the body in water retention and resulting in increased blood volume.

If these primary approaches don't work, doctors may resort to other blood pressure increasing drugs, such as ProAmatine (midodrine), a vasoconstrictor (a drug that increases blood pressure by constricting the blood vessels). Pressure stockings such as Jobst Stockings may also be administered in order to avoid pooling of the blood in the lower extremities, which is common in dysautonomic patients.