The Various Presentations of Autonomic Dysfunction

Low BP

Orthostatic Hypotension

The word hypotension means low blood pressure. “Orthostatic” refers to a change in posture, generally when a person stands up. Thus, orthostatic hypotension is a condition in which the blood pressure drops excessively with standing up. Most of the time, the autonomic nervous system tries to maintain a fairly stable blood pressure under normal circumstances. Blood pressure can vary quite a bit from one minute to the next, depending on the patient’s emotional state or physical activity. “Hypertension” or high blood pressure is generally defined as a resting blood pressure of greater than 135/85.  Blood pressures below that are considered “normal.” Young people can walk around with resting blood pressures in the 90s without symptoms, and for those people a blood pressure of 95/50 may be normal. However, when the blood pressure is inadequate to suit the individual patient and symptoms of reduced blood pressure occur, there is a problem. Symptoms of an excessively low blood pressure include lightheadedness, weakness, fatigue, visual symptoms like blurry or darkened vision or “seeing stars,” and even fainting.

Generally, the blood pressure should stay fairly steady despite changes in posture. Orthostatic hypotension is present when the upper (systolic) blood pressure number drops by more than 20 points or when the lower (diastolic) blood pressure number drops by more than 10 points when a person stands up. Often, this degree of a drop in blood pressure is not enough to cause symptoms, but much larger drops in blood pressure can occur in patients with this condition.  It’s not uncommon to see blood pressures in the 70 range when a person begins to feel lightheaded.

We all have certain reflexes in place to maintain blood flow in the face of a dropping blood pressure. The mechanism regulates the brain’s blood flow automatically, and for that reason it is given the name “autoregulation.”  The arteries leading to the brain are able to constrict when there is a high blood pressure, and they dilate (or open up) whenever the blood pressure drops. By dilating, the resistance to blood flow is reduced and the blood has an easier time getting up to the brain in the face of a low blood pressure. On the other hand, it is useful to have those blood vessels constrict when the blood pressure gets too high, mainly to prevent the blood vessels in the brain from bursting from an excessive amount of blood flowing into the head.

Most of the time, orthostatic hypotension occurs either because of an excessive amount of pooling of blood in the lower extremities or an inability of the autonomic nervous system to compensate for the normal amount of pooling. Certain medications are a common cause for orthostatic hypotension, and they can turn a mild case into a severe one, resulting in lightheadedness, weakness and even fainting. All blood pressure medications, many cardiac medications, and some medications used to treat prostate problems or even anxiety / depression have been implicated in causing orthostatic hypotension. Dehydration predisposes a person to developing orthostatic hypotension. Often, older people lose their thirst reflexes and have no desire to drink water even in the face of significant dehydration. Sweating during exercise and water vapor losses through breathing count can result in dehydration if those fluids are not replaced.  Potential aggravating factors such as extreme heat (hot showers), large meals, and prolonged standing should be avoided. Patients need to change positions slowly to avoid severe symptoms. Alcohol can make symptoms worse, so patients should keep drinking to a minimum.

Patients who develop orthostatic hypotension need to be evaluated for other signs of autonomic dysfunction, since orthostatic hypotension can be an early sign of more serious neurologic conditions. Other signs include a slow heart beat, a reduction in sweating, bowel and bladder problems, sexual dysfunction, and other effects of autonomic failure. A blood count or measurement of the concentration of red blood cells in the blood (hematocrit) should be done to rule out anemia. However, patients who are dehydrated often have a deceptively hematocrit, because a reduction in the liquid portion of the blood (the plasma) can mask a significant reduction in the red blood cells (a situation referred to as “hemoconcentration”).  Adrenal insufficiency, vascular disease, diabetes, other systemic medical conditions, and neurologic diseases such as Parkinson’s disease are associated with orthostatic hypotension. Lastly, in some patients orthostatic hypotension may be one of the presenting signs of certain cancers, and sometimes imaging studies such as CT scans should be done to rule out the presence of a tumor.

Treatment of orthostatic hypotension involves correction of any anemia or fluid deficit (dehydration). Sometimes support stockings (to help the blood return from the legs back to the heart) can relieve symptoms. Other means of improving the return of blood to the heart involve leg exercises to strengthen the muscles. There is a mechanism referred to as the “skeletal muscle pump,” which refers to the fact that when the leg muscles contract they generate pressure that is applied to the walls of the veins, “milking” the blood back up to the heart. Increasing the leg muscle tone improves the effectiveness of this skeletal muscle pump. It also helps to have patients with orthostatic hypotension sleep with their head elevated. This helps to reduce the normal amount of nighttime urine production, thus lessening the mild degree of dehydration that people wake up with in the morning (most people with orthostatic hypotension feel their worst when they first wake up). Finally, a variety of medications are available to help this condition. They work either by increasing fluid retention, constricting the blood vessels (to increase blood pressure), or by trying to rebalance the abnormalities in the autonomic nervous system. It is very helpful to see a specialist in fainting when trying to manage orthostatic hypotension, since the treatment must be individualized and several different approaches must often be used together to obtain acceptable outcomes.