sections include: problems and their causes, diagnosis and treatment
Our autonomic nervous system is essential for our survival. This system of nerve cells continuously monitors and controls our visceral organs: the heart and blood vessels; the pupils; the glands for tears, saliva, and sweat; the lungs’ bronchi; the stomach and intestines; the bladder; and the sexual organs. Control of these organs regulates our bodies’ response to exercise, emotion, and environmental challenges. Several areas of the brain are involved in the working of the autonomic nervous system, including the cerebral cortex, amygdala, hypothalamus, brain stem, and spinal cord. Neurons of the brain stem and spinal cord send nerve fibers to the autonomic ganglia, which, in turn, send nerve fibers to all visceral organs.
The autonomic nervous system has two main divisions, sympathetic and parasympathetic. The sympathetic system is activated in response to stress, exercise, exposure to heat or cold, low blood glucose, and other environmental challenges. This system is critical for maintaining blood pressure as we stand up; an autonomic reflex constricts the vessels in our legs and abdomen to keep blood from pooling in these regions and rushing away from our head. The sympathetic system also increases the frequency and strength of heartbeats during exercise, and controls sweating and blood flow to the skin to maintain healthy body temperature. The parasympathetic system is important for digesting and absorbing nutrients, slowing the heart during sleep, emptying the bladder and bowel, and penile erection. In many organs, the effects of the parasympathetic system oppose those of the sympathetic; for example, the sympathetic dilates the pupil and the parasympathetic constricts it.
Problems and Their Causes
Given how many parts of the nervous system control the visceral organs, and the many functions of the autonomic system, it is not surprising that problems with this system can show up in many ways. Any disorder affecting the hypothalamus and brain stem, the spinal cord, the autonomic ganglia, or the sympathetic or parasympathetic nerves may result in autonomic failure or, in rarer cases, excessive autonomic activity. For example, lesions in the hypothalamus, the spinal cord, or the sympathetic ganglia and nerves that connect to the sweat glands can produce an inability to sweat. Diseases of the spinal cord or parasympathetic nerves may make people retain urine and men become impotent. The body’s own immune system can be keyed off by an infection to mistakenly attack the autonomic nerves.
One of the most frequent and disabling forms of autonomic failure is chronic light-headedness or fainting when a person gets up from a chair or a bed. This problem can result from lesions in the medulla oblongata, the spinal cord, or the sympathetic ganglia or fibers. That damage blocks the autonomic reflex that normally keeps blood from rushing into our lower limbs as we stand. A person without this reflex instead experiences a drop in blood pressure, called orthostatic hypotension. When the blood pressure falls, so does the blood flow to the brain, and the person feels dizzy or faints. Orthostatic hypotension may also show up as blurred vision, fatigue, and neck and head pain that disappears when the individual sits or lies down. A person with this condition can learn to recognize all these symptoms and can sit down as soon as they appear to avoid fainting.
People with orthostatic hypotension commonly have high blood pressure when they are lying flat, and excrete excessive amounts of salt and water during the night. The symptoms of orthostatic hypotension are typically worse early in the morning, after a heavy meal rich in carbohydrates, after exposure to heat, or during heavy exercise or straining. Orthostatic hypotension can prevent people from engaging in normal daily activity. They may be unable to stand for more than a few minutes, or they have to sit down frequently to prevent fainting. Falling down, of course, can result in head injuries or bone fractures—creating even worse problems.
Most often, autonomic disorders show up as failures of both sympathetic and parasympathetic systems, and can thus cause multiple problems at once, affecting perspiration, appetite, excretion of waste, and sexual arousal. The consequences of these failures can be very harmful to our bodies and our sense of self. Inability to sweat means that a person cannot exercise in a hot environment and faces the risk of heatstroke. Feeling full after only a small meal, decreased appetite, and nausea may result in malnutrition and weight loss. Severe constipation may lead to fecal impaction. Incomplete voiding causes a person to retain urine in the bladder and poses the risk of recurrent urinary tract infections. Erectile impotence, an early symptom of autonomic failure, has profound psychological impact for men and their partners.
Autonomic failure occurs most commonly as a side effect of drugs a person is taking to treat other problems. These medications interfere with the normal transmission of chemicals from the autonomic nerves. The problem appears most frequently in elderly people because as we age we normally lose some autonomic nerve cells and the system becomes easier to disrupt. As a common example, a person found to have high blood pressure while lying down may adopt a low-salt diet and start taking antihypertensive drugs; under this new regime the person may develop orthostatic hypotension—low blood pressure when standing up. Obviously, such a person’s physician should adjust the medication dosage. Another familiar case is an individual who experiences a dry mouth or has difficulty emptying the bladder while using an antidepressant drug.
Several nervous system diseases can produce combined sympathetic and parasympathetic failure. These include some degenerative disorders affecting the brain stem and spinal cord, such as multiple system atrophy (previously referred to as the Shy-Drager syndrome) and Parkinson’s disease. In these diseases, autonomic failure occurs alongside symptoms, such as shuffling gait, unsteadiness, stiffness, or tremor. About 5 to 15 people out of 100,000 develop multiple system atrophy—not a large number. Parkinson’s disease is more common, but autonomic problems in this disease are less severe and occur much later.
The most common peripheral nerve disease, or neuropathy, that produces autonomic failure is diabetes mellitus. Diabetes affects approximately 1.3 percent of the population, and 5 percent to 7 percent of these people suffer damage to their autonomic nerves.
Some spinal cord disorders predominantly affect a person’s bladder, bowel, and sexual function; important examples are multiple sclerosis and injury to the spine.
Diagnosis and Treatment
Doctors diagnose autonomic disorders based on a person’s history, a physical examination, tests of the autonomic functions, and laboratory results. During the physical examination, physicians assess blood pressure and pulse while the individual is lying and standing, the pupils’ reaction to light, and the color and temperature of the skin. Autonomic tests measure sweat production and changes in the heart rate during breathing. The doctor will also check how the blood pressure responds to straining (the patient closes his or her mouth and nose and tries to blow out, called the Valsalva maneuver), to being switched from a horizontal to a vertical position as the patient lies on a tilt table, and to standing. It is sometimes necessary to check how well a person can urinate and move his or her bowels. Blood glucose and other blood tests are done to exclude diabetes and other conditions that may produce similar symptoms.
People diagnosed with an autonomic disorder should work with a health care team: a neurologist, a dietitian, a physical therapist, and in some cases, a urologist or gastroenterologist. The principles for managing these disorders are:
- Learn about your condition.
- Work with your doctor to correct potentially reversible causes, particularly unnecessary medications.
- Adjust your diet and physical activities as necessary.
- Take drugs specific to the autonomic condition, if prescribed.
As an example, here is the usual program of advice for people with orthostatic hypotension:
- Increase your intake of salt to 8 to 10 grams a day and of water to 2 to 2.5 liters (over half a gallon) a day.
- Sleep with the head of your bed raised 20 to 30 cm (8 to 12 inches) to prevent hypertension and excessive urination at night.
- Eat smaller, more frequent meals with low carbohydrate content, and a high-fiber diet to avoid constipation.
- Learn to use small postural maneuvers as standing with your legs crossed and squatting to prevent fainting.
- Perform regular exercise, but avoid heavy exercise and exposure to heat.
- Some people benefit from the use of support stockings.
- Drug treatment potentially includes fludrocortisone (Florinef), which increases the kidneys’ retention of sodium from salt, and midodrine (Proamatine), which constricts the blood vessels.
Other drugs used to treat symptoms of autonomic failure are metoclopramide (Reglan) to improve the working of the stomach and intestine, and sildenafil (Viagra) to treat erectile impotence. Although many elderly people take oxybutynin (Ditropan) or tolterodine (Detrol) to reduce excessive bladder contractions and incontinence, individuals with autonomic failure should not take these medicines. People suffering from urinary problems caused by an autonomic disorder need to follow a fluid schedule and may eventually have to learn to empty their bladders with a catheter.
For some people, doctors may recommend surgical procedures, such as a gastrostomy (a feeding tube is inserted into the stomach to bypass swallowing problems) or penile implant. Individuals whose autonomic problems stem from diabetes may be advised to have a pancreas or kidney transplant. These surgeries can’t fix the autonomic system itself, but they can either alleviate the underlying problem or counteract the troublesome symptoms.
The prognosis for autonomic disorders varies greatly because of their many causes. In multiple system atrophy, autonomic problems worsen along with the other manifestations of the disease. This illness has a poor prognosis; many patients experience potentially fatal breathing difficulties during sleep and may require a tracheotomy. On the other hand, about two thirds of acute autonomic failures following an infection and an immune attack on the autonomic nerves improve within two to four weeks. The prognosis of autonomic failure in diabetes parallels that of the underlying neuropathy and other manifestations of the disease, and may improve with appropriate control of blood glucose and, in some cases, surgery.
Intensive ongoing research is aimed at understanding the brain mechanisms that control autonomic function, as well as the causes of mechanisms of disorders in this system. These investigations may yield results that help prevent and treat not only the diseases associated with autonomic failure but also conditions such as panic attacks, high blood pressure, and sudden cardiac death.
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