The nervous system has three parts: motor, sensory and autonomic. The motor part takes care of movement of a muscle such as lifting an arm or turning the head. The sensory system takes care of any kind of perception from the external environment, such as seeing, or feeling a texture. The autonomic system handles everything else. This includes monitoring and control of all internal functions such as blood pressure, blood flow, sweating, bowel and bladder. There are many other functions that we do not yet understand.
Your doctor wishes to determine whether your autonomic nervous system is functioning normally. Certain diseases can attack the autonomic nervous system in isolation, or as part of a more widespread illness. In the second case, many functions of the nervous system, including autonomic, sensory and motor systems, may be affected, and the autonomic testing can be used as a "marker" to diagnose such a disease. In all of these cases, the autonomic nervous system will be functioning poorly or not at all. In contrast, when pain restricted to one part of the body is the main problem, your doctor will wish to determine if the autonomic nervous system on that side is functioning too much.
All testing is non-invasive and generally well-tolerated. Testing depends on the problem.
When the issue is whether the entire autonomic nervous system has been affected by a disease, some or all of the following tests may be performed:
First, we will monitor your blood pressure and heart rate, while you:
1) lie down on a tilt table, snugly secured. You are then raised to the upright position for 20 minutes, and taken back down again. This is called the tilt table test.
2) take deep breaths for a full minute. This is called the deep breathing test.
3) blow into a tube to maintain increase pressure in your chest. This is called the Valsalva manuever.
Next we will monitor your sweating (sweat glands do not sweat unless a nerve tells them to do so) with little capsules attached to the skin:
1) After you change into a disposable bathing suit, we apply an orange powder to your skin. You then go into a warm and humid large glass room (much like a sauna) for 20 to 30 minutes. The orange powder turns purple where you sweat, telling us which parts of the autonomic nervous system are working, and which are not. This is the thermoregulatory sweat test.
2) A small battery-operated current stimulates the sweat glands directly. This is the quantitative sweat axon reflex test.
When pain in one limb is the main problem, we will compare the one that hurts with the one that does not hurt. We may ask you to exercise both limbs for 2 minutes. Tests may include:
1) Small capsules attached to the skin, measuring sweating at rest and with a small battery-operated current that stimulates the sweat glands directly. This the resting sweat output test.
2) A laser taped to the skin measuring skin blood flow.
3) A blood pressure cuff inflated around the limb measuring muscle blood flow.
4) Any swelling is detected by putting the limb in luke-warm water. This is called limb-volume displacement.
5) A infrared probe that does not contact the skin measuring skin temperature
The sweat glands, heart rate, blood pressure, and blood flow in the limbs are all controlled by the autonomic nervous system. When we measure these functions, we can tell whether your autonomic nervous system is working normally, or if some of the symptoms you have could be related to under- or overfunction of the autonomic nervous system. We can also tell how likely you are to respond to certain treatments. A report will go to your referring physician within a week.
