Autonomic Function Tests
The autonomic nervous system controls the function of your internal organs, such as your heart rate, the movement within your stomach and intestines, and modulation of your blood pressure. Autonomic nerve fibers are small fibers similar to the nerve fibers that transmit pain. Your doctor may order autonomic function tests if you experience dizziness or fainting, or if a small fiber neuropathy is suspected. The test is sometimes referred to as “small fiber testing” or “tilt table testing.” The test, performed by a technician, takes 1½ to 2 hours but is not painful.
Preparing for the tests
In preparation for the tests, do not smoke or drink coffee, tea, or other caffeinated beverages for at least four hours preceding the test. If possible, avoid taking any medications that dry out your eyes or mouth, such as cold and allergy medications or antidepressants, for 24 hours before your visit.
What is involved?
Autonomic function tests come in three parts:
- Quantitative sudomotor axon reflex test (QSART). This test measures your sweat output, which may be impaired in disorders of the autonomic nervous system, such as neuropathy. A technician attaches four small plastic capsules to your arms and legs. These capsules contain a liquid that causes sweating. The capsules are attached to a computer, which sends a small amount of electricity through the liquid. It then measures your sweat response. The QSART test is not dangerous or painful. You will feel a slight pricking sensation under the capsule, and your skin may look a little red after the test, but this will go away in a few hours.
- Cardiovagal testing. This test measures how your heart rate and blood pressure respond to changes in your breathing pattern. The technician puts ECG stickers attached to wires on your chest to monitor your heart rate. A small cuff is placed on your finger to monitor your blood pressure. The cuff fills with air and squeezes your finger throughout the test. You then do two breathing exercises. The first exercise is called heart rate response to deep breathing. In the first exercise you take slow, deep breaths. The second exercise is called the Valsalva maneuver. In this exercise you blow hard into a tube.
- Tilt table testing. You lie flat on a table with a seatbelt across your body and your feet on a foot rest. After a period of rest, the table tilts up so that you are in a standing position. A technician will monitor you for 10 minutes. If you don’t feel well during this test, tell the technician and he or she will bring you back down right away.
Talk to your physician about whether autonomic function tests can assist in your diagnosis and treatment. For referral appointments, please call Jessica Robinson-Papp, MD, at 212-241-8390. The tests are performed in the clinical neurophysiology area, located in the Annenberg Building, second floor (area 218).