Nerves of the autonomic nervous system control heart rate and blood pressure, and they also control blood flow and sweat gland function. In the autonomics laboratory, we perform two types of studies. One is for complex regional pain syndrome (CRPS) or reflex sympathetic dystrophy, and the other is for small fiber neuropathy and other suspected autonomic disorders.
Complex regional pain syndrome
For this pain disorder, we assess skin temperatures on the affected and contralateral arms or legs by infrared thermography. We also assess the resting sweat levels on those limbs. Last, we perform quantitative sudomotor axon reflex testing (QSART) to measure stimulated sweat output in the affected and nonaffected limb. QSART consists of applying a small electric current and a chemical called acetylcholine to the skin. Sweat glands are stimulated and a capsule placed on the skin captures the sweat that is measured by the machine. With CRPS, there is an asymmetry in stimulated sweat output between an affected and unaffected limb. The testing is not very useful if symptoms are present in both arms or both legs. We do not perform testing for pain in the face or trunk.
Autonomic Reflex Screen
The autonomic reflex screen consists of QSART, tilt table test with measurement of heart rate and blood pressure, and measurement of parasympathetic function (heart rate to deep breathing and with Valsalva testing). The QSART is as described above but performed on the left leg at three sites and on the left forearm. With disorders that affect small nerve endings, there is often a reduction in stimulated sweat output.
For the tilt-table testing, the patient is strapped onto a table that tilts up to a standing position while blood pressure and heart rate are monitored for 10 minutes. No medications are administered. The entire test battery takes about an hour and a half.
Reasons to Undergo Autonomic Reflex Screen
- Small fiber neuropathy
- Orthostatic hypotension with suspected dysautonomia; for example, parkinsonian syndromes
- POTS (postural orthostatic tachycardia syndrome)
For probable cardiac disorders, patients should be seen by a cardiologist and have tilt-table testing done in Cardiology for safety.
You need a prescription from your physician prior to scheduling. Orders are placed electronically or Faxed to 412-647-5162
Preparation for Testing
For CRPS testing, medications that interfere with sweat production should be discontinued if possible. A list will be provided after scheduling. For the autonomic reflex screen, patients should be well-hydrated with non-caffeinated beverages, but they should not eat, smoke, or use caffeine for 3 hours prior to testing. Alcohol should be avoided for 12 hours prior to testing. There is also a long list of medications—mostly antidepressants and blood pressure medications-- that should be held prior to testing, if possible, and this list will be provided at the time of scheduling. Tilt testing cannot be performed on patients greater than 300 pounds. Notify the technicians if you have a history of retinal detachment as that limits the testing.