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Autonomic testing

Children’s Hospital of Wisconsin uses four tests when evaluating a patient for autonomic disorders:

Sweat response test

This test measures a child’s sweat response to see if autonomic nerves are intact or harmed. During the test, the technician will apply a few capsules to your child’s extremities that provoke sweating and then measure the volume of sweat on that section of your child’s skin.

Tilt table test

This test is helpful when diagnosing an autonomic disorder called postural orthostatic tachycardia syndrome, also known as POTS. The patient is strapped to a motorized table that moves into an upright position while measuring changes in the patient’s blood pressure and heart rate. A patient with POTS will have a heart rate that increases more than 40 beats a minute in the first 10 minutes upright with no significant change in blood. The test is also used in patients with fainting or near fainting. Some patients might faint as a result of this test.

A patient with orthostatic hypotension would show a progressive drop in blood pressure with or without heart rate changes in response to the tilt table test. Orthostatic hypotension is a more significant condition than POTS, but it is not as common in children.

Valsalva maneuver

In this test, the child blows for 15 seconds as if he or she is bearing down during a bowel movement, and then relaxes. That bearing down decreases the blood that comes back to the heart, which activates the sympathetic part of the autonomic nervous system, which then increases the blood pressure and the heart rate. When the patient stops blowing, more blood comes back to the heart. At this point, the parasympathetic nervous systems get activated with a decrease in heart rate. If a patient’s blood pressure does not increase while blowing (sympathetic function) and continues dropping, it could be a sign of autonomic dysfunction.

Deep breathing

This test evaluates parasympathetic function by measuring heart rate changes as a child breathes in and out.

All four tests take about 2 to 2.5 hours to complete, and your referring doctor should receive results after about a week.

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