Autonomic Nervous System Testing

Abstract

The clinical utility of autonomic function tests in pediatric gastroenterology is steadily evolving. The current tests available evaluate cardiac and sudomotor responses, and not direct gastrointestinal response. Therefore, when these tests are utilized in clinical practice, the results are extrapolated (in the appropriate clinical setting) to the abnormality of the gastrointestinal tract. The tests are divided into those of autonomic cardiovascular function (Cardiac response to deep breathing, Valsalva maneuver, head up tilt (HUT) table test, handgrip and cold pressor test) and those of sudomotor function (quantitative sudomotor test and thermoregulatory sweat test). Together, these two groups of tests evaluate the sympathetic adrenergic, sympathetic cholinergic, and parasympathetic cholinergic function in several organ systems, and assess for the presence or absence of a generalized autonomic neuropathy.

In preparation for the testing, the subject should be well hydrated, free of caffeine and nicotine exposure, and all medications that may interfere with the response of the autonomic nervous system should be stopped about 5-half lives to 5–7 days prior to the testing date. Such medications include α(alpha)- and β(beta)-receptor agonists and antagonists, pro- and anticholinergics and mineralocorticoids, selective serotonin reuptake inhibitors, and serotonin nonselective reuptake inhibitors.

Some data show altered electrical activity of the stomach in the upright position in subjects with postural tachycardia syndrome (POTS). In addition, treatment of the orthostatic intolerance in patients with POTS often benefits their gastrointestinal symptoms. Thus, there appear to be a significant physiologic relationship between orthostatic and gastrointestinal dysfunction, although the exact nature of this is yet to be elucidated.