Autonomic testing: common techniques and clinical applications.

Laboratories able to test autonomic function are increasingly available and rely on batteries of well-accepted, noninvasive tests. Tests of parasympathetic cardiovagal, sympathetic vasoconstriction, and sudomotor (sweating) function are most commonly employed. Common examples include heart rate variability to various challenges, Valsalva maneuver, standing and tilt-table studies, and various sudomotor methods. New techniques and technical refinements continue to be described. Most studies rely on perturbations of complex systems and not direct assessment. Testing has helped to improve disease recognition and prompted advances in classification, pathophysiology, and treatment. Major areas impacted include hereditary and immune-mediated autonomic neuropathy, diabetic autonomic neuropathy, distal symmetric polyneuropathy, Parkinson disease and other autonomic failure syndromes, orthostatic intolerance, and unexplained syncope.