Autonomic neuropathy (AN) involves dysfunction of the autonomic nervous system (ANS), the branch of the peripheral nervous system that is responsible for involuntary functions, including, but not limited to, heart contraction rate/force, blood vessel and pupillary dilation/constriction, gastrointestinal tract motility, and sweat gland secretion. AN may cause abnormality in any of the functions controlled by the ANS and is characterized by reductions in autonomic neurotransmitter levels, slowed conduction of autonomic impulses, and altered perception and response to external stimuli. A variety of tests and measures is used to detect AN. The most common of these identify N by evaluating heart rate and/or blood pressure at rest, routine activity, or in response to cardiovascular challenges or by evaluating conduction of autonomic impulses in nerves or muscle fibers, skin response to external stimuli, sweat response to external heat, perception of sensations or changes in blood flow induced by stimuli applied to the skin, pupillary response to external
stimuli, gastric emptying time, clinical AN symptoms, and/or neurotransmitter levels.