Autonomic Function Testing (AFT) is a series of diagnostic tests that evaluate the autonomic nervous system (ANS), which controls involuntary bodily functions like heart rate, blood pressure, digestion, and sweating. The tests measure the body's response to stimuli, such as breathing exercises, changes in posture, or other physical challenges, to identify if the ANS is working correctly. This can help diagnose conditions like autonomic neuropathy, which damages the nerves controlling internal organs.