Autonomic Physiology

Autonomic physiology encompasses diverse interactions between the nervous system and visceral effector organs, and their impairment in many neurological disorders can be measured noninvasively. Autonomic outflow is organized neuroanatomically and functionally. Sympathetic and parasympathetic nerves coordinate the cardiovascular, peripheral vascular, and sudomotor responses that regulate blood pressure, heart rate, thermal equilibrium, and other automatic bodily functions. Knowledge of autonomic physiology is key to the recognition and diagnosis of autonomic failure, orthostatic hypotension, autonomic neuropathies, localizable regional autonomic disorders, neurodegenerative and general medical disorders that affect autonomic function. An important example is neurogenic orthostatic hypotension, which can result from impaired sympathetic vasoconstriction of peripheral vascular beds, impaired carotid baroreflex responses, or impaired autonomic influence on cardiac output. Another example is thermoregulatory failure from ineffective cutaneous sudomotor or vasomotor responses. Accurate measurement and valid interpretation of autonomic responses in the clinical laboratory rest on an understanding of autonomic physiology.