Autonomic Nervous System Testing

The autonomic nervous system (ANS) regulates physiological processes, such as blood pressure, heart rate, body temperature, digestion, metabolism, fluid and electrolyte balance, sweating, urination, defecation, sexual response, and other processes. Regulation occurs without conscious control, i.e., autonomously. The ANS has two major divisions: the sympathetic and parasympathetic systems. Many organs are controlled primarily by either the sympathetic or parasympathetic system, although they may receive input from both; occasionally, functions are reciprocal (e.g., sympathetic input increases heart rate; parasympathetic decreases it).

Disorders of the ANS can affect any system of the body; they can originate in the peripheral or central nervous system and may be primary or secondary to other disorders. Symptoms suggesting autonomic dysfunction include orthostatic hypotension, heat intolerance, nausea, constipation, urinary retention or incontinence, nocturia, impotence, and dry mucous membranes. If a patient has symptoms suggesting autonomic dysfunction, cardiovagal, adrenergic, and sudomotor tests are usually done to help determine severity and distribution of the dysfunction.

Autonomic Regulation is the body’s ability to maintain homeostasis (stability and balance) during internal and external stimuli. Autonomic Regulation is always functioning, and we are often unaware of the important tasks it is performing. When the nerves that control Autonomic Regulation are damaged, Autonomic Dysfunction can develop. Autonomic Dysfunction can be temporary or chronic. Diabetes and Parkinson’s disease are two examples of chronic conditions that can lead to Autonomic Dysfunction.

To see if a disease is affecting the autonomic nervous system, several tests are done to monitor blood pressure, blood flow, heart rate, skin temperature, and sweating. By measuring these functions, it is possible to discover whether or not the autonomic nervous system is functioning normally.

Tests to measure blood pressure and heart rate include the tilt table test, a deep breathing test and the Valsalva maneuver. The tilt table test requires that the patient lie on a table that is then raised. The deep breathing test requires the patient to take deep breaths for a minute. The Valsalva maneuver requires that the patient blow into a tube to increase pressure in the chest. While these simple tests are performed, blood pressure and heart rate are monitored.

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