The autonomic nervous system (ANS) is a division of the peripheral nervous system that regulates the unconscious functions of the body such as heart rate, digestion, and respiration. It has two branches: the sympathetic nervous system, which prepares the body for “fight or flight” response, and the parasympathetic nervous system, which slows down the body and promotes “rest and digest” functions. These two branches work in balance to maintain the body’s homeostasis, or internal stability.

An autonomic nervous system test is a medical examination that assesses the functioning of the autonomic nervous system. This test measures the body’s responses to specific stimuli, such as changes in heart rate, blood pressure, or sweating, to evaluate the functioning of the sympathetic and parasympathetic branches of the autonomic nervous system. The results of the test can help diagnose various conditions such as autonomic neuropathy, Parkinson’s disease, and postural orthostatic tachycardia syndrome (POTS).

The procedure for an autonomic nervous system test may vary depending on the specific test being performed, but some common tests include:

1. Heart rate response test – measures the heart rate response to changes in position, breathing, or exercise.

2. Blood pressure response test – measures the blood pressure response to changes in position, deep breathing, or other stimuli.

3. Sweat test – measures the amount of sweat produced in response to certain stimuli, such as an increase in temperature.

4. Tilt table test – measures the heart rate and blood pressure response to a sudden change in position from lying down to standing up.

5. Deep breathing test – measures the heart rate response to deep breathing.

6. Valsalva maneuver test – measures the heart rate response to bearing down, as if having a bowel movement.

These tests are usually performed in a doctor’s office or medical facility, and can take anywhere from 30 minutes to several hours to complete. The patient may be connected to various monitoring devices such as an electrocardiogram (ECG) or blood pressure cuff to measure the autonomic responses.