Autonomic Testing

What is autonomic testing?

Autonomic testing helps find out if your autonomic nervous system (ANS) is working as well as it should. Your ANS controls body functions that happen automatically (without you thinking about them). These include breathing, heartbeat, body temperature, and digestion. If there are problems with the function of the ANS, it's known as autonomic neuropathy. The most common causes of autonomic neuropathy include diabetes, autoimmune diseases, some types of medicines, and certain infections, such as HIV/AIDS.

Autonomic testing can show which part of the ANS is affected and how seriously it's affected. This can help your provider develop the most effective treatment strategy.

Other names: tilt table test, quantitative sudomotor axon reflex test (QSART), thermoregulatory sweat test (TST)

What is it used for?

Autonomic testing is used to check for problems with your autonomic nervous system (ANS).

Why do I need autonomic testing?

You may need this test if you have symptoms of autonomic neuropathy. Symptoms will vary depending on which part of the nervous system is affected.

Stomach and gastrointestinal symptoms include:

• Constipation
• Diarrhea
• Nausea and vomiting

Bladder and urinary symptoms include:

• Difficulty urinating
• Leaking urine
• Urinating more often than usual

Heart and lung symptoms include:

• Rapid heart rate
• Shortness of breath with activity or exercise
• Dizziness
• Fainting
• Weakness

Other symptoms include:

• Too much or not enough sweating
• Sexual problems; erectile dysfunction in men; vaginal dryness in women

What happens during autonomic testing?

There are different types of autonomic tests. Depending on your symptoms, your health care provider may perform one or more of the following tests:

Deep Breathing Test and Valsalva Maneuver. These tests measure your heart rate and blood pressure while doing certain types of breathing.

• For both tests, a provider will place electrodes on your chest and a small blood pressure cuff on your finger.
• For a deep breathing test, you will take slow, deep breaths for one minute.
• For the Valsalva maneuver, you will breathe out forcefully through a mouthpiece while your nose is pinched shut.
• The electrodes and cuff will record your heart rate and blood pressure.

Tilt Table Test. This test measures your blood pressure and heart rate as you change your posture and position. During the test:

• You will lie flat on a motorized table that has a footrest.
• Soft safety straps will be placed across your body.
• A health care provider will put electrodes on your chest and blood pressure cuffs on one of your arms and a finger. An IV line may also be placed in your arm or hand to inject medicine or fluids if needed.
• You will remain flat on the table for about 15 minutes.
• A health care provider will tilt the table to an almost standing position for up to 45 minutes.
• Your provider will check your blood pressure and heart rate.
• If the test causes you to faint, the table will be quickly returned to the flat position.

Quantitative Sudomotor Axon Reflex Test (QSART). This test measures the function of the nerves that control sweating. During the test:

• Your provider will place electrodes on your foot, arm, and leg. The electrodes will contain a substance that stimulates sweating.
• A mild electrical current will be sent through the electrodes. You might feel a warm, tingling sensation as this is done.
• A computer will analyze how your nerves and sweat glands react to the electrical current.

The test takes about 45 minutes to an hour to complete.

Thermoregulatory Sweat Test (TST). This test measures how well your body sweats in a warm environment. During the test:

• A special powder will be applied to your skin.
• You will lie in a special room that will be slowly heated up to stimulate sweating. The heat and humidity may be a little uncomfortable.
• The powder will change color as you sweat.
• The pattern of your sweat can show if you are sweating normally.

The test takes usually takes 40-65 minutes to complete.

Bladder Ultrasound. This test is used to check for problems with your bladder, which is controlled by autonomic nerves. The ultrasound is done after you urinate to see how much urine is left in the bladder. During the test:

• You will lie on a table with your lower abdomen exposed.
• A health care provider will spread a special gel on the skin over that area.
• The provider will move a wand-like device, called a transducer, over the area.
• The device sends sound waves into your body.
• The waves are recorded and turned into images on a monitor.

Will I need to do anything to prepare for the test?

Your health care provider will give you specific instructions on how to prepare, but many autonomic tests require the following preparations:

• Don't eat or drink anything with caffeine for eight hours before your test.
• Keep well hydrated with noncaffeinated beverages the day before your test.
• Don't drink alcohol for 12 hours before your test.
• Don't smoke for three hours before your test.

Your provider will also let you know if you need to stop taking certain medicines before your test.

Are there any risks to the test?

Some people faint during a tilt table test. If that happens, you will be tilted back to a normal position immediately. During and after a tilt table test, you may experience nausea or vomiting and weakness. Weakness may last for a couple of hours, but other symptoms usually go away quickly.

There are no known risks to having ultrasound or sweat tests.

What do the results mean?

If any of your autonomic test results were not normal, your provider may recommend medicine and/or lifestyle changes to treat the disease that is causing your symptoms. Your provider may also recommend treatment strategies to help manage your symptoms. If the cause of your autonomic neuropathy is unknown, you may need more tests to help make a diagnosis.