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Autonomic Assessment


The autonomic nervous system controls many involuntary body functions, including heart rate, blood pressure, perspiration, bowel and bladder control, and digestion.


There are conditions affecting the autonomic nervous system, ranging from forms of peripheral neuropathy to conditons within the brain. Diabetic neuropathy is probably the most common condition affecting the autonomic nerves.


Autonomic neuropathy is a nerve disorder that affects these involuntary body functions. Damage to these nerves in an autonomic neuropathy disrupts signals between the brain and portions of the autonomic nervous system, such as with the heart, blood vessels, bowels, and sweat glands. This can cause either decreased or abnormal performance of one or more of these involuntary body functions.


Autonomic neuropathy can be a complication of a number of diseases and conditions. And some medications can cause autonomic neuropathy as a side effect. Signs, symptoms and treatment of autonomic neuropathy vary depending on the cause, and on which nerves are affected.


Signs and symptoms of autonomic neuropathy depend upon which parts of your autonomic nervous system are affected. These may include:

  • Dizziness and fainting upon standing due to a drop in blood pressure.

  • Urinary problems, including difficulty with starting a urinary stream, urinary incontinence (leakage) and an inability to empty your bladder fully. The last complication can lead to recurrent urinary tract infections.

  • Sexual difficulties, including problems achieving or maintaining erections or ejaculation problems in men. In women, this may lead to vaginal dryness and difficulties with arousal and orgasm.

  • Difficulty with digestion of food, due to abnormal movement of food through the digestive tract, along with slow emptying of the stomach, called gastroparesis. This may be noticed as a feeling of fullness after eating smaller than usual amounts, a loss of appetite, nausea, vomiting, diarrhea, constipation, abdominal fullness and bloating, problems with swallowing and even heartburn.

  • Sweating abnormalities, such as increased or decreased sweating patterns, which affects the ability to regulate body temperature.

  • Sluggish pupil reaction, which makes it difficult to adjust when you go from a light to dark room. This can also lead to problems with driving at night.

  • Exercise intolerance, due to a lack of change in heart rate instead of appropriately increasing and decreasing in response to your activity level. This may be occurring as fatigue with regular activities that are not strenuous.

What to do before your appointment:

  • You can write down any symptoms you're experiencing, including any that may seem unrelated to the reason you are being assessed.

  • Make a list of all medications, vitamins or supplements that you're taking, especially blood pressure medications.

  • Write down questions to ask your doctor.


What testing will be done for autonomic neuropathy?


Your medical history will be reviewed first. A thorough description of your symptoms is necessary and a physical exam will be performed.


There are several tests that your doctor may use to help with diagnosis will evaluate the reaction of several body functions controlled by the autonomic nervous system. These may include:


  • Breathing tests - these tests measure how your heart rate and blood pressure respond to different forms of breathing. For example, quiet, soft breathing will be performed for 1 minute, followed by deep breathing for another minute. Then, an exercise called the Valsalva maneuver, in which you exhale forcibly while contracting your abdominal muscles, will be performed. This involves having electrodes placed across your chest (see below left), just like a regular heart tracing

During breathing testing, a heart tracing similar to that performed during an electrocardiogram (ECG) is obtained to look for changes in heart rate during different forms of breathing.

An iodine and starch solution changes colours when sweating takes place. In this case, the left hand (on the right) is sweating moreso than the right hand (on the left).

  • Thermoregulatory sweat test - during this test, you will have body portions coated with a powder of iodine and starch. This will change color when you sweat (see below right). Your sweat pattern may help confirm a diagnosis of autonomic neuropathy or other causes for decreased or increased sweating.

  • Sympathetic skin testing - this also examines your ability to sweat. When you are frightened or scared, sweating normally takes place. In this case, electrodes are placed over your foot or your hand while a shock is given to you somewhere on your body to surprise you. If you sweat, a waveform will be present on the computer screen due to the presence of a salt bridge forming with the sweat (see below left). If no sweating occurs, then flat lines will be seen (see below right)

  • Orthostatic blood pressure checks  - your blood pressure is checked regularly, but in order to determine the function of the autonomic nervous system, it is important to check the blood pressure in different positions. First, the blood pressure will be checked while lying after being relaxed for several minutes. Then, you will sit up and the pressure will be checked again after a short delay. Finally, a standing blood pressure will be obtained after standing for 2 minutes. Your heart rate will also be measured during these positions. It is normal for your blood pressure and heart rate to change as your body position changes. In autonomic dysfunction, blood pressure may fall while standing or even sitting, while the heart rate fails to rise in order to accommodate the change in position.


Depending upon the laboratory that you are seen at, or if your doctor wishes to have you perform additional testing, you may also receive the following tests:

  • Tilt-table test - this monitors how your blood pressure and heart rate respond to changes in posture and position, simulating standing up after lying down. You will lie flat on a table that is tilted to raise you up. Normally, your body compensates for a drop in blood pressure when you stand up by clamping down on your blood vessels and increasing your heart rate. Blood pressure and heart rate are monitored throughout this test.

  • Gastric-emptying tests - these check for slowed movement of food through your system, delayed emptying of the stomach and other abnormalities. These tests are usually done by a gastroenterologist.

  • Quantitative sudomotor axon reflex test (QSART) - this evaluates how the nerves that regulate your sweat glands respond to stimulus. A small electrical current passes through four points at your forearm, foot and leg. A computer analysis examines how your nerves and sweat glands react. 

  • Urinalysis and bladder function (urodynamic) tests - these are performed by a Urologist and examine the dynamics of the flow of urine when voiding the bladder. 

  • Ultrasound of the bladder - after voiding, an ultrasound can show how much volume is left inside the bladder. In autonomic disorders, the bladder does not void fully.

This is an example of an abnormal sympathetic skin response in a patient with long standing diabetes. There are no waves seen after the stimulus is provided, indicating that no salt bridge formed due to absence of sweat.

This is an example of a normal sympathetic skin response in a control subject. There are waves for each of both hands and both feet after the stimull are provided, indicating that salt bridges formed due to sweating.

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