Diagnosing Autonomic Disorders
There are many types of autonomic disorders, some of which occur alone. Others occur as the result of another disease, such as Parkinson's disease or diabetes. To diagnose the conditions, a doctor performs a physical exam and reviews a person’s medical history.
Doctors at NYU Langone’s Dysautonomia Center are experienced at diagnosing autonomic disorders, as well as conditions that may be causing similar symptoms. They may perform the following tests.
A doctor performs a neurological examination to determine whether there are any underlying causes of autonomic dysfunction. He or she may assess how a person moves or walks and his or her ability to sense vibration, touch, or pain.
Autonomic testing is designed to determine how well the body regulates the internal organs. During these tests, doctors use an electrocardiogram, or EKG, to monitor electrical activity in the heart and special cuffs on the fingers to continuously measure blood pressure. Doctors may record other physiologic functions, depending on a person’s symptoms, including sweating, respiration, production of carbon dioxide, oxygen saturation, the amount of blood the heart pumps, and the amount of blood going through the brain.
The tests involve performing different breathing exercises and changing position, from lying down to standing upright. These activities are meant to stimulate the autonomic nervous system to produce changes in blood pressure, heart rate, sweating, and blood flow to the brain during a short period of time so the doctor can identify any autonomic disorder.
Doctors may also order blood tests to assess the release of neurotransmitters and hormones that help to control blood pressure.
To test the body’s ability to compensate for changes in the amount of blood that returns to the heart, a doctor asks a person to perform a test called the Valsalva maneuver. The Valsalva maneuver involves forcefully exhaling against a closed airway. This is usually done by breathing through a mouthpiece and pinching the nose shut while blowing hard, like you’re blowing up a balloon.
During this test, doctors record the strength and depth of respiration and changes in heart rate and blood pressure through electrodes on the chest and cuffs on the fingers. People with autonomic dysfunction have changes in heart rate, blood pressure, or both that are different from those in people who don’t have these disorders.
A doctor performs the deep breathing test to determine the function of the vagus nerve that controls the heart. The purpose of this test is to examine how much the heart rate changes in response to breathing in and breathing out. The test involves following commands to breathe slowly and deeply for one minute, while expansion of the chest, heart rate, and blood pressure are recorded through electrodes on the chest and cuffs on the fingers.
Tilt Table Test
A doctor performs a tilt table test to determine whether standing up provokes a drop in blood pressure or fainting. The purpose is to reproduce a person’s symptoms in a controlled laboratory setting.
During this test, a person’s heartbeat, blood pressure, respiration, and sweating are continuously recorded while he or she lies on a stretcher-like table relaxing and breathing normally for five minutes. Seatbelt-like straps are then attached around the abdomen and legs and the table tilts the person upright to a 60-degree angle. The tilting continues for up to 45 minutes or until the person has a drop in blood pressure and experiences low blood pressure symptoms such as dizziness, lightheadedness, or near fainting.
As soon as a person starts to feel symptoms of low blood pressure, the table is tilted back and the person is returned to the lying position, where symptoms get better.
Samples of blood are taken while the person is in the lying and the standing position to check the release of neurotransmitters and hormones that are involved in the control of blood pressure.
The team at the Dysautonomia Center may also measure blood supply to the brain using a small ultrasound probe mounted on a headband. This allows the doctors to see whether symptoms that a person has during a tilt table test are related to changes in blood supply to the brain.
In addition, specialists also measure breathing rate throughout the tilt table test using a small plastic nasal tube called a cannula that monitors the level of carbon dioxide in each breath.
A sweat test evaluates how the nerves that control sweat glands respond to stimulation. During this test, a mild, painless electrical current is passed through the forearms, foot, and leg. A computer analyzes how the nerves and sweat glands react.
These nerves can be affected by different autonomic disorders like pure autonomic failure and Parkinson’s disease. The test can pinpoint where in the autonomic nervous system the problem is.
Ambulatory Blood Pressure Monitoring
An ambulatory blood pressure machine is a portable device that you take home and wear. It is programmed to measure your blood pressure at intervals throughout the day and night. Depending on the results of the ambulatory blood pressure measurements, doctors may adjust any medications you are on, or prescribe different ones to help control blood pressure.
A bladder ultrasound is an imaging method to study the function of your bladder, which is controlled by autonomic nerves. The painless test is done after you urinate to measure how much urine is left in your bladder.