Familial amyloid polyneuropathy (FAP) is a rare genetic disorder where amyloids (protein deposits) accumulate in the peripheral nervous system and other tissues. Because of this amyloid buildup, signals from the autonomic nervous system can be slowed, resulting in delayed responses to changes in body position and blood pressure. A tilt table test is one method physicians can use to help diagnose FAP.
Why it is done
When a person stands up after lying down, the autonomic nervous system must make changes to prevent the blood from pooling in the legs. This is accomplished by sending signals to constrict (shrink) blood vessels and increase heart rate. In normal conditions, this happens rather quickly and can prevent a person from becoming lightheaded or faint. If a person has FAP, some of the nerves from the autonomic nervous system might be damaged. This could result in a much slower response to standing up and cause lightheadedness, nausea, or fainting. The tile table test is used to safely re-create this activity while monitoring vital signs.
How the test is performed
Patients are secured to a horizontal, motorized table for several minutes before the table is tilted vertically for up to an hour. Vital signs, including EKG, blood pressure, and oxygen levels in the blood, are taken when the patient is lying down and after being moved to an upright position. If the movement from lying to standing does not produce any of the symptoms of low blood pressure, a medication called isoproterenol can be given through the bloodstream to increase the heart rate and make symptoms more noticeable.
What the results mean
Doctors will monitor the vital signs and symptoms during the course of the test. Fainting or dizziness along with a slow change in heart rate and blood pressure recovery could be symptoms of FAP or another autonomic neuropathy disorder. The results of the test will be analyzed and can be used in conjunction with family history and the results of other tests to help reach a diagnosis.
The tilt table test is fairly safe. Possible complications include:
- Nausea and vomiting
- Prolonged low blood pressure
Because the test is performed in a medical facility and the patient monitored by medical professionals, there is very little risk associated with the test.
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