Ref. Cardiology: I have to attend a "Autonomic Function Test"Whats Involved?
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austin,
There are three basic types of autonomic function test, one of which is for cardiovagal response, or how well your heartbeat is regulated. There is more than one test for this.
You've been having trouble with fainting or dizziness?
One is a deep breathing test. Lying on your back, you may be required to breathe deeply. The heart normally does not beat at the same rate all the time. What is called "sinus arrhythmia" is absolutely normal and desirable. The heart also speeds up when we breathe in and slows down when we breathe out, which is also normal, and you will probably be tested for this regular irregularity.
You will probably be tested for heart response (heart rate) while lying down, standing up, squatting, and coughing.
All this is a test for the condition of your "vagus nerve," a very important nerve that, among other things, helps regulate heart rate and blood pressure.
So is the Valsalva Manuver, which strictly speaking is the same as holding your breath while straining against it, something like attempting a bowel movement while mildly constipated. The test won't be quite like that, however. It will most likely be blowing for 15 seconds into a tube with a small leak in it, maintaining a certain pressure in it (40 mm of mercury, if I remember right). This will test your vagus nerve's tone. Your heart should speed up during this test.
Another test is simply standing up after lying down. If there is fear of your fainting, you might simply have your head tilted up at about a 60-degree angle, or the whole bed could be tilted up. In this case, the examiners will be looking for a characteristic, very small, change in blood pressure, a slight increase in the lower number and a slight fall in the upper, with a rise in heart rate of about 20 beats per minute. This is completely normal. If you are asked to stand, your blood pressure will fall, but this, too is normal up to a point. If it's too much, you will become dizzy or faint, and that will be quite instructive to your doctor.
At any rate, the autonomic function test is not invasive or painful. It just takes time and is a bit inconvenient, but it is a very good diagnostic tool for differentiating benign signs from more serious ones.
Good luck.
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