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Pulmonary Function Test


This test measures the amount of air that can be taken in with a deep breath and how quickly it can be expelled from the lungs by a forceful exhalation. The tests can be used to diagnose & monitor lung conditions.

There are different tests in the series:

The match test - this is a simple test that checks the force of exhalations. It involves holding a lighted match six inches away from the mouth, then exhaling as hard as possible to blow out the flame. If the flame is blown out easily, the result is normal.

The forced expiratory time (FET) test - Involves taking a deep breath in, then exhaling as fast as possible with the mouth open wide. The exhalation time is measured in seconds. Normal values for test: all the air in the lungs is expelled in two to five seconds.

The peak expiratory flow (PEF) test - Involves inhaling deeply, then blowing as hard as possible into a peak flow meter. The highest of three values is recorded. Normal values for test: the value should be 80 percent of the predicted normal value.

The maximum ventilatory volume (MVV) test - Uses an instrument called a spirometer. Involves putting a mouthpiece in the mouth & blowing into into as hard as possible for 15 seconds. The result is recorded on a graph, and multiplied by four to give the value for 1 minute. Normal values for test should be 15 to 20 times the FVC.

The forced vital capacity (FVC) test and forced expiratory volume (FEV1) - Also uses the spirometer. Again, it involves blowing into the mouthpiece as hard & long as possible. It is repeated three times & the highest value recorded.

A test to measure your lung volume (size) will be done in one of two ways. One way to measure lung volume is to have you inhale a small carefully measured amount of a specific gas (such as helium) that is not ever absorbed into your bloodstream. This gas can mix with all of the air in your lungs before you breathe it out again. The air and helium that you breathe out will be tested to see how much the helium got diluted by the air in your lungs and a calculation using this information can decide how much air your lungs must have been holding in the first place.

The other way to measure lung volume is with a test called "plethysmography." In this test, you will sit inside an airtight cubicle that looks like a phone booth, and you will breath in and out through a pipe in the wall. The air pressure inside the box will change with your breathing because your chest expands and contracts while you breathe. This pressure change can be measured and used to calculate the amount of air you must be breathing.

Your lungs' efficiency at delivering oxygen and other gases to your bloodstream can be tested and is known as your "diffusion capacity." For this test, you will breathe in a small quantity of carbon monoxide (too small a quantity to do you any harm) and the amount you breathe out will be measured and compared. Your ability to absorb carbon monoxide into the blood is representative of your ability to absorb other gases such as oxygen.




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