Performing Spirometry

Performing a good FVC test is not easy! Explaining the patient how to perform the test is key to get a good result. Patient cooperation is very important as well.

The Forced Vital Capacity consists of a forced expiration in the spirometer followed by a forced inspiration.

Preparation

Although the test can be performed while standing up, most recommend to do it while sitting down.

It is recommended to loosen or take of tight cloths for the test (eg. a tie).

Explaining the patient what he needs to do is extremely important to get a good result. The better the test is explained (don't hesitate to show how to do it!) the better the patient will understand what is required and the more disappointment and demotivation are avoided.

Although not strictly necessary it is recommended to put a nose clip on the patient's nose during the test.

Many spirometers allow to perform a few respiratory cycles at rest before the FVC is performed. This tidal breathing can be helpful for the patient to understand better what needs to be done during the test. Other spirometers do not allow this tidal breathing and the patient will need to inspire completely before puttng the mouthpiece in his mouth. This way of performing a test is more error prone.

Performing FVC

After preparation and explaining the test very well to the patient he will do the following:

  1. Tidal breathing
    If the spirometer permits it, it is recommended to start with some tidal breathing and explaining the patient what he is doing while showing it on the screen of the spirometer or computer.
  2. Maximum inspiration
    The patient fills his lungs entirely. This first inspiration does no need to be forced but must be as deep as possible.
  3. Forced expiration
    Immediately after the complete inspiration the patient performs a maximal expiration during which all the air is blasted out of the lungs as fast, as hard and as long as he can. It is important to empty the lungs as much as possible. Some say patients should hold their breath shortly (but not more than 2 seconds) after complete inspiration, others say there does not need to be pause.
  4. Forced inspiration
    Immediately after the forced expiration a second inspiration is performed. The second inspiration will be forced and as quickly as possible.

The patient will need to keep a straight back during the test, a common error is that the patient will bend over during the forced expiration.

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