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.
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 putting the mouthpiece in his mouth. This way of performing a test is more error prone.
After preparation and explaining the test very well to the patient he will do the following:
- 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.
- Maximum inspiration
The patient fills his lungs entirely. This first inspiration does not need to be as quick as posibble, but it must be as deep (complete) as possible.
- (A short pause between maximum inspiration and forced expiration is permitted, although not necessary. In any case it should never exceed 2 seconds. Some patients will perform better without this pause, some will perform better with it.)
- Forced expiration
The patient performs a maximal expiration during which all the air is blasted out of the lungs as quick, as forcefully and as long as he can. It is important to empty the lungs as much as possible.
- Forced inspiration
Immediately after the forced expiration a second inhalation is performed. The second inspiration will be forced and as quickly as possible.
The patient should keep his back straight during the test, a common error is to bend over during the forced expiration.
After the flow-volume loop has been performed, put the spirometer down, assess the test quality and explain any errors the patient might have done.
A minimum of 3 well performed and reproducible flow-volume loops are necessary.