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:
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.
After the flow-volume loop has been performed, put the spirometer down, assess the test quality and explain the patient any errors he might have done.
A minimum of 3 well performed and reproducible tests are necessary.