Pulmonary Function Testing, Simplified


Pulmonary function testing, to some clinicians, can be a bit of a black box (black lung?). Yes, these are usually interpreted formally by a pulmonology, but, generalist interpretation can still be simplified significantly if done systematically, similar to EKG interpretation. In general, reports are standardized to all look about the same, so that this becomes essentially a cerebellar activity over time (a dance with the eyes). There are essentially three steps for most patients, and the fundamental question, usually, is: restriction or obstruction?

1.  Verify: Check to ensure appropriate patient and demographics. Once that is done, ensure the test is adequate by looking at the flow/time graph. An adequate test should show three efforts, all with FEV1 and FVC within about 200ml of each other. The flow/time graph should show a rapid rise with a plateau and be 6 seconds long. 

2. Identify: Look at three numbers: 1) FEV1/FVC, 2) FVC, and 3) TLC. The FEV1/FVC should be >70% or there is probably obstruction. If that number is >70%, a reduced FVC indicates restriction. TLC should be checked to confirm restriction, and should also be reduced if FVC is reduced. 

3. Evaluate: Once restriction or obstruction is identified, each has a couple of further steps for further evaluation. If restriction, check a DLCO. If DLCO is low, then it's probably a primary lung problem leading to restriction. If DLCO is normal or unimpressively low, it's probably an extra pulmonary problem leading to restriction. If obstruction, then check for bronchodilator to decided between asthma, then TLCO to look for emphysema, then reanalysis of FEV1 to grade severity.