Although the FEV1 was first described in 1949 by Tiffeneau the basic algorithm for interpreting spirometry using the FEV1/FVC ratio was developed by Gaensler in 1951. A reduction in the FEV1/FVC ratio has proven to be a reliable signal for the presence of airway obstruction and this approach towards interpreting spirometry has remained much the same since then.

Taken simplistically, all that is needed to interpret spirometry is to know whether the FEV1/FVC ratio and FVC are normal or reduced. This however, overlooks any issues about test quality and the effect they have on the reliability of the FVC, FEV1 and FEV1/FVC ratio.

Realistically, most spirometry tests will probably meet all testing criteria and will be either clearly normal or abnormal. When spirometry test quality if poor, this clarity no longer exists and it becomes necessary to think in terms of probabilities instead of a simple normal or abnormal. Even so, it is still possible for a reasonably reliable interpretation to be made using unreliable results when testing errors and their probable effects on results are understood.

The guidelines for the performance of spirometry come primarily from the ATS/ERS standards for spirometry which provides a number of objective criteria for assessing test quality. There are also a number of real-world common-sense criteria not included in the ATS/ERS guidelines that are usually gained only from experience in performing or interpreting spirometry.

It should be noted that at one time or another reductions in a number of other spirometry measurements such as the FEF25-75, MEF50% and Peak Expiratory Flow (PEF) have been proposed as additional ways to determine the presence of airway obstruction. All of these however, have been shown to have severe enough shortcomings that they are rarely, if ever, used for this purpose any more.

 

 

PFT Interpretation by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License