Study objectives: No recommendation currently exists for grading the severity of airway obstruction in the presence of additional restriction. The grading of airway obstruction is currently based on the FEV1 (American Thoracic Society [ATS] recommendations), while prior recommendations by the Intermountain Thoracic Society (ITS) graded the severity of obstruction based on the FEV1/FVC ratio. The objective was to compare the grading of airway obstruction using the percent predicted FEV1 (ATS) with a confidence interval-based system (ITS), with particular focus on pulmonary functions in patients having both airway obstructions and restrictions.
Design: Retrospective analysis.
Setting: Tertiary medical center.
Patients: A retrospective analysis of 21,499 patient pulmonary function tests (PFTs) was performed. The predicted values of Crapo and coworkers were used.
Measurements and results: The distribution of the severity of the obstruction was compared using the ATS and ITS methods for PFTs with normal, increased, or decreased total lung capacity (TLC). Analysis was performed using the χ2 method. Of the 21,499 PFTs that were analyzed, TLC was measured in 28% (5,962 PFTs). In this cohort, 44% (2,619 PFTs) gave evidence of obstruction. Of these, 147 PFTs demonstrated additional restriction. While the ATS criteria graded 133 of these PFTs (90%) as being severe, the ITS criteria graded only 4 PFTs (3%) as severe (the severity distribution between the methods was significantly different [p < 0.01]).
Conclusions: In view of the possible overestimation of the severity of obstruction in PFTs with concurrent restriction using the percentage of predicted FEV1 values, consideration should be given to grading the severity of obstruction on the basis of the FEV1/FVC ratio in this specific subset of PFTs.