Abstract
BACKGROUND: Although the ratio of FEV1 to the vital capacity (VC) is universally accepted as the cornerstone of pulmonary function test (PFT) interpretation, FVC remains in common use. We sought to determine what the differences in PFT interpretation were when the largest measured vital capacity (VCmax) was used instead of the FVC.
METHODS: We included 12,238 consecutive PFTs obtained for routine clinical care. We interpreted all PFTs first using FVC in the interpretation algorithm and then again using the VCmax, obtained either before or after administration of inhaled bronchodilator.
RESULTS: Six percent of PFTs had an interpretive change when VCmax was used instead of FVC. The most common changes were: new diagnosis of obstruction and exclusion of restriction (previously suggested by low FVC without total lung capacity measured by body plethysmography). A nonspecific pattern occurred in 3% of all PFT interpretations with FVC. One fifth of these 3% produced a new diagnosis of obstruction with VCmax. The largest factors predicting a change in PFT interpretation with VCmax were a positive bronchodilator response and the administration of a bronchodilator. Larger FVCs decreased the odds of PFT interpretation change. Surprisingly, the increased numbers of PFT tests did not increase odds of PFT interpretation change.
CONCLUSIONS: Six percent of PFTs have a different interpretation when VCmax is used instead of FVC. Evaluating borderline or ambiguous PFTs using the VCmax may be informative in diagnosing obstruction and excluding restriction.
- respiratory function tests
- vital capacity
- airway obstruction
- spirometry
- respiratory physiological phenomena
- FEV1
- PFT
Footnotes
- Correspondence: Denitza P Blagev MD, Intermountain Medical Center, Heart-Lung Building, 6th Floor, 5121 South Cottonwood Street, Murray, UT 84107. E-mail: Denitza.blagev{at}imail.org.
This work was supported by a grant from the Intermountain Research and Medical Foundation. The authors have disclosed no conflicts of interest.
Dr Blagev presented a version of this paper at the American Thoracic Society 2013 International Conference, held May 17–22, in Philadelphia, Pennsylvania, and at the European Respiratory Society International Congress 2014, held September 6–10, 2014, in Munich, Germany.
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