Evaluating How Post-Bronchodilator Vital Capacities Affect the Diagnosis of Obstruction in Pulmonary Function Tests.
BACKGROUND
Although the ratio of FEV1to 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 VCmaxwas 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 VCmaxwere 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 VCmaxis used instead of FVC. Evaluating borderline or ambiguous PFTs using the VCmaxmay be informative in diagnosing obstruction and excluding restriction.
Intermountain Healthcare, Division of Pulmonary and Critical Care Medicine, Murray, Utah. Denitza.blagev@imail.org.|Division of Pulmonary and Critical Care Medicine, University of Utah, Salt Lake City, Utah.
Denitza P
DP
Blagev
Intermountain Healthcare, Division of Pulmonary and Critical Care Medicine, Murray, Utah.|Division of Pulmonary and Critical Care Medicine, University of Utah, Salt Lake City, Utah.|Homer Warner Center for Informatics Research, Murray, Utah.
Dean
D
Sorenson
Intermountain Healthcare, Division of Pulmonary and Critical Care Medicine, Murray, Utah.
Olinto
O
Linares-Perdomo
School of Computing, University of Utah, Salt Lake City, Utah.
Stacy
S
Bamberg
Intermountain Healthcare, Division of Pulmonary and Critical Care Medicine, Murray, Utah.|Division of Pulmonary and Critical Care Medicine, University of Utah, Salt Lake City, Utah.
Matthew
M
Hegewald
Intermountain Healthcare, Division of Pulmonary and Critical Care Medicine, Murray, Utah.|Division of Pulmonary and Critical Care Medicine, University of Utah, Salt Lake City, Utah.
Alan H
AH
Morris
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001993:Bronchodilator Agents / Q000008:administration & dosage*; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012129:Respiratory Function Tests / Q000379:methods*; D012189:Retrospective Studies; D014797:Vital Capacity / Q000187:drug effects*
D001993:Bronchodilator Agents
FEV1; PFT; airway obstruction; respiratory function tests; respiratory physiological phenomena; spirometry; vital capacity