Chest
Volume 114, Issue 6, December 1998, Pages 1607-1612
Journal home page for Chest

Clinical Investigations
Airways
Assessing the Reversibility of Airway Obstruction

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Study objective

To determine whether changes of partial expiratory flow-volume curve (PEFV) and inspiratory capacity (IC) detect functional responses to bronchodilator in patients who do not meet the FEV1 criteria for reversibility of airway obstruction.

Design/methods

The effects of salbutamol (200 μg by metered-dose inhaler) on lung function were examined in 50 patients with asthma and 28 patients with COPD. Measurements evaluated were FEV1, forced expiratory flow at 30% of control FVC from maximal expiratory flow-volume curve ( V˙m30), forced expiratory flow at 30% of control FVC from PEFV ( V˙p30), and IC. On a separate occasion, a representative sample of 26 subjects inhaled placebo to determine the 95% confidence limits (CLs) of each of the parameters.

Results

A percent and absolute increment of FEV1 above the upper CL was recorded in 28 patients. Of these, 26 had a percent and absolute increase of V˙p30, 21 of V˙m30, 9 of FVC, and 11 of IC above the 95% CL. Of the 50 patients who did not have an increase in FEV1 above the 95% CL, 25 had a percent and absolute increase in V˙p30, 15 of V˙m30, 3 of FVC, and 13 of IC above the 95% CL. On average, the percent and absolute increase V˙p30 above the 95% CL significantly identified more responders than every other parameter.

Conclusion

Increases in maximal flow detected by PEFV and/or changes in IC may be substantially obscured by the effects of inspiration to total lung capacity required for the measurement of FEV1 in patients with chronic bronchoconstriction. Decreases in functional residual capacity (FRC) manifested by an increase of IC occur because, in patients whose FRC is dynamically determined, bronchodilatation that increases maximal flow in the tidal breathing range allows patients to breathe at lower lung volumes. Changes of FEV1 frequently fail to detect significant functional response to bronchodilators in patients with chronic airflow obstruction.

Section snippets

Subjects

The study participants were 78 outpatients with chronic airflow obstruction who were referred to a pulmonary function laboratory by their family physician. Fifty patients (37 men) met the American Thoracic Society criteria for bronchial asthma and 28 patients (27 men) met the criteria for COPD.9 To enter the study, the patients were required to have an FEV1/FVC below the lower normal limit,10 not to have suffered from exacerbations in the previous month, and to be able to abstain from

Results

Under control conditions (Table 1), all patients were obstructed, with a mean (±SD) FEV1 63 ± 19% of predicted and FVC 86 ± 18% of predicted, and moderately hyperinflated (FRC 136 ± 29% of predicted). The FEV1 was slightly but significantly less in COPD patients than in asthma patients (58 ± 20% vs 67 ± 18%; p < 0.05). V˙m30 was on average similar to V˙p30, though their ratio (M/P) was slightly greater in asthma patients than in COPD patients (1.05 ± 0.42 vs 0.88 ± 0.24; p < 0.06).

Discussion

The FEV1 is the traditional measure for the diagnosis of COPD and detection of reversibility of airway obstruction. Normal values are well established from population-based studies and the FEV1 is quite reproducible.1 Flow at 50% of FVC and below on both MEFV and PEFV is more variable because it is sensitive to changes in the depth of inhalation3, 4, 5 and compression of intrathoracic gas during a forced expiration.12 Furthermore, normal values are not well established. Until recently,

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