Study objectives: To determine the correlates of static
lung volumes in patients with airways obstruction, and to determine if
static lung volumes differ between asthma and COPD.
and methods: We examined the data from all of the adult patients
(mean age of 69) who were referred to a pulmonary function laboratory
from January 1990 through July 1994 with an FEV1/FVC ratio
of < 0.70 and tested using a body plethysmograph. Correlates were
determined using regression analysis.
results: Of the 4,774 patients observed with evidence of
airways obstruction, 61% were men. Self-reported diagnoses included
asthma, 19%; emphysema or COPD, 23%; chronic bronchitis, 1.5%; andα
1-antiprotease deficiency, 0.6%. Fifty-six percent of
the patients did not report a respiratory disease. The degree of
hyperinflation, as determined by the residual volume (RV)/total lung
capacity (TLC) ratio, or the RV % predicted (but not the TLC %
predicted), was strongly associated with the degree of airways
obstruction (the FEV1 % predicted). Patients with moderate
to severe airways obstruction and high RV and TLC levels were more
likely to have COPD than asthma. Of the 1,872 patients with a reduced
vital capacity determined by spirometry testing, 87% had
hyperinflation as defined by the RV/TLC, and 9.5% had a low TLC
(with less severe airways obstruction).
Conclusion: In patients found to have airways obstruction
by spirometry, the additional measurement of static lung volumes added
little to the clinical interpretation.
Abbreviations: AAP = α1-antiprotease;
ATS = American Thoracic Society; FRC = functional residual
capacity; PF = pulmonary function; RV = residual volume;
TGV = thoracic gas volume; TLC = total lung capacity; VC = vital