Closing volume as a simple, sensitive test for the detection of peripheral airway disease.

T he diagnosis of early obstructive airway disease has long been a source of frustration to physicians. Conventional tests of pulmonary function such as the measurement of lung volumes, flow rates, airway resistance and diffusing capacity have not proved sensitive enough to detect small airway involvement. The flieasureflieilt of “closing volume” ( CV) first described by Dollfuss in 1967’ seems to be particularly well suited to detect early changes in the lung whether these changes are due to intrinsic sniall airway disease or loss in lung elastic recoil. Anthonisen and colleagues2 first described, in 1969, the use of a modification of Fowler’s single breath nitrogen test to measure closing volume. We have also used the single breath technique to derive residual volume ( RV ) . In order to do this, total lung capacity ( TLC ) is estimated by application of the conventional alveolar dilution equation.’ We obtain mean alveolar nitrogen concentration after dilution with oxygen by planimetric determination of mean expired nitrogen concentration and correction for dead space admixture. RV is then derived by sul)tractiOn of the largest recorded vital capacity ( VC ) from TLC. Thus, from a single breath, the following subdivisions of lung volume were obtamed: VC, RV, TLC, CV, and the ratios CV/VC percent aild CV/TLC percent were derived. Using this technique, we have tested 284 asymptomatic nonsmokers ( 132 men, 152 women). Using data from these subjects, regression equations were established for the normal predicted values of CV/VC percent and CV/TLC percent both cxpressed as a function of age. These confirmed the findings of others2’4’5 that closing volume increases linearly with age. Data obtained from 200 cigarette smokers ( 100 men, 100 women-all voluntary screenees at an emphysema screening center ) were then compared with these normal standards. Of the 100 men smokers, 84 were symptomatic; 56 had a CV/TLC percent ratio greater than 2 SEE above the mean value; 44 had a CV/VC percent ratio greater than 2 SEE above the mean value and 12 had an abnor-