Lung volumes in 4,774 patients with obstructive lung disease

Study objectives: To determine the correlates of static lung volumes in pat ients with airways obstruction, and to determine if static lung volumes dif fer between asthma and COPD, Patients 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 J anuary 1990 through July 1994 with an FEV1/FVC ratio of < 0.70 and tested u sing a body plethysmograph. Correlates were determined using regression ana lysis. Measurements ann results: Of the 4,774 patients observed with evidence of a irways obstruction, 61% were men. Self-reported diagnoses included asthma, 19%; emphysema or COPD, 23%; chronic bronchitis, 1.5%; and alpha(1)-antipro tease deficiency, 0.6%. Fifty-six percent of the patients did not report a respiratory disease. The degree of hyperinflation, as determined by the res idual volume (RV)/total lung capacity (TLC) ratio, or the RV % predicted (b ut not the TLC % predicted), was strongly associated with the degree of air ways obstruction (the FEV, predicted). Patients with moderate to severe air ways obstruction and high RV and TLC levels were more likely to have COPD t han 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, th e additional measurement of static lung volumes added little to the clinica l interpretation.