Chest
Volume 115, Issue 1, January 1999, Pages 68-74
Journal home page for Chest

Clinical Investigations
COPD
Lung Volumes in 4,774 Patients With Obstructive Lung Disease

https://doi.org/10.1378/chest.115.1.68Get rights and content

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.

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 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.

Measurements and 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.

Section snippets

Materials and Methods

The study population was comprised of adult outpatients of> 30 years old who were referred to the Mayo Clinic outpatient pulmonary function (PF) laboratory in Rochester, MN between January 1990 and July 1994, and who had completed measurements of spirometry and static lung volumes. All of the patients with a prebronchodilator FEV1/FVC of > 0.70 were excluded from the study. The FEV1, the FVC, and the slow vital capacity (VC) were measured according to ATS recommendations3 using a model 1070

Results

There were 4,774 adult patients who met the entry criteria of an FEV1/FVC of < 0.70; 61% were men, and the mean age was 69 (see Fig 1 for the age distribution). At the time of testing, 908 patients (19%) reported a diagnosis of asthma, 1,099 patients (23%) reported a diagnosis of emphysema or COPD, 70 patients (1.5%) reported chronic bronchitis, 31 patients (0.6%) reported anα 1-antiprotease (AAP) deficiency, and 56% did not report having a respiratory disease. More than one respiratory

Discussion

In this large retrospective study of patients referred to a single PF laboratory, we have confirmed that hyperinflation of lung volumes is associated with the degree of airway obstruction. However, the strength of this association, as well as other clinical correlates, vary considerably according to whether “hyperinflation” is defined as a high RV/TLC, a high RV, or a high TLC. The RV or the RV/TLC are much more sensitive than the TLC to the degree of airways obstruction (see Figs 2, 3,4). As

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