ORIGINAL ARTICLERetrospective Study of Pulmonary Function Tests in Patients Presenting With Isolated Reduction in Single-Breath Diffusion Capacity: Implications for the Diagnosis of Combined Obstructive and Restrictive Lung Disease
Section snippets
PATIENTS AND METHODS
With Mayo Foundation Institutional Review Board approval, we retrospectively reviewed the pulmonary function database at the Mayo Clinic in Jacksonville, Fla, to identify complete PFTs performed between January 1, 1990, and June 30, 2000, in patients complaining of dyspnea. Pulmonary function studies included measurements of airflow, plethysmographic lung volumes, and Dlco (measured by the single-breath diffusion capacity method), with the aim of identifying patients with reduced Dlco but
Patient Cohort
Of the 38,095 patients who had pulmonary function studies archived in our database during the period of this study, 179 had an isolated reduction in Dlco (0.47%; 95% confidence interval [CI], 0.40%-0.54%). Twenty-seven of these 179 patients (15.1%; 95% CI, 10.2%-21.2%) had also undergone standard chest CT and echocardiography within 1 month of their PFTs, 16 of whom had also undergone HRCT.
Clinical Diagnoses and Physiologic Assessments
Final diagnosis, demographic data, PFT results, Dlco measurements, oxygen saturation values, and
DISCUSSION
Measurements of Dlco assess the transfer of gases from the alveoli to red blood cells. The frequency and importance of reduced Dlco in patients with otherwise normal PFT results have not been systematically explored. This retrospective clinical study provides some insight into this situation.
We have determined that in patients with dyspnea, an isolated reduction in Dlco is extremely rare (<1%). However, when present, it is commonly associated with emphysema and a concurrent restrictive process.
CONCLUSION
Reduction in Dlco in the context of normal lung volumes and airflows is an uncommon finding among patients evaluated for dyspnea. Isolated reduction in Dlco can frequently be explained by the association of emphysema with a restrictive lung process such as ILD or pulmonary edema/CHF. Interstitial lung disease, pulmonary vascular conditions, or both explain most of the remaining cases. Isolated reduction in Dlco should prompt further clinical investigation and evaluation with HRCT and
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