COMPARISON OF 4 METHODS FOR CALCULATING DIFFUSING-CAPACITY BY THE SINGLE-BREATH METHOD

In 283 patients referred for testing in an outpatient pulmonary functi on laboratory, we studied the single-breath diffusing capacity of the lungs for carbon monoxide (Dco) using the Ogilvie (Og), Jones-Meade (J M), Epidemiological Standardization Project (ESP), and three-phase ite rative methods (SPIT, similar to the three equation method). The Dco m aneuvers were performed using automated equipment and American Thoraci c Society (ATS) recommended procedures. There were small but significa nt differences in mean Dco, the ESP method yielding the largest, follo wed in order by JM, 3PIT, and Og methods. The SPIT and JM Dcos were in close agreement in all degrees and patterns of pulmonary function abn ormality. The Og Dco method was G percent less than JM in patients wit h normal pulmonary function, although the difference was less in patie nts with expiratory flow limitation, restriction, or reduced Dco. Ther e were no differences in the reproducibility of Dco measurements among the methods. Based on these results and a review of the literature, w e conclude the following: (1) when measuring single-breath Dco using a utomated equipment that follows ATS recommended procedures for collect ing a single expired gas sample of 500-ml volume, calculated Dco is la rgest using ESP method, following by JM, 3PIT, and Og methods; (2) in patients with reduced Dco associated with obstructive or restrictive a bnormalities, the Og, 3PIT, and JM timing methods are nearly equivalen t; and (3) reproducibility of Dco is the same by all methods.