SINGLE-BREATH DIFFUSING-CAPACITY FOR CARBON-MONOXIDE - EFFECTS OF ADJUSTMENT FOR INSPIRED VOLUME DEAD SPACE, CARBON-DIOXIDE, HEMOGLOBIN ANDCARBOXYHEMOGLOBIN

In order to assess the additive effects of taking into account dead sp ace volume (V-D), carbon dioxide, hemoglobin (Hb) and carboxyhemoglobi n on computation of single breath carbon monoxide diffusing capacity ( D(L)COsb), we sequentially applied all the corrections recommended by the 1987 American Thoracic Society (ATS) document on D(L)COsb standard ization. We used data from 739 men (333 nonsmokers and 406 current smo kers) and 475 women (403 nonsmokers and 72 current smokers) who underw ent measurement of D(L)COsb in the decade 1985-1994 at the Lung Functi on Laboratory of our institute. With respect to the unadjusted D(L)COs b value, significant small differences were found for all the correcte d formulas, ranging from -0.18 to 1.48 ml/min/mm Hg in men and from -0 .24 to 1.57 ml/min/mm Hg in women. After computing the percent change of D(L)COsb [(unadjusted-adjusted value) x 100/unadjusted value], we o bserved that the correction for V-D caused an underestimation of D(L)C Osb of about 5.8% in men and 7.7% in women. However, when all the corr ections were considered, these figures decreased to about 0.9% in male s and 2.9% in females. Regarding specifically the correction for Hb, t he adjusted value was slightly lower in men, while it was somewhat hig her in women, with respect to the unadjusted D(L)COsb. In conclusion, the corrections suggested by ATS in the computation of D(L)COsb, when considered altogether, seem to account for a limited proportion of tes t variability in usual clinical conditions, especially in males.