Nonuniformity of diffusing capacity: DISCUSSION (5)

Previous reports found that the conventional single breath diffusing capacity for carbon monoxide (DLcoSb) was reduced in smokers and correlated with macroscopic disease, as detected by CT scan techniques . However, in seated patients at rest DLcoSb was insensitive to the interregional nonuniformity in the distribution of emphysema that often preferentially affects the apex of the lung in smokers . Conventional DLcoSb testing, as distinct from the DLcoSb-3EQ , was also less useful as a screening tool because the method was spuriously affected by the variations in the way the single breath test was performed . Interpretation of DLcoSb in smokers has also been potentially confounded by uncertainties about precise corrections of DLcoSb for carbon monoxide back pressure, carboxy-hemoglobin and the binding affinity of hemoglobin . In the present study we corrected all measurements of DLcoSb-3EQ for the carbon monoxide back pressure by measuring the carbon monoxide in the exhaled gas during the exhalation phase of the deep breath of room air preceding each DLcoSb-3EQ manoeuvre . The infrared carbon monoxide analyzer was sufficiently sensitive to allow measurement of background carbon monoxide in nonsmokers at levels of 0 to 70 ppm . The carbon monoxide analyzer was linear in this range and was checked daily .

Category: Increased in smokers

Tags: Diffusion index, Inhomogeneity, Slope of phase III, Small airways, Three-equation diffusing capacity, Tobacco smoking