Using the phase III slope of exhaled methane during a single breath DLCO test to assess ventilation heterogeneity

The Phase III slope from a single breath nitrogen washout test provides information about ventilation heterogeneity (VH) in the lungs. To determine if the Phase III slope from the exhaled tracer gas concentration during a standard, single breath DLCO test using rapid gas analysis provides similar information about VH. Retrospective analysis of clinical pulmonary function laboratory data including spirometry, lung volumes, and DLCO. The normalized Phase III slope from the exhaled CH4 concentration (SnCH4) was compared among different patterns of physiologic abnormality and with VA/TLC as an indicator of VH. SnCH4 was the steepest in the group with “Obstruction and Low DLCO”, with significant differences between this group and the “Normal”, “Obstruction with Normal DLCO”, “Mixed Obstruction and Restriction” and “Isolated Low DLCO” groups. SnCH4 was steeper in current and former smokers compared to non-smokers. Among the entire study sample, SnCH4 correlated with VA/TLC (Spearman rho = −0.56, p