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

Background

The Phase III slope from a single breath nitrogen washout test provides information about ventilation heterogeneity (VH) in the lungs.

Purpose

To determine if the Phase III slope from the exhaled tracer gas concentration during a standard, single breath D_LCO test using rapid gas analysis provides similar information about VH.

Basic procedures

Retrospective analysis of clinical pulmonary function laboratory data including spirometry, lung volumes, and D_LCO. 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.

Main findings

SnCH₄ was the steepest in the group with “Obstruction and Low D_LCO”, with significant differences between this group and the “Normal”, “Obstruction with Normal D_LCO”, “Mixed Obstruction and Restriction” and “Isolated Low D_LCO” 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 < 0.01) and remained a significant determinant of VA/TLC by regression modeling.

Principal conclusions

The SnCH₄ derived from a standard, single breath D_LCO test using rapid gas analysis varied among distinct patterns of physiologic abnormalities and was associated with VA/TLC as a measure of VH.