Background: Traditional approaches to measuring the diffusing capacity of the lung for carbon monoxide (Dlco) treat the lung as a single, well-mixed compartment and produce a single value for Dlco to represent an average diffusing capacity of the lung (DL). Because DL distribution in the lung is inhomogeneous, and changes in the DL in diseased lungs may be regional, measuring regional DL, especially during exercise, may be more sensitive in detecting pulmonary vascular diseases.
Objectives: To characterize regional changes in DL in healthy individuals from rest to exercise, and to provide normal references for future studies in pulmonary vascular disorders.
Methods: We reanalyzed Dlco and phase III CH4 slopes that were obtained during a slow, single exhalation at rest and during exercise in our extended database of 105 healthy individuals. Dlco profiles between 20% and 80% of exhaled vital capacity (VC) (ie, the intrabreath Dlco) were analyzed by calculating the average Dlco measured at midlung volume (ie, 30 to 45% of exhaled VC [DlcoMLV]) and by fitting the whole curve with a third-order polynomial equation.
Results: Dlco decreased nonlinearly by approximately 30%, from 20 to 80% of exhaled VC at rest. Dlco during exercise was greater than that at rest, and the increase was similar at all lung volumes. The CH4 slopes at rest and during exercise were similar. Prediction equations based on regressions on age, sex, and height were computed for resting and exercise DlcoMLV and the phase III CH4 slope (an index of ventilation distribution).
Conclusions: Capillary recruitment/dilation during exercise in healthy individuals is a uniform process throughout the lungs. Our analyses provide a database for a noninvasive method that can incorporate exercise to evaluate the volume-dependent distribution of Dlco in lung diseases.