Conductive and acinar lung-zone contributions to ventilation inhomogeneity in COPD

We investigated ventilation inhomogeneity in patients with chronic obstructive pulmonary disease (COPD) through use of the multiple breath Nz washout test (MBW). From an alveolar slope analysis throughout the MEW, we derived two indices, S-cond and S-acin, as a measure of ventilation inhomogeneity in conductive and acinar zones of the lungs, respectively (J. Appl. Physiol. 1997;83:1807-1816). We evaluated the relationship of S-cond and S-acin to standard lung-function indices by means of a principal-components factor analysis, which linked correlated indices to independent factors accounting for 81% of the total variance within the COPD group. S-acin was linked to the so-called acinar lung-zone factor, which also comprises diffusion capacity measurements. S-cond was linked to the so-called conductive lung-zone factor, which also comprises specific airway conductance (SGaw) and forced expiratory flows. FEV1 divided by NC (FEV1/FVC) was the only variable linked to both the conductive and the acinar lung-zone factors. The fact that S-cond and S-acin were linked to independent factors provides statistical confirmation of the hypothesis that S-cond and S-acin reflect independent lung alterations, whereas FEV1/FVC behavior indicates a combined conductive and acinar contribution to airways obstruction.