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 N2 washout test (MBW). From an alveolar slope analysis throughout the MBW, 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 (S(Gaw)) and forced expiratory flows. FEV1 divided by FVC (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.