Partitioning of airway and respiratory tissue mechanical impedances by body plethysmography.

We have tested the feasibility of separating the airway (Zaw) and tissue (Zti) components of total respiratory input impedance (Zrs,in) in healthy subjects by measuring alveolar gas compression by body plethysmography (Vpl) during pressure oscillations at the airway opening. The forced oscillation set up was placed inside a body plethysmograph, and the subjects rebreathed BTPS gas. Zrs,in and the relationship between Vpl and airway flow (Hpl) were measured from 4 to 29 Hz. Zaw and Zti were computed from Zrs,in and Hpl by using the monoalveolar T-network model and alveolar gas compliance derived from thoracic gas volume. The data were in good agreement with previous observations: airways and tissue resistance exhibited some positive and negative frequency dependences, respectively; airway reactance was consistent with an inertance of 0.015 +/- 0.003 hPa.s2.l-1 and tissue reactance with an elastance of 36 +/- 8 hPa/I. The changes seen with varying lung volume, during elastic loading of the chest and during bronchoconstriction, were mostly in agreement with the expected effects. The data, as well as computer simulation, suggest that the partitioning is unaffected by mechanical inhomogeneity and only moderately affected by airway wall shunting.