MECHANICAL IMPEDANCE OF THE LUNG PERIPHERY

The mechanics of the regional airways and tissues was studied in isola ted dog lobes by means of a modified wave-tube technique. Small-amplit ude pseudorandom forced oscillations between 0.1 and 48 Hz were applie d through catheters wedged in a-mm-diameter bronchi in three regions o f each lobe at translobar pressures (PL) of 10, 7, 5, 3, 2, and 1 cmH( 2)O. The measured regional input impedances were fitted by a model con taining the resistance (R-1) and inertance (I) of the regular (segment al) airways, the resistance of the collateral channels (R-2), and the damping (G) and elastance (H) of the local tissues. This model gave fa r better fits to the data on impedance of the lung periphery than when CT and H were replaced by a single tissue compliance, which explains why interruption of segmental flow did not lead to monoexponential pre ssure decay in previous studies. The interlobar and intralobar varianc es of the parameters were equally significant, and poor correlations w ere found between the airway parameters R-1 and R-2 and between any ai rway and tissue parameter (e.g., R-1 and H). R-2 was On average simila r to 10 times higher than R-1, although the R-2-to-R-1 ratios and thei r dependencies on PL were regionally highly variable. However, for the total of 33 regions studied, the PL dependence was the same for R-1 a nd R-2, which may reflect similar morphological structures for the reg ular and collateral airways. The dependencies of G and H on PL showed high interregional variations; generally, however, they assumed their minima at medium PL values (similar to 5 cmH(2)O).