Linear-lumped-parameter modeling of pulmonary impedance in monkeys

Pulmonary impedance, ZL, measured from 2 to 32 Hz in anesthetized, intubated and paralyzed bonnet monkeys (Macaca radiata) was fitted to a variety of linearlumped parameter mechanical networks. Parameter values for each network were obtained by minimizing the average of the percent distance, Dr, between the computed network impedance and measured ZL at all frequencies. Measured resistance, RL, decreased from 2 to 8 Hz and increased from 8 to 32 Hz indicating that a single series resistance-inertance-compliance (RIC) network was not optimal (Dr∼19%). Networks consisting of two series RIC pathways in parallel resulted in a lower Dr (∼14%), but parameter values were difficult to interpret. Despite not modeling the decrease in RL with frequency below 8 Hz, an airway wall compliance, C aw , network in which the airways were separated into central and peripheral components resulted in an even lower Dr (∼11%). In addition, parameter values were easy to interpret, consistent among our “normal” monkeys and changed consistently and explainably with change in lung mechanics induced by decrease in lung volume. We conclude that (1) networks containing both parallel pathways and C aw are necessary to model ZL over the entire frequency range (2–32 Hz), (2) the effect of C aw is an important determinant of ZL above 8 Hz, and (3) a six-parameter C aw network with the ratio of C aw to parenchymal compliance, Cp, fixed may prove useful in interpreting changes in ZL induced by alterations in lung mechanics in monkeys.