Linear-lumped-parameter modeling of pulmonary impedance in monkeys

Abstract

Pulmonary impedance, Z_L, 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, D_r, between the computed network impedance and measured Z_L at all frequencies. Measured resistance, R_L, 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 (D_r∼19%). Networks consisting of two series RIC pathways in parallel resulted in a lower D_r (∼14%), but parameter values were difficult to interpret. Despite not modeling the decrease in R_L 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 D_r (∼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 Z_L over the entire frequency range (2–32 Hz), (2) the effect of C _aw is an important determinant of Z_L above 8 Hz, and (3) a six-parameter C _aw network with the ratio of C _aw to parenchymal compliance, C_p, fixed may prove useful in interpreting changes in Z_L induced by alterations in lung mechanics in monkeys.