Input impedance and peripheral inhomogeneity of dog lungs

TLDR

The study measured tracheal, airflow, and alveolar pressures in open‑chest dogs during 0.1–20 Hz pseudorandom oscillations, fitted the input impedance with four‑parameter models (airway resistance, inertance, tissue resistance, elastance), and simulated a heterogeneous lung model to reproduce the data. The impedance models fit both control and histamine states, regional transfer impedance variability increased with frequency and histamine, and simulations showed that extreme peripheral inhomogeneity can still produce a nearly homogeneous input response.

Abstract

Tracheal pressure, central airflow, and alveolar capsule pressures in cardiac lobes were measured in open-chest dogs during 0.1- to 20-Hz pseudorandom forced oscillations applied at the airway opening. In the interval 0.1-4.15 Hz, the input impedance data were fitted by four-parameter models including frequency-independent airway resistance and inertance and tissue parts featuring a marked negative frequency dependence of resistance and a slight elevation of elastance with frequency. The models gave good fits both in the control state and during histamine infusion. At the same time, the regional transfer impedances (alveolar pressure-to-central airflow ratios) showed intralobar and interlobar variabilities of similar degrees, which increased with frequency and were exaggerated during histamine infusion. Results of simulation studies based on a lung model consisting of a central airway and a number of peripheral units with airway and tissue parameters that were given independent wide distributions were in agreement with the experimental findings and showed that even an extremely inhomogeneous lung structure can produce virtually homogeneous mechanical behavior at the input.