Airway geometry by analysis of acoustic pulse response measurements

TLDR

The serial distribution of airway properties influences how the lung responds to high‑frequency oscillations. The authors measured high‑frequency acoustic responses of excised dog lungs and lobes (156–10 kHz) to derive an area‑distance function of an acoustically equivalent rigid‑wall, regularly branching model, and evaluated its sensitivity to air trapping, pleural removal, and airway smooth‑muscle tone. The technique produced a strong correlation between changes in equivalent acoustic area and radiographically measured airway area, indicating that the computed area‑distance function reliably estimates the magnitude and serial distribution of real airway cross‑sectional changes.

Abstract

Serial distribution of airway properties determines in part the response of the lung to high frequency oscillations. We measured the response of excised dog lungs and lobes between 156 and 10,000 Hz and determined the area-distance function of the acoustically equivalent structure having rigid walls, regular branching, and negligible internal losses. The utility of this techique was tested by determining the effects of air trapping, removal of pleura from a dried lung, central airway smooth muscle tone. A strong correlation was found between relative changes in equivalent acoustic area and relative area changes measured radiographically in individual airways at corresponding distances. We conclude that despite departures of the properties of the real lung from the characteristics of the acoustically equivalent structure, changes in the area-distance function computed by this technique provide reasonable estimates of the magnitude and serial distribution of actual changes in airway cross-sectional area.