Effects of chest wall on volume and strain patterns in canine lungs

Abstract

Lobar functional residual capacity-to-total lung capacity ratios (FRC/TLC) and strains in five supine anesthetized dogs were determined from volumes and side lengths of tetrahedra formed by multiple intraparenchymal markers whose positions were determined roentgenographically. Strain is related to fractional changes in length of elements in a Cartesian coordinate system and was used to describe parenchymal distortion. Volumes and strain patterns were compared in three states: intact dogs, after transection of forelimb structures to relieve traction on the chest wall, and in dogs' excised lungs. Removing traction (NT) decreased the plethysmographically determined FRC and the upper-to-lower lobe ratio (UL/LL) for FRC/TLC. The ratio in the NT state was more like the ratio in the excised lungs (UL/LL approximately equal to 1) than in the intact dog (UL/LL greater than 1). Strain patterns were similar between the intact and the NT states, indicating no lobar shape change at FRC between these two states. Strain in the excised lungs differed greatly from strains in the intact and NT states. We conclude that forelimb traction alters volume distribution between lobes and that lung-chest wall interactions are important in determining volume and strain patterns.

Computed Tomography Studies of Lung Mechanics

“…Using metal parenchymal markers implanted in animals and a biplane X-ray cine system that tracked the marker positions during spontaneous and controlled ventilation, a series of landmark studies was performed that examined regional lung expansion under a variety of conditions. Comparing results in intact animals as well as excised lungs, these studies demonstrated differences in the distribution of lung expansion between prone and supine positioning (7), the uniformity of expansion within lobes and the motion of lobes relative to each other within the chest (7), and the importance of chest wall-lung interactions in determining regional lung expansion and mechanical strain (35)(36)(37). Subsequent applications of this method examined the heterogeneity of bronchoconstriction (38), regional diaphragm function (39), and most recently the controversy over flooding versus collapse in acute lung injury (40,41).…”