Nonuniform expansion of constricted dog lungs

Abstract

The parenchymal marker technique was used to measure regional tidal volumes of samples of lung parenchyma in four open-chest supine dogs. Radiopaque markers that had been implanted in the lower lobe were tracked by biplane video fluoroscopy during sinusoidal volume oscillations at tidal volumes of approximately 20% of total lung capacity and frequencies of 1-40 breaths/min before and after methacholine was administered by aerosol. The volumes of tetrahedrons with apexes at four markers were computed, and sine waves were fit to the data for volume vs. time for each tetrahedron. The ratio of mean regional volume to mean airway pressure decreased by 10-45% after exposure to methacholine. Dynamic lung elastance and resistance of the constricted lungs were larger than control, and both were frequency dependent. Regional elastance and resistance varied considerably among tetrahedrons, and these were also frequency dependent. The data were fit by a model in which tissue elastance was uniform and nearly equal to elastance in the control state, but small-airway resistance was high and variable. We conclude that the lung contracts under bronchoconstriction but that the increased dynamic elastance and resistance of the constricted lung may be primarily the result of nonuniform increased airway resistance at the level of the terminal bronchioles.

Computed Tomography Studies of Lung Mechanics

“…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). At about the same time, the dynamic spatial reconstructor, a predecessor of modern volumetric CT scanners, was built (42).…”

Magnetic resonance elastography of the lung: Technical feasibility

“…Within the asthma model, both the parenchymal bulk, K (volumetric stress/strain) and shear moduli, μ (shear stress/shear strain), have been reported to increase with bronchoconstriction in the rat lung (2), which suggests that parenchyma stiffness should increase with asthma severity. Simulation studies have also identified the relationship between airway patency and the mechanical properties of the parenchyma (3–5). In particular, bronchioconstriction has been identified as a method by which these elastic properties can increase (2, 5), which highlights the relationship between asthma and parenchymal stiffness.…”

Lung Tissue Resistance Measured in Saline-Filled Guinea Pig Lungs by Micropuncture

“…Thus stress adaptation should be reduced in saline-filled lungs. R ti could be caused by airway heterogeneity during inflation or deflation instead of by stress adaptation [10]. Heterogeneity in alveolar pressure of air-filled lungs has been observed by Fredberg et al [5].…”

“…The effects of alveolar surface tension and alveolar distortion caused by alveolar duct constriction have been proposed as reasons for the differences between in situ and in vitro measurements of R ti . A recent study has suggested that heterogeneity of small airway resistance might contribute the measurements of R ti [10]. Thus we wondered whether the effects observed in air-filled lungs can be demonstrated in liquid-filled lungs with the elimination of alveolar surface forces.…”