Locally measured shear moduli of pulmonary tissue and global lung mechanics in mechanically ventilated rats

Abstract

Schwenninger D, Runck H, Schumann S, Haberstroh J, Guttmann J. Locally measured shear moduli of pulmonary tissue and global lung mechanics in mechanically ventilated rats. J Appl Physiol 113: 273-280, 2012. First published May 24, 2012 doi:10.1152/japplphysiol.01620.2011.-This study was aimed at measuring shear moduli in vivo in mechanically ventilated rats and comparing them to global lung mechanics. Wistar rats (n ϭ 28) were anesthetized, tracheally intubated, and mechanically ventilated in supine position. The animals were randomly assigned to the healthy control or the lung injury group where lung injury was induced by bronchoalveolar lavage. The respiratory system elastance Ers was analyzed based on the single compartment resistance/elastance lung model using multiple linear regression analysis. The shear modulus (G) of alveolar parenchyma was studied using a newly developed endoscopic system with adjustable pressure at the tip that was designed to induce local mechanostimulation. The data analysis was then carried out with an inverse finite element method. G was determined at continuous positive airway pressure (CPAP) levels of 15, 17, 20, and 30 mbar. The resulting shear moduli of lungs in healthy animals increased from 3.3 Ϯ 1.4 kPa at 15 mbar CPAP to 5.8 Ϯ 2.4 kPa at 30 mbar CPAP (P ϭ 0.012), whereas G was ϳ2.5 kPa at all CPAP levels for the lung-injured animals. Regression analysis showed a negative correlation between G and relative Ers in the control group (r ϭ Ϫ0.73, P ϭ 0.008 at CPAP ϭ 20 mbar) and no significant correlation in the lung injury group. These results suggest that the locally measured G were inversely associated with the elastance of the respiratory system. Rejecting the study hypothesis the researchers concluded that low global respiratory system elastance is related to high local resistance against tissue deformation.

Endoscopic Imaging to Assess Alveolar Mechanics During Quasi-static and Dynamic Ventilatory Conditions in Rats With Noninjured and Injured Lungs*

“…In contrast, in our study we exclusively focused on the local mechanics of alveolar tissue in vivo under conditions of intact thorax. Accordingly, our study aimed at investigating alveolar mechanics during quasi-static and dynamic ventilatory maneuvers in noninjured and injured lungs using our recently reported endoscopie method (29)(30)(31). We hypothesized that alveolar mechanics vary with quasi-static and dynamic ventilatory conditions and lung conditions.…”

A micromechanical model for estimating alveolar wall strain in mechanically ventilated edematous lungs

“…Furthermore, the bulk modulus changes roughly exponentially with transpulmonary pressure, whereas the shear modulus is nearly proportional to the transpulmonary pressure over a wide range of volumes. Using a newly developed endoscopic system, Schwenninger et al (32) measured shear moduli in vivo in mechanically ventilated rats. The shear modulus in healthy animals increased from 3.3 Ϯ 1.4 kPa at 15 cmH 2 O continuous positive-airway pressure (CPAP) to 5.8 Ϯ 2.4 kPa at 30 cmH 2 O, whereas the shear modulus was 2.5 kPa at all CPAP levels in the lung-injured animals.…”