Lung tissue properties obtained by optical alveolar elastometry

Introduction

Knowledge of micromechanical properties of lung parenchyma is essential for understanding macroscopic lung mechanics. The first results of in vivo and in situ measurements using an endomicroscopic device [1] are reported. The degree of local lung deformation in dependence of locally applied pressure is shown.

Methods

An endoscopic system including two concentric trocars was constructed to apply a defined local pressure within the field of view (P_fov). The endoscopic system was placed between the ribs of mechanically ventilated rats with the tip placed on the pleura. P_fov was applied to a circular area on to the lungs' surface and led to a local deformation. By adjusting the flow rate of the flushing fluid from the outer trocar to the inner trocar, P_fov was varied. The resulting local deformation of lung parenchyma was optically measured by estimating the diameter of ceramic particles, fixed on the pleura for that purpose. Deformation was measured at different levels of airway pressure (P_aw) with P_fov ramped from 0 to -40 mbar.

Results

The healthy lung (Figure 1A) parenchyma showed less deformation caused by fluidic pressure compared with the lavaged lung (Figure 1B). In contrast to the lavaged lung, the deformation of the healthy lung was less when higher P_aw was present.

Figure 1

Conclusions

Micromechanical properties of lung parenchyma can be analyzed in vivo at an alveolar level. The healthy lung parenchyma appears to be stiffer (less deformation) at higher P_aw. The stronger deformation and less dependence on airway pressure in the lavaged lung support the hypothesis that small lung compliance in lavaged lungs might not be reasoned by stiff lung parenchyma, but rather by regional collapse.