Use of optical techniques applied to the measurement of lung deformations and vibrations for the assessment of viscoelastic models of the bronchial tree and parenchyma at various dynamic regimens

The interest of the Ecole Polytechnique Federale de Lausanne (EPFL) group is focused on the study of the biomechanical properties of soft tissues, in particular, bronchi and parenchymatous tissues. Model studies have been developed, which treat the fluid structure interaction in detail. They are based on the theory of the mechanics of continuous media. The case of the vibrations of the prestressed eye has been treated by the finite element method [1]. A similar approach could be developed for the calculation of the dynamic behaviour of the bronchial tree and lung parenchyma coupled to airflow. Such a model accounts for the distributed nature of the lung structures. Experimental work should be carried out to prove the validity of the distributed biomechanical models of lung tissues. Because of the lack of other investigatory methods, such as ultrasound or Magnetic Resonance Imaging (MRI) (for dynamic studies), optical measuring techniques present a major and unique interest in the study of the dynamic behaviour of the lung: optical holography (in particular the double pulse technique) and interferometry can be used to quantify local deformations of tissues, with a particular emphasis on their vibratory behaviour. Microendoscopy (<0.5 mm in diameter) may also facilitate valuable measurements of local tissue deformation [2]. Transillumination of lung tissues is another technique which is expected to yield valuable data on densities and blood perfusion of lung tissues. Imaging can be obtained by optical tomography, based on time resolved photon migration measurements [3]. Syntheses of experimental and model studies are expected to provide important help in the understanding of correlations of respiratory impedance with the biomechanical characteristics of the lung.