On Mechanisms of Formation of Acoustic Properties of Pulmonary Parenchyma

Abstract

The anatomic structure of human respiratory system is analyzed. For frequencies typical for the respiratory sounds a possibility of representing of lung's respiratory zone as a continuum with microstructure is justified. An acoustic model of pulmonary parenchyma is developed on the basis of physical study of sound dispersion and attenuation in emulsions. For the case of thermal independence of grains of emulsion (alveoles) the analytical expression describing the sound speed and attenuation decrement in the parenchyma is obtained. It is shown that behavior of the sound speed foreseen in the emulsion model is similar to tendencies depicted by simple gas-liquid models. A strong dependence of the attenuation decrement on the frequency and concentration of parenchyma's gas phase is shown. It is outlined that at low values of air filling of lungs the frequency dependence of damping in the studied range is a square law. As for high air filling, a transition to the square root tendency with the increase of frequency is demonstrated. This peculiarity is conditioned by strong resizing of the alveoles during the respiratory cycle. A considerable decrease of the sound attenuation at deep inspiration is stated.