Photoacoustic technique: a new method for measuring the rheologic properties of human bronchial mucus

Abstract

Patients affected by obstructive pulmonary diseases exhibit typical characteristics of airway mucus hypersecretion, including sputum production, increased luminal mucus, goblet cell hyperplasia and submucosal gland hypertrophy. The mucociliary system is a sophisticated defense mechanism to maintain the homeostasis of the respiratory tract by means of the bronchial mucus transport, the process in which airway mucus together with substances trapped within are moved out of the lungs. In the end, the mucus together with the substances trapped within are swallowed or coughed up. It is an important defense mechanism of the human body [1]. Mucociliary clearance is influenced by viscosity and elasticity, that are the fundamental rheologic properties of the respiratory mucus and important determinants of its transportability in the mucociliary system [2]. It has been observed that the rheologic properties of mucus are often abnormal in patients with airways disease [3]. A retardation in mucociliary transport may lead to mucus retention, a condition which predisposes to bacterial colonization and may eventually lead to pneumonia. Drugs may alter the process of mucociliary transport, such that it is necessary to know the effect of the drugs on the rheologic properties of human bronchial mucus. Understanding the interaction of a specific drug with human bronchial mucus may lead to a better therapeutic use of such medication. The photoacoustic technique (PAT) is a new method that permits to monitor indirectly the rheologic properties of any mucus sample [3,4]. PAT enables to study the interaction between therapeutic aerosols and bronchial mucus, making it possible to determine the typical time of interaction between the aerosol and the mucus (T0) and the solubilization period (Δt). According to our knowledge it is important to have an experimental technique that permits the monitoring of the rheologic properties of mucus during the interaction with the specific drug.