Photoacoustic technique: a new method for measuring the rheologic properties of human bronchial mucus
© Novamedia srl 2011
Received: 23 June 2011
Accepted: 8 July 2011
Published: 31 August 2011
Tecnica fotoacustica: un nuovo metodo per studiare le proprietà reologiche del muco bronchiale umano
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 .
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 . It has been observed that the rheologic properties of mucus are often abnormal in patients with airways disease . 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.
Photoacoustic Technique (PAT)
In our preliminary study, we performed photoacoustic analyses according to the protocol described by Dumas et al. . Each sputum sample was evaluated for a period of 5 min to measure the baseline photoacoustic signal.
In our preliminary study, conducted according to Dumas et al. , mucus was obtained from 11 volunteers, divided into two groups: five patients presenting respiratory impairment symptoms (group I) and six healthy subjects (group II). The photoacoustic signal of the mucus absorbing the isotonic saline solution was monitored as a function of time, with measurements being performed each 10 min, up to 120 min. A characteristic time for the half saturation of the absorption process was obtained. The mean values and standard deviations obtained for parameters t0 and Δt were 23.3 ± 5.3 min and 4.5 ± 1.9 min for group I, and 55.0 ± 7.7 min and 16.6 ± 3.4 min for group II respectively, presenting a significant difference (Student's t-test, p < 0.05).
This study has shown that human bronchial mucus from subjects with different health status presents different rheological properties and characteristic times for absorption of the isotonic saline solution. The results confirm the feasibility of using PAT on the study of the solubility behavior of human bronchial mucus after specific therapeutic aerosols.
A number of diseases of the chest are characterized by increased mucus production, including chronic obstructive pulmonary disease (COPD), bronchiectasis and cystic fibrosis, which, in concert with damage to cilia from a variety of host and bacterial sources, can lead to impairment of the mucociliary escalator and retention of secretions within the bronchial tree. Secretion retention can also contribute to airflow obstruction, wheeze, shortness of breath and cough, and the poor clearance of airway secretions promotes recurrent cycles of pulmonary infection and inflammation. Mucociliary clearance, the process in which mucus together with substances trapped within are moved out of the lungs, is an important defense mechanism of human body. Drugs may alter this process, such that it is necessary to know the effect of these drugs on mucociliary clearance. PAT measurements as a function of time permit to characterize the solubilization kinetics of pulmonary secretions, and to know the effects of mucolytic drugs in samples of mucus derived from different respiratory pathologies.
Conflict of interest statement
The authors declare that there is no associaton with any commercial enterprise that has interest in the object of this study.
The authors thank Fundação de Amparo à Pesquisa (Fapesp, acronym in Portuguese) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, acronym in Portuguese) for supporting this research.
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