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The role of pulmonary surfactant in airway obstruction and its influence on airway reopening - review

Kuraszkiewicz B.

Biocybernetics and Biomedical Engineering

2006

Vol. 26, no. 2

75-83

Our knowledge about the role of pulmonary surfactant in obstructive airways disease is stiII limited, but there is convincing evidence that pulmonary surfactant plays a role in keeping the airways open. Whereas lung damage with dysfunction of alveolar surfactant is of importance in various respiratory diseases, such as ARDS (adult respiratory distress syndrome) or pneumonia, alveolar surfactant dysfunction does not seem to play a major role in obstructive airways disease. On the contrary, surfactant impairment in the airways as a secondary consequence of airway inflammation might have a major impact on the small airway function. Thus, dysfunction of surfactant in the airways might be a contributory factor to airway obstruction and increased airway resistance in obstructive lung disease. In last years, direct and indirect evidence has emerged for surfactant as a factor in the regulation of airway calibers. Surfactant may be of a greater importance in the airways than it has previously been recognized. This review will discuss those aspects of the airway mechanics that are closely related to the function of pulmonary surfactant. Some of the mechanisms discussed may be of secondary rather than primary importance in obstructive airways disease.

Mathematical modelling of airway reopening

Kuraszkiewicz B.

Biocybernetics and Biomedical Engineering

2004

Vol. 24, no. 3

67-75

The theoretical and experimental investigations of the airway reopening by simulation of the progression of airflow through a fluid or liquid-filled rigid-walled tube (an initial model of pulmonary airway reopening) were performed. Positive pressure drove the "finger" of the air forward to displace the liquid and to obtain the interfacial movement. The air-liquid interface was assumed to be a simple axisymmetric meniscus. In this study the rigid tube radius was R and the "finger" of the air was (1-m)1/2R, where m was a fraction of the viscous fluid left behind on the walls of the tube. The liquid had constant surface tension and viscosity. The capillary number defined the state of the system (the air-liquid interface). This number is the dimensionless velocity that represents the ratio of the viscous to the capillary stresses. A quasi-steady state solution as a function of this parameter using the flow analysis was examined. A semi-empirical formula for the interface was generated by dimensional analysis. The results suggested that the pressures, required to reopen the collapsible airway and non-collapsible airway with the same radius, are similar in the magnitude. These studies showed that the air-liquid interface in the airway collapsible tube model could be sumulated by the meniscus of the air-liquid flow in a rigid circular tube model of the same radius.