Effects of surface tension and intraluminal fluid on mechanics of small airways

• Published in: Journal of applied physiology (1985) 1997-01, Vol.82 (1), p.233-239
• Main Authors: Hill, Mark J, Wilson, Theodore A, Lambert, Rodney K
• Format: Article
• Language: English
• Subjects: Air breathing; Airway Resistance - physiology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Models, Biological; Respiratory Physiological Phenomena; Respiratory system: anatomy, metabolism, gas exchange, ventilatory mechanics, respiratory hemodynamics; Surface Tension; Vertebrates: respiratory system
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1997.82.1.233

Mark J. Hill 1 , Theodore A. Wilson 1 , and Rodney K. Lambert 2 1  Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, Minnesota 55455; and 2  Department of Physics and Biophysics, Massey University, Palmerston North, New Zealand Received 13 March 1996; accepted in final form 9 September 1996. Hill, Mark J., Theodore A. Wilson, and Rodney K. Lambert. Effects of surface tension and intraluminal fluid on the mechanics of small airways. J. Appl. Physiol. 82(1): 233-239, 1997. Airway constriction is accompanied by folding of the mucosa to form ridges that run axially along the inner surface of the airways. The muscosa has been modeled (R. K. Lambert. J. Appl. Physiol. 71: 666-673, 1991) as a thin elastic layer with a finite bending stiffness, and the contribution of its bending stiffness to airway elastance has been computed. In this study, we extend that work by including surface tension and intraluminal fluid in the model. With surface tension, the pressure on the inner surface of the elastic mucosa is modified by the pressure difference across the air-liquid interface. As folds form in the mucosa, intraluminal fluid collects in pools in the depressions formed by the folds, and the curvature of the air-liquid interface becomes nonuniform. If the amount of intraluminal fluid is small, 2%, the area of the air-liquid interface decreases as airway cross-sectional area decreases, and surface tension contributes to airway compression. The model predicts that surface tension plus intraluminal fluid can cause an instability in the area-pressure curve of small airways. This instability provides a mechanism for abrupt airway closure and abrupt reopening at a higher opening pressure. mathematical model; airway compliance; airway closure; airway opening pressure 0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society