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Absolute instability in the proximal airways
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DOI：10.1017/jfm.2026.11416.png)
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Abstract
En 中文
Camassa et al. (J. Fluid Mech. 745; 2014; 682–715) demonstrated excellent agreement between the theoretical predictions using the longwave equation and experimental observations for the absolute instability-induced plug formation in the gravity-driven flow of a liquid coating the inner surface of a tube. A similar flow of airway surface liquid (ASL) exists in the proximal airways; driven by the turbulent airflow in addition to gravity. Motivated by the conclusions of previous studies; we probe for the existence of absolute instability in the proximal airways in the present study to determine plug formation and subsequent airway closure by considering ASL elasticity; cylindrical flow geometry and the effect of inhaled air temperature. To accomplish this; we derive a longwave evolution equation; which is then used to obtain the dispersion relation. In contradistinction to the distal airways; the analysis predicts the absence of absolute instability-induced airway closure in the proximal airways for a healthy lung. However; an increased ASL thickness and/or elasticity due to excessive secretion of mucus and mucins in a diseased lung could lead to airway closure due to ASL plugs. Furthermore; inhaling colder air (than body temperature) enhances the absolute instability region; and the opposite is true for inhaling warmer air (than body temperature). For lungs with increased ASL thickness (due to diseases); plug formation is aggravated by colder air inhalation; thus demonstrating that inhaling colder (warmer) air is detrimental (beneficial) for diseased lungs. The predictions of the present analysis are in agreement with clinical observations.
Keywords:
pulmonary fluid mechanics
absolute/convective instability
viscoelasticity
Journal
IF:
3.9
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2.0W
Citations:
9.4W