Wall motion in expiratory flow limitation: choke and flutter

Abstract

Limitation of expiratory airflow from mammalian airways is currently understood to be due to choking at wave speed (S. V. Dawson and E. A. Elliott. J. Appl. Physiol. 43: 498-515, 1977). A critical weakness of the theory is the lack of a mechanism for the dissipation of energy when effort exceeds that needed for maximal flow. We have observed substantial wall motion with flow limitation in a physical model of a trachea. Therefore we have examined a simple two-dimensional mathematical model, designed to approximate the behavior of the physical model of the trachea, to try to identify a relationship between flow limitation and wall oscillation. The model matches wave-speed predictions when only long waves are considered. The model predicts that aerodynamic flutter will occur in the zone of supercritical flow described in wave-speed theory. Aerodynamic flutter in the zone of supercritical flow provides a potential mechanism for the energy dissipation necessary for transition from supercritical to subcritical flow and explains the high-frequency pure tone heard with flow limitation.

The effects of wall inertia on flow in a two-dimensional collapsible channel

“…There have, however, been many experiments on collapsible tubes, and we have already confirmed that some features of the lowfrequency oscillations found numerically are qualitatively similar to those observed experimentally (Luo & Pedley 1996). Experimental studies in which high-frequency oscillations are observed, sometimes superimposed on lower-frequency oscillations, include those of Weaver & Paidoussis (1977), Webster et al (1985), Sakurai & Ohba (1986), Bertram (1986), Gavriely et al (1989) and Bertram et al (1990Bertram et al ( , 1991. The studies of Bertram and his colleagues involved water flow in thick-walled tubes, so both the effective value of m would be relatively large and the elastic properties of the tube would have been very different from those assumed in this paper.…”

“…Wall mass would have been even more dominant in the experiments of Gavriely et al (1989) who studied airflow in a thick-walled tube; they found, nevertheless, that there was reasonable agreement with a two-dimensional flutter model, in which the bending stiffness of the wall was more important than longitudinal tension. Webster et al (1985) studied airflow in a 'mechanical trachea', consisting of a tube with square cross-section (when undeformed), one side of which was replaced with a membrane under biaxial tension; when deformed, this system is not approximately two-dimensional nor tube-like. Weaver & Paidoussis (1977) studied the stability of thin-walled tubes conveying water, and reported a flapping-mode flutter and classical shell-mode flutter depending on the initial collapsed states of the tubes.…”

“…The study of flow-induced oscillation in tubes and channels has a long history, with proposed applications in either engineering (Carpenter & Garrad 1986;Carpenter & Morris 1990) or physiology, notably in the context of expiratory wheezing in airways (Gavriely & Grotberg 1988;Gavriely et al 1989;Webster et al 1985). Almost all these studies, however, consisted of linear or nonlinear instability theories for flow in a long, parallel-sided channel, so in the basic state the steady flow is unidirectional and the elastic walls are planar.…”

The cascade structure of linear instability in collapsible channel flows

“…Stability of a plane channel flow between compliant walls has also been studied previously from a variety of points of view (Green & Ellen 1972;Webster et al 1985;Carpenter & Garrad 1986;Grotberg & Gavriely 1989;Ehrenstein & Rossi 1993;Davies & Carpenter 1997a, b). Most of these studies considered the instability of flow in a long parallel-sided channel, so, in the basic state, the steady flow is unidirectional and the elastic walls are planar.…”

Μηχανική Της Αναπνοής Και Εφαρμογή Τεχνητής Αρνητικής Πίεσης Σε Ασθενείς Με Σύνδρομο Απνοιών Στον Ύπνο Και Χρόνιας Αποφρακτικής Πνευμονοπάθειας

“…ην θάξπγγα, ε ζηξνβηιψδεο ξνή, απνηειεί ηελ θχξηα πεγή θαηαλάισζεο ησλ πηέζεσλ. Απηή ε κεγάιε θαηαλάισζε ελέξγεηαο ηεο P alv (πνπ ζπκβαίλεη ζε ζηξνβηιψδε ξνή), απνζηαζεξνπνηεί ην θάξπγγα ζχκθσλα κε ην Webster θαη ζπλεξγάηεο (1985) [129], πξνθαιψληαο ηνηρσκαηηθή θίλεζε (ηαιάλησζε) θάησ απφ (ακέζσο πξηλ απφ) ην ζεκείν ζχζθημεο, ε νπνία ζε ηερλεηή ηξαρεία έρεη 1 κνλαδηθή θνξπθή (peak) ζπρλφηεηαο 1 KHz. Αληηζέησο, πάλσ απφ ην ζεκείν ζχζθημεο, δελ ππάξρεη ηαιάλησζε.…”