Open AccessAirflow limitation in a collapsible model of the human pharynx: physical mechanisms studied with fluid‐structure interaction simulations and experiments
Author(s) -
Le Trung B.,
Moghaddam Masoud G.,
Woodson B. Tucker,
Garcia Guilherme J. M.
Publication year - 2019
Publication title -
physiological reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.918
H-Index - 39
ISSN - 2051-817X
DOI - 10.14814/phy2.14099
Subject(s) - pharynx , mechanics , choke , airway , airflow , fluid–structure interaction , compressibility , flow (mathematics) , airway resistance , materials science , medicine , physics , anatomy , surgery , thermodynamics , finite element method , quantum mechanics
The classical Starling Resistor model has been the paradigm of airway collapse in obstructive sleep apnea ( OSA ) for the last 30 years. Its theoretical framework is grounded on the wave‐speed flow limitation ( WSFL ) theory. Recent observations of negative effort dependence in OSA patients violate the predictions of the WSFL theory. Fluid‐structure interaction ( FSI ) simulations are emerging as a technique to quantify how the biomechanical properties of the upper airway determine the shape of the pressure‐flow curve. This study aimed to test two predictions of the WSFL theory, namely (1) the pressure profile upstream from the choke point becomes independent of downstream pressure during flow limitation and (2) the maximum flowrate in a collapsible tube isV I max = A 3 / 2( ρ d A / d P ) − 1 / 2, where ρ is air density and A and P are the cross‐sectional area and pressure at the choke point respectively. FSI simulations were performed in a model of the human upper airway with a collapsible pharynx whose wall thickness varied from 2 to 8 mm and modulus of elasticity ranged from 2 to 30 kP a. Experimental measurements in an airway replica with a silicone pharynx validated the numerical methods. Good agreement was found between our FSI simulations and the WSFL theory. Other key findings include: (1) the pressure‐flow curve is independent of breathing effort (downstream pressure vs. time profile); (2) the shape of the pressure‐flow curve reflects the airway biomechanical properties, so that V I maxis a surrogate measure of pharyngeal compliance.