Airflow limitation in a collapsible model of the human pharynx: physical mechanisms studied with fluid‐structure interaction simulations and experiments

• Published in: Physiological reports Vol. 7; no. 10; pp. e14099 - n/a
• Main Authors: Le, Trung B., Moghaddam, Masoud G., Woodson, B. Tucker, Garcia, Guilherme J. M.
• Format: Journal Article
• Language: English
• Published: United States John Wiley & Sons, Inc 01.05.2019; John Wiley and Sons Inc; Wiley
• Subjects: Airflow limitation; Apnea; Biomechanics; Control of Breathing; fluid‐structure interaction simulations and experiments; Mathematical models; Mechanical properties; NMR; Nuclear magnetic resonance; obstructive sleep apnea; Original Research; Patient compliance; Pharynx; Physiology; Pressure; Respiratory Conditions Disorder and Diseases; Respiratory tract; Silicones; Sleep; Sleep apnea; Sleep disorders; Starling Resistor biomechanical model of airway collapse; Studies; Theory; wave‐speed flow limitation theory; obstructive sleep apnea; fluid-structure interaction simulations and experiments; Starling Resistor biomechanical model of airway collapse; wave-speed flow limitation theory; Airflow limitation
• ISSN: 2051-817X
• DOI: 10.14814/phy2.14099

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 is VImax=A3/2(ρdA/dP)−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 kPa. 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 VImax is a surrogate measure of pharyngeal compliance. Fluid‐structure interaction simulations of airflow limitation in a collapsible model of the human pharynx support two predictions of the wave‐speed flow limitation theory, namely (1) the pressure profile upstream from the choke point is independent of downstream pressure during flow limitation and (2) the maximum flowrate in collapsible tubes is inversely proportional to the square root of pharyngeal compliance (VImax∝C−1/2). This suggests that pharyngeal compliance can be estimated from peak flow measurements.