Date of Award
Fall 2017
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Biomedical Engineering
First Advisor
Garcia, Guilherme J. M.
Second Advisor
LaDisa, John F.
Third Advisor
Audi, Said
Abstract
Obstructive sleep apnea (OSA) is characterized by recurrent episodes of airway collapse and airflow limitation during sleep. Fragmented sleep and reductions in blood oxygen saturation lead to several comorbidities, including hypertension, cardiovascular disease, and cerebrovascular disease. Longitudinal forces (tracheal traction) acting on the soft tissues surrounding the upper airway have been proposed to play a significant role in stabilizing the airway and preventing collapse. However, the relative contribution of longitudinal forces as compared to other factors that affect airway stability (airway geometry, tissue properties, muscle activity) remains unclear. This in-vitro study aimed to investigate to what extent longitudinal forces can stabilize the upper airway against flow-induced collapse. Collapsible silicone tubes of varying lengths (L = 75 to 125mm), diameters (D = 12.70 to 31.75mm), and wall thicknesses (h = 0.98 to 2.22mm) were fabricated in-house. An experimental setup was developed that included a pressure catheter to measure air pressure in the tube lumen, a pump that generated sinusoidal bidirectional flow, and a laser line scanner to monitor deformations of the tube wall. The buckling pressure (pressure at which the tube collapses) was quantified as a function of tube geometry and longitudinal stretching. The silicone tubes collapsed at a similar range of transmural pressures (0 to 10 cmH2O) and flowrates (0 to 250ml/s) as observed in the human airway during sleep. Tube length had no clear effect on the buckling pressure, but mechanical stability increased when the wall-thickness-to-radius ratio ( = 2h/D) increased. The buckling pressured measured experimentally was in good agreement with the theory for tubes exposed to transmural pressure alone (zero flow), suggesting that tube collapse was determined primarily by the transmural pressure (rather than by fluid-structure interactions). Longitudinal stretching (5% strain) reduced the buckling pressure by 0.5 to 1.0 cmH2O, which was smaller than the effect of changes in tube diameter and wall thickness. Longitudinal stretching improved the stability of cylindrical silicone tubes, but its effect was smaller than the effect of changes in tube geometry.