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Peripharyngeal tissue deformation, stress distributions, and hyoid bone movement in response to mandibular advancement.

Mandibular advancement (MA) increases upper airway (UA) patency and decreases collapsibility. Furthermore, MA displaces the hyoid bone in a cranial-anterior direction, which may contribute to MA-associated UA improvements via redistribution of peripharyngeal tissue stresses (extraluminal tissue pressure, ETP). In the present study, we examined effects of MA on ETP distributions, deformation of the peripharyngeal tissue surface (UA geometry), and hyoid bone position. We studied 13 supine, anesthetized, tracheostomized, spontaneously breathing adult male New Zealand White rabbits. Graded MA was applied from 0 to ∼4.5 mm. ETP was measured at six locations distributed throughout three UA regions: tongue, hyoid, and epiglottis. Axial computed tomography images of the UA (nasal choanae to glottis) were acquired and used to measure lumen geometry (UA length; regional cross-sectional area) and hyoid displacement. MA resulted in nonuniform decreases in ETP (greatest at tongue region), ranging from -0.11 (-0.15 to -0.06) to -0.82 (-1.09 to -0.54) cmH2O/mm MA [linear mixed-effects model slope (95% confidence interval)], across all sites. UA length decreased by -0.5 (-0.8 to -0.2) %/mm accompanied by nonuniform increases in cross-sectional area (greatest at hyoid region) ranging from 7.5 (3.6-11.4) to 18.7 (14.9-22.5) %/mm. The hyoid bone was displaced in a cranial-anterior direction by 0.42 (0.36-0.44) mm/mm MA. In summary, MA results in nonuniform changes in peripharyngeal tissue pressure distributions and lumen geometry. Displacement of the hyoid bone with MA may play a pivotal role in redistributing applied MA loads, thus modifying tissue stress/deformation distributions and determining resultant UA geometry outcomes.