MRI study of regional variations of pharyngeal wall compliance in cats

Upper airway compliance indicates the potentialof the airway to collapse and is relevant to the pathogenesis ofobstructive sleep apnea. We hypothesized that compliance would varyover the rostral-to-caudal extent of the pharyngeal airway. In aparalyzed isolated upper airway preparation in cats, we controlledstatic upper airway pressure during magnetic resonance imaging (MRI, 0.391-mm resolution). We measured cross-sectional area andanteroposterior and lateral dimensions from three-dimensionalreconstructed MRIs in axial slices orthogonal to the airway centerline.High-retropalatal (HRP), midretropalatal (MRP), and hypopharyngeal(HYP) regions were defined. Regional compliance was significantlyincreased from rostral to caudal regions as follows: HRP < MRP < HYP (P < 0.0001), and compliancedifferences among regions were directly related to collapsibility. Thusour findings in the isolated upper airway of the cat support thehypothesis that regional differences in pharyngeal compliance exist andsuggest that baseline regional variations in compliance andcollapsibility may be an important factor in the pathogenesis andtreatment of obstructive sleep apnea.