UPPER AIRWAY AND SOFT-TISSUE STRUCTURAL-CHANGES INDUCED BY CPAP IN NORMAL SUBJECTS

Nasal continuous positive airway pressure (CPAP) is the treatment of c hoice for adults with obstructive sleep apnea. CPAP is known to increa se upper airway size; however, the direct effects of CPAP on soft tiss ue structures surrounding the upper airway are less well understood. M agnetic resonance imaging was used to study the effect of incremental levels (0, 5, 10, and 15 cm H2O) of CPAP on the upper airway and surro unding soft tissue structures in 10 normal subjects, Progressive incre ases in CPAP resulted in the following major findings: (1) airway volu me and airway area (measured at several different locations [midregion , minimal, maximal]) within the retropalatal and retroglossal regions increased; (2) lateral airway dimensional changes were greater than an terior-posterior changes; (3) lateral upper airway soft tissue structu ral changes were significantly greater than anterior-posterior changes ; (4) lateral pharyngeal wall thickness decreased and the distance bet ween the lateral parapharyngeal fat pads increased. An inverse relatio nship was demonstrated between CPAP level acid pharyngeal wall thickne ss; (5) minimal changes were noted in the soft palate and tongue. Thes e data suggest that the lateral pharyngeal walls are more ''compliant' ' than the soft palate and tongue. This investigation provides further evidence that the lateral pharyngeal walls play an important role in mediating upper airway caliber.