Upper airway and soft tissue structural changes induced by CPAP in normal subjects.

TLDR

CPAP, the standard treatment for obstructive sleep apnea, enlarges the upper airway but its impact on surrounding soft tissues remains poorly characterized. Using MRI, the study examined the effects of 0, 5, 10, and 15 cm H₂O CPAP on the upper airway and adjacent soft tissues in ten healthy volunteers. Incremental CPAP increased airway volume and area in retropalatal and retroglossal regions, with greater lateral than anterior‑posterior changes, reduced lateral pharyngeal wall thickness inversely related to pressure, expanded lateral parapharyngeal fat pad spacing, minimal soft palate/tongue alterations, and evidence that the compliant lateral pharyngeal walls play a key role in airway caliber.

Abstract

Nasal continuous positive airway pressure (CPAP) is the treatment of choice for adults with obstructive sleep apnea. CPAP is known to increase upper airway size; however, the direct effects of CPAP on soft tissue structures surrounding the upper airway are less well understood. Magnetic 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 surrounding soft tissue structures in 10 normal subjects. Progressive increases in CPAP resulted in the following major findings: (1) airway volume 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 anterior-posterior changes; (3) lateral upper airway soft tissue structural changes were significantly greater than anterior-posterior changes; (4) lateral pharyngeal wall thickness decreased and the distance between the lateral parapharyngeal fat pads increased. An inverse relationship was demonstrated between CPAP level and pharyngeal wall thickness; (5) minimal changes were noted in the soft palate and tongue. These 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.