PHARYNGEAL NARROWING AND CLOSING PRESSURES IN PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA

Based on previous studies, we hypothesized that the pharynx collapses at multiple sites in most patients with obstructive sleep apnea (OSA). The purpose of this study was to document, in a population of apneic subjects, the site(s) of narrowing and closing pressure of the hypoton ic pharynx. We endoscopically examined the pharynx in 45 OSA patients during sleep while they received nasal continuous positive airway pres sure (CPAP), which produces hypotonia of pharyngeal muscles. Intraphar yngeal images and pressures were obtained at the end of expiration dur ing single-breath tests (SBT). The fractional narrowing (FN) of each p haryngeal segment (nasopharynx, oropharynx, and hypopharynx) was calcu lated as the relative change in area when nasal airway pressure was re duced from a pressure that held the pharynx fully distended to the pre ssure at which the airway closed. The frequency distribution of FN for the nasopharynx was skewed toward larger values, and the frequency wa s relatively evenly distributed for the oropharynx and hypopharynx. A site having FN greater than 0.75 was defined as a site of primary narr owing, and a site showing FN 0.25 to 0.75 was defined as a site of sec ondary narrowing. The nasopharynx was a site of primary narrowing in 8 0% of patients, and two or more sites of narrowing were commonly obser ved (82%). Four categories of combined narrowing were identified: (1) primary narrowing only at the nasopharynx (18%); (2) primary narrowing at the nasopharynx plus other sites of secondary narrowing (40%); (3) primary narrowing at the nasopharynx plus other sites of primary narr owing (22%); and (4) other patterns (20%). Closing pressures ranged fr om -2 to 8 cm H2O, and 85% of values were equal to or greater than 0 c m H2O. Our results demonstrate that the hypotonic pharynx of sleeping apneic subjects commonly collapses at multiple sites, that the nasopha rynx is a site of primary narrowing in the vast majority of patients, and that closing pressure is equal to or greater than atmospheric pres sure in most cases.