PHARYNGEAL FUNCTION AND SNORING CHARACTERISTICS IN APNEIC AND NONAPNEIC SNORERS

Abnormalities in pharyngeal function, manifested even when the patients are awake, are thought to play an important role in the pathogenesis of sleep apnea. Tests of awake pharyngeal function continue to stimulate interest because it is hoped that they may allow physicians to distinguish patients with sleep apnea from those without it, and therefore reduce the number of unnecessary sleep studies. We elected to study two measures of pharyngeal function: changes in pharyngeal area with lung volume (PLVD) and changes in pharyngeal area in response to externally applied positive pressure, i.e., pharyngeal distensibility (Cph). Both measurements have been employed for assessment of pharyngeal function, and both are thought to reflect pharyngeal "floppiness." Measurement of PLVD is technically very simple, whereas the measurement of Cph is technically more complex. It the two measurements are highly correlated, it might be possible to replace the technically more difficult one by the simpler one. Consequently, the purpose of this study was two-fold: first, to examine the relationship between pharyngeal distensibility and lung volume dependence of pharyngeal area, and second, to compare these parameters in a large group of confirmed snorers with and without obstructive sleep apnea (OSA). We studied 75 unselected patients referred for the investigation of snoring and suspected sleep apnea. All patients had nocturnal polysomnography, pulmonary function tests, and measurement of pharyngeal areas at TLC, FRC, and residual volume (RV) employing the acoustic reflection technique. The area measurement at FRC was performed at zero and at 4.1 cm H2O positive airway pressure to calculate pharyngeal distensibility. We found no significant correlation between PLVD and Cph (r = 0.15, p = 0.20). Using a stepwise, forward, multiple linear regression model, we found that only body mass index and PLVD, but not Cph, were significant determinants of the variability in apnea/hypopnea index (AHI) (multiple r2 = 0.33, p < 0.005). Neither PLVD nor Cph correlated with snoring. When we divided our patients into four groups based on an AHI of less than 10 (controls), between 11 and 30 (mild OSA), between 31 and 50 (moderate OSA), and greater than 50 (severe OSA), we found that PLVD, but not Cph, separated the severe group from the control and the mild groups. We conclude that (1) measurements of PLVD and pharyngeal compliance are not equivalent, and (2) lung-volume-associated changes in pharyngeal area are related to the severity of sleep apnea.