Differences in pharyngeal properties between snorers with predominantly central sleep apnea and those without sleep apnea.

The underlying cause of idiopathic central sleep apnea syndrome is not well understood. We therefore examined the possibility that patients with idiopathic central sleep apnea may have abnormalities of upper airway mechanics that might contribute to the pathogenesis of central apneas. The acoustic reflection technique was used to assess pharyngeal size, lung volume dependence, and pharyngeal "compliance" in 8 patients with idiopathic central sleep apnea, all of whom were snorers, and in 8 weight-matched, snoring control subjects with normal sleep studies. Patients with central sleep apnea when compared with control subjects exhibited markedly increased specific pharyngeal "compliance" (0.12 +/- 0.05 versus 0.03 +/- 0.01 cm H2O-1; p less than 0.001), increased change in pharyngeal area from FRC to RV (0.8 +/- 0.5 versus 0.03 +/- 0.3 cm2; p less than 0.05), and a larger pharyngeal area at FRC (4.7 +/- 0.9 versus 3.8 +/- 0.8 cm2; p less than 0.03). We conclude that increased pharyngeal "compliance" and lung volume dependence may play a role in the etiology of central apneas in this syndrome.