Dysfunctional mechanical coupling of upper airway tissues in sleep apnea syndrome.

The mechanical effect of musculus uvulae (MU) contraction on in vitro uvular shortening and/or displacement was measured in 15 patients with a sleep apnea hypopnea syndrome (SAHS) and in 8 snorers. Using freshly resected uvular tissues, passive and active uvular tissue-specific elastance and shortening were determined during stimulation of MU. No difference was found in maximum tetanic tension measured on uvular tissue between the two groups (47.2 +/- 14.8 g in SAHS and 39.1 +/- 16.5 g in snorers). Passive uvular-specific elastance was significantly less in snorers (0.36 +/- 0.27 g/% Lo) compared with patients with SAHS (0.84 +/- 0.39 g/% Lo) (p = 0.006). There was a negative correlation between uvular shortening and passive uvular specific elastance (r = 0.69, p = 0. 05). Maximal tetanic tension developed by isolated MU was higher in SAHS than in snorers (45.8 +/- 23.1 and 30.0 +/- 8.3 g, respectively, p = 0.04). A strong positive relationship was found between the apnea index and specific uvular elastance (r = 0.55, p = 0.007). We conclude that there is a significant difference between the uvular tissue elastance of SAHS and snorers, and that this difference influences the mechanical efficiency of MU contraction.