Patients with obstructive sleep apnea exhibit genioglossus dysfunction that is normalized after treatment with continuous positive airway pressure

Obstructive sleep apnea syndrome (OSAS) is characterized by repetitive epis odes of pharyngeal closure during sleep. The pathogenesis of OSAS is unclea r. We hypothesized that the genioglossus (CC), the most important pharyngea l dilator muscle, would be abnormal in patients with OSAS. Further, because treatment with continuous positive airway pressure (CPAP) is very effectiv e clinically in these patients, we investigated the effects of CPAP upon th e structure and function of the CC. We studied 16 patients with OSAS (nine of them at diagnosis and seven after having been under treatment with CPAP for at least 1 yr) and 11 control subjects in whom OSAS was excluded clinic ally. A biopsy of the CC was obtained in each subject, mounted in a tissue bath, and stimulated through platinum electrodes. The following measurement s were obtained: maximal twitch tension, contraction time, half-relaxation time, the force-frequency relationship, and the response to a fatiguing pro tocol. The percentage of type I ("slow twitch") and type II ("fast twitch") fibers was also quantified. Patients with OSAS showed a greater GG fatigab ility than did control subjects (ANOVA, p < 0.001). Interestingly, this abn ormality was entirely corrected by CPAP. Likewise, the percentage of type I I fibers was significantly higher in patients with OSAS (59 +/- 4%) than in control subjects (39 +/- 4%, p < 0.001) and, again, these structural chang es were corrected by CPAP (40 +/- 3%, p < 0.001). These results show that t he function and structure of the GG is abnormal in patients with OSAS. Beca use these abnormalities are corrected by CPAP, we suggest that they are lik ely a consequence, not a cause, of the disease.