Parameters affecting pharyngeal response to genioglossus stimulation in sleep apnoea

Chronic stimulation of the hypoglossus nerve may provide a new treatment modality for obstructive sleep apnoea (OSA). In previous studies we observed large differences in response to stimulation of the genioglossus (GG). We hypothesised that both individual patient characteristics and the area of the GG stimulated are responsible for these differences. In the present study, we compared the response to GG electrical stimulation at the anterior area (GGa-ES), which activates the whole GG and the posterior area (GGp-ES), which activates preferentially the longitudinal fibres. Studies were performed in 14 propofol-sedated OSA patients. The parameters evaluated included cephalometry, pressure-flow relationship and pharyngeal shape and compliance assessed by pharyngoscopy. Compared with GGa-ES, GGp-ES resulted in significantly larger decreases in the critical value of end-expiratory pressure (P(crit)) (from 3.8 ± 2.2 to 2.9 ± 3.3 and -2.0 ± 3.9 cmH(2)O, respectively (p<0.001)). Both tongue size and velopharyngeal shape (anteroposterior to lateral ratio) correlated significantly with the decrease in P(crit) during GGp-ES (R = 0.53 and -0.66, respectively; p<0.05). In the patients with the larger tongue size (n = 7), the decrease in P(crit) reached 8.0 ± 2.2 cmH(2)O during GGp-ES. We conclude that directing stimulation to longitudinal fibres of the GG improves the flow-mechanical effect. In addition, patients with large tongues and narrow pharynx tend to respond better to GGp-ES.