Parameters affecting pharyngeal response to genioglossus stimulation in sleep apnoea

Abstract

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 (Pcrit) (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 Pcrit during respectively; p,0.05). In the patients with the larger tongue size (n57), the decrease in Pcrit reached 8.0¡2.2 cmH 2 O during GGp-ES.We conclude that directing stimulation to longitudinal fibres of the GG improves the flowmechanical effect. In addition, patients with large tongues and narrow pharynx tend to respond better to GGp-ES.

Effect of upper-airway stimulation for obstructive sleep apnoea on airway dimensions

“…These findings of multilevel opening at the different collapsible levels of the upper airway with stimulation probably explain the effectiveness of UAS therapy in reducing AHI severity in a recent multicentre, prospective trial evaluating this UAS therapy, as well as explain the return to baseline AHI in patients who were randomised to therapy withdrawal [15]. The findings of improvement in upper-airway cross-sectional area at the retropalatal level during unilateral hypoglossal nerve stimulation are in line with the results from groups visualising retropalatal area during direct genioglossus muscle stimulation under anaesthesia [6,8], as well as others visualising palatal anterior displacement and thinning from fluoroscopic images during intraoperative testing of an implantable hypoglossal neurostimulator [16]. The present study found this result in patients undergoing a therapeutic clinical trial.…”

“…Therapeutic applications using neuromuscular electrical stimulation of the hypoglossal nerve and genioglossus muscle have been designed and evaluated as a potential alternative to positive airway pressure therapy and upper-airway surgical procedures [6][7][8][9][10][11][12][13]. The therapy consists of an implanted, programmable neurostimulation system, with a stimulation electrode around the protrusor branches of the right hypoglossal nerve and a respiration sensor placed in the right intercostal space to detect respiration [10,14,15].…”

Dissociation of electromyogram and mechanical response in sleep apnoea during propofol anaesthesia

“…It should be noted that we have previously found that the mechanical effect of GG stimulation during sleep and anaesthesia is similar [33]. Moreover, the site used for electrode placement in the current study produces a substantially smaller effect than a location that activates preferentially the protrusive GG fibres [34]. In addition, electrical stimulation produces a much smaller protrusive force than volitional activation [35].…”

“…Nevertheless, lack of adequate activation of muscles not evaluated in this study cannot be excluded. Anaesthesia-induced general hypotonia that includes the trunk and neck muscles may affect the forces arising from the chest and increase extrapharyngeal pressure within the maxillo-mandibular bony structures that enclose the soft tissue surrounding the collapsible segment of the pharynx [34,40]. Such alterations may affect GG contraction and/or the negative dependence of flow and downstream pressure.…”

“…In addition to intermuscular coordination, intramuscular coordination of fibre activity may also be important. Although the GG is considered to be a single muscle, its fan-like fibre orientation results in different mechanical activity depending on the fibres recruited [34]. Recent studies that have evaluated single motor-units of the GG have shown that this muscle's EMG is composed of several populations of units that are activated differently during breathing [29,43].…”