Effect of coactivation of tongue protrusor and retractor muscles on pharyngeal lumen and airflow in sleep apnea patients

Abstract

The present study evaluated the effect of coactivation of tongue protrusors and retractors on pharyngeal patency in patients with obstructive sleep apnea. The effect of genioglossus (GG), hyoglossus (HG), and coactivation of both on nasal pressure (Pn):flow relationships was evaluated in a sleep study (SlS, n = 7) and during a propofol anesthesia study (AnS, n = 7). GG was stimulated with sublingual surface electrodes in SlS and with intramuscular electrodes in AnS, while HG was stimulated with surface electrodes in both groups. In the AnS, the cross-sectional area (CSA):Pn relationships was measured with a pharyngoscope to estimate velopharyngeal compliance . In the SlS, surface stimulation of GG had no effect on the critical pressure (Pcrit), HG increased Pcrit from 2.8 +/- 1.7 to 3.7 +/- 1.6 cmH(2)O, but coactivation lowered Pcrit to 0.2 +/- 1.9 cmH(2)O (P < 0.01 for both). In the AnS, intramuscular stimulation of GG lowered Pcrit from 2.6 +/- 1.3 to 1.0 +/- 2.8 cmH(2)O, HG increased Pcrit to 6.2 +/- 2.5 cmH(2)O (P < 0.01), and coactivation had a similar effect to that of GG (Pcrit = 1.2 +/- 2.4 cmH(2)O, P < 0.05). None of the interventions affected significantly velopharyngeal compliance. We conclude that the beneficial effect of coactivation depends on the pattern of GG fiber recruitment: although surface stimulation of GG failed to protrude the tongue, it prevented the occlusive effect of the retractor, thereby improving pharyngeal patency during coactivation. Stimulation of deeper GG fibers with intramuscular electrodes enlarged the pharynx, and coactivation had no additive effect.

Acute Upper Airway Responses to Hypoglossal Nerve Stimulation during Sleep in Obstructive Sleep Apnea

“…In these prior studies, investigators scrutinized EEG and ECG signals to exclude responses associated with cortical or autonomic activation (13,18,19). Additional studies with implantable nerve cuff (13) and fine-wire electrodes have demonstrated responses to selective lingual muscle stimulation during sleep and anesthesia (13)(14)(15)(16)(17). The present study also screened for evidence of cortical and autonomic activation, and further required strict temporal synchrony between the stimulus burst and airflow response to exclude arousal responses from the analysis.…”

“…These increases have been attributed to decreases in pharyngeal collapsibility (14,16,17), which decreases the back pressure to inspiratory airflow (27). In previous studies, stimulating the genioglossus muscle and hypoglossal nerve led to an approximately 3-to 5-cm H 2 O decrease in critical pressure, which can account for an approximately 150-to 250-ml/s increase in maximal inspiratory airflow (18,19).…”

“…Rather, peak flow was achieved at lower stimulation amplitudes in the non-flow-limited group, suggesting enhanced mechanical effects of lingual muscle contraction on the pharynx. This effect could reflect greater linkage between the tongue and other pharyngeal structures, because of differences in lingual muscle fiber orientation, lingual-palatine linkage, or pharyngeal site of collapse (14,28,29). Alternatively, lingual muscle recruitment patterns could differ among patients, as suggested by observed decreases in inspiratory airflow in one patient at stimulation amplitudes well above the peak flow threshold, which were also associated with tongue retraction during wakefulness and sedation.…”

“…Implantable HGNS systems have been developed to stimulate the hypoglossal nerve during inspiration, and recruit the lingual musculature, leading to decreases in pharyngeal collapsibility during sleep (14)(15)(16)(17). Motor activity protrudes the tongue, and mitigates airflow obstruction during sleep (18,19).…”

Positive airway pressure and electrical stimulation methods for obstructive sleep apnea treatment: a patent review (2005 – 2014)

“…Moreover, selective stimulation of both the lateral XII nerve branches and the medial nerve branch seems to increase maximum rate of airflow and mechanical stability [42,58,59]. Recent studies assessing efficacy of current commercial devices for electrical neurostimulation report significant improvement in AHI and quality of life measures [60][61][62].…”