Effects of selective hypoglossal nerve stimulation on canine upper airway mechanics.
Electrical stimulation of the hypoglossal (XII) nerve has been demonstrated as an effective approach to treating obstructive sleep apnea. The physiological effects of conventional modes of stimulation (i.e., genioglossus activation or whole XII nerve stimulation), however, have yielded inconsistent and only partial alleviations of hypopneic or apneic events. Although selective stimulation of the multifasciculated XII nerve offers many stimulus options, it is not clear how these will functionally affect the upper airway (UAW). To study these effects, animal experiments in eight beagles were performed to investigate changes in the UAW resistance and critical pressure during simulated expiration (n = 4) and inspiration (n = 4). During expiration, nonselective XII nerve stimulation yielded the greatest improvement in UAW resistance (-0.66 +/- 0.11 cm H2O x l(-1) x min(-1)), compared with that for selective activation of the geniohyoid (-0.29 +/- 0.09 cm H2O x l(-1) x min(-1)), genioglossus (-0.31 +/- 0.12 cm H2O x l(-1) x min(-1)), and hyoglossus/styloglossus (0.37 +/- 0.06 cm H2O x l(-1) x min(-1)) muscles. For simulated inspiration, on the other hand, only whole XII nerve stimulation (-0.9 +/- 0.4 cm H2O) and coactivation of the genioglossus + hyoglossus/styloglossus muscles (-1.18 +/- 0.6 cm H2O) produced significant (P < 0.05) improvements in UAW stability (i.e., lowered critical pressure), compared with baseline (-0.52 +/- 0.32 cm H2O). The results of this study suggest that a multicontact nerve electrode can be used to achieve both UAW dilation and patency, comparable to that obtained with nonselective stimulation, by selectively activating the various branches of the XII nerve.