Figure 2. Polysomnography during hypoglossal nerve stimulation.

Initially, hypoglossal nerve stimulation is off, with periods of obstructive apnoea accompanied by oxygen desaturation and arousal. Stimulation is then turned on at a level above the capture threshold, in this example at 2·5 mA. Regular impulses can be seen in the electromyography. Improvement is noted in flow characteristics such that desaturation and arousal are no longer present, however, flow limitation remains. Variable response to hypoglossal nerve stimulation between patients emphasises the importance of refining patient selection. By permission of Inspire Medical Systems.