摘要：

The genioglossus (GG) is known to be the main tongue protrusor, and therefore plays a major role in breathing. However, due to the fan shape of the GG fibers, it could be assumed that contraction of the anterior fibers of the GG do not cause tongue protrusion. In this study, we examined the effect of contraction of the anterior-vertical fibers of the GG (GGV) on the tongue and their EMG activity during wakefulness and sleep. The findings were compared to those of the longitudinal fibers (GGL), which, based on their orientation, are responsible for tongue protrusion. Fine-wire electrode pairs were placed into the GGV and GGL in 11 patients with untreated OSA. Movement of the tongue during electrical stimulation at each site was videoed. The same electrodes were used to record EMG from both sites during respiratory stimulation by inspiratory loading and CO2 rebreathing during wakefulness. During sleep, repetitive flow limitation events were induced with low-level CPAP to augment GG activity. In all participants, electrical stimulation of GGL and GGV protruded and retracted the tongue, respectively. Respiratory stimulation increased GG activity, but GGV reached only 39 % and 23 % of peak GGL activity during high resistive loading and PCO2 of 65 mmHg, respectively. Flow limitation during sleep increased GGL to levels that were considerably higher than awake baseline, but GGV activity remained tonic or with minimal phasic activity, reaching on average 15 % of GGL peak activity. Our electrical stimulation findings indicate that GGV is a tongue retractor and depressor. Tongue stimulation for OSA should avoid this area. The EMG results demonstrate that the anterior part of the GG is controlled very differently from the longitudinal protrusive fibers. The GGV responses are similar to those previously found in tongue retractors and peri-pharyngeal muscles other than the GG, in which diminished activation during sleep is likely to be involved in the failure of increasing GGL activity to alleviate flow limitation.

收起

展开 