Improved upper airway patency elicited by electrical stimulation of the hypoglossus nerves.

The present study evaluated the mechanisms by which upper airway (UAW)-dilating muscle contraction, elicited by hypoglossus nerve (HGN) stimulation, improved UAW patency. Pressure-flow (P-V) relationships of the isolated UAW as well as the negative intraluminal pressures required to cause UAW collapse were assessed before and during electrical stimulation of the HGN in 8 anesthetized, ventilated dogs. Sectioning of the HGN shifted the P-V relationship to the left, while electrical stimulation resulted in a substantial shift of the curve to the right, indicating UAW dilatation. UAW resistance decreased from 9.0 +/- 1.5 to 0.3 +/- 0.1 cm H2O.1(-1).s during HGn stimulation (p < 0.01). The magnitude of negative intraluminal pressure at which UAW collapse occurred (the critical pressure) increased from -2.7 +/- 0.7 to -13.2 +/- 2.1 cm H2O (p < 0.002). The increase in UAW conductance and stability raised the maximal flow which could be sustained without collapse from 0.28 +/- 0.07 to 2.07 +/- 0.35 l/s during HGN stimulation (p < 0.001). These findings indicate that in the anesthetized dog, UAW muscle contraction improves UAW patency both by dilating the UAW and by stiffening its walls.