EFFECT OF UPPER AIRWAY MUSCLE-CONTRACTION ON SUPRAGLOTTIC RESISTANCE AND STABILITY

The activation of upper airway (UAW) muscles is believed to increase U AW patency to air flow. To evaluate the mechanisms by which UAW muscle s act to prevent UAW collapse, pressure-flow relationships of the isol ated UAW as well as the negative pressure required to cause UAW collap se (P(crit)) were assessed before and during electrical stimulation of four UAW muscle pairs in anesthetized dogs. Stimulation of each of th e muscles shifted the pressure-flow curve toward lower pressures for a ny given flow rate, indicating UAW dilatation. UAW resistance decrease d from 7.9 +/- 0.6 to 0.4 +/- 0.1, 2.7 +/- 0.6, 2.3 +/- 0.8 and to 4.8 +/- 1.5 cmH2O.L-1. sec during genioglossus, geniohyoid, sternothyroid and sternohyoid stimulation respectively (P < 0.01 in all cases). How ever, only genioglossus stimulation significantly increased P(crit) (f rom -3.4 +/- 0.6 to -12.0 +/- 1.8 cmH2O, P < 0.001). Relaxation of the genioglossus thus appears to produce the main impediment to air flow through the UAW, and contraction of this muscle improves UAW patency b oth by dilating the supraglottic airway and by stiffening its walls.