HYPOGLOSSAL NERVE-STIMULATION AFFECTS THE PRESSURE-VOLUME BEHAVIOR OFTHE UPPER AIRWAY

To determine the effects of electrical hypoglossal nerve and submental stimulation on upper airway collapsibility, we examined the pressure- volume (P-V) relationships during bilateral supramaximal stimulation o f the distal cut hypoglossal nerve ends over a range of frequencies fr om zero to 100 Hz in the sealed upper airway of 10 anesthetized supine dogs. Animals were artificially ventilated with 50% O-2 and maintaine d under relative hyperoxia and hypocapnia during the study to eliminat e the ventilatory drive output. Sealed upper airway pressures were obt ained during random injections of different volumes of air from zero t o 50 ml with and without hypoglossal nerve stimulation, and the upper airway P-V curves were obtained. The characteristics of the P-V curves were as follows: (1) the upper airway compliance defined as the slope of the regression of P-V curves fell from 4.07 +/- 0.33 ml/cm H2O wit hout stimulation to 3.02 +/- 0.30 ml/cm H,O with stimulation at 50 Hz and plateaued at frequencies greater than 50 Hz, and (2) the volume at a given pressure during stimulation was larger than that without stim ulation. The effects of submental stimulation on upper airway collapsi bility were similar to those of hypoglossal nerve stimulation. These r esults suggest that the increase of upper airway muscle tone by hypogl ossal nerve or submental stimulation stiffens the upper airway and tha t increases in muscle tone expand the upper airway.