Comparison of the responses of the diaphragm and upper airway muscles to central stimulation of the sciatic nerve.

Electrical stimulation of the central end of the sciatic nerve was used to assess the effect of increased somatic sensory input on respiratory muscle electrical activity in anesthetized, spontaneously breathing dogs. Graded electrical stimulation of the sciatic nerve was associated with progressively greater activity of the upper airway dilating muscles (alae nasi, genioglossus, and posterior cricoarytenoid) as well as the diaphragm. Breathing frequency also increased because of a reduction in inspiratory and expiratory time. After cessation of stimulation of the sciatic nerve, increased activity of all the muscles studied persisted and only gradually returned to control levels. The responses to sciatic nerve stimulation were independent of the CO2 concentration of the inspired gas mixture. At any level of chemical drive electrical stimulation caused greater increases in the electrical activity of upper airway dilating muscles than that of diaphragm. Based on these results, it is concluded that stimulation of sciatic nerve activates upper airway muscles as well as the diaphragm, and the upper airway muscle activity is augmented to a greater degree than diaphragm activity. It seems possible that somatosensory afferent input produces unequal effects on different respiratory motoneurons.