Dilatory effects of upper airway muscle contraction induced by electrical stimulation in awake humans.

During sleep, diminished activity of upper airway dilator muscles (UADMs) is believed to increase upper airway (UAW) resistance and ultimately cause collapse of the UAW. In anesthetized dogs, electrically induced UADM contraction reduces UAW resistance and collapsibility. In this study, we measured the effects of electrically induced contraction of UADMs on pharyngeal resistance (Rph) in seven awake healthy subjects. UAW partial occlusion was achieved by applying external pressure to the submental hyoid region, leading to increased Rph. Transmucosal electrical stimulation (ES) of the base of the tongue was used to preferentially stimulate the genioglossus muscle. Transcutaneous ES using submental and paralaryngeal electrodes were used to preferentially stimulate the geniohyoid and the sternohyoid and sternothyroid muscles, respectively. During the unobstructed state, Rph averaged 6.11 +/- 0.48 cmH2O.l-1.s, and ES produced minimal resistance changes for all stimulation sites tested. In contrast, during the application of external pressure, when Rph was raised to an average of 190 +/- 14% of the baseline value, sublingual ES reduced resistance from 11.67 +/- 1.90 to 6.77 +/- 1.30 cmH2O.l-1.s (P < 0.01). ES at the other sites during the raised Rph state produced only minor statistically insignificant changes in Rph, even when combined submental and paralaryngeal ES was applied. Likewise, only sublingual ES produced measurable anterior movement of the tongue. We conclude that when Rph is raised by exogenous means, sublingual transmucosal ES effectively reduces Rph in awake humans.