Figure 1.

(A) Simplified conceptual diagram illustrating the separate major pathways for chemoreceptor “drive” and mechanoreceptor “pressure” inputs that determine genioglossus activity (EMGgg) during sleep. Laryngeal negative pressures are transduced by mechanoreceptors in the upper airway via the superior laryngeal nerve to the NTS to provide negative pressure reflex input to the hypoglossal motor nucleus (HGN). Hypercapnia is sensed by peripheral and central chemoreceptors and transduced to chemosensitive neurons in the medulla (e.g., at the RTN) that innervate the RPGs, which provide a common ventilatory drive signal to both the hypoglossal and phrenic motor nuclei. Additional pathways, including wakefulness or arousal inputs and (potential) pulmonary stretch receptor inputs to the HGN, are not shown. (B) Directed acyclic graph summarizing the statistical analysis approach. Multivariable regression was used to quantify separate mechanoreceptor and chemoreceptor inputs to the hypoglossal motor nucleus and the downstream EMGgg; Pes was used to represent mechanoreceptor input, and EMGdi was used to represent chemoreceptor input. EMGdi = diaphragm electromyography; NTS = nucleus tractus solitarius; Pes = esophageal pressure; RPG = respiratory pattern generator; RTN = retrotrapezoid nucleus.