Regional genioglossus reflex responses to negative pressure pulses in people with obstructive sleep apnea.

Tongue and upper airway dilator muscle movement patterns during quiet breathing vary in people with obstructive sleep apnea (OSA). Many patients have inadequate or counterproductive responses to inspiratory negative airway pressure that likely contributes to their OSA. This may be due, at least in part, to inadequate or nonhomogeneous reflex drive to different regions of the largest upper airway dilator, genioglossus. To investigate potential regional heterogeneity of genioglossus reflex responses in OSA, brief suction pulses were applied via a nasal breathing mask and an electromyogram (EMG) was recorded in four regions (anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal) using intramuscular fine wire electrodes in 15 people with OSA. Genioglossus short-latency reflex excitation amplitude had regional heterogeneity (horizontal vs. oblique regions) when expressed in absolute units but homogeneity when normalized as a percentage of the immediate (100 ms) prestimulus EMG. Regional variability in reflex morphology (excitation and inhibition) was present in one-third of the participants. The minimum cross-sectional area (CSA) of the pharyngeal airway was quantified using MRI and may be related to the amplitude of the short-latency reflex response to negative pressure as we found that people with a smaller CSA tended to have a greater reflex amplitude (e.g., horizontal region r2 = 0.41, P = 0.01). These findings highlight the complexity of genioglossus reflex control, the potential for regional heterogeneity, and the functional importance of upper airway anatomy in mediating genioglossus reflex responses to rapid changes in negative pressure in OSA.NEW & NOTEWORTHY Our findings indicate that 30% of participants had regional heterogeneity in reflex morphology (excitation/inhibition) to brief pulses of negative upper-airway pressure across anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal regions of the genioglossus muscle. Reflex excitation amplitude was proportional to prestimulus drive, with increased activation in oblique compared with horizontal regions of the posterior tongue. People with narrower upper-airway anatomy tended to have increased genioglossus reflex amplitude to negative pressure pulses during wakefulness.