Genioglossal and diaphragmatic EMG responses to hypoxia during sleep

Activation of pharyngeal dilator muscles, such as the genioglossus, during hypoxia must be sufficient to overcome the increased subatmospheric pressure generated by the diaphragm. This is particularly important during sleep, when upper airway resistance is greater. We measured ventilatory, genioglossal (EMGgg) and diaphragmatic (EMGdi) electromyogram responses to isocapnic hypoxia during wakefulness (W), slow-wave sleep (SWS), and rapid eye movement (REM) sleep in seven chronically instrumented adult goats. We also compared the EMG responses to hypoxia to response to CO₂ during W. ΔEMGdi/ΔSa(O₂) decreased progressively from W to SWS (p < 0.05) to REM sleep (p < 0.05 versus SWS), paralleling the corresponding ventilatory responses. EMGgg was activated only below and Sa(O₂) threshold, similar during W (69.8 ± 6.3%) and SWS (67.2 ± 4.3%), beyond which there was a brisk linear increase. During REM sleep, arousal preceded activation of EMGgg in each animal, although Sa(O₂) at arousal (61.3 ± 4.4%) was less than the Sa(O₂) threshold for EMGgg activation during W or SWS (p < 0.05). Despite state-related differences in the individual muscle responses, simultaneous EMGgg and EMGdi during hypoxia or hypercapnia in W, and during hypoxia in SWS and REM sleep, were linked in a constant manner. This suggests common integration of central and peripheral chemoreceptor inputs. Furthermore, these relationships are unaffected by either SWS or REM sleep.