Muscle relaxation attenuates the reflex response to laryngeal negative pressure

Negative pressure (NP) within the upper airway (UA) excites the activity of the genioglossus muscle and other UA dilators. For unknown reasons this reflex response is attenuated during sleep. Sleep reduces skeletal muscle tone, therefore we hypothesized that the magnitude of the pressure reflex is modulated by muscle tension. We have compared the threshold and the magnitude of the reflex response to laryngeal NP before and during muscle relaxation in 16 rabbits. The threshold increased from 7 +/- 2 (mean +/- S.D.) to 17 +/- 4 cm H2O. Peak amplitude during NP pulse dropped from 167 to 139 arbitrary units (a.u.) for the hypoglossal nerve (n.XII) and from 134 to 114 a.u. for the facial nerve (n.VII). Independently of the pressure reflex muscle relaxation reduced the phasic n.XII activity by 18% and tonic activity by 20%. We conclude that muscle atonia attenuates n.XII activity and the response to UA pressure change. Our findings when extrapolated to state of sleep suggest that sleep-induced muscle relaxation may be an independent factor suppressing pressure reflex. (C) 1997 Elsevier Science B.V.