Inhibition of inspiratory motor output by high-frequency low-pressure oscillations in the upper airway of sleeping dogs

1. We utilized a chronically tracheostomized, unanaesthetized dog model to study the reflex effects: on inspiratory motor output of low-amplitude, hig h-frequency pressure oscillations (HFPOs) applied to the isolated upper air way (UA) during stable non-rapid eye movement (NREM) sleep. 2. HFPOs (30 Hz and +/-2 to +/-4 cmH(2)O) were applied via a piston pump du ring eupnoea, inspiratory resistive loading and tracheal occlusion. 3. When applied to the patent UA during expiration, and especially during l ate expiration, HFPOs prolonged expiratory time (T-E) and tonically activat ed the genioglossus muscle EMG. When applied to the patent UA during inspir ation, HFPOs caused tonic activation of the genioglossus muscle EMG and inh ibition of inspiratory motor output by either: (a) a shortening of inspirat ory time (T-I), as inspiration was terminated coincident with the onset of HFPOs; or (b) a prolonged T-I accompanied by a decreased rate of rise of di aphragm EMG and rate of fall of tracheal pressure. These effects of HFPOs w ere observed during eupnoea, and inspiratory resistive loading, but were ma ximal during tracheal occlusion where the additional inhibitory effects of lung inflation reflexes were minimized. 4. During eupnoea, topical anaesthesia of the UA abolished the HFPO-induced prolongation of T-E, suggesting that the response was mediated primarily b y mechanoreceptors close to the mucosal surface, whereas the T-E-prolonging effects of a sustained square wave of negative pressure (range, -4.0 to -1 4.9 cmH(2)O) sufficient to close the airway mere preserved following anaest hesia. 5. These results demonstrate that high-frequency, low-amplitude oscillatory pressure waves in the UA, similar to those found in snoring, produce refle x inhibition of inspiratory motor output. This reflex may help maintain UA patency by decreasing the collapsing pressure generated bg the inspiratory pump muscles and transmitted to the UA.