EFFECT OF UPPER AIRWAY NEGATIVE-PRESSURE ON INSPIRATORY DRIVE DURING SLEEP

To determine the effect of upper airway (UA) negative pressure and col lapse during inspiration on regulation of breathing, we studied four u nanesthetized female dogs during wakefulness and sleep while they brea thed via a fenestrated tracheostomy tube, which was sealed around the permanent tracheal stoma. The snout was sealed with an airtight mask, thereby isolating the UA when the fenestration (Fen) was closed and ex posing the UA to intrathoracic pressure changes, but not to flow chang es, when Fen was open. During tracheal occlusion with Fen closed, insp iratory time (TI) increased during wakefulness, non-rapid-eye-movement (NREM) sleep and rapid-eye-movement (REM) sleep (155 +/- 8, 164 +/- 1 1, and 161 +/- 32%, respectively), reflecting the removal of inhibitor y lung inflation reflexes. During tracheal occlusion with Fen open (vs . Fen closed) 1) the UA remained patent; 2) TI further increased durin g wakefulness and NREM (215 +/- 52 and 197 +/- 28%, respectively) but nonsignificantly during REM sleep (196 +/- 42%); 3) mean rate of rise of diaphragm EMG (EMGdi/TI) and rate of fall of tracheal pressure (Ptr /TI) were decreased, reflecting an additional inhibitory input from UA receptors; and 4) both EMGdi/TI and Ptr/TI were decreased proportiona tely more as inspiration proceeded, suggesting greater reflex inhibiti on later in the effort. Similar inhibitory effects of exposing the UA to negative pressure (via an open tracheal Fen) were seen when an insp iratory resistive load was applied over several breaths during wakeful ness and sleep. These inhibitory effects persisted even in the face of rising chemical stimuli. This inhibition of inspiratory motor output is alinear within an inspiration and reflects the activation of UA pre ssure-sensitive receptors by UA distortion, with greater distortion po ssibly occurring later in the effort.