EFFECT OF TOPICAL UPPER AIRWAY ANESTHESIA ON APNEA DURATION THROUGH THE NIGHT IN OBSTRUCTIVE SLEEP-APNEA

It has previously been reported that the duration of obstructive apnea s increases from the beginning to the end of the night (M. Charbonneau , J. M. hlarin, A. Olha, R. J. Kimoff, R. D. Levy, and M. Cosio. Chest 106: 1695-1701, 1994). The purpose of this study was to test the hypo thesis that stimulation of upper airway (UA) sensory receptors during obstructed inspiratory efforts contributes to arousal and apnea termin ation and that a progressive attenuation of this mechanism through the night contributes to apnea lengthening. We studied seven patients (si x men, one woman) with severe obstructive sleep apnea (apnea-hypopnea index = 93 +/- 26 events/h) during two consecutive nights of polysomno graphic monitoring. On one night (random order), we performed topical UA anesthesia with 0.2% tetracaine and on the control night, sham anes thesia. We measured apnea duration, esophageal pressure (Pes) during a pneas, and apneic O-2 desaturation. Consistent with previous findings, apnea duration, number of efforts per apnea, and peak Pes at end apne a increased from the beginning to the end of the control nights. UA an esthesia produced a significant increase in apnea duration at the begi nning of the night but no change in apnea length at the end of the nig ht. Peak Pes and the rate of increase in Pes during the anesthesia nig hts were greater than during control nights, but the rate of increase in Pes was similar for the beginning and end of the control and anesth esia nights. These findings suggest that UA sensory receptors play a r ole in mediating apnea termination at the beginning of the night but t hat the contribution of these receptors diminishes as the night progre sses such that greater inspiratory efforts are required to trigger aro usal, leading to apnea prolongation.