RESPIRATORY AND AROUSAL RESPONSES TO ACOUSTIC STIMULATION

Study objectives: Although sleep-related obstructive apnea is most oft en associated with transient arousal, the impact of this arousal on re spiratory control remains unclear. We tested the hypotheses that acous tic arousing stimulation can generate a significant respiratory respon se during sleep in healthy subjects and that the magnitude or timing o f this response is affected by the presence of electrocortical arousal or inhaled carbon dioxide. Design: We employed binaural tone bursts ( 0.5-s duration, 4-KHz center frequency, 99-s interstimulus interval) t o elicit repetitive transient arousals from sleep during nocturnal pol ysomnographic recordings beginning at 10 PM and ending at 6 AM. Partic ipants: Recordings mere conducted in five healthy adult volunteers age d 24 to 37 rears. Interventions: Inspired gas was alternated between r oom air and 3% to 7% CO2 (titrated to yield an approximate 50% increas e in minute ventilation) at l-h intervals. Measurements and results: E ach 30-s epoch was scored for sleep/wake stage according to standard c riteria. Only results obtained during nonrapid eve movement sleep are presented herein. Tone-evoked arousals were detected by computer analy sis as increased EEG frequency occurring within 3 s of acoustic stimul ation. For each tone, respiratory parameters for each of three prestim ulus and four poststimulus breaths were normalized to the overall mean of prestimulus breaths measured during room air breathing for each su bject. Tone bursts elicited repetitive transient arousals with a mean duration of approximately 10 s from all stages of sleep. With respect to the three prestimulus breaths, acoustic stimulation was associated with increased tidal volume and decreased inspiratory duration for at least four breaths. These respiratory responses to acoustic stimulatio n were not significantly influenced by either presence of transient ar ousal from sleep or inspired gas. Conclusions: We conclude that transi ent EEG arousal may be repeatedly evoked from nonrapid eye movement sl eep by transient acoustic stimulation in normal sleepers. This sensory stimulation is associated with augmented ventilation, a response that is not significantly affected by inspired hypercapnia or the presence of generalized EEG arousal.