Respiratory and arousal responses to acoustic stimulation.

STUDY OBJECTIVES

Although sleep-related obstructive apnea is most often associated with transient arousal, the impact of this arousal on respiratory control remains unclear. We tested the hypotheses that acoustic arousing stimulation can generate a significant respiratory response during sleep in healthy subjects and that the magnitude or timing of 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) to elicit repetitive transient arousals from sleep during nocturnal polysomnographic recordings beginning at 10 PM and ending at 6 AM.

PARTICIPANTS

Recordings were conducted in five healthy adult volunteers aged 24 to 37 years.

INTERVENTIONS

Inspired gas was alternated between room air and 3% to 7% CO2 (titrated to yield an approximate 50% increase in minute ventilation) at 1-h intervals.

MEASUREMENTS AND RESULTS

Each 30-s epoch was scored for sleep/wake stage according to standard criteria. Only results obtained during nonrapid eye movement sleep are presented herein. Tone-evoked arousals were detected by computer analysis as increased EEG frequency occurring within 3 s of acoustic stimulation. For each tone, respiratory parameters for each of three prestimulus and four poststimulus breaths were normalized to the overall mean of prestimulus breaths measured during room air breathing for each subject. 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 stimulation were not significantly influenced by either presence of transient arousal from sleep or inspired gas.

CONCLUSIONS

We conclude that transient EEG arousal may be repeatedly evoked from nonrapid eye movement sleep 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.