DECREASED CARDIAC RESPONSES TO AUDITORY-STIMULATION DURING PRONE SLEEP

Objective. To evaluate the relationship between body position during s leep and the infants' cardiac responses to auditory stimulation. Metho ds. Thirty healthy infants with a median age of 11 weeks were studied polygraphically for one night, while sleeping successively prone and s upine, or vice versa. Their behavioral and cardiac responses were reco rded during rapid eye movement (REM) sleep, both before and after expo sure to 90 dB (A) of white-noise. Results. Ten infants were excluded f rom the study, because they woke up during the challenge. For the 20 i nfants included in the analysis, no significant difference was seen be tween the prone and the supine position for total sleep time, sleep ef ficiency, percent of REM and nonrapid eye movement sleep, number of gr oss body movements, transcutaneous oxygen saturation levels, mean card iac rate, heart rate variability, number of heart rate drops; mean res piratory rate, and number or duration of central or obstructive apneas . Auditory challenges induced significantly less overall changes in he art rate, less heart rate drops, less heart rate variability, as well as fewer and shorter central apneas in the prone than in the supine po sition. Autoregressive power spectral analysis of the heart rate was c onsistent with a possible increase in orthosympathetic tone in the pro ne position. Conclusion. Prone sleeping was associated with a decrease in cardiac responses to auditory stimulation and a possible increase in orthosympathetic activity. Prone positioning could favor a reduced reactivity to danger-signaling stimuli during REM sleep.