Increased cardiac autonomic responses to auditory challenges in swaddled infants.

STUDY OBJECTIVES: When infants have been swaddled and sleep supine, their risk of dying from sudden infant death syndrome (SIDS) is reduced with an odds ratio of 0.64 to 0.69. Alternatively, the risk for SIDS in swaddled infants shows a 3-fold increase in the prone position. The protective role of swaddling during supine sleep has remained unexplained. This study was designed to evaluate the effects of swaddling on cardiac reactivity to auditory stimuli during sleep in both the prone and the supine position. DESIGN: Thirty healthy infants with a median age of 11 weeks (range 8 to 15 weeks) were studied polygraphically for 1 night while sleeping successively prone and supine, or vice versa. The infants were studied while swaddled and nonswaddled in both positions. Heart rates were studied during rapid eye movement sleep, before and after exposure to 90 dB(A) of white-noise. RESULTS: Ten infants were excluded from the study because they woke up during the position change or the auditory challenge. Before the administration of the noise stimulus, swaddling decreased values of basal heart rates in the supine position only (P = .049). Following swaddling, the values of basal heart rate were significantly lower in the supine than in the prone position (P = .003). Auditory challenges were followed by a greater increase in heart rate when the supine sleeping infants were swaddled than when not swaddled (P = .018). When swaddled, beat-to-beat heart-rate variability increased following auditory stimulation in the supine position only (P = .012). CONCLUSION: When sleeping supine, swaddled infants had greater cardiac autonomic changes in response to noise challenges than when they were not swaddled.