Inverse association between Slow Wave Activity per cycle and the number of ultradian sleep cycles per night in healthy humans.

OBJECTIVE: Comparisons of sleep Slow Wave Activity (SWA) during successive sleep cycles rely on the assumption that SWA in a given cycle is independent of the number of ultradian cycles present in a night. This assumption was evaluated here. METHODS: Twenty-six healthy controls with no medical, sleep or psychiatric disorders were selected among 84 candidates and their sleep was recorded at home across 2 consecutive nights after two habituation nights. RESULTS: In comparison with nights with less cycles, nights with more cycles showed significantly more REMS but not more NREMS. No correlation was found between the number of cycles and the integrated SWA per night (epochs visually scored as NREMS). However, inverse correlations were found between the number of cycles and the SWA per cycle. This was significant on both nights in Cycle 1 and strong trends were found for the two subsequent cycles on Night 2. Comparable results were found after removal of nights containing suspected Skipped First REMS episodes. CONCLUSIONS: The SWA in a cycle was found to be inversely correlated to the number of cycles in the first 3 cycles in at least one of the two analyzed nights. SIGNIFICANCE: Differences in the number of cycles per night are a potential bias in the comparisons of SWA per cycles.

Physiological relationship between autonomic reactions and arousals in infancy.

OBJECTIVE: Changes in blood pressure (BP) were measured following auditory stimuli in the prone and the supine position to study the correlation between arousal from sleep and autonomic responses. METHOD: Two newborns born at term, two infants and four children were recorded polygraphically during one night, while sleeping in the prone and the supine position. They were exposed to white noises of increasing intensities during both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep in each position. BP changes were measured by Finapress in the children and by pulse transient time (PTT) in the infants and newborns. RESULTS: Basal systolic BP pressures were lower (P<0.001) and PTT were higher (P=0.008) in the prone than in the supine position in children and in infants. Following the auditory stimulations, the increases in systolic BP (P=0.024) and the decreases in PTT (P=0.006) were smaller in prone than in supine position. During cortical arousals, the same findings were found, independently of sleep stages. CONCLUSION: Compared with when they are sleeping supine, children and infants sleeping prone had lower basal BP and higher PTT and smaller changes in BP and PTT after auditory stimulation. Reduced BP changes to stimuli could be implicated in the increased arousal thresholds in prone position.

Pacifier use modifies infant's cardiac autonomic controls during sleep.

OBJECTIVE: The risk for sudden infant death (SIDS) was postulated to decrease with the use of a pacifier and by conditions increasing parasympathetic tonus during sleep. We evaluated the influence of a pacifier on cardiac autonomic controls in healthy infants. STUDY DESIGN: Thirty-four healthy infants were studied polygraphically during one night: 17 infants regularly used a pacifier during sleep and 17 never used a pacifier. Thumb users or occasional pacifier users were not included in the study. The infants were recorded at a median age of 10 weeks (range 6-18 weeks). Autonomic nervous system (ANS) was evaluated by spectral analysis of the heart rate (HR). The high frequency component of HR spectral analysis reflected parasympathetic tonus and the low frequency on high frequency ratio corresponded to the sympathovagal balance. RESULTS: Most infants (63.6%) lost their pacifier within 30 min of falling asleep. Sucking periods were associated with increases in cardiac sympathovagal balance. During non-sucking periods, in both REM and NREM sleep, infants using a pacifier were characterized by lower sympathetic activity and higher parasympathetic tonus compared with non-pacifier users. CONCLUSIONS: The use of pacifiers modifies cardiac autonomic controls during both sucking and non-sucking sleep periods. Non-nutritive sucking could regulate autonomic control in infants. These findings could be relevant to mechanisms implicated in the occurrence of sudden infant deaths during sleep.