Decreased autonomic responses to obstructive sleep events in future victims of sudden infant death syndrome

To evaluate changes in autonomic nervous system controls in response to obs tructive events in future victims of sudden infant death syndrome (SIDS), w e studied the polysomnographic sleep recordings of 18 future SIDS infants a nd those of 36 matched control infants. A heart rate autoregressive power s pectral analysis was performed preceding and after the obstructive apneas. The low-frequency to high-frequency power ratio was computed to evaluate sy mpathovagal balance, Future SIDS victims had significantly more obstructive apneas (p = 0.001) and mixed apneas (p = 0.005) than control infants. Obst ructive events occurred mainly during rapid eye movement sleep in the two p opulations (84.5% in future SIDS victims and 95.8% in control infants; p = NS). Comparing heart rate power spectral analysis before and after obstruct ive apneas in rapid eye movement sleep, high-frequency power values were si gnificantly lower and low-frequency to high-frequency power ratios higher i n future SIDS victims than in control infants. Compared with preapnea value s, low-frequency to high-frequency power ratios significantly decreased aft er obstructive apneas in control infants (p < 0.001) but not in the future SIDS victims. When the obstructive apneas were divided according to duratio n, the findings were seen mainly for long apneas. In conclusion, future SID S victims were characterized by different autonomic status and responses to obstructive apneas during sleep. These findings could be relevant to mecha nisms implicated in some cases of SIDS.