Respiratory frequency during sleep in siblings of sudden infant death syndrome victims. A comparison with control, normal infants.

The present study was carried out on 76 polygraphic recordings performed on 38 siblings of sudden infant death syndrome victims and on 38 control (2 days to 18 weeks old) infants. Each sibling corresponded to a control infant according to gender, gestational age at birth and postnatal age criteria. We found that in siblings as in controls, respiratory frequency (RF) was higher in active sleep (AS) compared to quiet sleep (QS) state (P less than 0.05 for 11-18 week siblings, p less than 0.01 for the other groups). During the transitional sleep (TS), RF was on an intermediate level (AS greater than TS greater than QS). There were no significant differences between RF of siblings compared to controls, except that RF during QS in 6-10 week control infants was higher than in siblings of the same age (P less than 0.05). We found a wide variability between RF of different individuals within all the age groups of siblings and of controls (P less than 0.001). However, a high correlation was usually noted between RF found in different sleep states: some infants (siblings or controls) breathed more rapidly and others more slowly in all states studied. In siblings, as previously described in other groups of normal infants, RF seems to be an individual characteristic. In addition, the present work shows that according to RF criterion, healthy siblings are similar to normal infants.