Sudden infant death syndrome, sleep, and seizures.

WORKING HYPOTHESIS: benign febrile seizures seen in 7% of infants before 6 months play a role in the terminal pathway in a subset of sudden infant death syndrome victims. Supporting evidence: (1) lack of 5-hydroxitryptamine, one consistent finding in sudden infant death syndrome that Kinney et al coined a developmental serotonopathy, is consistent with risk for seizures. (2) Non-rapid eye movement sleep increasing during the age of highest risk for sudden infant death syndrome facilitates some seizures (seizure gate). (3) Sudden unexpected death in epilepsy is associated with severe hypoxemia and hypercapnia during postictal generalized electroencephalographic (EEG) suppression. In toddlers, sudden unexplained deaths are associated with hippocampal abnormalities and some seizures. (4) The sudden nature of both deaths warrants an exploration of similarities in the terminal pathway. Moreover, sudden infant death syndrome, febrile seizures, sudden unexplained death in childhood, and sudden unexpected death in epilepsy share some of the following risk factors: prone sleeping, infections, hyperthermia, preterm birth, male gender, maternal smoking, and mutations in genes that regulate sodium channels. State-of-the-art molecular studies can be exploited to test this hypothesis.

The development of the circadian heart rate rhythm (CHR) in Asian infants.

OBJECTIVE: To test the hypothesis that term-born Asian infants, at reduced risk to die of Sudden Infant Death Syndrome (SIDS) exhibit a circadian heart rate rhythm (CHR) at a later age than non-Asian term infants. METHOD: Repeated overnight heart rate (HR) traces obtained with a battery-operated Polar S810i heart-rate monitor at home in 17 Asian Torajan infants in Indonesia, were compared with those of 52 non-Asian infants monitored as part of the Collaborative Home Infant Monitoring Evaluation (CHIME). HR was determined using a moving window averaging technique. A comparison of median HR during quiet sleep (QS) episodes (identified by minimum HR variability), established the presence of CHR. RESULTS: Seventy three percent of non-Asian CHIME infants ≤7 weeks exhibited CHR compared to 45% of Asian Torajan infants. Between 8 and 12 weeks, 94% of non-Asian CHIME infants exhibited CHR, compared to 33% of Asian Torajan infants (p<0.001). Forty seven and 56% of Asian Torajan infants exhibited the CHR at the age intervals of 16-20 weeks and 21-25 weeks respectively. Active wakefulness percentages as a function of the entire recording and median QS HR were not significantly different in the two groups. CONCLUSION: Despite the fact that Asian Torajan infants were on average a week older than non-Asian CHIME babies, between two and three months of age only one in three exhibited the CHR, compared to virtually all non-Asian CHIME infants. We speculate that the cause of this difference rests in the infants' environment rather than their genetic origin.

Extreme and conventional cardiorespiratory events and epidemiologic risk factors for SIDS.

OBJECTIVE: To test the hypotheses that there is a lack of correlation between extreme events and epidemiologic risk factors for sudden infant death syndrome (SIDS), and if conventional events are normal, their numbers should increase once a circadian decrease in breathing rate is established. In addition, the number of events should decrease with maternal smoking. STUDY DESIGN: Three outcome variables were derived from the Collaborative Home Infant Monitoring Evaluation (CHIME) of 1082 infants: (1) at least 1 extreme event lasting > or = 30 seconds, (2) at least 1 conventional event lasting > or = 20 seconds, and (3) being part of the 50% of infants with the most events. RESULTS: Multivariate logistic regression analyses found that extreme events were not statistically associated with any known SIDS risk factors and occurred less often during the early morning. Healthy term infants had significantly fewer of these events compared with preterm infants, subsequent siblings of infants with SIDS, and infants with an apparent life-threatening event, a finding that was not evident after 43 weeks (3 weeks postterm). Conventional events increased during the night, whereas maternal smoking was associated with a decrease in conventional events. Apneic episodes persisting for > or = 40 seconds occurred in 1.8% of the infants. CONCLUSIONS: Extreme events are associated with immaturity and do not seem to be immediate precursors of or causally related to SIDS.

Apparent life-threatening events and sudden infant death syndrome: comparison of risk factors.

OBJECTIVE: To compare the risk factors of 153 cases of apparent life-threatening event (ALTE) enrolled in the multicenter Collaborative Home Infant Monitoring Evaluation (CHIME) from 1994 to 1998 with the published risk factors for sudden infant death syndrome (SIDS). STUDY DESIGN: Trained CHIME interviewers gathered histories of infants with ALTE who met the criteria. The following risk factors were analyzed: male predominance, gestational age, low birth weight, very low birth weight, incidence of small for gestational age (SGA), age at the event, multiparity, maternal age, and smoking. Population-based SIDS studies with >100 deaths, focusing on 1 or more pertinent risk factors and carried out during the decade in which CHIME data were collected, were chosen for comparison. RESULTS: One of the 153 infants with ALTE in this study died during follow-up (0.6%). CHIME ALTE differed significantly from SIDS in 4 respects: fewer infants with low birth weight and SGA at birth, fewer teenage pregnancies, and a younger infant age at ALTE. CONCLUSIONS: Although a number of risk factors for ALTE are similar to those for SIDS, the differences warrant a separate focus on ALTE beyond that on SIDS.

Sleep architecture in term and preterm infants beyond the neonatal period: the influence of gestational age, steroids, and ventilatory support.

STUDY OBJECTIVE: To examine (1) sleep architecture of infants at varied risk for sudden infant death syndrome, (2) delays or advances in preterm infants at term postmenstrual age, (3) whether ventilatory support and gestational age alter sleep, (4) whether steroids alter sleep, (5) confounding influences of sex, small for gestational age, and maternal smoking. DESIGN: Overnight polysomnography. DEPENDENT VARIABLES: Percentage of active sleep, quiet sleep, indeterminate, and awake time per total recording time; mean and longest duration of state epochs; number of episodes > or = 10 minutes; and sleep efficiency. SETTING: Collaborative Home Infant Monitoring Evaluation (CHIME). PARTICIPANTS: Two hundred one preterm and 198 term infants between 33 and 58 weeks postmenstrual age during polysomnography. Fifty-one term infants with an apparent life-threatening event without known etiology (apnea of infancy), 59 subsequent siblings of babies who died of sudden infant death syndrome, and 88 healthy term infants. RESULTS: Tracings of infants with apnea of infancy and healthy term infants were similar. Subsequent siblings of babies who died of sudden infant death syndrome spent less time in quiet sleep. Preterm infants (< or = 37 weeks postmenstrual age) exhibited immature architecture compared with infants of term postmenstrual age. The latter exhibited similar sleep except that they had a lower percentage of quiet sleep and longer mean indeterminate and longest indeterminate episodes. Preterm infants with the youngest gestational age lagged behind older preterm infants. Neither sex nor use of steroids affected sleep. Assisted ventilation was associated with a delay in maturation, small-for-gestational age status with increased active sleep, and smoking with increased awake time. CONCLUSION: With few exceptions, asymptomatic premature infants do not exhibit significant delays in sleep architecture compared with term infants at comparable postmenstrual age. The preterm infant with an early gestational age and morbidity exhibited delayed sleep architecture.

Factors that influence use of a home cardiorespiratory monitor for infants: the collaborative home infant monitoring evaluation.

BACKGROUND: As part of the Collaborative Home Infant Monitoring Evaluation, a home monitor was developed to record breathing, heart rate, other physiologic variables, and the time the monitor was used. OBJECTIVE: To determine the frequency of monitor use, factors that influence use, and validity of a model developed to predict use. DESIGN: We developed a model to predict monitor use using multiple linear regression analysis; we then tested the validity of this model to predict adherence for the first week of monitoring and for the subsequent 4-week period (weeks 2-5). SETTING: Clinical research centers in Chicago, Ill; Cleveland, Ohio; Honolulu, Hawaii; Los Angeles, Calif; and Toledo, Ohio. Patients Preterm infants, infants younger than 1 month with a history of autopsy-confirmed sudden infant death syndrome in a sibling, and infants with an idiopathic apparent life-threatening event were divided into 2 cohorts based on enrollment date. Main Outcome Measure Mean hours of monitor use per week. RESULTS: In cohort 1, the variables available before monitoring were only weakly associated with total hours of monitor use in weeks 2 to 5 (total model r(2) = 0.08). However, when hours of monitor use in week 1 were included as a variable to predict monitor use in weeks 2 to 5, the r(2) increased to 0.64 for hours of monitor use per week. CONCLUSIONS: Our data show that monitor use in the first week was the most important variable for predicting subsequent monitor use. The study suggests that a major focus of home monitoring should be adherence in the first week, although it remains to be tested whether this adherence can be altered.