Sudden Infant Oeath Syndrome (SIOS): An Integration of Ontogenetie Pathologie, Physiologie and Epidemiologie Faetors1

Sudden Infant Death Syndrome (SIDS) is the most prevalent cause of death in infants between one and six months of age. Epidemiologie pathologie and physiologie data suggest tbe meehanism of SIDS is complex, characterized by interactions at many levels of the neuraxis, between the organism and tbe environment and spanning both preand post-natal life. Details of one such model are presented here. The model is based on I) systematic physiological studies of two groups of infants at statistically inereased risk for SIDS: subsequent siblings and near-miss for SIDS. 2) An epidemiological study of approximately 800 SIDS in Los Angeles County, and 3) clinical perinatal data and fetal heart rate recordings of a subset oftbese 800 SIDS. Data from other investigators are incorporated as weil. Factors unique to SIDS are: Age of death, association with sleep, seasonal distribution and increased risk for the second born. Tbe proposed core deficit eonsists of mild hypoxia, sustained during preand post-natal life, for which the majority of infants successfully eompensates. Previously not fully appreciated changes between one and three months of age in development and integration of the central nervous system, give rise to increased vulnerability to endogenous and exogenous deleterious influences at this time. Altered sleep state distributions consisting of an increase in Quiet sleep (QS) and a decrease in Aetive sleep (AS), are temporally and funetionally associated with alterations in respiratory and eardiae regulation. Some infants pass through this age period sooner, at a faster rate and with less reserve and thus are more susceptible to additional stress. Althougb the etiology of the core deficit is unknown, many factors can potentiate an existing mild hypoxia. One such potential mechanism is the influenee of amI This research was supported by the National Institute of Child Health and Human Development Contract :#: No I-HD-2-2777, HD4-2810 and Grant :#: HO 13689-02, donations in memory of SIDS and contributions from the San Gabriel and Orange County chapters ofthe Guild for Infant Survival. bient pollutants. Other mild deficieneies ofvaried origin operate as predisposing faetors to risk or preeipitating events causing death. A large number of infants would be expected to be stressed but only an unfortunate interseetion ofprior vulnerability and one or more aggravating conditions encountered during a diserete limited age of risk would result in death. Many nonspeeifie factors associated with SIDS are identical to those assoeiated with perinatal morbidity and mortality. Programs aimed at reducing the latter should substantially reduee the rate ofSIDS as weIl.