Arousal responses and risk factors for sudden infant death syndrome
Introduction
Despite the dramatic decline in the incidence of sudden infant death syndrome (SIDS) following world-wide education programmes, SIDS still remains the major cause of death in infants between 1 month and 1 year of age [1], [2]. Arousal from sleep is believed to be an important survival mechanism that may be impaired in victims of SIDS [3]. A prospective study found that infants who subsequently died from SIDS had fewer body movements during sleep compared with controls [4]. Additionally, post-mortem examinations of infants dying of SIDS have identified abnormalities in brain regions associated with arousal [5].
Epidemiological studies in a number of western countries have identified various factors, which increase the risk of an infant dying from SIDS. The prone sleeping position has been identified as one of the major risk factors for SIDS in numerous studies [6], [7], [8], [9], [10], [11]. With the reduction in the incidence of infants being put to sleep prone, maternal smoking has become the major modifiable risk factor for SIDS [6]. Preterm and low birth-weight infants are also at increased risk for SIDS, and this increase is inversely related to gestational age [12], [13], [14], [15], [16], [17]. It has been estimated that approximately 20% of all SIDS cases occur in the preterm population [15], [16], [17]. Approximately half of the SIDS victims in some studies had slight respiratory infection prior to death [18]. Many of the developmental and environmental risk factors associated with SIDS, such as peak age of occurrence, seasonal distribution, prone sleeping and maternal smoking, are also associated with susceptibility of infants to infection, particularly that of upper respiratory tract infection [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29].
This paper will review the effects of these major risk factors for SIDS on infant arousability. The studies will focus on the work carried out by our laboratory over the past 5 years.
Section snippets
Methods
All subjects were recruited from the Monash Medical Centre, Melbourne, Australia. Written informed consent was obtained from parents prior to commencement of the study, and no monetary incentive was provided for participation. The Monash Medical Centre Human Ethics Committee granted approval for these projects.
Sleep state
Our studies have shown that arousal from sleep in response to air-jet stimulation is affected by sleep state in both term and preterm infants, with arousal thresholds being significantly elevated in QS compared to AS [31], [32], [33], [34], [35], [36], [37]. We have recently demonstrated that the same sleep-state difference in arousability occurs in response to 15% O2 over the first 6 months of life when arousability is measured as both probability of arousal and arousal latency [38].
Sleeping position
We have
Discussion
Arousal from sleep is an important response that may protect an infant from a life-threatening event and impairment in arousability has been postulated as a likely mechanism to explain SIDS [3]. Our studies have demonstrated that the major risk factors for SIDS identified from epidemiological studies, prone sleeping position, maternal smoking, prematurity and recent infection, also decrease arousability from sleep in infants. We propose that this decreased arousability from sleep may be
Acknowledgements
This project was supported by SIDSaustralia, Sudden Infant Death Research Foundation of South Australia and SIDassist.
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