Maternal smoking and sudden infant death syndrome: epidemiological study related to pathology

Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part II. Age-associated alterations in serotonin receptor binding profiles within medullary nuclei supporting cardiorespiratory homeostasis

The failure of chemoreflexes, arousal, and/or autoresuscitation to asphyxia may underlie some sudden infant death syndrome (SIDS) cases. In Part I, we showed that some SIDS infants had altered 5-hydroxytryptamine (5-HT)2A/C receptor binding in medullary nuclei supporting chemoreflexes, arousal, and autoresuscitation. Here, using the same dataset, we tested the hypotheses that the prevalence of low 5-HT1A and/or 5-HT2A/C receptor binding (defined as levels below the 95% confidence interval of controls-a new approach), and the percentages of nuclei affected are greater in SIDS versus controls, and that the distribution of low binding varied with age of death. The prevalence and percentage of nuclei with low 5-HT1A and 5-HT2A/C binding in SIDS were twice that of controls. The percentage of nuclei with low 5-HT2A/C binding was greater in older SIDS infants. In >80% of older SIDS infants, low 5-HT2A/C binding characterized the hypoglossal nucleus, vagal dorsal nucleus, nucleus of solitary tract, and nuclei of the olivocerebellar subnetwork (important for blood pressure regulation). Together, our findings from SIDS infants and from animal models of serotonergic dysfunction suggest that some SIDS cases represent a serotonopathy. We present new hypotheses, yet to be tested, about how defects within serotonergic subnetworks may lead to SIDS.

Autopsy for Medical Diagnostics: Finding the Cause of Sudden Unexpected Death through Investigation of the Cardiac Conduction System by Serial Sections

Sudden unexpected death (SUD) is a fatal event that occurs in an apparently healthy subject in a way that such an abrupt outcome could have not been predicted. SUD-including sudden intrauterine unexplained death (SIUD), sudden neonatal unexpected death (SNUD), sudden infant death syndrome (SIDS), sudden unexpected death of the young (SUDY), and sudden unexpected death in the adult (SUDA)-occurs as the first manifestation of an unknown underlying disease or within a few hours of the presentation of a disease. SUD is a major unsolved, shocking form of death that occurs frequently and can happen at any time without warning. For each case of SUD, a review of clinical history data and performance of a complete autopsy, particularly focused on the study of the cardiac conduction system, were carried out according to the necropsy protocol devised by the Lino Rossi Research Center, Università degli Studi di Milano, Italy. Research cases collected and selected for this study were represented by 75 SUD victims that were subdivided into 15 SIUD, 15 SNUD, 15 SUDY, and 15 SUDA victims. After a routine autopsy and clinical history analysis, death remained unexplained, and hence a diagnosis of SUD was assigned to 75 subjects, which included 45 females (60%) and 30 (40%) males ranging in age from 27 gestational weeks to 76 years. Serial sections of the cardiac conduction system disclosed frequent congenital alterations of the cardiac conduction system in fetuses and infants. An age-related significant difference in distribution among the five age-related groups was detected for the following anomalies of the conduction system: central fibrous body (CFB) islands of conduction tissue, fetal dispersion, resorptive degeneration, Mahaim fiber, CFB cartilaginous meta-hyperplasia, His bundle septation, sino-atrial node (SAN) artery fibromuscular thickening, atrio-ventricular junction hypoplasia, intramural right bundle branch, and SAN hypoplasia. The results are useful for understanding the cause of death for all SUD cases that were unexpected and would have otherwise remained unexplained, so as to motivate medical examiners and pathologists to perform more in-depth studies.

Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part I. Tissue-based evidence for serotonin receptor signaling abnormalities in cardiorespiratory- and arousal-related circuits

The sudden infant death syndrome (SIDS), the leading cause of postneonatal infant mortality in the United States, is typically associated with a sleep period. Previously, we showed evidence of serotonergic abnormalities in the medulla (e.g. altered serotonin (5-HT)1A receptor binding), in SIDS cases. In rodents, 5-HT2A/C receptor signaling contributes to arousal and autoresuscitation, protecting brain oxygen status during sleep. Nonetheless, the role of 5-HT2A/C receptors in the pathophysiology of SIDS is unclear. We hypothesize that in SIDS, 5-HT2A/C receptor binding is altered in medullary nuclei that are key for arousal and autoresuscitation. Here, we report altered 5-HT2A/C binding in several key medullary nuclei in SIDS cases (n = 58) compared to controls (n = 12). In some nuclei the reduced 5-HT2A/C and 5-HT1A binding overlapped, suggesting abnormal 5-HT receptor interactions. The data presented here (Part 1) suggest that a subset of SIDS is due in part to abnormal 5-HT2A/C and 5-HT1A signaling across multiple medullary nuclei vital for arousal and autoresuscitation. In Part II to follow, we highlight 8 medullary subnetworks with altered 5-HT receptor binding in SIDS. We propose the existence of an integrative brainstem network that fails to facilitate arousal and/or autoresuscitation in SIDS cases.

The Effect of Active and Passive Maternal Smoking During Pregnancy on the Uterine Artery Blood Flow and Obstetric Outcomes: A Prospective Study

BACKGROUND AND AIM

Maternal smoking is associated with an increased risk of obstetric and neonatal complications during pregnancy. We aimed to investigate the effects of active and passive smoking on fetal-maternal blood flow and fetal complications in mid-trimester pregnant women.

METHODS

This prospective study was conducted at Zekai Tahir Burak Women's Research and Training Hospital and included women who were 20 to 22 weeks old, with no fetal anomalies, and with a singleton pregnancy. The data used in the analysis were obtained from a total of 168 pregnant women (50 smokers, 50 passive smokers, and 68 non-smokers). Starting from their 20^th week of pregnancy, the women were examined at least once in each trimester. Fetal and maternal pregnancy results were evaluated. Fetal biometry, umbilical, and uterine artery Doppler ultrasonography were performed. To evaluate the flow in these veins, the pulsatility index, resistance index, and systole/diastole (S/D) ratio were performed.

RESULTS

The mean age of study patients was 25.06 ± 4.36 years and the mean gestational week was 20.03 ± 0.6 weeks. In terms of the umbilical artery pulsatility index (UMBAPI), umbilical artery systolic/diastolic ratio (UMBAS/D),uterine artery resistance index (UARI), uterine artery pulsatility index (UAPI), and uterine artery systolic/diastolic ratio (UAS/D) levels, the mean value of the smoker group was significantly higher compared to the non-smoker group (p<0.001, p=0.043, p=0.021, p=0.020, and p=0.037, respectively). The birth weight of the fetus was significantly lower in the active and passive smoker groups than in the non-smoker group (p=0.009 and p=0.006, respectively). The number of patients diagnosed with intrauterine growth restriction (IUGR) and oligohydramnios were significantly higher in the smoker group than in the passive smoker and non-smoker groups (p=0.003 and p<0.001, respectively). The risk of low birth weight (OR, (95% CI): 3.38 (2.05 - 5.57); p=0.024), oligohydramnios (OR (95% CI): 13.44 (5.22 - 34.57); p=0.001), IUGR (OR (95% CI): 9.33 (4.50 - 19.33); p=0.001), and preterm birth (OR (95% CI): 4.56 (1.25 - 17.32); p=0.001) increased significantly in the active and passive cigarette exposure groups, compared to the non-smokers.

CONCLUSION

During pregnancy, both smoking and passive exposure to cigarette smoke adversely affect the fetus and the newborn. Uterine and umbilical artery Doppler measurements in pregnant women who smoke are significantly higher than the pregnant women who do not smoke.

Risk of Sudden Infant Death Syndrome Among Siblings of Children Who Died of Sudden Infant Death Syndrome in Denmark

IMPORTANCE

Sudden infant death syndrome (SIDS) remains a leading cause of death during the first year of life. The etiology of SIDS is complex and remains largely unknown.

OBJECTIVE

To evaluate whether siblings of children who died of SIDS have a higher risk of SIDS compared with the general pediatric population.

DESIGN, SETTING, AND PARTICIPANTS

This register-based cohort study used Danish nationwide registers. Participants were all infants (<1 year) in Denmark between January 1, 1978, and December 31, 2016, including siblings of children who died of SIDS. Siblings were followed up from the index cases' date of SIDS, date of birth, or immigration, whichever came first, and until age 1 year, emigration, developing SIDS, death, or study end. The median (IQR) follow-up was 1 (1-1) year. Data analysis was conducted from January 2017 to October 2022.

MAIN OUTCOMES AND MEASURES

Standardized incidence ratios (SIRs) of SIDS were calculated with Poisson regression models relative to the general population.

RESULTS

In a population of 2 666 834 consecutive births (1 395 199 [52%] male), 1540 infants died of SIDS (median [IQR] age at SIDS, 3 [2-4] months) during a 39-year study period. A total of 2384 younger siblings (cases) to index cases (first sibling with SIDS) were identified. A higher rate of SIDS was observed among siblings compared with the general population, with SIRs of 4.27 (95% CI, 2.13-8.53) after adjustment for sex, age, and calendar year and of 3.50 (95% CI, 1.75-7.01) after further adjustment for mother's age (<29 years vs ≥29 years) and education (high school vs after high school).

CONCLUSIONS AND RELEVANCE

In this nationwide study, having a sibling who died of SIDS was associated with a 4-fold higher risk of SIDS compared with the general population. Shared genetic and/or environmental factors may contribute to the observed clustering of SIDS. The family history of SIDS should be considered when assessing SIDS risk in clinical settings. A multidisciplinary genetic evaluation of families with SIDS could provide additional evidence.

Pre- and early postnatal nicotine exposure exacerbates autoresuscitation failure in serotonin-deficient rat neonates

KEY POINTS

Sudden infant death syndrome (SIDS) is one of the leading causes of death during the first year of life and abnormalities linked to serotonin (5-HT) have been identified in many SIDS cases. Cigarette smoking and associated exogenous stressors, e.g. developmental nicotine exposure, may compound these serotonergic defects and any associated defects in cardiorespiratory function. Using neonatal rodent pups subjected to medullary 5-HT deficiency and perinatal nicotine exposure, we examined the impact of this interplay of factors on the neonates' ability to autoresuscitate at specific ages. In perinatal nicotine-exposed 5-HT deficient pups, impaired autoresuscitation along with significantly delayed post-anoxic recovery of normal breathing and heart rate was observed at postnatal day 10 (P10). We found that the interaction between 5-HT deficiency and perinatal nicotine exposure can significantly increase pups' vulnerability to environmental stressors and exacerbate defects in cardiorespiratory protective reflexes to repetitive anoxia during the development period.

ABSTRACT

Cigarette smoking during pregnancy increases the risk of sudden infant death syndrome (SIDS), and nicotine replacements, a key ingredient of cigarettes, have been recently prescribed to women who wish to quit smoking during their pregnancy. Serotonin (5-HT) abnormalities have been consistently identified in many SIDS cases. Here we investigated the effects of perinatal nicotine exposure in mild 5-HT deficiency rat neonates on autoresuscitation, a protective cardiorespiratory reflex. The mild 5-HT deficiency was induced by a maternal tryptophan-deficient diet, and nicotine was delivered from embryonic day (E) 4 to postnatal day (P) 10 at 6 mg kg^-1  day^-1 through an osmotic pump. In P10 rats, nicotine exposure exacerbates autoresuscitation failure (mortality) in mildly 5-HT-deficient rats to a greater extent than in controls (P = 0.029). The recovery of eupnoea and heart rate to baseline values following repetitive anoxic events (which elicit an apnoea accompanied by a bradycardia) is significantly delayed in 5-HT-deficient rats treated with nicotine, making them more susceptible to failure of autoresuscitation (eupnoea recovery: P = 0.0053; heart rate recovery: P = < 0.0001). Neither 5-HT deficiency nor nicotine exposure alone appears to affect the ability to autoresuscitate significantly when compared among the four treatments. The increased vulnerability to environmental stressors, e.g. severe hypoxia, asphyxia, or anoxia, in these nicotine-exposed 5-HT-deficient neonates during postnatal developmental period is evident.

Update on congenital heart disease and sudden infant/perinatal death: from history to future trends

During the 20th century, expert pathologists contributed an in-depth characterisation of the anatomical pathology and associated pathophysiology of congenital heart disease (CHD). Starting in the 1970s, the reported CHD birth prevalence has been increasing, owing to advances in diagnostic methods. Over the years, surgical treatments have been associated with an enormous reduction of CHD mortality. Advances also have been made in understanding the developmental biology and molecular pathogenesis of CHD. In developed countries, sudden infant death syndrome (SIDS) is the most frequent form of death during the first year of life, with a death rate of 0.42 every 1000 births. Unexpected stillbirth has a six- to eightfold greater incidence than that of SIDS and remains unexplained in 40–80% of cases even after autopsy. Specific environmental risk factors, such as maternal smoking, air and water pollution, food contamination, pesticides, etc, can interact with the genetic constitution in complex ways, which may lead to polymorphisms and/or mutations of specific genes, such as polymorphisms in the serotonin transporter gene 5-HTT, the regulator of the synaptic serotonin concentration. Current directions of research in this area are reviewed.

Anatomopathological changes of the cardiac conduction system in sudden cardiac death, particularly in infants: advances over the last 25 years

Sudden cardiac death (SCD) is defined as the unexpected death without an obvious noncardiac cause that occurs within 1 h of witnessed symptom onset (established SCD) or within 24 h of unwitnessed symptom onset (probable SCD). In the United States, its incidence is 69/100,000 per year. Dysfunctions of the cardiac conduction and autonomic nervous systems are known to contribute to SCD pathogenesis, even if most clinicians and cardiovascular pathologists lack experience with detailed examination of the cardiac conduction system and fail to recognize lesions that are crucial to explain the SCD itself. In this review, we sought to describe the advances over the last 25 years in the study of the anatomopathological changes of the conducting tissue, in SCD, in mature hearts and particularly in sudden infant death syndrome (SIDS) and sudden intrauterine unexpected death syndrome (SIUDS), through the articles published in our journal Cardiovascular Pathology (CVP). We carried out an extensive Medline search to retrieve and review all articles published in CVP in which the sudden unexpected death of one or more subjects believed healthy was reported, especially if associated with lesions of the conducting tissue in settings that revealed no other explained causes of death, particularly in infants and fetuses. The cardiac conduction findings of resorptive degeneration, His bundle dispersion, Mahaim fibers, cartilaginous meta-hyperplasia, persistent fetal dispersion, left-sided His bundle, septation of the bifurcation, atrioventricular node dispersion, sinus node hypoplasia, Zahn node, His bundle hypoplasia, atrioventricular node, and His bundle dualism were similarly detected in SIDS and SIUDS victims.

Parental smoking during pregnancy shortens offspring's legs

One of the most severe detrimental environmental factors acting during pregnancy is foetal smoke exposure. The aim of this study was to assess the effect of maternal, paternal and parental smoking during pregnancy on relative leg length in 7- to 10-year-old children. The research conducted in the years 2001-2002 included 978 term-born children, 348 boys and 630 girls, at the age of 7-10 years. Information concerning the birth weight of a child was obtained from the health records of the women. Information about the mother's and the father's smoking habits during pregnancy and about the mothers' education level was obtained from a questionnaire. The influence of parental smoking on relative leg length, controlled for age, sex, birth weight and the mother's education, as a proxy measure of socioeconomic status, and controlled for an interaction between sex and birth weight, was assessed by an analysis of covariance, where relative leg length was the dependent variable, smoking and sex were the independent variables, and birth weight as well as the mother's education were the covariates. Three separate analyses were run for the three models of smoking habits during pregnancy: the mother's smoking, the father's smoking and both parents' smoking. Only both parents' smoking showed a significant effect on relative leg length of offspring. It is probable that foetal hypoxia caused by carbon monoxide contained in smoke decelerated the growth of the long bones of foetuses.

Impaired hypercarbic and hypoxic responses from developmental loss of cerebellar Purkinje neurons: implications for sudden infant death syndrome

Impaired responsivity to hypercapnia or hypoxia is commonly considered a mechanism of failure in sudden infant death syndrome (SIDS). The search for deficient brain structures mediating flawed chemosensitivity typically focuses on medullary regions; however, a network that includes Purkinje cells of the cerebellar cortex and its associated cerebellar nuclei also helps mediate responses to carbon dioxide (CO2) and oxygen (O2) challenges and assists integration of cardiovascular and respiratory interactions. Although cerebellar nuclei contributions to chemoreceptor challenges in adult models are well described, Purkinje cell roles in developing models are unclear. We used a model of developmental cerebellar Purkinje cell loss to determine if such loss influenced compensatory ventilatory responses to hypercapnic and hypoxic challenges. Twenty-four Lurcher mutant mice and wild-type controls were sequentially exposed to 2% increases in CO2 (0-8%) or 2% reductions in O2 (21-13%) over 4 min, with return to room air (21% O2/79% N2/0% CO2) between each exposure. Whole body plethysmography was used to continuously monitor tidal volume (TV) and breath frequency (f). Increased f to hypercapnia was significantly lower in mutants, slower to initiate, and markedly lower in compensatory periods, except for very high (8%) CO2 levels. The magnitude of TV changes to increasing CO2 appeared smaller in mutants but only approached significance. Smaller but significant differences emerged in response to hypoxia, with mutants showing smaller TV when initially exposed to reduced O2 and lower f following exposure to 17% O2. Since cerebellar neuropathology appears in SIDS victims, developmental cerebellar neuropathology may contribute to SIDS vulnerability.

The impact of intrauterine tobacco exposure on the cerebral mass of the neonate based on the measurement of head circumference

The objective of the study was to assess cerebral mass, based on head circumference measurements in neonates exposed to tobacco smoke in utero, and to determine the relative proportions of the cerebral and body mass. The study included 147 neonates born in the period 2003-2004 at the Princess Anna Mazowiecka University Hospital and admitted to the Neonatal and Intensive Care Department of the Medical University in Warsaw. Subjects were divided into three groups on the basis of maternal status as active, passive, or nonsmokers determined by maternal urinary cotinine concentration and a questionnaire. Neonates whose mothers were active smokers throughout the whole period of pregnancy had a lower head circumference and in consequence a lower cerebral mass significantly more frequently when compared with those whose mothers were nonsmokers, P= 0.002. (Median difference in cerebral mass was 48.27 g.) The risk of lower cerebral mass was 3.9 (1.4-10.8, CI 95%) in the group of neonates whose mothers actively smoked cigarettes during pregnancy. A negative correlation was seen between cerebral mass and maternal urinary cotinine concentration (correlation coefficient r=-23, P= 0.006). The ratio of the cerebral to body mass was similar for neonates in all three groups. Active smoking during pregnancy had a negative effect on the cerebral mass of the neonate, however no such effect was observed in neonates whose mothers were passive smokers. The deficiency in cerebral mass increased with greater smoking intensity. Active smoking by the mother during pregnancy inhibits the growth of the brain as well as that of the body mass of the neonate.

Cardiovascular control during sleep in infants: Implications for Sudden Infant Death Syndrome

In infants the cardiorespiratory system undergoes significant functional maturation after birth and these changes are sleep-state dependent. Given the immaturity of these systems it is not surprising that infants are at risk of cardiorespiratory instability, especially during sleep. A failure of cardiovascular control mechanisms in particular is believed to play a role in the final event of Sudden Infant Death Syndrome (SIDS). The "triple risk model" describes SIDS as an event that results from the intersection of three overlapping factors: (1) a vulnerable infant, (2) a critical development period in homeostatic control, and (3) an exogenous stressor. This review summarises normal development of cardiovascular control during sleep in infants and describes the association of impaired cardiovascular control with the three overlapping factors proposed to be involved in SIDS pathogenesis.

The brainstem and serotonin in the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is the sudden death of an infant under one year of age that is typically associated with sleep and that remains unexplained after a complete autopsy and death scene investigation. A leading hypothesis about its pathogenesis is that many cases result from defects in brainstem-mediated protective responses to homeostatic stressors occurring during sleep in a critical developmental period. Here we review the evidence for the brainstem hypothesis in SIDS with a focus upon abnormalities related to the neurotransmitter serotonin in the medulla oblongata, as these are the most robust pathologic findings to date. In this context, we synthesize the human autopsy data with genetic, whole-animal, and cellular data concerning the function and development of the medullary serotonergic system. These emerging data suggest an important underlying mechanism in SIDS that may help lead to identification of infants at risk and specific interventions to prevent death.

Evidence for oxidative stress in the developing cerebellum of the rat after chronic mild carbon monoxide exposure (0.0025% in air)

BACKGROUND

The present study was designed to test the hypothesis that chronic very mild prenatal carbon monoxide (CO) exposure (25 parts per million) subverts the normal development of the rat cerebellar cortex. Studies at this chronic low CO exposure over the earliest periods of mammalian development have not been performed to date. Pregnant rats were exposed chronically to CO from gestational day E5 to E20. In the postnatal period, rat pups were grouped as follows: Group A: prenatal exposure to CO only; group B: prenatal exposure to CO then exposed to CO from postnatal day 5 (P5) to P20; group C: postnatal exposure only, from P5 to P20, and group D, controls (air without CO). At P20, immunocytochemical analyses of oxidative stress markers, and structural and functional proteins were assessed in the cerebellar cortex of the four groups. Quantitative real time PCR assays were performed for inducible (iNOS), neuronal (nNOS), and endothelial (eNOS) nitric oxide synthases.

RESULTS

Superoxide dismutase-1 (SOD1), SOD2, and hemeoxygenase-1 (HO-1) immunoreactivity increased in cells of the cerebellar cortex of CO-exposed pups. INOS and nitrotyrosine immunoreactivity also increased in blood vessels and Purkinje cells (PCs) of pups from group-A, B and C. By contrast, nNOS immunoreactivity decreased in PCs from group-B. Endothelial NOS immunoreactivity showed no changes in any CO-exposed group. The mRNA levels for iNOS were significantly up-regulated in the cerebellum of rats from group B; however, mRNA levels for nNOS and eNOS remained relatively unchanged in groups A, B and C. Ferritin-H immunoreactivity increased in group-B. Immunocytochemistry for neurofilaments (structural protein), synapsin-1 (functional protein), and glutamic acid decarboxylase (the enzyme responsible for the synthesis of the inhibitory neurotransmitter GABA), were decreased in groups A and B. Immunoreactivity for two calcium binding proteins, parvalbumin and calbindin, remained unchanged. The immunoreactivity of the astrocytic marker GFAP increased after prenatal exposure.

CONCLUSION

We conclude that exogenously supplied CO during the prenatal period promotes oxidative stress as indicated by the up-regulation of SOD-1, SOD-2, HO-1, Ferritin-H, and iNOS with increased nitrotyrosine in the rat cerebella suggesting that deleterious and protective mechanisms were activated. These changes correlate with reductions of proteins important to cerebellar function: pre-synaptic terminals proteins (synapsin-1), proteins for the maintenance of neuronal size, shape and axonal quality (neurofilaments) and protein involved in GABAergic neurotransmission (GAD). Increased GFAP immunoreactivity after prenatal CO-exposure suggests a glial mediated response to the constant presence of CO. There were differential responses to prenatal vs. postnatal CO exposure: Prenatal exposure seems to be more damaging; a feature exemplified by the persistence of markers indicating oxidative stress in pups at P20, following prenatal only CO-exposure. The continuation of this cellular environment up to day 20 after CO exposure suggests the condition is chronic. Postnatal exposure without prenatal exposure shows the least impact, whereas prenatal followed by postnatal exposure exhibits the most pronounced outcome among the groups.

Respiratory dysfunctions induced by prenatal nicotine exposure

1. Maternal tobacco smoking is the principal risk factor associated with sudden infant death syndrome (SIDS), a leading cause of death of infants under 1 year of age. Victims of SIDS show a higher incidence of respiratory control abnormalities, including central apnoeas, delayed arousal responses and diminished ventilatory chemoreflexes. 2. Nicotine is likely the link between maternal tobacco smoking and SIDS. Prenatal nicotine exposure can alter the breathing pattern and can reduce hypoxia- and hypercarbia-induced ventilatory chemoreflexes. In vitro approaches have revealed that prenatal nicotine exposure impairs central chemosensitivity, switching the cholinergic contribution from a muscarinic to a nicotinic receptor-based drive. In addition, serotonergic, noradrenergic, GABAergic, glycinergic and glutamatergic, among others, are affected by prenatal nicotine. 3. Here we propose that prenatal nicotine affects the respiratory network through two main processes: (i) reorganization of neurotransmitter systems; and (ii) remodelling of neural circuits. These changes make breathing more vulnerable to fail in early postnatal life, which could be related to the pathogenesis of SIDS.

Maternal smoking impairs arousal patterns in sleeping infants

OBJECTIVE

Impairment of the arousal process from sleep is thought to be involved in the pathogenesis of sudden infant death syndrome (SIDS). We hypothesized that a greater propensity for cortical arousal in the prone position may, in a normal infant, be a protective mechanism to promote complete arousal in a vulnerable sleeping position, a protection that is absent in SIDS victims. We aimed to examine the arousal process in a group of infants exposed to maternal smoking, who are thus at higher risk for SIDS.

DESIGN

Twelve healthy, full-term infants born to smoking mothers were studied using daytime polysomnography at 2 to 4 weeks, 2 to 3 months and 5 to 6 months postnatal age. Data were compared with 13 healthy infants born to nonsmoking mothers. Arousal was induced by pulsatile air-jet stimulation to the nostrils during active and quiet sleep, in both supine and prone positions. For each stimulus, physiologic and electroencephalogram changes were visually assessed and arousal responses were classified as sub-cortical activation or cortical arousal.

RESULTS

In smoke-exposed infants, the progression from sub-cortical activation to cortical arousal was depressed at 2 to 4 weeks and 5 to 6 months. There was no effect of maternal smoking observed at 2 to 3 months; however, a significant dose-dependent relationship between cortical activation proportions and urinary cotinine levels was present in both supine and prone positions.

CONCLUSION

We have shown that maternal smoking is associated with impaired arousal processes to trigeminal stimulation that may increase the risk for SIDS. This further highlights the importance of public education of the risks of maternal smoking.

Heart rate and blood pressure control in infants exposed to maternal cigarette smoking

AIM

Exposure to maternal cigarette smoking is a major risk factor for sudden infant death syndrome (SIDS). Foetal and postnatal smoke-exposure may alter cardiovascular control in infants. We studied heart rate (HR) and blood pressure (BP) responses in smoke-exposed infants.

METHODS

Eleven infants exposed to maternal cigarette smoking were studied at the age of 12 +/- 2.1 (range 10-16) weeks. Twenty healthy, age-matched infants from non-smoking families served as controls. During confirmed slow-wave sleep (NREM3), 3-5 sec side motion and 45 sec 45 degrees head-up tilt tests were performed.

RESULTS

Control infants showed consistent biphasic HR and BP responses to side motion, with an initial 2-5% increase followed by a 2% decrease (p < 0.0001). In smoke-exposed infants, the initial HR (p = 0.009) and BP responses (p < 0.0001) were markedly reduced, and the subsequent decrease in BP was more prominent (systolic blood pressure, SBP, p = 0.005; diastolic blood pressure, DBP, p = 0.03). No differences were observed between the groups in tilt test results, HR variability or HR responses to spontaneous arousals.

CONCLUSION

Maternal cigarette smoking may alter vestibulo-mediated cardiovascular control in early infancy. This may contribute to increased SIDS risk.

Air pollutant effects on fetal and early postnatal development

Numerical research on the health effects of air pollution has been published in the last decade. Epidemiological studies have shown that children's exposure to air pollutants during fetal development and early postnatal life is associated with many types of health problems including abnormal development (low birth weight [LBW], very low birth weight [VLBW], preterm birth [PTB], intrauterine growth restriction [IUGR], congenital defects, and intrauterine and infant mortality), decreased lung growth, increased rates of respiratory tract infections, childhood asthma, behavioral problems, and neurocognitive decrements. This review focuses on the health effects of major outdoor air pollutants including particulates, carbon monoxide (CO), sulfur and nitrogen oxides (SO(2), NOx), ozone, and one common indoor air pollutant, environmental tobacco smoke (ETS). Animal data is presented that demonstrate perinatal windows of susceptibility to sidestream smoke, a surrogate for ETS, resulting in altered airway sensitivity and cell type frequency. A study of neonatal monkeys exposed to sidestream smoke during the perinatal period and/or early postnatal period that resulted in an altered balance of Th1-/Th2-cytokine secretion, skewing the immune response toward the allergy-associated Th2 cytokine phenotype, is also discussed.

Epidemiology of prenatal smoking and perinatal outcomes

During the previous two decades smoking among pregnant women in the developed world declined by about 60-75%. Nevertheless, prenatal smoking remains a common habit and accounts for a significant proportion of fetal morbidity and mortality through both a direct (fetal) and an indirect (placental) effect. The most important smoking-induced placental pathology is placental abruption with reported risk estimates ranging from 1.4 to 4.0. It is almost a consensus that prenatal smoking is a causative factor for placental abruption. Although the evidence is less compelling, smoking mothers are at an increased risk for placenta previa and placenta-previa-accreta combination. There is no association between maternal smoking and the syndrome of idiopathic uterine bleeding. The relationship between maternal smoking and fetal growth is causal, and includes significant reduction in growth of head circumference, abdominal circumference and femur length, with the largest reduction in size observed for femur length. Prenatal smoking is associated with a 20-30% higher likelihood for stillbirth, a 40% elevation in the risk for infant mortality and a 2-fold increase in the incidence of SIDS.

CONCLUSION

Despite a temporal decline in maternal smoking, it still accounts for significant feto-infant morbidity and mortality, and efforts to discourage prenatal smoking need to be intensified.

Sudden infant death syndrome: another year of new hope but no cure

PURPOSE OF REVIEW

Sudden infant death syndrome has inspired increasingly sophisticated studies at a time when rates are declining because of the Back-to-Sleep campaign, but ethnic disparities are widening. This review evaluates and discusses original, recent research in this area.

RECENT FINDINGS

The epidemiology of sudden infant death syndrome was evaluated, corroborating known risk factors and identifying new risk factors such as socioeconomic depression and air pollution. Deficits in our understanding of risk factors for this syndrome persist, suggesting a need for ethnicity-specific education, especially among the underserved. Both autopsy and genetic testing were found to improve diagnostic accuracy or identify other causes of death (e.g. long Q-T syndrome). Debate persists over counseling regarding pacifiers and co-sleeping within the context of breastfeeding. Support was found for a relationship between sudden infant death syndrome and autonomic dysregulation via the serotonergic pathway, but more research is needed.

SUMMARY

The cause of sudden infant death syndrome remains elusive. Recent studies, however, suggest that improved culturally sensitive educational programs, increased diagnostic specificity, and further clarification of the link between genetics and developmental stage might further decrease the number of infants lost to this devastating disease and elucidate the mechanism(s) responsible for this syndrome.

The effect of maternal smoking and drinking during pregnancy upon (3)H-nicotine receptor brainstem binding in infants dying of the sudden infant death syndrome: initial observations in a high risk population

The high rate of the sudden infant death syndrome (SIDS) in American Indians in the Northern Plains (3.5/1000) may reflect the high incidence of cigarette smoking and alcohol consumption during pregnancy. Nicotine, a neurotoxic component of cigarettes, and alcohol adversely affect nicotinic receptor binding and subsequent cholinergic development in animals. We measured (3)H-nicotine receptor binding in 16 brainstem nuclei in American Indian SIDS (n = 27) and controls (n = 6). In five nuclei related to cardiorespiratory control, (3)H-nicotinic binding decreased with increasing number of drinks (P < 0.03). There were no differences in binding in SIDS compared with controls, except upon stratification of prenatal exposures. In three mesopontine nuclei critical for arousal there were reductions (P < 0.04) in binding in controls exposed to cigarette smoke compared with controls without exposure; there was no difference between SIDS cases with or without exposure. This study suggests that maternal smoking and alcohol affects (3)H-nicotinic binding in the infant brainstem irrespective of the cause of death. It also suggests that SIDS cases are unable to respond to maternal smoking with the "normal" reduction seen in controls. Future studies are needed to establish the role of adverse prenatal exposures in altered brainstem neurochemistry in SIDS.