Abnormal maturation of sleep states in infants with aborted sudden infant death syndrome

Decreased orexin (hypocretin) immunoreactivity in the hypothalamus and pontine nuclei in sudden infant death syndrome

Infants at risk of sudden infant death syndrome (SIDS) have been shown to have dysfunctional sleep and poor arousal thresholds. In animal studies, both these attributes have been linked to impaired signalling of the neuropeptide orexin. This study examined the immunoreactivity of orexin (OxA and OxB) in the tuberal hypothalamus (n = 27) and the pons (n = 15) of infants (1-10 months) who died from SIDS compared to age-matched non-SIDS infants. The percentage of orexin immunoreactive neurons and the total number of neurons were quantified in the dorsomedial, perifornical and lateral hypothalamus at three levels of the tuberal hypothalamus. In the pons, the area of orexin immunoreactive fibres were quantified in the locus coeruleus (LC), dorsal raphe (DR), laterodorsal tegmental (LDT), medial parabrachial, dorsal tegmental (DTg) and pontine nuclei (Pn) using automated methods. OxA and OxB were co-expressed in all hypothalamic and pontine nuclei examined. In SIDS infants, orexin immunoreactivity was decreased by up to 21 % within each of the three levels of the hypothalamus compared to non-SIDS (p ≤ 0.050). In the pons, a 40-50 % decrease in OxA occurred in the all pontine nuclei, while a similar decrease in OxB immunoreactivity was observed in the LC, LDT, DTg and Pn (p ≤ 0.025). No correlations were found between the decreased orexin immunoreactivity and previously identified risk factors for SIDS, including prone sleeping position and cigarette smoke exposure. This finding of reduced orexin immunoreactivity in SIDS infants may be associated with sleep dysfunction and impaired arousal.

Fewer spontaneous arousals in infants with apparent life-threatening event

STUDY OBJECTIVES

A deficit in arousal process has been implicated as a mechanism of sudden infant death syndrome (SIDS). Compared with control infants, SIDS victims showed significantly more subcortical activations and fewer cortical arousals than matched control infants. Apparent life-threatening event (ALTE) is often considered as an aborted SIDS event. The aim of this study was to study the arousal characteristics of ALTE infants during the first months of life.

DESIGN

35 ALTE infants were studied with nighttime polysomnography at 2-3, 5-6, and 8-9 months of age. Eighteen of the infants had mothers who smoked. The infants were born full term and were usually supine sleepers. Sleep state and cardiorespiratory parameters were scored according to recommended criteria. Arousals were differentiated into subcortical activations or cortical arousals, according to the presence of autonomic and/or electroencephalographic changes. The results were compared with those of 19 healthy infants with nonsmoking mothers.

RESULTS

During NREM sleep, the ALTE infants had fewer total arousals, cortical arousals, and subcortical activations at 2-3 and 5-6 months (P < 0.001) than control infants. ALTE infants with smoking mothers had more obstructive apnea (P = 0.009) and more subcortical activations during REM sleep at 2-3 months of age (P < 0.001) than ALTE infants with nonsmoking mothers.

CONCLUSIONS

Spontaneous arousals were differently altered in ALTE infants than in SIDS infants, suggesting an entity different from SIDS. ALTE infants with smoking mothers had arousal and respiratory characteristics that were similar to future SIDS victims, suggesting some common abnormalities in brainstem dysfunction.

Sleep Biological Rhythms in Normal Infants and those at High Risk for SIDS

The focus of this study was on daytime and nighttime sleep and wakefulness during the peak age for Sudden Infant Death Syndrome (SIDS), two to four months, to determine whether there are differences between at-risk for SIDS (R) and control (C) infants. Such differences may provide insight on the frequent occurrence of SIDS in the early morning hours, when most babies are asleep. This is the only study in which R and C infants were continuously monitored for long periods of time (24-48 h) and then followed and recorded at monthly intervals until the age of 4-6 months. Data analyses indicate that ultradian REM/NREM cyclicity becomes stabilized into a regular pattern at three months of age. Infants at this age convert from a polyphasic sleep/wakefulness pattern to a circadian one. Among the changes that occur is a lengthening of short sleep periods that consolidate at night and wake periods that consolidate in the daytime. The most striking effects are related to sleep state and vary according to age and sex. The lengthening of single sleep and wakeful periods is coupled with the maturation of the brain. The development of the central nervous system facilitates the synchronization of sleeping patterns with external light input and social entrainment. One or more biological clocks or oscillators may be responsible for these REM/NREM patterns and circadian cycles. These differences during the early morning hours, when the occurrence of SIDS peaks, may have important implications for understanding the pathophysiological mechanism of SIDS.

Is SIDS associated with sleep? : A report of six cases demonstrating difficulty in this determination

Epidemiological studies suggest an important association of sudden infant death syndrome (SIDS) with sleep. Because these deaths are very rarely observed, this association is difficult to confirm. When nearby caretakers hear noises suggesting that some infants are awake before their deaths from SIDS, this determination may be even more difficult. We report six cases illustrating the difficulty in determining the sleep status of SIDS infants immediately prior to their deaths. A retrospective analysis was undertaken of the San Diego SIDS/SUDC Research Project database and the new SIDS definition proposed at the January 2004 conference in San Diego, California was applied. The circumstances surrounding the deaths of six infants led nearby caretakers to speculate that all were awake before dying. However, careful analyses suggest that all but one infant were actually sleeping before their deaths. This study strengthens the association of SIDS with sleep and emphasizes the importance of very detailed evaluation of the circumstances of death in all cases of sudden infant death. The use of the recently stratified definition for SIDS as well as the new category of unclassified sudden infant death (USID) is recommended.

Temperature differences during sleep between fullterm and preterm neonates at matched post-conceptional ages

OBJECTIVE

Altered physiologic behaviors during sleep have been described for healthy preterm neonates at post-conceptional fullterm ages. These differences may reflect brain dysmaturity as a result of conditions of prematurity. The present study examines if differences in state-specific temperature changes exist in a healthy preterm cohort as another expression of brain dysmaturity.

METHODS

Rectal and skin temperatures during sleep state transitions are reported in 59 asymptomatic post-conceptional age term infants, comparing 25 full term and 34 preterm infants. Three-hour 24-channel electroencephalogram (EEG)-sleep studies were recorded for each child. One of 4 sleep states were assigned for each of 7339 min, based on both cerebral and non-cerebral measures. For each study, average rectal and skin temperatures for each sleep state were calculated. Repeated measures MANOVA were performed using 4 explanatory variables, average skin and rectal temperatures and variance of rectal and skin temperatures, comparing preterm/fullterm status and 4 sleep states.

RESULTS

Rectal temperature differences between neonatal cohorts during specific sleep states were noted: F=8.58, P<0.0001. Significant differences were noted for both average and variance of rectal temperatures during all 4 sleep states with higher temperatures in the preterm group. For all neonates, both skin and rectal temperature differences were also noted among sleep states (F=4.22, P<0.0004). Differences were specifically noted between two specific EEG segments, mixed frequency active sleep and tracé alternant quiet sleep (P<0.0004).

CONCLUSIONS

In summary, significant differences in temperatures were noted across sleep state transitions for two neonatal cohorts, with higher average rectal temperatures in the preterm cohort. These findings highlight an altered measure of brain function during sleep in preterm infants affecting temperature regulation. This altered physiologic behavior reflects adaptation of the infant's brain function to conditions of prematurity which may contribute to vulnerabilities at older ages.

Effects of temperature on sleep in the developing rat

In altricial species, such as humans and rats, much of the development of autonomic systems occurs postnatally. Consequently, vulnerabilities exist early in postnatal development when immature autonomic functions are challenged by external factors such as variations in ambient temperature (Ta). Ta profoundly influences sleep/wake state structure in adult animals and humans, and exposure to excessive warmth has been implicated as a risk factor in sudden infant death syndrome. To better understand the relationship between temperature and sleep during development, we investigated the effect of Ta variation on sleep/wake state structure and sleep intensity in developing rats. In this experiment, sleep intensity was measured by the intensity of slow-wave activity during slow-wave sleep. Neonatal Long-Evans hooded rat pups were surgically prepared for chronic sleep/wake state and brain temperature (Tbr) recording. Two-hour recordings of sleep/wake state and Tbr were obtained from rats on postnatal day 12 (P12), P14, P16, P18, and P20 at a Ta of either 28.0-30.0, 33.0-35.0, or 38.0-40.0 degrees C. Ta significantly influenced sleep/wake state structure but had little, if any, effect on sleep intensity in developing rats.

Infant arousals during mother-infant bed sharing: implications for infant sleep and sudden infant death syndrome research

OBJECTIVE

Normative values for infant sleep architecture have been established exclusively in the solitary sleeping environment. However, most of the world's cultures practice some form of parent-infant cosleeping. In addition, no previous polysomnographic studies in infants examined the frequency of electroencephalogram (EEG) arousals. This is the first study to assess (a) EEG arousals in infants and their relationship to sleep stages; (b) the impact on arousals of mother-infant bed sharing; and (c) the temporal overlap of infant with maternal arousals during bed sharing.

METHODOLOGY

Three nights of polysomnography were performed in 35 breastfeeding mother-infant pairs when the infants were 11 to 15 weeks old. An adaptation night was followed by one bed sharing night and one solitary sleeping night. Twenty infants had been bed sharing since birth and 15 were routine solitary sleepers. Both epochal awakenings (EWs), based on 30-second epoch scoring of sleep-wake stages, and more transient arousals (TAs) >/=3 seconds were quantified.

RESULTS

Stage 3-4 sleep was associated with a striking paucity of EWs and TAs compared with stages 1-2 or rapid eye movement sleep. Bed sharing facilitated EWs and TAs selectively during stage 3-4 sleep. EWs from stage 3-4 sleep were more frequent on the bed sharing night than on the solitary night in both infant groups. Routinely bed sharing infants also exhibited more frequent TAs in stage 3-4 than the routine solitary sleepers in both conditions. In both groups, the number of infant arousals (EWs + TAs) that overlapped the mother's was doubled during bed sharing, with infant arousals leading most often.

CONCLUSIONS

Mother-infant bed sharing promotes infant arousals. Together with a previous report that bed sharing reduces stage 3-4 sleep, this suggests that normative values for infant sleep must be interpreted within the context of the sleeping environment in which they were established. Given that arousability is diminished in stage 3-4, we speculate that, under otherwise safe conditions, the observed changes in stage 3-4 sleep and arousals associated with bed sharing might be protective to infants at risk for SIDS because of a hypothesized arousal deficit. The responsivity of the mother to infant arousals during bed sharing might also be protective.

Sudden Infant Death Syndrome: The Role of Central Chemosensitivity

Clinical and basic research on Sudden Infant Death Syndrome (SIDS) has focused on sleep-disordered cardiorespiratory control during a critical period of brainstem maturation. Recently, some SIDS cases have been reported to have abnormalities of the arcuate nucleus of the medulla. The human arcuate nucleus is thought to be homologous to the medullary raphe in rats and cats, a widely projecting serotonergic system that is functionally linked to both respiration and sleep. Neurons of the medullary raphe are now known to be highly sensitive to respiratory acidosis in vitro and are candidates for central chemoreceptors. The relevance of changes in the arcuate nucleus to the mechanisms of death in SIDS remains controversial. However, based on this new data, a specific hypothesis is proposed here. In combination with Immaturity of respiratory control mechanisms, dysfunction of arcuate neurons may lead to a fatal exaggeration of a normal physiologic inhibition of central chemoreception during sleep. The major elements of this working hypothesis are testable in animal experiments and clinical studies.

Gastroesophageal reflux in childhood

Gastroesophageal reflux (GER) is one of the most frequent symptomatic clinical disorders affecting the gastrointestinal tract of infants and children. During the past 2 decades, GER has been recognized more frequently because of an increased awareness of the condition and also because of the more sophisticated diagnostic techniques that have been developed for both identifying and quantifying the disorder. Gastroesophageal fundoplication is currently one of the three most common major operations performed on infants and children by pediatric surgeons in the United States. Normal gastroesophageal function is a complex mechanism that depends on effective esophageal motility, timely relaxation and contractility of the lower esophageal sphincter, the mean intraluminal pressure in the stomach, the effectiveness of contractility in emptying of the stomach, and the ease of gastric outflow. More than one of these factors are often abnormal in the same child with symptomatic GER. In addition, in patients with GER disease, and particularly in those patients with neurologic disorders, there appears to be a high prevalence of autonomic neuropathy in which esophagogastric transit and gastric emptying are frequently delayed, producing a somewhat complex foregut motility disorder. GER has a different course and prognosis depending on the age of onset. The incompetent lower esophageal sphincter mechanism present in most newborn infants combined with the increased intraabdominal pressure from crying or straining commonly becomes much less frequent as a cause of vomiting after the age of 4 months. Chalasia and rumination of infancy are self-limited and should be carefully separated from symptomatic GER, which requires treatment. The most frequent complications of recurrent GER in childhood are failure to thrive as a result of caloric deprivation and recurrent bronchitis or pneumonia caused by repeated pulmonary aspiration of gastric fluid. Children with GER disease commonly have more refluxing episodes when in the supine position, particularly during sleep. The reflux of acid into the mid or upper esophagus may stimulate vagal reflexes and produce reflex laryngospasm, bronchospasm, or both, which may accentuate the symptoms of asthma. Reflux may also be a cause of obstructive apnea in infants and possibly a cause of recurrent stridor, acute hypoxia, and even the sudden infant death syndrome. Premature infants with respiratory distress syndrome have a high incidence of GER. Esophagitis and severe dental carries are common manifestations of GER in childhood. Barrett's columnar mucosal changes in the lower esophagus are not infrequent in adolescent children with chronic GER, particularly when Heliobacter pylori is present in the gastric mucosa. Associated disorders include esophageal dysmotility, which has been recognized in approximately one third of children with severe GER. Symptomatic GER is estimated to occur in 30% to 80% of infants who have undergone repair of esophageal atresia malformations. Neurologically impaired children are at high risk for having symptomatic GER, particularly if nasogastric or gastrostomy feedings are necessary. Delayed gastric emptying (DGE) has been documented with increasing frequency in infants and children who have symptoms of GER, particularly those with neurologic disorders. DGE may also be a cause of gas bloat, gagging, and breakdown or slippage of a well-constructed gastroesophageal fundoplication. The most helpful test for diagnosing and quantifying GER in childhood is the 24-hour esophageal pH monitoring study. Miniaturized probes that are small enough to use easily in the newborn infant are available. This study is 100% accurate in diagnosing reflux when the esophageal pH is less than 4.0 for more than 5% of the total monitored time.

Fetal behaviour and the sudden infant death syndrome (SIDS)

To examine whether differences in sleep maturation could be identified before birth, behavioural studies were carried out in 28 fetuses. Studies were possible in all 28 fetuses at 28 weeks, but only in 26 fetuses at 36 weeks (two fetuses delivered before 36 weeks). The risk of sudden infant death syndrome (SIDS) was determined using the Oxford SIDS scoring system. The fetuses at greater risk of SIDS had coincidence of behavioural characteristics for a significantly lower percentage of the time than those at low risk. This difference reached significance (p < or = 0.05) only at 36 weeks.

Plasma levels of DSIP in infants in the first year of life and SIDS risk

In searching for abnormalities related to the sudden infant death syndrome (SIDS), delta sleep-inducing peptide (DSIP), a regulatory peptide with sleep promoting actions, was investigated in the first year of life in four groups of children: (1) preterm infants (n = 28), (2) infants with a high mean apnea duration evaluated polysomnographically (n = 26), (3) healthy full-term infants (n = 37) and (4) siblings of SIDS-victims (n = 26). DSIP was radioimmunoassayed in plasma. Half of the infants were also investigated polygraphically during sleep. The ratio between quiet sleep and active sleep was determined. There was no age dependence of the plasma level of DSIP in the first year of life but there was an increase in the ratio of quiet/active sleep depending of maturity. The level of DSIP in healthy full-term infants was significantly higher (P less than 0.05) (median: 1885 pmol/l, interquartile range: 757 pmol/l) than in preterms (1595; 385) and in infants with a high mean apnea duration (1542; 373). There was no significant difference in DSIP concentrations between healthy full-term infants and SIDS-siblings (1605; 271).

Prolonged QT interval: a marker of sudden infant death syndrome?

A prospective electrocardiographic study was performed in 1830 newborns to evaluate the predictive value of QT interval for sudden infant death syndrome (SIDS). Standard ECG, with babies asleep, was recorded at the ages of 4 days, 2, 4, 6 months, and 1 year. The QTc (+/- SD) was 392 +/- 22 at 4 days, 410 +/- 16 (p less than 0.0001) at 2 months (n = 1256), 404 +/- 16 at 4 months (n = 1015), 400 +/- 16 at 6 months (n = 895), and 398 +/- 15 at 1 year (n = 890). QTc values longer than the mean plus 3 standard deviations were considered prolonged. Heart rate values (beats/min) were 138 +/- 19 at 4 days, 141 +/- 13 at 2 months, 134 +/- 13 at 4 months, 133 +/- 13 at 6 months, and 128 +/- 14 at 1 year. In 34 babies the QT interval was prolonged (mean + 3SD) and 3 of these died suddenly: the first, at 3 months (QTc = 470 and HR = 147 at 4 days); the second after 7 weeks (QTc = 514, HR = 115); the third at 3 months (QTc = 464 and HR = 140 at 4 days).

The relationship between sleep and sudden infant death

Infants epidemiologically at high risk for SIDS demonstrate a variety of abnormalities in sleep-state organization, maturation, and sleep-state modulation of cardio-respiratory control mechanisms. These involve both the REM and quiet-sleep states and are seen in twins who have had no evidence of clinical cardio-respiratory compromise during infancy as well as in near-miss infants who have suffered serious cardio-respiratory failure. Although these infants have higher levels of REM sleep around 40 weeks, of special concern is the decrease in the maturation of the quiet system, which becomes evident after 44 weeks, and the reported quiet-sleep abnormalities in reflex control of respiration and arousal. The source of these abnormalities is environmental rather than genetic and most likely occurs prenatally. During the critical period for SIDS, infant sleep begins to coalesce from a series of naps to more prolonged night time sleep periods that last up to 8 hours. We believe that the ability to maintain physiologic homeostasis during prolonged sleep is a challenge facing infants who are epidemiologically at risk for sudden infant death. The challenge facing sleep research is the more complete understanding of the relationship between prolonged inhibition, homeostasis, arousal, and development.

Feeding, behavioural state and cardiorespiratory control

The aim of the present study was to examine whether immaturity of cardiorespiratory control corresponds to a less mature behavioural state pattern and/or to less efficient feeding behaviour. Fifty-four infants were observed and data polygraphically recorded for 6 hours; a feeding session was included. It was found that infants with immature cardiorespiratory control spent more time in REM-sleep, less time in the active awake state, and were more likely to be inefficient feeders. In addition, 100 infants were observed for risk signs of sudden infant death syndrome and their parents were asked to answer a questionnaire on the sleeping and feeding behaviour of their infants. The majority of the infants with immature cardiorespiratory control were described as bad feeders but good sleepers. We conclude that gathering information about sleeping and feeding behaviour is useful when screening for immaturity of cardiorespiratory control.

Are there tests predictive for prolonged apnoea and SIDS? A review of epidemiological and functional studies

Sudden infant death syndrome (SIDS) remains the predominant cause of postneonatal mortality. Epidemiological studies have led to the definition of populations with an increased risk for SIDS: subsequent siblings of SIDS victims, infants with near miss for SID episodes, prematurely born infants with perinatal risk factors, and infants of drug dependent mothers. Furthermore, a variety of additional although rarely independent factors regarding both mothers and infants have been found to be associated with an increased risk for SIDS. Despite of this, the majority of infants still dying from SIDS do not belong to one or more of these risk groups and even within a group considered to be at increased risk it is impossible so far to identify individual infants at highest risk on the basis of an infant's history and clinical data. Therefore, different methods have been applied during the last several years in order to detect functional abnormalities of cardiorespiratory control during sleep with the aim of obtaining more specific and sensitive predictors of subsequent severe apnoea and SIDS. In an attempt to evaluate the predictive power of these various methods the present article reviews their results in relation to the follow up data of the infants under study. The results of the meanwhile innumerous studies were found to be at variance and often controversial. At the present time, none of these tests may be looked at as virtually improving our ability to predict the risk for prolonged apnoea and SIDS. One of the reasons for this may be the lack of standardisation of the particular methods with respect to both definition of study groups and conditions of testing infants. Since all of these tests have mainly been performed in infants of epidemiological risk groups, the definition of which is an indispensable prerequisite for the evaluation of both the indication and the results of such tests, an updated survey of the more recent epidemiological studies is given as an introduction.

A hypothesis: sudden infant death syndrome is a disorder of entrainment

A hypothesis is presented that explains Sudden Infant Death Syndrome (SIDS) as a disorder of entrainment. This hypothesis fits the known characteristics of SIDS i.e., age at death, sleep-related, natural death and absence of a lethal lesion. The spectrum from reversible hypoxia (near-miss SIDS) to irreversible hypoxia (SIDS) can be explained by the presence or absence of brainstem lesions in infants with a disorder of entrainment.

Brainstem auditory evoked responses in infants at risk of sudden infant death

Brainstem auditory evoked responses (BAERs) were recorded from 63 near-miss Sudden Infant Death Syndrome (NMSIDS) infants, 26 siblings of SIDS (SSIBS) infants and 67 control infants between 0 and 30 weeks post-term. The majority of BAERs recorded from the NMSIDS and SSIBS infants had normal form and interpeak intervals (V-I and V-IIn) within normal limits for their age. However, 15% of these infants had interpeak intervals outside the normal range, suggesting abnormal neural function in these cases. The distributions of interpeak intervals for all NMSIDS and SSIBS infants were skewed towards longer times compared to control infants. The distributions of V-IIn intervals for both groups of at risk infants were significantly different to that of control infants. While the observations confirm that the recording of BAERs is not suitable for identifying infants at risk of SIDS, they suggest, however, that maturation of neural processing in the brainstem of these infants may be delayed.

Sudden infant death syndrome: increased carotid-body dopamine and noradrenaline content

Carotid bodies from infants dying of sudden infant death syndrome contained significantly higher concentrations of dopamine (10-fold) and noradrenaline (3-fold) than those from age-matched control infants. Administration of dopamine inhibits respiration by direct action on the carotid body, and it is suggested that the elevated levels of endogenous catecholamines found in victims of sudden infant death syndrome may compromise the normal function of the carotid body, particularly the ventilatory response to hypoxia.

Use of the SCSB method for monitoring of respiration, body movements and ballistocardiogram in infants

A new method for long-term monitoring of respiration, the ballistocardiogram (BCG), heart rate and body movements in newborn infants and children is presented. The design of the static charge-sensitive bed (SCSB) method for the monitoring of newborn infants and children is described. The method is simple and inexpensive. No electrodes or cables need to be connected to the subject. The SCSB method allows continuous long-term monitoring of body movements, respiratory movement, the BCG and heart rate. The results of about 40 neonatal recordings made in our clinic with the SCSB method demonstrate that recording body movements and respiration is possible in ordinary hospital wards. The infra-acoustic noise due to air-conditioning which is usually present in ordinary wards disturbs the BCG recordings in neonates. To obtain adequate BCG recordings this noise must be eliminated from recording rooms. Low-frequency noise is low enough to allow good BCG recordings in private dwellings. The SCSB method opens up new approaches to long-term studies of the regulation of respiration, body movements and the ballistocardiogram in newborn infants and children. Possible clinical applications of the SCSB method are discussed.

Biochemical and histological assessment of hepatic lipid in sudden infant death syndrome

A biochemical and histological study of hepatic lipid in children dying from the sudden infant death syndrome (SIDS) and children of a similar age dying explicably are reported. Contrary to a previous report based on histological assessment of hepatic lipid, no significant increase of total lipid content in livers of children dying from SIDS was found. Analysis of hepatic phospholipid fatty acid esters, however, revealed a significant difference between SIDS and children of similar age dying acutely and explicably. The phospholipid abnormality found in SIDS was similar to that found in children dying subacutely with hypoxia and would be consistent with increased cell membrane fluidity. The implications of these findings in the pathogenesis of SIDS are discussed.

Development of sleep-waking temporal sequencing in infants at risk for the Sudden Infant Death Syndrome

The periodic organization of waking, quiet sleep, and active sleep was studied in control infants and siblings of victims of the Sudden Infant Death Syndrome. Spectral estimates of all-night binary state time series recorded at 1 week and 1, 2, 3, 4, and 6 months of age revealed disturbed patterns of sleep states, especially in active sleep, from as early as the first week of life. These disruptions continued until at least 6 months of age. These data support the contention that the temporal patterning of sleep state can be used as an important neurologic marker for development.