Factors affecting heart rate variability and heart rate responses to tilting in infants aged 1 and 3 months

Characterising the motion and cardiorespiratory interaction of preterm infants can improve the classification of their sleep state

AIM

This study aimed to classify quiet sleep, active sleep and wake states in preterm infants by analysing cardiorespiratory signals obtained from routine patient monitors.

METHODS

We studied eight preterm infants, with an average postmenstrual age of 32.3 ± 2.4 weeks, in a neonatal intensive care unit in the Netherlands. Electrocardiography and chest impedance respiratory signals were recorded. After filtering and R-peak detection, cardiorespiratory features and motion and cardiorespiratory interaction features were extracted, based on previous research. An extremely randomised trees algorithm was used for classification and performance was evaluated using leave-one-patient-out cross-validation and Cohen's kappa coefficient.

RESULTS

A sleep expert annotated 4731 30-second epochs (39.4 h) and active sleep, quiet sleep and wake accounted for 73.3%, 12.6% and 14.1% respectively. Using all features, and the extremely randomised trees algorithm, the binary discrimination between active and quiet sleep was better than between other states. Incorporating motion and cardiorespiratory interaction features improved the classification of all sleep states (kappa 0.38 ± 0.09) than analyses without these features (kappa 0.31 ± 0.11).

CONCLUSION

Cardiorespiratory interactions contributed to detecting quiet sleep and motion features contributed to detecting wake states. This combination improved the automated classifications of sleep states.

Baseline heart rate in infants with prenatal alcohol exposure: A systematic review and independent analysis

BACKGROUND

Infants with fetal alcohol syndrome exhibit a range of developmental anomalies, many related to the heart (e.g., decreased heart rate variability). However, the baseline heart rate in this population remains unclear. We hypothesized that the age at which heart rate was measured or the age during exposure to alcohol affects the baseline heart rate.

METHODS

First, we conducted a systemic review to determine the published heart rate of infants with prenatal alcohol exposure (PAE). Exclusion criteria included potentially confounding factors, including the commonly associated phenotypes of small for gestational age and premature birth. Risk of bias was evaluated based on case study limitations, and data were compared with established heart rate norms. Then, we evaluated the precise age at heart rate measurement using existing datasets from the Collaborative Initiative on Fetal Alcohol Spectrum Disorders and the Maternal Lifestyle Study.

RESULTS

Based on the weighted means of six studies, the baseline heart rate was 4.6 bpm higher in infants with PAE (n = 253) than in control infants (n = 152). Using the individual patient data, baseline heart rates were similar between age-matched infants with PAE and control infants who were born full-term and showed no signs of growth restriction (ANOVA, p > .05; n = 49-124 infants per age and exposure).

CONCLUSIONS

A systematic literature review suggested that heart rate is elevated in infants with PAE, but these findings are limited by the number of studies and how few studies included control infants. The analysis of individual patient data indicates that infants with PAE have normal baseline heart rates. This knowledge may help clinicians detect changes in cardiac function in infants with PAE. (Registered via PROSPERO, #CRD42020191212.).

Evidence Base for 2022 Updated Recommendations for a Safe Infant Sleeping Environment to Reduce the Risk of Sleep-Related Infant Deaths

Every year in the United States, approximately 3500 infants die of sleep-related infant deaths, including sudden infant death syndrome (SIDS) (International Statistical Classification of Diseases and Related Health Problems 10th Revision [ICD-10] R95), ill-defined deaths (ICD-10 R99), and accidental suffocation and strangulation in bed (ICD-10 W75). After a substantial decline in sleep-related deaths in the 1990s, the overall death rate attributable to sleep-related infant deaths have remained stagnant since 2000, and disparities persist. The triple risk model proposes that SIDS occurs when an infant with intrinsic vulnerability (often manifested by impaired arousal, cardiorespiratory, and/or autonomic responses) undergoes an exogenous trigger event (eg, exposure to an unsafe sleeping environment) during a critical developmental period. The American Academy of Pediatrics recommends a safe sleep environment to reduce the risk of all sleep-related deaths. This includes supine positioning; use of a firm, noninclined sleep surface; room sharing without bed sharing; and avoidance of soft bedding and overheating. Additional recommendations for SIDS risk reduction include human milk feeding; avoidance of exposure to nicotine, alcohol, marijuana, opioids, and illicit drugs; routine immunization; and use of a pacifier. New recommendations are presented regarding noninclined sleep surfaces, short-term emergency sleep locations, use of cardboard boxes as a sleep location, bed sharing, substance use, home cardiorespiratory monitors, and tummy time. In addition, additional information to assist parents, physicians, and nonphysician clinicians in assessing the risk of specific bed-sharing situations is included. The recommendations and strength of evidence for each recommendation are published in the accompanying policy statement, which is included in this issue.

Prenatal nicotine exposure was associated with long-term impact on the cardiovascular system and regulation-Review

AIM

The aim of this structured review was to discuss knowledge of nicotine use during pregnancy and long-term effects on children's cardiovascular function.

METHODS

PubMed and MEDLINE were searched for original papers that covered various forms of nicotine exposure during pregnancy and this identified 314 papers published in English from inception of the databases to 1 March 2021. The research focus was prenatal exposure that had long-term effects on the cardiovascular system. The search was expanded from the reference list of the selected papers, which identified another 17 papers.

RESULTS

The 34 original papers that were included covered 172,696 subjects from foetuses to 19 years of age. Cardiovascular autonomic dysfunction was discussed in 12 of the papers and 16 studies reported on blood pressure. The remaining studies covered structural or functional changes in arterial wall or heart. There were convincing data on autonomic dysfunction and increased blood pressure. Some data were conflicting and problems with misclassification of exposure were evident.

CONCLUSION

Prenatal nicotine exposure was associated with long-term developmental changes in the cardiovascular system and regulation. There were no safe periods, doses or nicotine products during pregnancy and women should abstain when planning a pregnancy.

Effects of tilt on cerebral hemodynamics measured by NeoDoppler in healthy neonates

BACKGROUND

Today, there are conflicting descriptions of how neonates respond to tilt. Examining physiologic responses of cerebral blood flow velocities (BFVs) in challenging situations like a tilt requires equipment that can cope with positional changes. We aimed to characterize how healthy term neonates respond to mild cerebral hemodynamic stress induced by a 90° tilt test using the recently developed NeoDoppler ultrasound system.

METHODS

A small ultrasound probe was fixated to the neonatal fontanel by a cap, and measured cerebral BFV in healthy neonates during and after a 90° head-up tilt test, five min in total, at their first and second day of life. Unsupervised k-means cluster analysis was used to characterize common responses.

RESULTS

Fifty-six ultrasound recordings from 36 healthy term neonates were analyzed. We identified five distinct, immediate responses that were related to specific outcomes in BFV, heart rate, and pulsatility index the next two min. Among 20 neonates with two recordings, 13 presented with different responses in the two tests.

CONCLUSIONS

Instant changes in cerebral BFV were detected during the head-up tilt tests, and the cluster analysis identified five different hemodynamic responses. Continuous recordings revealed that the differences between groups persisted two min after tilt.

IMPACT

NeoDoppler is a pulsed-wave Doppler ultrasound system with a probe fixated to the neonatal fontanel by a cap that can measure continuous cerebral blood flow velocity. Healthy neonates present with a range of normal immediate cerebral hemodynamic responses to a 90° head-up tilt, categorized in five groups by cluster analysis. This paper adds new knowledge about connection between immediate responses and prolonged responses to tilt. We demonstrate that the NeoDoppler ultrasound system can detect minute changes in cerebral blood flow velocity during a 90° head-up tilt.

Exposures influencing the developing central autonomic nervous system

Autonomic nervous system function is critical for transition from in-utero to ex-utero life and is associated with neurodevelopmental and neuropsychiatric outcomes later in life. Adverse prenatal and neonatal conditions and exposures can impair or alter ANS development and, as a result, may also impact long-term neurodevelopmental outcomes. The objective of this article is to provide a broad overview of the impact of factors that are known to influence autonomic development during the fetal and early neonatal period, including maternal mood and stress during and after pregnancy, fetal growth restriction, congenital heart disease, toxic exposures, and preterm birth. We touch briefly on the typical development of the ANS, then delve into both in-utero and ex-utero maternal and fetal factors that may impact developmental trajectory of the ANS and, thus, have implications in transition and in long-term developmental outcomes. While many types of exposures and conditions have been shown to impact development of the autonomic nervous system, there is still much to be learned about the mechanisms underlying these influences. In the future, more advanced neuromonitoring tools will be required to better understand autonomic development and its influence on long-term neurodevelopmental and neuropsychological function, especially during the fetal period.

Heart rate variability for determining autonomic nervous system effects of lifestyle behaviors in early life: A systematic review

BACKGROUND

An unhealthy lifestyle negatively alters autonomic nervous system (ANS) activity as reflected by decreased heart rate variability (HRV), increasing cardiovascular disease (CVD) risk. Research investigating the effect of modifiable lifestyle factors on ANS activity in young children is limited. Early identification of these risk factors is vital to improving long-term individual and public health outcomes. A systematic review was conducted to assess the effect of maternal or child modifiable lifestyle factors on child ANS activity.

METHODS

Following the 2009 PRISMA guidelines, three electronic databases were searched from February 2018 - July 2019 for articles describing human trials between 1996 - 2019. Included studies examined ANS activity of children between 28 weeks gestational age - 6 years in relation to modifiable lifestyle CVD risk factors.

RESULTS

Twenty-six studies fulfilled inclusion criteria. Sixteen studies reported that modifiable lifestyle factors significantly influenced the HRV of children. Increased HRV was significantly associated with higher maternal zinc and omega-3 fatty acid intake, regular maternal aerobic exercise and a non-smoking environment. Child diet and body composition demonstrated some support for an association between these modifiable lifestyle factors and child HRV.

CONCLUSION

There is cross-sectional evidence supporting an association between maternal lifestyle factors and child HRV. Evidence is less supportive of a relationship between child modifiable lifestyle factors and child HRV. Monitoring the effects of lifestyle interventions on the ANS via HRV measurements of both mother and child may identify child CVD risk.

Heart Rate Dynamics in Patients with Obstructive Sleep Apnea: Heart Rate Variability and Entropy

Background: Obstructive sleep apnea (OSA), a highly prevalent sleep disorder, is closely related to cardiovascular disease (CVD). Our previous work demonstrated that Shannon entropy of the degree distribution (E_DD), obtained from the network domain of heart rate variability (HRV), might be a potential indicator for CVD. Method: To investigate the potential association between OSA and E_DD, OSA patients and healthy controls (HCs) were identified from a sleep study database. Then E_DD was calculated from electrocardiogram (ECG) signals during sleep, followed by cross-sectional comparisons between OSA patients and HCs, and longitudinal comparisons from baseline to follow-up visits. Furthermore, for OSA patients, the association between E_DD and OSA severity, measured by apnea-hypopnea index (AHI), was also analyzed. Results: Compared with HCs, OSA patients had significantly increased E_DD during sleep. A positive correlation between E_DD and the severity of OSA was also observed. Although the value of E_DD became larger with aging, it was not OSA-specified. Conclusion: Increased E_DD derived from ECG signals during sleep might be a potential dynamic biomarker to identify OSA patients from HCs, which may be used in screening OSA with high risk before polysomnography is considered.

Combined effects of body position and sleep status on the cardiorespiratory stability of near-term infants

The purpose of this study was to determine the effects of body position (prone, supine and lateral) together with sleep status (wake and sleep) on the cardiorespiratory stability of near-term infants. A total of 53 infants (gestational age at birth 33.2 ± 3.5 weeks; birth weight 1,682 ± 521 g; gestational age at recording 38.6 ± 2.1 weeks; weight at recording: 2,273 ± 393 g) were monitored for 24 hours for clinically significant apnea (>15 seconds), bradycardia (<100 bpm), and oxygen desaturation (SpO₂ < 90%) in alternating body positions (prone, supine and lateral) by cardiorespiratory monitors and 3-orthogonal-axis accelerometers. Sleep status of the infants was also continuously monitored by actigraphs. No apnea was observed. During wake, severe bradycardia was most frequently observed in the lateral position while, during sleep, severe bradycardia was most frequently observed in the supine position. Desaturation was most frequently observed in the supine and lateral positions during both wake and sleep. Our study suggests that the cardiorespiratory stability of infants is significantly compromised by both body position and sleep status. During both wake and sleep, prone position induces the most stable cardiorespiratory functions of near-term infants.

Changes in cardiac output and cerebral oxygenation during prone and supine sleep positioning in healthy term infants

OBJECTIVE

To investigate the changes in systemic and cerebral haemodynamics between supine and prone sleep in healthy term infants during the early postnatal period.

DESIGN/METHODS

Healthy term infants without congenital anomalies, patent ductus arteriosus and/or small for gestational age status were enrolled. Infants were placed in supine (SP₁), prone (PP) and back in supine (SP₂) position for 15 min each while asleep. Cardiac output (CO) and stroke volume (SV) were assessed by electrical velocimetry (EV) and echocardiography (echo), and cerebral regional oxygen saturation (CrSO₂) in the frontal lobes was monitored by near-infrared spectroscopy. Heart rate (HR) and SpO₂ were continuously monitored by conventional monitoring.

RESULTS

In 34 healthy term infants (mean age 3.7±1.2 days; 16 females), 66 sets of serial CO measurements (34 EV and 32 echo) in three sleep positions were obtained. Mean CO_EV and CO_echo were 182±57 (SP₁), 170±50 (PP) and 177±54 (SP₂), and 193±48 (SP₁), 174±40 (PP) and 192±50 (SP₂) mL/kg/min, respectively. Mean SV_EV and SV_echo were 1.46±0.47 (SP₁), 1.36±0.38 (PP) and 1.37±0.39 (SP₂), and 1.54±40 (SP₁), 1.38±0.38 (PP) and 1.51±0.41 (SP₂) mL/kg, respectively. Repeated measures analysis of variance revealed a decrease in CO and SV during prone positions by both EV and echo, while HR, SpO₂ and CrSO₂ did not change. Thirty-eight per cent of the CO measurements decreased≥10% during prone positioning.

CONCLUSIONS

In healthy term infants, CO decreases in prone position due to a decrease in SV and not HR. CO recovers when placed back in supine. However, frontal lobe CrSO₂ does not change in the different positions.

Entropy Information of Cardiorespiratory Dynamics in Neonates during Sleep

Sleep is a central activity in human adults and characterizes most of the newborn infant life. During sleep, autonomic control acts to modulate heart rate variability (HRV) and respiration. Mechanisms underlying cardiorespiratory interactions in different sleep states have been studied but are not yet fully understood. Signal processing approaches have focused on cardiorespiratory analysis to elucidate this co-regulation. This manuscript proposes to analyze heart rate (HR), respiratory variability and their interrelationship in newborn infants to characterize cardiorespiratory interactions in different sleep states (active vs. quiet). We are searching for indices that could detect regulation alteration or malfunction, potentially leading to infant distress. We have analyzed inter-beat (RR) interval series and respiration in a population of 151 newborns, and followed up with 33 at 1 month of age. RR interval series were obtained by recognizing peaks of the QRS complex in the electrocardiogram (ECG), corresponding to the ventricles depolarization. Univariate time domain, frequency domain and entropy measures were applied. In addition, Transfer Entropy was considered as a bivariate approach able to quantify the bidirectional information flow from one signal (respiration) to another (RR series). Results confirm the validity of the proposed approach. Overall, HRV is higher in active sleep, while high frequency (HF) power characterizes more quiet sleep. Entropy analysis provides higher indices for SampEn and Quadratic Sample entropy (QSE) in quiet sleep. Transfer Entropy values were higher in quiet sleep and point to a major influence of respiration on the RR series. At 1 month of age, time domain parameters show an increase in HR and a decrease in variability. No entropy differences were found across ages. The parameters employed in this study help to quantify the potential for infants to adapt their cardiorespiratory responses as they mature. Thus, they could be useful as early markers of risk for infant cardiorespiratory vulnerabilities.

SIDS and Other Sleep-Related Infant Deaths: Evidence Base for 2016 Updated Recommendations for a Safe Infant Sleeping Environment

Approximately 3500 infants die annually in the United States from sleep-related infant deaths, including sudden infant death syndrome (SIDS), ill-defined deaths, and accidental suffocation and strangulation in bed. After an initial decrease in the 1990s, the overall sleep-related infant death rate has not declined in more recent years. Many of the modifiable and nonmodifiable risk factors for SIDS and other sleep-related infant deaths are strikingly similar. The American Academy of Pediatrics recommends a safe sleep environment that can reduce the risk of all sleep-related infant deaths. Recommendations for a safe sleep environment include supine positioning, use of a firm sleep surface, room-sharing without bed-sharing, and avoidance of soft bedding and overheating. Additional recommendations for SIDS risk reduction include avoidance of exposure to smoke, alcohol, and illicit drugs; breastfeeding; routine immunization; and use of a pacifier. New evidence and rationale for recommendations are presented for skin-to-skin care for newborn infants, bedside and in-bed sleepers, sleeping on couches/armchairs and in sitting devices, and use of soft bedding after 4 months of age. In addition, expanded recommendations for infant sleep location are included. The recommendations and strength of evidence for each recommendation are published in the accompanying policy statement, "SIDS and Other Sleep-Related Infant Deaths: Updated 2016 Recommendations for a Safe Infant Sleeping Environment," which is included in this issue.

The role of physiological studies and apnoea monitoring in infants

There is evidence that failure of cardio-respiratory control mechanisms plays a role in the final event of the Sudden Infant Death Syndrome (SIDS). Physiological studies during sleep in both healthy term born infants and those at increased risk for SIDS have been widely used to investigate how the major risk and protective factors for SIDS identified from epidemiological studies might alter infant physiology. Clinical polysomnography (PSG) in infants who eventually succumbed to SIDS however demonstrated abnormalities that were neither sufficiently distinctive nor predictive to support routine use of PSG for infants at risk for SIDS. PSG findings have also been shown to be not predictive of recurrence of Apparent Life Threatening Events (ALTE) and thus international guidelines state that PSG is not indicated for routine evaluation in infants with an uncomplicated ALTE, although PSG may be indicated when there is clinical evidence of a sleep related breathing disorder. A decision to undertake home apnoea monitoring should consider the potential advantages and disadvantages of monitoring for that individual, in the knowledge that there is no evidence of the efficacy of such devices in preventing SIDS.

Sudden unexpected death in infancy: biological mechanisms

Sudden unexpected death in infancy (SUDI) covers both explained and unexplained deaths. Unexplained cases or SIDS are likely to have multiple neural mechanisms contributing to the final event. The evidence ranges from subtle physiological signs related to autonomic control, to findings at autopsy of altered neurotransmitter systems, including the serotonergic system, a network that has an extensive homeostatic role in cardio-respiratory and thermoregulatory control. Processes may be altered by the vulnerability of the infant due to age, poor motor ability, or a genetic predisposition. The fatal event may occur in response to an environmental stress. A single final physiological route to death seems unlikely. An understanding of the reasons for explained SUDI also reminds us that a thorough investigation is required after each death occurs.

Cardio-respiratory control during sleep in infancy

During the first year of life and particularly the first 6 months autonomic control of the cardio-respiratory system is still undergoing maturation and infants are at risk of cardio-respiratory instability. These instabilities are most marked during sleep, which is important as infants spend the majority of each 24 hours in sleep. Sleep state has a marked effect on the cardio-respiratory system with instabilities being more common in active sleep compared to quiet sleep. Responses to hypoxia are also immature during infancy and may make young infants more vulnerable to cardio-respiratory instability. It has been proposed that an inability to respond appropriately to a life threatening event underpins the Sudden Infant Death Syndrome (SIDS). The major risk factors for SIDS, prone sleeping and maternal smoking, both impair cardio-respiratory control in normal healthy term infants.

Heart rate variability in sleeping preterm neonates exposed to cool and warm thermal conditions

Sudden infant death syndrome (SIDS) remains the main cause of postneonatal infant death. Thermal stress is a major risk factor and makes infants more vulnerable to SIDS. Although it has been suggested that thermal stress could lead to SIDS by disrupting autonomic functions, clinical and physiopathological data on this hypothesis are scarce. We evaluated the influence of ambient temperature on autonomic nervous activity during sleep in thirty-four preterm neonates (mean ± SD gestational age: 31.4±1.5 weeks, postmenstrual age: 36.2±0.9 weeks). Heart rate variability was assessed as a function of the sleep stage at three different ambient temperatures (thermoneutrality and warm and cool thermal conditions). An elevated ambient temperature was associated with a higher basal heart rate and lower short- and long-term variability in all sleep stages, together with higher sympathetic activity and lower parasympathetic activity. Our study results showed that modification of the ambient temperature led to significant changes in autonomic nervous system control in sleeping preterm neonates. The latter changes are very similar to those observed in infants at risk of SIDS. Our findings may provide greater insight into the thermally-induced disease mechanisms related to SIDS and may help improve prevention strategies.

Laboratory evaluation of pediatric autonomic disorders

The autonomic nervous system controls a variety of fundamental physiological processes in the human body including regulation of breathing, heart rate, blood pressure, temperature, and gastrointestinal motility. Although, methods of testing autonomic function have been developed and normative data have been collected in adults, development of child-friendly testing and the field of pediatric autonomic medicine is just beginning. These noninvasive testing methods serve to identify changes in autonomic functioning and to clarify whether dysfunction is isolated or crosses into multiple systems. Methods for testing cardiovagal, adrenergic, sudomotor, pupillary, enteric, and bladder function need to be refined and made more child friendly at the same time that age and gender appropriate normative values are developed for children.

Swaddling: will it get babies onto their backs for sleep?

INTRODUCTION

The supine sleep position is recommended to reduce sudden infant death syndrome risk. Swaddling may improve adherence with supine placement.

AIM

To assess knowledge, attitudes, and practice regarding swaddling among adult caregivers of 0- to 3-month-old infants.

METHODS

Cross-sectional descriptive survey.

RESULTS

All 103 adults interviewed had swaddled their infant. Common reasons for swaddling included infant comfort and warmth. Almost 80% of those who swaddled their infant found it effective, 80% believed it to be comfortable, and ~90% believed swaddling to be safe. Parents who routinely used swaddling were more likely to find it effective and to place their infant supine when swaddled (P < .01).

CONCLUSIONS

Parents often use swaddling to comfort the infant, and most find it effective. Parents who routinely use swaddling are more likely to place their infant supine if swaddled. Swaddling may be a strategy for parents of infants who have difficulty sleeping in the supine position.

Maturation of heart rate and blood pressure variability during sleep in term-born infants

STUDY OBJECTIVES

Abnormal blood pressure control is implicated in the sudden infant death syndrome (SIDS). However, no data exist on normal development of blood pressure control during infancy. This study assessed maturation of autonomic control of blood pressure and heart rate during sleep within the first 6 months of life.

PARTICIPANTS

Term infants (n = 31) were studied longitudinally at 2-4 weeks, 2-3 months, and 5-6 months postnatal age.

INTERVENTIONS

Infants underwent daytime polysomnography at each age studied. Blood pressure and heart rate were recorded during quiet (QS) and active (AS) sleep in undisturbed baseline and head-up tilt conditions.

MEASUREMENTS AND RESULTS

Autonomic control was assessed using spectral indices of blood pressure and heart rate variability (BPV and HRV) in ranges of low frequency (LF, reflecting sympathetic + parasympathetic activity) and high frequency (HF, parasympathetic activity), total power (LF+HF), and LF/HF ratio (sympathovagal balance). With increasing postnatal age and predominantly during QS, HRV-LF, HRV-HF, and HRV total power increased, while HRV-LF/HF decreased. BPV-LF/HF also decreased with postnatal age. All changes were evident in both baseline and head-up tilt conditions. BPV-LF and BPV total power during tilts were markedly reduced in QS versus AS at each age.

CONCLUSIONS

In sleeping infants, sympathetic vascular modulation of the circulation decreases with age, while parasympathetic control of heart rate is strengthened. These normative data will aid in the early identification of conditions where autonomic function is impaired, such as in SIDS.

SIDS and other sleep-related infant deaths: expansion of recommendations for a safe infant sleeping environment

Despite a major decrease in the incidence of sudden infant death syndrome (SIDS) since the American Academy of Pediatrics (AAP) released its recommendation in 1992 that infants be placed for sleep in a nonprone position, this decline has plateaued in recent years. Concurrently, other causes of sudden unexpected infant death occurring during sleep (sleep-related deaths), including suffocation, asphyxia, and entrapment, and ill-defined or unspecified causes of death have increased in incidence, particularly since the AAP published its last statement on SIDS in 2005. It has become increasingly important to address these other causes of sleep-related infant death. Many of the modifiable and nonmodifiable risk factors for SIDS and suffocation are strikingly similar. The AAP, therefore, is expanding its recommendations from being only SIDS-focused to focusing on a safe sleep environment that can reduce the risk of all sleep-related infant deaths including SIDS. The recommendations described in this report include supine positioning, use of a firm sleep surface, breastfeeding, room-sharing without bed-sharing, routine immunization, consideration of a pacifier, and avoidance of soft bedding, overheating, and exposure to tobacco smoke, alcohol, and illicit drugs. The rationale for these recommendations is discussed in detail in this technical report. The recommendations are published in the accompanying "Policy Statement--Sudden Infant Death Syndrome and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment," which is included in this issue (www.pediatrics.org/cgi/doi/10.1542/peds.2011-2220).

Baroreflex sensitivity during sleep in infants: impact of sleeping position and sleep state

STUDY OBJECTIVES

The prone sleeping position is a major risk for the sudden infant death syndrome (SIDS) and has been associated with lowered blood pressure and impaired blood pressure control. This study aimed to assess the effects of sleeping position, sleep state, and postnatal age on baroreflex control of heart rate.

PARTICIPANTS

Term infants (n = 31) were studied at 2-4 weeks, 2-3 months, and 5-6 months with daytime polysomnography.

INTERVENTIONS

Blood pressure and heart rate were recorded during quiet (QS) and active (AS) sleep in both the supine and prone positions. In each condition, three 1-2 minute baseline measurements and three 15° head-up tilts were performed.

MEASUREMENTS AND RESULTS

Baroreflex sensitivity (BRS) was assessed using cross-spectral analysis (BRS(SP)) and sequence analysis (BRS(SEQ)) in the baseline condition and with BRS(SP) during head-up tilting (BRS(SP) Tilt). BRS was usually lower prone compared to supine, reaching significance at 2-3 months (BRS(SP), P < 0.05; BRS(SP) Tilt, P < 0.05) and 5-6 months (BRS(SEQ), P < 0.05). BRS was lower in AS than QS supine at 5-6 months for all BRS estimates (P < 0.05). During QS, BRS increased with postnatal age in both sleeping positions (P < 0.05 for all BRS estimates); during AS, the postnatal age-related increase was limited to the prone position (BRS(SEQ), P < 0.05).

CONCLUSIONS

Sleeping position, sleep state and postnatal age all affect infant baroreflex function. Reduced BRS in the younger infants sleeping prone could increase the vulnerability to hypotensive events during sleep and thus play a vital role in conditions where circulatory failure may be involved, such as SIDS.

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.

Effects of alcohol and smoking during pregnancy on infant autonomic control

Prenatal exposure to smoking and alcohol increases the risk for Sudden Infant Death Syndrome (SIDS). Physiological changes associated with these exposures are not well studied. Full-term infants were tested within the first 3 days of life. We hypothesized that maternal alcohol consumption and/or smoking during pregnancy would alter autonomic nervous system function. Newborns whose mothers smoked during pregnancy had lower beat-to-beat heart rate variability in quiet sleep. Infants whose mothers consumed alcohol had lower global heart rate variability, but only in active sleep. Unexposed infants demonstrated increases in heart rate with head-up tilt and decreases in heart rate with head-down tilt, but smoking and alcohol-exposed infants showed no significant responses. These results indicate that autonomic function is altered by prenatal exposure to alcohol and smoking. Such markers may provide early identification of infants at greatest risk for SIDS.

Blood pressure and heart rate patterns during sleep are altered in preterm-born infants: implications for sudden infant death syndrome

OBJECTIVE

Preterm infants are at an increased risk of sudden infant death syndrome, which may result from immature autonomic control of heart rate and blood pressure. Previous studies have demonstrated that preterm infants have altered heart rate and blood pressure control at term-equivalent age; however, little information is available beyond this age. The aim of this study was to determine the effect of preterm birth on heart rate and blood pressure control over the first 6 months of life after reaching term-equivalent age, including the age at which sudden infant death syndrome risk is increased, to understand the pathogenesis of sudden infant death syndrome.

METHODS

Preterm (n=25) and term (n=20) infants were studied longitudinally at 2 to 4 weeks', 2 to 3 months', and 5 to 6 months' term-corrected age by using daytime polysomnography. A photoplethysmographic cuff (Finometer) around the infant's wrist measured blood pressure during quiet and active sleep.

RESULTS

Blood pressure was lower in the preterm group during both quiet and active sleep at all ages studied. In contrast, there were no differences between groups in heart rate. Within the infants in the preterm group, blood pressure averaged lower at 2 to 3 months' corrected age compared with both 2 to 4 weeks' and 5 to 6 months' corrected age and was lower in quiet sleep compared with active sleep at all ages studied. Heart rate decreased with increasing age and was lower in quiet sleep compared with active sleep at 5 to 6 months' corrected age.

CONCLUSIONS

Sleep state and age affect heart rate and blood pressure patterns in prematurely born infants over the first 6 months of term-corrected age. It is notable that preterm infants had persistently lower blood pressure compared with age-matched term infants, signifying long-term alterations in cardiovascular control in infants born prematurely.

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.

Autonomic cardiac control of very preterm newborns: a prolonged dysfunction

BACKGROUND

Autonomic nervous system (ANS) activity is fundamental to infant health. ANS activity of preterm newborns seems to be reduced at term equivalent age, but follow-up of ANS activity has rarely been performed in that population during the weeks after birth. The aim of the study was to perform such a follow-up in preterm newborns of different gestational ages, up to their term equivalent ages.

METHODS

Prolonged electrocardiographic recordings were prospectively performed in a group of 39 premature newborns, each week, up to term equivalent age before discharge. Control values were obtained from a group of 19 full-term newborns, recorded at the first week of their life. ANS indices were calculated from recordings during quiet sleep periods by spectral-domain analysis (Fourier transform): Ptot (total power), VLF (very low-frequencies), LF (low-frequencies), HF (high-frequencies), LF/HF ratio, LFnu (normalized low-frequencies) and HFnu (normalized high-frequencies) values.

RESULTS

Ptot, VLF, LF and HF were significantly lower in the preterm group at birth compared to the control group, while LFnu, HFnu and LF/HF ratio were not significantly different. The results were similar when comparing the control group to any ANS values at a given post-natal corrected age of preterm newborns. Furthermore, preterm newborns did not demonstrate any significant increase in ANS values from birth to theoretical term.

CONCLUSION

The finding of substantial reduced ANS activity and failure of maturation in preterm infants up to term equivalent age needs confirming by other research groups, and mechanisms and implications for infant health explored.

Sudden infant death syndrome

Despite declines in prevalence during the past two decades, sudden infant death syndrome (SIDS) continues to be the leading cause of death for infants aged between 1 month and 1 year in developed countries. Behavioural risk factors identified in epidemiological studies include prone and side positions for infant sleep, smoke exposure, soft bedding and sleep surfaces, and overheating. Evidence also suggests that pacifier use at sleep time and room sharing without bed sharing are associated with decreased risk of SIDS. Although the cause of SIDS is unknown, immature cardiorespiratory autonomic control and failure of arousal responsiveness from sleep are important factors. Gene polymorphisms relating to serotonin transport and autonomic nervous system development might make affected infants more vulnerable to SIDS. Campaigns for risk reduction have helped to reduce SIDS incidence by 50-90%. However, to reduce the incidence even further, greater strides must be made in reducing prenatal smoke exposure and implementing other recommended infant care practices. Continued research is needed to identify the pathophysiological basis of SIDS.

Autonomic nervous system activity in premature and full-term infants from theoretical term to 7 years

The premature population reaching theoretical term suffers from a major deficit in autonomic nervous system (ANS) activity, as can be seen from heart rate variability indices. Whether this autonomic function recovers in the long term is not yet established. Thus, we analyzed and compared ANS activity indices, at birth or at the time of the theoretical term, and at ages 2-3 and 6-7 years, in two populations: a group of 30 premature children and a reference group of 14 full-term age-matched newborns. Using Fourier Transform analysis, we studied 24-h ECG Holter recordings to establish heart rate variability indices: Ptot, VLF, LF, HF, ratio LF/HF, LFnu, HFnu. In the neonatal period, sympathetic and even more markedly, parasympathetic activities were very low in prematures compared to the reference full-term group. At ages 2-3 and 6-7 years, prematures had recovered and had similar ANS activity as the full-term group. These data suggest a fast ANS maturation in prematures during the two first years of life, with a higher speed of recovery for the parasympathetic arm. Furthermore, compared evolution shows a faster ANS maturation in premature. Potential mechanisms are discussed.

Effects of prematurity on heart rate control: implications for sudden infant death syndrome

In Western countries, 5-11% of all infants are born before 37 weeks of gestation, and with improvements in modern intensive care techniques the number of these preterm infants that survive continues to increase. Preterm birth is one of the leading causes of neonatal morbidity and mortality in developed countries, accounting for 60-80% of infant deaths in those without congenital anomalies. Furthermore, in the post-neonatal period, preterm infants are at four-times greater risk of sudden infant death syndrome. It has been suggested that this increased risk is due to immature autonomic control. This article provides an overview of studies assessing autonomic control of the cardiovascular system in preterm infants.

Fewer spontaneous arousals during prone sleep in preterm infants at 1 and 3 months corrected age

OBJECTIVE

This study was performed to determine if there were fewer spontaneous arousals in prone sleep than in supine sleep.

STUDY DESIGN

Home polysomnography/video recordings were done during daytime naps in 14 preterm infants: four at corrected age of 1 month, nine at both 1 and 3 months, and one only at 3 month. A body movement lasting 3 to 60 s during sleep was used as an indicator of spontaneous arousals.

RESULTS

Most arousals had a heart rate increase and change in respiration pattern. The mean duration of the intervals between successive arousals in active and quiet sleep was significantly longer in prone at 1 and 3 months of age. The duration of arousals was significantly shorter at 3 months corrected age compared with one month corrected age during active sleep. The duration of arousals was shorter during quiet sleep at one month compared with active sleep.

CONCLUSION

There were fewer spontaneous arousals that is, longer interval between successive arousals in prone, which may, in part, explain the increase in risk of Sudden Infant Death Syndrome.

Interactions between sleeping position and feeding on cardiorespiratory activity in preterm infants

Infants sleeping in the prone position are at greater risk for sudden infant death syndrome (SIDS). Sleep position-dependent changes in cardiorespiratory activity may contribute to this increased risk. Cardiorespiratory activity is also affected by feeding. Twenty prematurely-born infants were studied at 31-36 weeks postconceptional age while sleeping in the prone and supine positions. Heart rate, respiratory rate, and patterns of variability were recorded during interfeed intervals, and effects of position and time after feeding were analyzed by repeated measures analyses of variance. There were significant effects of both sleeping position and time after feeding. Heart rate is higher and heart period variability is lower in the prone position, and the effects of sleeping position on cardiac functioning are more pronounced during the middle of the intrafeed interval. In preterm infants, autonomic responses to nutrient processing modulate the cardiorespiratory effects of sleeping position. Prone sleeping risk may vary with time after feeding.

Heart rate variability and cardiac reflexes in small for gestational age infants

To assess the influence of intrauterine growth retardation and postnatal development on heart rate variability (HRV) and cardiac reflexes, we studied 27 healthy small for gestational age (SGA) and 23 appropriate for gestational age (AGA) infants during a nap study. Resting HRV was assessed by point dispersion of Poincaré plots for overall (SDRR) and instantaneous beat-to-beat variability (SDΔRR) and the ratio (SDRR/SDΔRR). Heart rate reflex and arousal responses to a 60° head-up tilt were determined. All tests/measures were repeated twice in quiet and active sleep and in prone and supine sleep positions at 1 and 3 mo of age. SGA infants exhibited higher resting sympathetic tone [SDRR/SDΔRR: 1.9 (95% confidence interval: 1.7, 2.0) and 1.7 (95% confidence interval: 1.5, 1.8) in SGA and AGA, respectively; P = 0.046] and a tendency for a smaller tachycardic reflex response to the tilt [Δheart rate: 24 beats/min (95% confidence interval: 20, 28) and 30 (95% confidence interval: 25, 34)] in SGA and AGA, respectively; P = 0.06]. HRV indexes were reduced in the prone compared with supine position ( P < 0.0001), but reflex tilt responses were unchanged with position. SGA/AGA differences were independent of sleep position. Gestational age weight status did not influence the likelihood of arousal, but prone sleeping per se reduced the odds 2.5-fold. The findings suggest reduced autonomic activity and cardiac reflexes in SGA infants. The finding that the sympathetic component of the control of HRV was higher in SGA infants could link with findings in adulthood of an association between being born SGA and a higher risk of cardiovascular disease.

Arterial blood flow and autonomic function in full-term infants

OBJECTIVES

To investigate variations in the autonomic functions and blood-flow velocity of the arteries supplying to the brainstem in supine and prone positions.

METHODS

Forty-one full-term infants were studied at the age of 24-72 h. Each infant underwent respiratory, cardiac and eye movement analyses in supine and prone positions. In addition, blood-flow velocity of the basilar and vertebral arteries was measured with a 2 MHz probe for 5 min in each position. Two time domain measures of heart rate variability (HRV) (Standard deviation of normal R-R intervals for long-term and pNN50 for short-term variability) were employed.

RESULTS

Significantly decreased short- (P<0.001) and long (P = 0.003)-term variabilities were observed in prone when compared with supine position. Increased short-term variability in active sleep with no interaction with position was observed (P = 0.005). A significant decreased mean (P = 0.001) and peak (P = 0.001-0.003) blood-flow velocity in prone when compared with supine position were measured in all three arteries supplying to the brainstem. No significant correlation between HRV and arterial blood-flow velocity (ABFV) was observed in either position.

COMMENT

The results of the present study in agreement with previous studies reflect the vulnerability of infants in prone position as related to brainstem function. However, it appears that ABFV and autonomic functions as reflected by HRV are independent physiological measures, possibly indicating regulation autonomy of the central nervous system.

Developmental changes in infant heart rate responses to head-up tilting

AIM

Newborn infants produce significant heart rate responses to both head-up and head-down tilting: heart rate increases with head-up tilting and decreases with head-down tilting. However, previously we found that, at 2-4 mo of age, heart rate increases were no longer significant following slow head-up tilting. This study was designed to determine if 2-4-mo-old infants have significant increases in heart rate when tilted rapidly.

METHODS

Fifty-four infants were tested as newborns or at 2-4 mo of age. Heart rate was measured while infants were tilted to a 30 degrees head-up angle either slowly over a period of 30 s or rapidly in 5 s.

RESULTS

Newborns exhibited increases in heart rate using both tilt speeds; however, at 2-4 mo of age, heart rate did not change significantly using either speed of tilting.

CONCLUSION

There are significant early developmental changes in cardiac responses to hypotensive challenge. Newborns react like adults, mounting sustained increases in heart rate in response to head-up tilting, but at 2-4 mo of age sustained heart rate responses are no longer significant. Tilt tests may provide a standardized method for assessing autonomic competence during the period of maximum vulnerability to sudden infant death syndrome.

Postnatal development of ventilatory and arousal responses to hypoxia in human infants

During the first year of life there is significant maturation of the hypoxic ventilatory response (HVR) in human infants. Compared with adults, healthy term infants have an immature HVR until at least 6 months of age. There are few studies in infants on the effects of sleep state on the HVR but these suggest that at early postnatal ages there is initially no sleep-state related difference; this is followed by a developmental trend towards the adult situation in which the response is depressed in REM sleep compared with NREM. Maternal cigarette smoking is a major risk factor for SIDS and the mechanism for this may involve a depressed HVR in the exposed infant; however studies are limited and the wide variation in cigarette consumption makes interpretation of results difficult. Arousal responses to hypoxia are of vital importance and a failure to arouse has been implicated in SIDS. Sleeping infants frequently fail to arouse in response to hypoxia in QS, whereas in AS they invariably arouse; furthermore arousal latency is longer in QS compared with AS. The oxygen saturation at which infants arouse is not different between sleep states, suggesting that desaturation is more rapid in AS. In QS younger infants arouse more readily than at older ages and arousal is depressed by maternal smoking. These findings suggest that depression of the arousal response to hypoxia in AS may have life-threatening consequences. Infants at increased risk for SIDS have been shown to have both depressed ventilatory and arousal responses to hypoxia, thus they may be at even greater risk.

Topographic localization of electrocortical activation in newborn and two- to four-month-old infants in response to head-up tilting

AIMS

(1) To confirm that head-up tilting causes sustained increases in the heart rate (HR) of newborn infants but not during the period of maximum vulnerability to SIDS at 2-4 mo of age, and (2) to determine whether electrocortical activation (changes in high-frequency EEG power) also shows topographic and age-dependent effects of tilting.

METHODS

HR and electrocortical activity were recorded in 15 newborn and 12 2- to 4-mo-old infants during head-up tilting. Infants were tilted, three times, to a 30 degrees head-up position. Electrocortical activity was acquired using a 128-lead EEG system. Changes in HR and high-frequency (12-50 Hz) power in the electrocortical signal were computed from the flat to the head-up position.

RESULTS

Newborn infants had significant increases in HR and robust increases in high-frequency power in the left frontal, right frontal-temporal, and occipital regions following head-up tilt. At 2 to 4 mo of age, HR did not change significantly and tilt-related increases in high-frequency power were smaller.

CONCLUSION

The patterns of HR change and electrocortical activation with tilting of newborn infants are different from infants at the age of highest risk for SIDS.

Heart rate responses to non-arousing trigeminal stimulation in infants: effects of sleep position, sleep state and postnatal age

AIMS

The aim of this study was to examine the effects of maternal smoking, sleeping position, sleep state and postnatal age on heart rate changes following non-arousing trigeminal stimulation in infants.

SUBJECTS

We studied healthy term infants, 13 of whom were born to mothers who did not smoke and 11 to mothers who smoked during pregnancy. Each infant was studied using daytime polysomnography on 3 occasions: (a) 2-3 weeks, (b) 2-3 months and (c) 5-6 months after birth. Nasal air-jet stimulation was presented in both active sleep (AS) and quiet sleep (QS) when infants slept both prone and supine.

RESULTS

We found no difference between infants of smoking and non-smoking mothers in any of the parameters measured. Minimum HR (MinHR) following non-arousing trigeminal stimulation was significantly lower in the supine compared to the prone sleeping position at 2-3 weeks and 2-3 months of age (p<0.05) in AS, and at all 3 ages in QS (p<0.01). MinHR was significantly lower in QS compared to AS at 2-3 months when infants slept prone and at 5-6 months when sleeping supine (p<0.01). In QS, MinHR became lower with increasing postnatal age in both sleep positions (p<0.01). In AS, there was no maturational effect. The normalized bradycardia (DeltaHR%) was significantly greater in AS than in QS at 2-3 weeks of age (p<0.05) when infants slept supine.

CONCLUSION

Our study has shown that there was a decrease in heart rate (MinHR) following trigeminal stimulation in infants up to 6 months of age and this was affected by sleep position and sleep state, being larger in the supine sleeping position and the QS state.

Cardiorespiratory effects of nicotine exposure during development

Exposure to tobacco smoke is a major risk factor for the sudden infant death syndrome. Nicotine is thought to be the ingredient in tobacco smoke that is responsible for a multitude of cardiorespiratory effects during development, and pre- rather than postnatal exposure is considered to be most detrimental. Nicotine interacts with endogenous acetylcholine receptors in the brain and lung, and developmental exposure produces structural changes as well as alterations in neuroregulation. Abnormalities have been described in sympathicovagal balance, arousal threshold and latency, breathing pattern at rest and apnea frequency, ventilatory response to hyperoxia or hypoxia, heart rate regulation and ability to autoresuscitate during severe hypoxia. This review discusses studies performed on infants of smoking mothers and nicotine-exposed animals yielding varying and sometimes inconsistent results that may be due to differences in experimental design, species and the dose of exposure. Taken together however, developmental nicotine exposure appears to induce vulnerability during hypoxia and a potential inability to survive severe asphyxia.

Comparison of postnatal development of heart rate responses to trigeminal stimulation in sleeping preterm and term infants

Autonomic dysfunction has been regarded as a possible cause of the sudden infant death syndrome (SIDS) and it has been suggested that preterm infants, who are at a greater risk of SIDS than term infants, may have immature autonomic control. Our aim was to compare the maturation of cardiac autonomic control during sleep in preterm and term infants by examining heart rate responses to arousing and non-arousing trigeminal stimuli. Preterm infants (n = 15) and term infants (n = 24) were studied longitudinally with daytime polysomnography. Air-jet stimulation of the nares was delivered in both active sleep (AS) and quiet sleep (QS), and heart rate (HR) changes recorded for both arousal and non-arousal responses. Changes in HR (DeltaHR%) were calculated as the relative differences between baseline HR (BHR) and either MaxHR (arousal) or MinHR (non-arousal). Comparisons of HR changes between sleep states and postnatal ages were made with two-way anova for repeated measures and between groups with two-way anova. The increase in HR (DeltaHR%) was greater in term than preterm infants (P < 0.05), but only at 2-3 weeks corrected postnatal age (CPA). In preterm infants, there were no differences in BHR between sleep states, whereas in term infants, BHR was higher in AS than in QS at 2-3 weeks and 2-3 months of age. The smaller DeltaHR% to arousing stimuli in preterm infants compared with term infants at 2-3 weeks suggests that cardiac sympathetic activity in preterm infants may be lower than in term infants. This mechanism may account for the increased risk for SIDS of preterm infants.

Sleeping and waking state development in preterm infants

BACKGROUND

Most studies of sleep-wake states of preterm infants have been cross-sectional. Thus, the extent to which sleep-wake development occurs within individuals and how environmental factors affect the development of sleeping and waking is unclear.

AIMS

This study examined the development of sleeping and waking during the preterm and early post-term periods and the effects of infant health and environmental characteristics.

DESIGN

Longitudinal, descriptive design.

PARTICIPANTS

134 preterm infants at high risk for developmental problems because of birthweights under 1500 g or mechanical ventilation.

OUTCOME MEASURES

Weekly 2-h behavioral observations were conducted from the time infants were no longer critically ill until 43 weeks post-conceptional age or discharge. A single follow-up observation was conducted 1-3 months later.

RESULTS

Active sleep, large body movements and the percent of no REM during active sleep decreased with age, and quiet waking, active waking, quiet sleep and regularity of respiration in active sleep and quiet sleep increased. The state of sleep-wake transition increased until 40 weeks and then decreased after 43 weeks CA. Negative facial expressions showed a quadratic decrease over age. Active waking, active sleep, negative facial expressions and quiet sleep regularity showed a change of development after term. Infant characteristics, illness severity and medical treatments, the handling due to performing an EEG and hospital had only minor effects.

CONCLUSIONS

Significant development of sleeping and waking occurs over the preterm period. Additional research is needed to determine how the change from the hospital to the home environment affects on these developmental trajectories.

Respiratory control and arousal in sleeping infants

Control of the cardiovascular and respiratory systems undergoes rapid maturation during infancy. Sleep is at a lifetime maximum during this period and has a marked influence on cardiorespiratory function. The mechanisms leading to sudden infant death syndrome (SIDS) may include a failure in the neural integration of the cardiovascular and respiratory systems, with a concomitant failure to arouse from sleep. Studies have shown that sleep states exert a marked influence on respiratory control and arousability. Infants are more arousable in active sleep compared with quiet sleep from both somatosensory and respiratory stimuli. Post-natal and gestational age at birth also have a marked influence on arousability. Arousability is depressed by the major risk factors for SIDS (prone sleeping, maternal smoking, prematurity and recent infection) and is increased by factors that decrease the risk for SIDS (e.g. use of dummies, breastfeeding).

Influences of maternal cigarette smoking on infant arousability

Since the reduction in the incidence of the prone sleeping position, maternal cigarette smoking has become the strongest modifiable risk factor for Sudden Infant Death Syndrome (SIDS). This risk is dose dependent. Various mechanisms have been postulated to explain the increased risk of SIDS associated with maternal smoking, among these, impairment of arousal from sleep. This paper reviews the effects of maternal smoking on infant arousability from sleep, cardiorespiratory controls and sleep architecture. Infants exposed to maternal smoking have been shown to have both decreased spontaneous and evoked arousability from sleep. Such impairment of arousal has been demonstrated to be associated with changes in control of autonomic cardiac function. Sleep architecture appears not to be altered by smoking. During arousal, heart rate, blood pressure and breathing movements increase, while gross body movements occur to avoid the stimulus. Any impairment in arousability from sleep could occur when infants are exposed to maternal cigarette smoking, and could possibly contribute to the final pathway to SIDS.