Effects of sleep position, sleep state and age on heart rate responses following provoked arousal in term infants

Effect of sleep position in term healthy newborns on sudden infant death syndrome and other infant outcomes: A systematic review

Background

Though recommended by numerous guidelines, adherence to supine sleep position during the first year of life is variable across the globe.

Methods

This systematic review of randomized trials and observational studies assessed the effect of the supine compared to non-supine (prone or side) sleep position on healthy newborns. Key outcomes were neonatal mortality, sudden infant death syndrome (SIDS), sudden unexpected death in infancy (SUDI), acute life-threatening event (ALTE), neurodevelopment, and positional plagiocephaly. We searched MEDLINE via PubMed, Cochrane CENTRAL, EMBASE, and CINAHL (updated till November 2021). Two authors separately evaluated the risk of bias, extracted data, and synthesised effect estimates using relative risk (RR) or odds ratio (OR). The GRADE approach was used to assess the certainty of evidence.

Results

We included 54 studies (43 observational studies and 11 intervention trials) involving 474 672 participants. A single study meeting the inclusion criteria suggested that the supine sleep position might reduce the risk of SUDI (0-1 year; OR = 0.39, 95% confidence interval (CI) = 0.23-0.65; 384 infants), compared to non-supine position. Supine sleep position might reduce the risk of SIDS (0-1 year; OR = 0.51, 95% CI = 0.42-0.61; 26 studies, 59332 infants) and unexplained SIDS/severe ALTE (neonatal period; OR = 0.16, 95% CI = 0.03-0.82; 1 study, 119 newborns), but the evidence was very uncertain. Supine sleep position probably increased the odds of being 0.5 standard deviation (SD) below mean on Gross Motor Scale at 6 months (OR = 1.67, 95% CI = 1.22-2.27; 1 study, 2097 participants), but might have little to no effect at 18 months of age (OR = 1.16, 95% CI = 0.96, 1.43; 1 study, 1919 participants). An increase in positional plagiocephaly at 2-7 months of age with supine sleep position is possible (OR = 2.77, 95% CI = 2.06-3.72; 6 studies, 1774 participants).

Conclusions

Low- to very low-certainty evidence suggests that supine sleep position may reduce the risk of SUDI (0-1 year) and SIDS (0-1 year). Limited evidence suggests that supine sleeping probably delays short-term ‘gross motor’ development at 6 months, but the effect on long-term neurodevelopment at 18 months may be negligible.

Impact of diaper change frequency on preterm infants' vital sign stability and skin health: A RCT

BACKGROUND

Bundling nurse caregiving interventions are promoted to minimize infant stress.

PURPOSE

To evaluate impact of bundled nursing care and diaper change frequency on vital sign stability and skin health of preterm infants born ≤32 weeks gestation.

METHOD

Stable preterm infants on a 3-hour feeding schedule were randomly assigned to 3- vs. 6-hour diaper changes. Diapers were changed prior to 6 h if stool was present. Direct observation of bundled care events (BCE) identify caregiving activities during each BCE. Skin pH, transepidermal water loss (TEWL), and neonatal skin condition scores (NSCS) were obtained. Vital sign data (HR, RR, O₂ saturation) was downloaded from bedside monitors.

RESULTS

Forty-six infants contributed to 605 BCEs. BCEs lasted on average 28 min and included nine different activities (e.g., vital signs, feeding). Significant increases in heart rate during BCEs occurred in approximately half of the observations. Among observations with a diaper change increases in heart rate during diapering occurred in over 74% of observations Infants who were awake at the beginning of BCEs had 48% lower odds of having a change in heart rate than infants who were sleeping (p = .02). There were no group differences (3- vs. 6-hour diaper change) in skin health outcomes (TEWL, pH, NSCS).

CONCLUSION

Reducing diaper change frequency without stool present should be considered to minimize caregiving stress in preterm infants. Additional research should evaluate the intrusiveness and clusters of activities that significantly impact physiologic stability to better individualize the timing of routine yet intrusive activities. Clinicaltrials.gov registry # NCT03370757.

Bedsharing and Breastfeeding: The Academy of Breastfeeding Medicine Protocol #6, Revision 2019

A central goal of the Academy of Breastfeeding Medicine is the development of clinical protocols for managing common medical problems that may impact breastfeeding success. These protocols serve only as guidelines for the care of breastfeeding mothers and infants and do not delineate an exclusive course of treatment or serve as standards of medical care. Variations in treatment may be appropriate according to the needs of an individual patient.

Is prone sleeping dangerous for neonates? Polysomnographic characteristics and NDN gene analysis

Objective:

Prone sleep is an identified risk factor for sudden infant death syndrome, possibly due to reduced blood pressure, cerebral oxygenation, and impaired cerebral vascular control. Cardiac and respiratory responses in neonates during supine and prone sleep have not been reported.

Materials and Methods:

In this study, daytime polysomnography (PSG) data from 17 neonates aged 2–3 days during supine and prone sleep were reported and the NDN gene, an important gene for neonatal respiratory control, was sequenced for correlation with neonatal respiratory parameters. Heart rate (HR), oxygen saturation, carbon dioxide concentration, sleep stages, central apnea index (CAI), obstructive apnea/hypopnea index (OAHI), and oxygen nadir were compared between supine and prone sleep and between participants with different single-nucleotide polymorphisms (SNPs) in the NDN gene.

Results:

During prone sleep, neonates had a faster HR, decreased oxygen saturation, and a longer duration of oxygen saturation <90% than during supine sleep, suggesting that cardiopulmonary responsiveness was impaired. Sleep efficiency, sleep stages, oxygen nadir, and carbon dioxide tension were not different during supine and prone sleep. Central apnea occurred more significantly than obstructive apnea. During supine and prone sleep, the CAI was 3.3 ± 2.9/h and 2.3 ± 2.6/h and the OAHI was 0.6 ± 0.7/h and 0.6 ± 0.8/h, respectively. We found one SNP rs3743340 in the NDN gene that had no effect on the sleep and respiratory parameters of PSG.

Conclusion:

Tachycardia and respiratory instability were recorded in neonates during prone sleep, suggesting that neonates are vulnerable to cardiopulmonary events during prone sleep. Therefore, young neonates should be kept in the supine sleep position unless there are contraindications.

Cardiovascular autonomic dysfunction in sudden infant death syndrome

A failure of cardiorespiratory control mechanisms, together with an impaired arousal response from sleep, are believed to play an important 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 developmental period in homeostatic control and (3) an exogenous stressor. In an attempt to understand how the triple risk hypothesis is related to infant cardiorespiratory physiology, many researchers have examined how the known risk and protective factors for SIDS alter infant cardiovascular control during sleep. This review discusses the association between the three components of the triple risk hypothesis and major risk factors for SIDS, such as prone sleeping, maternal smoking, together with three "protective" factors, and cardiovascular control during sleep in infants, and discusses their potential involvement in SIDS.

Sleep positions and nocturnal body movements based on free-living accelerometer recordings: association with demographics, lifestyle, and insomnia symptoms

BACKGROUND

In order to establish normative values for body positions and movements during sleep, the objective of this study was to explore the distribution of sleep positions and extent of nocturnal body moments and the association with sex, age, body-mass index (BMI), smoking, alcohol consumption, and insomnia symptoms.

MATERIALS AND METHODS

This cross-sectional study comprised data on a working population (363 men and 301 women) who participated in the Danish Physical Activity Cohort with Objective Measurements (DPHACTO). Measures of body position and movements were obtained from actigraph accelerometers on the thigh, upper back, and upper arm. Linear regression was used to estimate adjusted mean differences in movements among categories of demographic and lifestyle characteristics.

RESULTS

During their time in bed, participants spent 54.1% (SD 18.1%) in the side position, 37.5% (SD 18.2%) in the back position, and 7.3% (SD 12.3%) in the front position. Increasing age and BMI were associated with increased time in the side position and a proportional reduction in time in the back position. There were on average 1.6 (SD 0.7) position shifts per hour. Compared to males, females had fewer position shifts (-0.37, 95% CI -0.48 to -0.24) and fewer arm, thigh, and upper-back movements. Participants aged 20-34 years had more arm, thigh, and upper-back movements compared to participants ≥35 years. Obese participants had fewer shifts in body position (-0.15, 95% CI -0.27 to 0), but more arm, thigh, and upper-back movements compared to normal-weight participants. Smokers had fewer shifts in body position than nonsmokers (-0.27, 95% CI -0.4 to -0.13).

CONCLUSION

The predominant sleep position in adults is on the side. This preference increases with age and BMI. The extent of nocturnal body movements is associated with sex, age, BMI, and smoking.

Cerebral oxygenation in preterm infants

BACKGROUND AND OBJECTIVE

Prone sleeping is a major risk factor for sudden infant death syndrome (SIDS) and preterm infants are at significantly increased risk. In term infants, prone sleeping is associated with reduced mean arterial pressure (MAP) and cerebral tissue oxygenation index (TOI). However, little is known about the effects of sleeping position on TOI and MAP in preterm infants. We aimed to examine TOI and MAP in preterm infants after term-equivalent age, during the period of greatest SIDS risk.

METHODS

Thirty-five preterm and 17 term infants underwent daytime polysomnography, including measurement of TOI (NIRO-200 spectrophotometer, Hamamatsu Photonics KK, Japan) and MAP (Finapress Medical Systems, Amsterdam, Netherlands) at 2 to 4 weeks, 2 to 3 months, and 5 to 6 months postterm age. Infants slept prone and supine in active and quiet sleep. The effects of sleep state and position were determined by using 2-way repeated measures analysis of variance and of preterm birth by using 2-way analysis of variance.

RESULTS

In preterm infants, TOI was significantly lower when prone compared with supine in both sleep states at all ages (P < .05). Notably, TOI was significantly lower in preterm compared with term infants at 2 to 4 weeks, in both positions (P < .05), and at 2 to 3 months when prone (P < .001), in both sleep states. MAP was also lower in preterm infants in the prone position at 2 to 3 months (P < .01).

CONCLUSIONS

Cerebral oxygenation is reduced in the prone position in preterm infants and is lower compared with age-matched term infants, predominantly in the prone position when MAP is also reduced. This may contribute to their increased SIDS risk.

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.

Arousal from sleep mechanisms in infants

Arousals from sleep allow sleep to continue in the face of stimuli that normally elicit responses during wakefulness and also permit awakening. Such an adaptive mechanism implies that any malfunction may have clinical importance. Inadequate control of arousal in infants and children is associated with a variety of sleep-related problems. An excessive propensity to arouse from sleep favors the development of repeated sleep disruptions and insomnia, with impairment of daytime alertness and performance. A lack of an adequate arousal response to a noxious nocturnal stimulus reduces an infant's chances of autoresuscitation, and thus survival, increasing the risk for Sudden Infant Death Syndrome (SIDS). The study of arousability is complicated by many factors including the definition of an arousal; the scoring methodology; the techniques used (spontaneous arousability versus arousal responses to endogenous or exogenous stimuli); and the confounding factors that complicate the determination of arousal thresholds by changing the sleeper's responses to a given stimulus such as prenatal drug, alcohol, or cigarette use. Infant age and previous sleep deprivation also modify thresholds. Other confounding factors include time of night, sleep stages, the sleeper's body position, and sleeping conditions. In this paper, we will review these different aspects for the study of arousals in infants and also report the importance of these studies for the understanding of the pathophysiology of some clinical conditions, particularly 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.

Unchanged heart rate-respiratory frequency ratio in preterm infants during spontaneous arousals

AIM

To find out whether a correlation of heart rate (HR) and respiratory frequency (RF) defined as HR-RF-ratio (HRR) may be helpful to identify arousals in term and preterm infants.

METHODS

Polygraphic recordings were performed in 25 term infants (gestational age 40.1 +/- 1.1 weeks) and 25 preterm infants (gestational age 31.1 +/- 1.3 weeks) during undisturbed daytime sleep. Arousals were scored as suggested by the 'International Paediatric Work Group on Arousals' and divided into cortical arousals and subcortical arousals. HRR was defined as HR over RF. Arousals were compared to a 30-sec period preceding an arousals.

RESULTS

Two hundred arousals were scored (100 cortical arousals and 100 subcortical arousals). HRR increased during arousals in term infants (p < 0.001). This was true for cortical arousals (p < 0.001) and subcortical arousals (p < 0.05) of term infants. In contrast, in preterm infants HRR remained unchanged during cortical arousals and subcortical arousals.

CONCLUSION

An increase of HRR during arousals is a simple parameter to identify arousals in term infants, but not in preterm infants suggesting that an unchanged HRR might be an indicator of an immature arousal response.

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.

Is bladder voiding in sleeping preterm infants accompanied by arousals?

BACKGROUND

As it has been reported that bladder voiding in sleeping full-term infants is consistently accompanied by a cortical arousal, it was the aim of the present study to find out whether this could also hold true for preterm infants.

METHODS

Polygraphic recordings were performed in 21 healthy preterm infants (10 female). The infants' gestational age at birth was 31+/-2.7 weeks and postnatal age at study entry was 26+/-8 days (mean+/-standard deviation). Bladder voiding was recorded by an adapted enuresis detector which was connected to the polygraphic computer unit. Arousals were defined as suggested by the International Paediatric Work Group on Arousals.

RESULTS

Bladder voiding was recorded 50+/-7 min after sleep onset and occurred during quiet sleep (QS) only. Heart rate (HR), respiratory frequency (RF) and electroencephalographic (EEG) frequency did not change during bladder voiding. Body movements were recorded in 52% of all preterm infants.

CONCLUSION

We found that bladder voiding was not accompanied by arousals, suggesting that the arousal process in preterm infants may be delayed due to immaturity.

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.

Comparison of heart rate responses during cortical and subcortical arousals in term and preterm infants

The aim of this study was to determine whether prematurity affects heart rate responses during spontaneous arousals. Polygraphic recordings were performed during undisturbed daytime naps in 35 preterm infants (gestational age at birth 32+/-2 weeks) and 35 term infants. Arousals were scored according to the recommendations of the International Paediatric Work Group on Arousals and categorized either as cortical arousals (CA) or subcortical arousals (SCA). Heart rate (HR) and respiratory frequency (RF) were measured during arousal and during the 10-s and 30-s period before and after arousal. Changes in HR and RF were expressed as the percentage of modification normalized for the 30-s period preceding arousal. Altogether, 122 arousals in preterm infants (66 CA, 56 SCA) and 105 arousals in term infants (57 CA, 48 SCA) were scored. Mean duration of the arousal period was 9+/-4 s and 8+/-3 s, respectively. In term infants, a significant increase in HR during arousal could be shown (11.3+/-8.2%; p<0.001), whereas this increase was significantly greater during CA compared to SCA (13.7+/-6.2% versus 8.4+/-9.4%; p<0.001). In contrast, HR decreased during arousal in preterm neonates (-3.9+/-19.3%; p<0.05). These findings suggest that cardiovascular control seems to be maturationally delayed in preterm infants, which may contribute to their increased risk for Sudden Infant Death Syndrome (SIDS).

Cerebral hemodynamics during arousals in preterm infants

The aim of the study was to evaluate potential changes of cerebral blood volume (CBV) related to arousals in preterm infants. As arousals are known to change different physiological parameters, it was postulated that this could also hold true for CBV. Polygraphic recordings were performed in 38 preterm infants (18 female, 20 male). The infants' gestational age at birth was 32.0+/-2.3 weeks, postconceptional age was 35.1+/-1.2 weeks and postnatal age at study entry was 24.3+/-2.9 days, birth weight was 1793+/-527 g and actual weight at study entry was 2011+/-324 g [mean (+/- standard deviation)]. CBV was measured using near infrared spectroscopy. Arousals were scored due to the guidelines of the "International Paediatric Work Group on Arousals" and categorized as either cortical (CA) or subcortical arousals (SCA). Altogether, 122 arousals (66 CA, 56 SCA) were scored. According to sleep stage, 77 arousals were analyzed in active sleep, 23 in quiet sleep and 22 in intermediate sleep. Mean duration of arousals was 8.8+/-0.3 s. CBV, cerebral vascular oxygenation and the balance between oxygen delivery and oxygen consumption remained constant during arousals in preterm infants. This was demonstrated for both CA and SCA and was independent of sleep stage, suggesting that the impact of arousals in stable preterm infants is too small to alter cerebral vascular autoregulation.

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.

Neurophysiologic assessment of neonatal sleep organization: preliminary results of a randomized, controlled trial of skin contact with preterm infants

BACKGROUND

Sleep is important to brain organization, but few strategies to promote sleep among premature infants have been tested. Behaviorally based measures of sleep have shown increased quiet sleep (QS) and decreased active sleep (AS) during skin-to-skin contact (SSC) with the mother, but these results have not been confirmed with objective electroencephalographic/polysomnographic measures of sleep organization. Important differences exist between behavioral and electroencephalographic/polysomnographic definitions of sleep state.

METHODS

Data for the first 28 relatively healthy, preterm subjects of an ongoing randomized trial of one 2- to 3-hour session of SSC or incubator care between feedings are reported here. Infants were positioned prone, inclined, and nested in an incubator during the 2- to 3-hour pretest period, were fed, and then went into the test period of SSC or incubator care. Infants were left largely undisturbed throughout testing. A mixed-model regression analysis compared the test-pretest differences in outcome measures within and between groups.

RESULTS

Results showed that arousals were significantly lower in the SSC group, compared with the control group, for the entire study period and for test-pretest matched segments of QS and AS. Rapid eye movement was significantly lower for the SSC group for the study period and AS segments. Indeterminate sleep was significantly lower for the SSC group when confounding environmental variables were included in the regression analysis. When 4 subjects who experienced excessive ambient light levels during SSC were removed from analysis, QS increased during SSC.

CONCLUSIONS

The patterns demonstrated by the SSC group are analogous to more-mature sleep organization. SSC may be used as an intervention to improve sleep organization in this population of preterm infants.

Bladder voiding in sleeping infants is consistently accompanied by a cortical arousal

The aim of the study was to find out whether bladder voiding in healthy sleeping infants was accompanied by any arousal reaction. Polygraphic recordings were performed in 21 healthy infants (11 female) born at term. The infants' age at study entry was 42 +/- 4 days and actual body weight was 4852 +/- 689 g (mean +/- SD). Bladder voiding was recorded by an adapted enuresis detector which was connected to the polygraphic computer unit. Arousals were defined as suggested by the 'International Paediatric Work Group on Arousals'. Awakenings were excluded from the study. Bladder voiding was recorded at a mean time of 68 +/- 7 min after the infant had fallen asleep and occurred during quiet sleep (QS). Electroencephalogram frequency (P < 0.01) and heart rate (P < 0.05) were higher during the 5-s period before and after bladder voiding when compared with a 30-s interval before voiding. Furthermore, bladder voiding was accompanied by body movements in all infants. Respiratory frequency did not change significantly. We could demonstrate for the first time in sleeping infants, that bladder voiding during QS was accompanied by a cortical arousal.

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.

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.