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

Maturation of the cardiac autonomic regulation system, as function of gestational age in a cohort of low risk preterm infants born between 28 and 32 weeks of gestation

OBJECTIVES

The maturation of the sympathetic nervous system (SNS) occurs steadily throughout gestation while the myelinated vagus has accelerated maturation periods, between 25 and 32 weeks of gestation and a further increase around 37-38 weeks of gestation. The aim was to quantify the cardiac autonomic regulation maturation, as a function of gestational age (GA) in a cohort of low risk preterm infants born between 28 and 32 weeks of gestation by assessing heart rate variability (HRV) at week 32, and at week 35 postmenstrual age (PMA).

METHODS

Forty preterm infants were recruited, 24 h recordings of breathing rate and RR intervals were obtained at week 32 and week 35 PMA.

RESULTS

A significant difference was noted between preterm infants born before 32 weeks GA and preterm infants born at week 32; the latter present higher HRV values throughout the follow-up period. No significant change over time was noted for the parasympathetic HRV measures while a significant increase was found in the sympathetic system. Moreover, a significant interaction effect of time and system was found, the increase in values of the sympathetic system over time was significantly larger than the change noted in the vagal HRV measures.

CONCLUSIONS

Given the beneficial influence of vagal tone on health and developmental outcomes in preterm infants, the findings of the current study highlight the need for further studies on the impact of specifics gestational age on vagal development and later assessing interventions associate with its continue development and maturation at these specific periods.

Genetic Factors Underlying Sudden Infant Death Syndrome

Sudden Infant Death syndrome (SIDS) is a diagnosis of exclusion. Decades of research have made steady gains in understanding plausible mechanisms of terminal events. Current evidence suggests SIDS includes heterogeneous biological conditions, such as metabolic, cardiac, neurologic, respiratory, and infectious conditions. Here we review genetic studies that address each of these areas in SIDS cases and cohorts, providing a broad view of the genetic underpinnings of this devastating phenomenon. The current literature has established a role for monogenic genetic causes of SIDS mortality in a subset of cases. To expand upon our current knowledge of disease-causing genetic variants in SIDS cohorts and their mechanisms, future genetic studies may employ functional assessments of implicated variants, broader genetic tests, and the inclusion of parental genetic data and family history information.

Avoidable mortality from respiratory tract infection and sudden unexplained death in children with chronic conditions: a data linkage study

OBJECTIVE

To determine the risk of death from two potentially avoidable causes with different aetiologies: respiratory tract infection (RTI) and sudden unexplained death (SUD) in children with and without chronic conditions.

DESIGN

Whole-country, birth cohort study using linked administrative health databases from Scotland.

SETTING AND PARTICIPANTS

Children aged 2 months to less than 5 years in Scotland between 2000 and 2014.

MAIN OUTCOME MEASURES

Relative risk of death (expressed as the HR) related to RTIs or SUD, in children with and without chronic conditions. We separately analysed deaths at ages 2-11 months and at 1-4 years and adjusted for birth characteristics, socioeconomic status and vaccination uptake using Cox regression.

RESULTS

The cohort comprised 761 172 children. Chronic conditions were recorded in 9.6% (n=72 901) of live births, 82.4% (n=173) of RTI-related deaths and 17.4% (n=49) of SUDs. Chronic conditions were very strongly associated with RTI mortality (2-11 months: HR 68.48, 95% CI (40.57 to 115.60), 1-4 years: HR 38.32, 95% CI (23.26 to 63.14)) and strongly associated with SUD (2-11 months: HR 2.42, 95% CI (1.67 to 3.63), 1-4 years: HR 2.53, 95% CI (1.36 to 4.71)).

CONCLUSIONS

The very strong association with chronic conditions suggests that RTI-related mortality may sometimes be a consequence of a terminal decline and not possible to defer or prevent in all cases. Recording whether death was expected on death certificates could indicate which RTI-related deaths might be avoidable through healthcare and public health measures.

In-utero exposure to nicotine alters the development of the rabbit cardiac conduction system and provides a potential mechanism for sudden infant death syndrome

In-utero exposure to tobacco smoke remains the highest risk factor for sudden infant death syndrome (SIDS). To alleviate the risks, nicotine replacement therapies are often prescribed to women who wish to quit smoking during their pregnancy. Cardiac arrhythmias is considered the final outcome leading to sudden death. Our goal in this study was to determine if exposing rabbit fetus to nicotine altered the cardiac conduction system of newborn kittens in a manner susceptible to cause SIDS. Using neuronal markers and a series of immunohistological and electrophysiological techniques we found that nicotine delayed the development of the cardiac pacemaker center (sinoatrial node) and decreased its innervation. At the molecular level, nicotine favored the expression of cardiac sodium channels with biophysical properties that will tend to slow heart rate and diminish electrical conduction. Our results show that alterations of the cardiac sodium current may contribute to the bradycardia, conduction disturbances and other cardiac arrhythmias often associated to SIDS and raise awareness on the use of replacement therapy during pregnancy.

Parents need support to find ways to optimise their own sleep without seeing their preterm infant's sleeping patterns as a problem

AIM

This study described how parents perceived their own sleep, and their infants', during neonatal intensive care unit (NICU) admission and after discharge. It also explored the infants' sleeping location at home.

METHODS

The study was conducted in the NICUs of two Swedish university hospitals. The parents of 86 infants - 86 mothers and 84 fathers - answered questionnaires during their infants' hospital stay, at discharge and at the infants' corrected ages of two, six and 12 months. The parents' own sleep was explored with the Insomnia Severity Index.

RESULTS

Mothers reported more severe insomnia than fathers during their infants' hospitalisation, and these higher insomnia severity scores were associated with more severe infant sleep problems at discharge (p = 0.027) and at two months (p = 0.006) and 12 months (p = 0.002) of corrected age. During the study period, 4%-10% of the parents reported severe or very severe infant sleeping problems. The bed-sharing rate was 75% after discharge and about 60% at the corrected age of 12 months.

CONCLUSION

Maternal insomnia during an infant's hospital stay was associated with later perceptions of sleep problems in their children. Parents need support to find solutions for optimal sleep without seeing their child's sleeping patterns as a problem.

Dummy/pacifier use in preterm infants increases blood pressure and improves heart rate control

BACKGROUND

Preterm infants are at increased risk of sudden infant death syndrome (SIDS). Use of a dummy/pacifier is thought to be protective against SIDS; accordingly, we assessed the effects of dummy/pacifier use on blood pressure, cerebral oxygenation, and heart rate control over the first 6 mo of life after term corrected age (CA) when SIDS risk is greatest.

METHODS

Thirty-five preterm infants were studied longitudinally at 2-4 wk, 2-3 mo, and 5-6 mo CA. Cardiac control was assessed from spectral indices of heart rate variability (HRV) in the low frequency (LF) and the high frequency (HF) range, and the ratio of HF/LF indicating sympathovagal balance was calculated.

RESULTS

Overall, at 2-3 mo, mean arterial pressure was significantly higher in the supine position in dummy/pacifier users in both quiet sleep (70 ± 2 vs. 60 ± 2 mm Hg; P < 0.05) and active sleep (74 ± 3 vs. 69 ± 2 mm Hg; P < 0.05). Dummy/pacifier users had higher LF HRV and LF/HF ratio and lower HF HRV.

CONCLUSION

Dummy/pacifier use increased blood pressure during sleep, at the age of greatest SIDS risk. Overall, LF HRV was elevated and HF HRV reduced in dummy/pacifier users, suggesting that dummy use alters cardiac control in preterm infants.

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.

Cardiorespiratory coupling in health and disease

Cardiac and respiratory activities are intricately linked both functionally as well as anatomically through highly overlapping brainstem networks controlling these autonomic physiologies that are essential for survival. Cardiorespiratory coupling (CRC) has many potential benefits creating synergies that promote healthy physiology. However, when such coupling deteriorates autonomic dysautonomia may ensue. Unfortunately there is still an incomplete mechanistic understanding of both normal and pathophysiological interactions that respectively give rise to CRC and cardiorespiratory dysautonomia. Moreover, there is also a need for better quantitative methods to assess CRC. This review addresses the current understanding of CRC by discussing: (1) the neurobiological basis of respiratory sinus arrhythmia (RSA); (2) various disease states involving cardiorespiratory dysautonomia; and (3) methodologies measuring heart rate variability and RSA.

Kangaroo care with twins: a case study in which one infant did not respond as expected

PURPOSE

The purposes were to relate responses (including unacceptable ones) of twins to shared kangaroo care (KC), to provide explanations for the unexpected responses, and to offer suggestions for safe nursing practice.

DESIGN

A descriptive, evaluative case study was conducted. Both twins received KC while their vital signs and maternal breast temperatures were manually recorded every 30 seconds. Descriptive statistics were computed.

SAMPLE

Identical twins, born to a 19-year-old African-American primigravada, were 34 3/7 weeks postconceptional age with weights of 1,760 and 1,480 g, respectively, when tested. Preterm labor resulted in spontaneous vaginal birth at 30 weeks gestation.

MAIN OUTCOME VARIABLES

Infant heart and respiratory rates, oxygen saturations, abdominal temperatures, and maternal breast temperatures.

RESULTS

Infant A's vital signs exceeded acceptable clinical limits during shared KC; vital signs returned to normal range once Infant A was returned to the incubator. Infant B's vital signs approximated clinically acceptable ranges throughout the session. Breast temperatures did not differ. Individuality mandates vigilant assessment of infant responses to shared KC.

The brainstem and serotonin in the sudden infant death syndrome

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

The effect of fish oil supplementation on heart rate in healthy Danish infants

Polyunsaturated n-3 fatty acids (n-3PUFA) may improve brain development and prevent cardiovascular disease. Heart rhythm is autonomically controlled and among the affected cardiovascular risk markers in adults. The aim of the study was to examine whether fish oil supplementation in late infancy could modify heart rate (HR) and heart rate variability (HRV). In a 2 x 2-intervention, 83 healthy Danish infants were randomized to +/- fish oil (3.4 +/- 1.1 mL/d) and cow's milk or infant formula from 9 to 12 mo of age. In 57 infants, 0.5-h ECG recordings were successfully obtained before and after the intervention and erythrocyte fatty acid composition was determined in 30 of these. Fish oil supplementation raised erythrocyte n-3PUFA content (p < 0.001). No significant group differences were seen in HR or HRV. However, a fish-oil x gender interaction was observed on mean RR interval (p = 0.001) with a 6% longer mean RR interval in fish-oil-supplemented boys (p = 0.007). Irrespective of gender, there was a positive association between the 9- and 12-mo changes in RR interval and erythrocyte n-3PUFA (p < 0.001). In infants with confirmed changes in erythrocyte n-3PUFA, mean RR interval was found to be longer (p = 0.011) in the fish-oil-supplemented groups. The study suggests that fish oil may affect heart rhythm in infants similar to that observed in adults. This may imply low n-3PUFA-status in late infancy and n-3PUFA influence on CNS function.