Development of baroreflex control of heart rate in preterm and full term infants

Mechanisms of Cardiovascular Changes of Phototherapy in Newborns with Hyperbilirubinemia

During phototherapy of jaundiced newborns, vasodilation occurs in the skin circulation compensated by vasoconstriction in the renal and mesenteric circulation. Furthermore, there is a slight decrease in cardiac systolic volume, and blood pressure, as well as an increase in heart rate and discrete changes in the heart rate variability (HRV). The primary change during phototherapy is the skin vasodilation mediated by multiple mechanisms: 1) Passive vasodilation induced by direct skin heating effect of the body surface and subcutaneous blood vessels, modified by myogenic autoregulation. 2) Active vasodilation mediated via the mechanism provided by axon reflexes through nerve C-fibers and humoral mechanism via nitric oxide (NO) and endothelin 1 (ET-1). During and after phototherapy is a rise in the NO:ET-1 ratio. 3) Regulation of the skin circulation through the sympathetic nerves is unique, but their role in skin vasodilation during phototherapy was not studied. 4) Special mechanism is a photorelaxation independent of the skin heating. Melanopsin (opsin 4) - is thought to play a major role in systemic vascular photorelaxation. Signalling cascade of the photorelaxation is specific, independent of endothelium and NO. The increased skin blood flow during phototherapy is enabled by the restriction of blood flow in the renal and mesenteric circulation. An increase in heart rate indicates activation of the sympathetic system as is seen in the measures of the HRV. High-pressure, as well as low-pressure baroreflexes, may play important role in these adaptation responses. The integrated complex and specific mechanism responsible for the hemodynamic changes during phototherapy confirm adequate and functioning regulation of the neonatal cardiovascular system, including baroreflexes.

Cardiovascular changes during phototherapy in newborns

Phototherapy is the most effective non-invasive method of neonatal hyperbilirubinemia treatment. Application of this method can be associated with side effects including changes in the cardiovascular system. During phototherapy, the primary effects in the cardiovascular system include cutaneous vasodilation leading to skin hyperperfusion and subsequent redistribution of blood. The increased blood flow through the skin is associated with increased transepidermal water loss. Further effects include an increase in cerebral blood flow. Redistribution of blood to the cutaneous bed is compensated by hypoperfusion in the splanchnic area (mostly postprandial) and a significant reduction of the renal blood flow. Regarding closure/reopening of the ductus arteriosus, the results suggest that that phototherapy does not affect ductal patency. During phototherapy the cardiac output can be slightly reduced due to a decreased stroke volume, especially in preterm newborns. Systemic blood pressure is decreased and heart rate is elevated in both preterm and term newborns during phototherapy. The heart rate variability is slightly reduced. Symbolic dynamics analysis of the short-term HRV showed that during phototherapy the activity of the ANS regulating the heart rate is shifted towards the dominancy of the sympathetic activity. The responses in the cardiovascular system of premature/mature newborns without other pathology confirm a well physiologically functioning control of this system, even under specific conditions of phototherapy.

Baroreflex Sensitivity and Blood Pressure in Premature Infants – Dependence on Gestational Age, Postnatal Age and Sex

To characterize the differences in baroreflex sensitivity (BRS), blood pressure (BP), heart rate (HR) and respiration rate (RR) in preterm infants with a similar postconceptional age reached by various combinations of gestational and postnatal ages. To detect potential sex differences in assessed cardiovascular parameters. The study included 49 children (24 boys and 25 girls), postconceptional age 34.6±1.9 weeks. Two subgroups of infants were selected with the similar postconceptional age (PcA) and current weight, but differing in gestational (GA) and postnatal (PnA) ages, as well as two matched subgroups of boys and girls. Blood pressure (BP) was recorded continuously using Portapres device (FMS). A stationary segment of 250 beat-to-beat BP values was analyzed for each child. Baroreflex sensitivity (BRS) was calculated by cross-correlation sequence method. Despite the same PcA age and current weight, children with longer GA had higher BRS, diastolic and mean BP than children with shorter GA and longer PnA age. Postconceptional age in preterm infants is a parameter of maturation better predicting baroreflex sensitivity and blood pressure values compared to postnatal age. Sex related differences in BRS, BP, HR and RR were not found in our group of preterm infants.

Physiology of Low Blood Pressure During the First Day After Birth Among Extremely Preterm Neonates

OBJECTIVE

To investigate the circulatory physiology of hypotension during the first day after birth among stable extremely preterm neonates.

STUDY DESIGN

Case-control study of neonates born at ≤27^6/7 weeks gestational age with hypotension, defined as mean blood pressure in mmHg less than gestational age in weeks for at least 1 hour during the first 24 hours after birth, who underwent comprehensive echocardiography assessment before commencement of cardiovascular drugs. Neonates with hypotension (n = 14) were matched by gestational age and intensity of respiratory support with normotensive neonates (n = 27) who underwent serial echocardiography during the first day after birth, and relatively contemporaneous echocardiography assessments were used for comparison.

RESULTS

Neonates with hypotension had a higher frequency of patent ductus arteriosus ≥1.5 mm (71% vs 15%; P < .001) and ductal size (median diameter, 1.6 mm [IQR, 1.4-2.1] vs 1.0 mm [IQR, 0-1.3]; P = .002), higher echocardiography indices of left ventricular systolic function (mean shortening fraction, 34 ± 7% vs 26 ± 4%; P < .001; mean longitudinal strain, -16 ± 5% vs -14 ± 3%; P = .04; and mean velocity of circumferential fiber shortening, 1.24 ± 0.35 circ/s vs 1.01 ± 0.28 circ/s; P = .03), lower estimates of left ventricular afterload (mean end-systolic wall stress, 20 ± 7 g/cm² vs 30 ± 9 g/cm²; P < .001 and mean arterial elastance, 43 ± 19 mmHg/mL vs 60 ± 22 mmHg/mL; P = .01), without significant difference in stress-velocity index z-score (-0.42 ± 1.60 vs -0.88 ± 1.30; P = .33). Neonates with hypotension had higher rates of any degree of intraventricular hemorrhage (71% vs 22%; P = .006).

CONCLUSIONS

Low blood pressure in otherwise well extremely low gestational age neonates was associated with low systemic afterload and larger patent ductus arteriosus, but not left ventricular dysfunction.

Prone sleeping affects cardiovascular control in preterm infants in NICU

BACKGROUND

Prone sleeping is used in preterm infants undergoing intensive care to improve respiratory function, but evidence suggests that this position may compromise autonomic cardiovascular control. To test this hypothesis, this study assessed the effects of the prone sleeping position on cardiovascular control in preterm infants undergoing intensive care treatment during early postnatal life.

METHODS

Fifty-six preterm infants, divided into extremely preterm (gestational age (GA) 24-28 weeks, n = 23) and very preterm (GA 29-34 weeks, n = 33) groups, were studied weekly for 3 weeks in prone and supine positions, during quiet and active sleep. Heart rate (HR) and non-invasive blood pressure (BP) were recorded and autonomic measures of HR variability (HRV), BP variability (BPV), and baroreflex sensitivity (BRS) using frequency analysis in low (LF) and high (HF) bands were assessed.

RESULTS

During the first 3 weeks, prone sleeping increased HR, reduced BRS, and increased HF BPV compared to supine. LF and HF HRV were also lower prone compared to supine in very preterm infants. Extremely preterm infants had the lowest HRV and BRS measures, and the highest HF BPV.

CONCLUSIONS

Prone sleeping dampens cardiovascular control in early postnatal life in preterm infants, having potential implications for BP regulation in infants undergoing intensive care.

Bioreactance-derived haemodynamic parameters in the transitional phase in preterm neonates: a longitudinal study

Bioreactance (BR) is a novel, non-invasive technology that is able to provide minute-to-minute monitoring of cardiac output and additional haemodynamic variables. This study aimed to determine the values for BR-derived haemodynamic variables in stable preterm neonates during the transitional period. A prospective observational study was performed in a group of stable preterm (< 37 weeks) infants in the neonatal service of Tygerberg Children's Hospital, Cape Town, South Africa. All infants underwent continuous bioreactance (BR) monitoring until 72 h of life. Sixty three preterm infants with a mean gestational age of 31 weeks and mean birth weight of 1563 g were enrolled. Summary data and time series graphs were drawn for BR-derived heart rate, non-invasive blood pressure, stroke volume, cardiac output and total peripheral resistance index. All haemodynamic parameters were significantly associated with postnatal age, after correction for clinical variables (gestational age, birth weight, respiratory support mode). To our knowledge, this is the first paper to present longitudinal BR-derived haemodynamic variable data in a cohort of stable preterm infants, not requiring invasive ventilation or inotropic support, during the first 72 h of life. Bioreactance-derived haemodynamic monitoring is non-invasive and offers the ability to simultaneously monitor numerous haemodynamic parameters of global systemic blood flow. Moreover, it may provide insight into transitional physiology and its pathophysiology.

Blood Pressure Variability and Baroreflex Sensitivity in Premature Newborns-An Effect of Postconceptional and Gestational Age

Introduction: Cardiovascular system is the vitally important system in the dynamical adaptation process of the newborns to the extrauterine environment. To reliably detect immaturity in the given organ system, it is crucial to study the development of the organ functions in relation to maturation process. Objectives: The objective was to determine the changes in the spontaneous short-term blood pressure variability (BPV) and baroreflex sensitivity (BRS) reflecting various aspects of cardiovascular control during the process of maturation in preterm babies and to separate effects of gestational age and postnatal age. Methods: Thirty-three prematurely born infants without any signs of cardio-respiratory disorders (gestational age: 31.8, range: 27-36 weeks; birth weight: 1,704, range: 820-2,730 grams) were enrolled. Continuous peripheral blood pressure signal was obtained by non-invasive volume-clamp photoplethysmography method during supine rest. The recordings of 250 continuous beat-to-beat blood pressure values were processed by spectral analysis of BPV (assessed measures: total power, low frequency and high frequency powers of systolic BPV) and BRS calculation. For each infant we also assessed systolic, diastolic and mean blood pressures, heart rate and respiratory rate. Results: With the postconceptional age, BPV measures decreased (for total power: Spearman correlation coefficient r_s = -0.345, P = 0.049; for low frequency power: r_s = -0.365, P = 0.037; for high frequency power r_s = -0.349; P = 0.046); and BRS increased significantly (r_s = 0.448, P = 0.009). The further analysis demonstrated that these effects were more attributable to gestational age than to postnatal age. BRS correlated negatively with BPV magnitude (r_s = -0.479 to -0.592, P = 0.001-0.005). Mean blood pressure and diastolic blood pressure increased during maturation (r_s = 0.517 and 0.537, P = 0.002 and 0.001, respectively) while heart rate and respiratory rate decreased (r_s = -0.366 and -0.516, P = 0.036 and 0.002, respectively). Conclusion: We conclude that maturation process is accompanied by an increased involvement of baroreflex buffering of spontaneous short-term blood pressure oscillations. Gestational age plays a dominant role not only in BPV changes but also in BRS, mean blood pressure, diastolic blood pressure and heart rate changes.

The effect of sleeping position on heart rate variability in newborns

Background

Lower heart rate variability (HRV) in a newborn might represent a risk factor for unfavourable outcome, a longer recovery after illness, and a sudden infant death. Our aim was to determine whether the newborn’s sleeping position is associated with HRV.

Methods

We performed a prospective clinical study in 46 hospitalized cardiorespiratory stable term newborns. During sleeping, we measured the parameters of HRV in four body positions (supine, supine with tilt, prone, prone with tilt).

Results

The TP (total power spectral density) was significantly higher when lying supine in comparison to prone (p = 0,048) and to prone with tilt (p = 0,046). The HF (high frequency of power spectral density) in the supine position without tilt tended to be higher compared to prone without tilt (p > 0,05). The LF (low frequency power) was significantly higher when lying supine compared to prone, both without tilt (p = 0,018). TP and HF showed a positive correlation with gestational but not postmenstrual age (p = 0.044 and p = 0.036, respectively).

Conclusions

In term newborns, sleeping position is associated with HRV. Higher TP and HF were found in the supine position, which might reflect better ANS stability. Gestational age positively correlated with TP and HF power, but only in supine position.

Trial registration

ISRCTN11702082, date of registration: March, 13th, 2020; retrospectively registered.

Repeated high blood pressure at 6 and 11 years at the Pelotas 2004 birth cohort study

Background

We evaluated the prevalence and the factors associated with repeated high systolic (SBP) and diastolic blood pressure (DBP) at 6- and 11-year follow-ups of children from the Pelotas (Brazil) 2004 Birth Cohort.

Methods

All live births to mothers living in the urban area of Pelotas were enrolled in the cohort. Blood pressure (BP) values were transformed into Z-scores by sex, age, and height. High SBP and DBP were defined as repeated systolic and diastolic BP Z-scores on the ≥95th percentile at the two follow-ups. Prevalence (95% confidence interval) of repeated high SBP, DBP, and both (SDBP) were calculated. Associations with maternal and child characteristics were explored in crude and adjusted logistic regression analyses.

Results

A total of 3182 cohort participants were analyzed. Prevalence of repeated high SBP, DBP and SDBP was 1.7% (1.2–2.1%), 2.3% (1.8–2.9%) and 1.2% (0.9–1.6%), respectively. Repeated high SBP was associated with males, gestational diabetes mellitus (2.92; 1.13–7.58) and obesity at 11 years (2.44; 1.29–4.59); while repeated high DBP was associated with females, family history of hypertension from both sides (3.95; 1.59–9.85) and gestational age < 34 weeks (4.08; 1.52–10.96). Repeated high SDBP was not associated with any of the characteristics investigated.

Conclusion

Prevalence of repeated high SBP, DBP, and SDBP were within the expected distribution at the population level. Nonetheless, gestational diabetes mellitus, obesity, family history of hypertension, and prematurity increased the risk of repeated high blood pressure measured at two occasions 5 years apart.

Common Genetic Variants Link the Abnormalities in the Gut-Brain Axis in Prematurity and Autism

This review considers a link between prematurity and autism by comparing symptoms, physiological abnormalities, and behavior. It focuses on the bidirectional signaling between the microbiota and the brain, here defined as the microbiota-gut-vagus-heart-brain (MGVHB) axis and its systemic disruption accompanying altered neurodevelopment. Data derived from clinical and animal studies document increased prevalence of gastrointestinal, cardiovascular, cognitive, and behavioral symptoms in both premature and autistic children and suggest an incomplete maturation of the gut-blood barrier resulting in a “leaky gut,” dysbiosis, abnormalities in vagal regulation of the heart, altered development of specific brain regions, and behavior. Furthermore, this review posits the hypothesis that common genetic variants link the abnormalities in the MGVHB axis in premature and autistic pathologies. This hypothesis is based on the recently identified common genetic variants: early B cell factor 1 (EBF1), selenocysteine tRNA-specific eukaryotic elongation factor (EEFSEC), and angiotensin II receptor type 2 (AGTR2), in the maternal and infant DNA samples, associated with risk of preterm birth and independently implicated in a risk of autism. We predict that the AGTR2 variants involved in the brain maturation and oxytocin-arginine-vasopressin (OXT-AVP) pathways, related to social behavior, will contribute to our understanding of the link between prematurity and autism paving a way to new therapies.

The effect of sex and prematurity on the cardiovascular baroreflex response in sheep

NEW FINDINGS

What is the central question of this study? Late preterm infants are often assumed to escape long-term morbidities known to impact earlier preterm offspring. Is this true for the cardiovascular system? What is the main finding and its importance? We show that late preterm birth is a risk factor for cardiovascular dysfunction in early adulthood and is influenced by sex. Early signs of cardiovascular dysfunction might predispose to heart disease in adulthood. Very preterm infants have an increased risk of cardiovascular disease; however, the effects of a late preterm birth on future cardiovascular function are not known. We hypothesized that after a late preterm birth, the well-described impairments in heart rate variability and baroreflex sensitivity would persist into adulthood. To test this hypothesis, sheep born preterm (0.9 gestation; nine male and seven female) or term (11 male and six female) underwent surgery at 14 months of age for insertion of femoral arterial and venous catheters and a femoral flow probe. After recovery, heart rate variability was assessed, followed by a baroreflex challenge (using the vasoactive agents phenylephrine and sodium nitroprusside) in conscious adult lambs. Our data demonstrate decreased low-frequency normalised units (LFnu) and low-frequency/high-frequency ratio in female but not male ex-preterm sheep at rest. When challenged, mature male ex-preterm sheep have an increased blood pressure response but dampened heart rate baroreflex response. We show that even a late preterm birth leads to cardiovascular dysfunction in adulthood. These early signs of cardiovascular dysfunction might underpin the later hypertension and increased risk of heart disease observed in adults born preterm. These findings are particularly important because late preterm infants are often assumed to escape the long-term morbidities known to impact on very preterm and extremely preterm offspring.

Baroreflex Sensitivity in Premature Infants – Relation to the Parameters Characterizing Intrauterine and Postnatal Condition

At present, there are insufficient information about baroreflex sensitivity (BRS) and factors that determine BRS in premature newborns. The objective of this study was to determine the relationship between BRS and the characteristics that reflecting the intrauterine development (gestational age and birth weight), as well as postnatal development (postconception age and the actual weight of the child at the time of measurement). We examined 57 premature infants, who were divided into groups according to gestational age and postconception age as well as birth weight, and weight at the time of measurement. Continuous and noninvasive registration of peripheral blood pressure (BP) was performed in every child within 2-5 min under standard conditions using a Portapres (FMS) device. The results showed a close correlation of baroreflex sensitivity, heart rate and respiratory rate with gestational age, postconception age, birth weight and actual weight at the time of measurement premature newborns. An increase in the characteristics (ages and weights) resulted in increased BRS and diastolic arterial pressure (DAP), and in decreased heart and respiratory rates. Baroreflex sensitivity in the first week was in the group of very premature newborns the lowest (4.11 ms/mmHg) and in the light premature newborns was almost double (8.12 ms/mmHg). BRS increases gradually in relation to postnatal (chronological) and to postconception age as well as to birth and actual weight. The multifactor analysis of BRS identified birth weight and postconception age as the best BRS predictors. The two independent variables together explained 40 % of interindividual BRS variability.

Heart Rate Variability in Newborns

Heart rate (HR) and heart rate variability (HRV) in newborns is influenced by genetic determinants, gestational and postnatal age, and other variables. Premature infants have a reduced HRV. In neonatal HRV evaluated by spectral analysis, a dominant activity can be found in low frequency (LF) band (combined parasympathetic and sympathetic component). During the first postnatal days the activity in the high frequency (HF) band (parasympathetic component) rises, together with an increase in LF band and total HRV. Hypotrophy in newborn can cause less mature autonomic cardiac control with a higher contribution of sympathetic activity to HRV as demonstrated by sequence plot analysis. During quiet sleep (QS) in newborns HF oscillations increase – a phenomenon less expressed or missing in premature infants. In active sleep (AS), HRV is enhanced in contrast to reduced activity in HF band due to the rise of spectral activity in LF band. Comparison of the HR and HRV in newborns born by physiological vaginal delivery, without (VD) and with epidural anesthesia (EDA) and via sectio cesarea (SC) showed no significant differences in HR and in HRV time domain parameters. Analysis in the frequency domain revealed, that the lowest sympathetic activity in chronotropic cardiac chronotropic regulation is in the VD group. Different neonatal pathological states can be associated with a reduction of HRV and an improvement in the health conditions is followed by changes in HRV what can be use as a possible prognostic marker. Examination of heart rate variability in neonatology can provide information on the maturity of the cardiac chronotropic regulation in early postnatal life, on postnatal adaptation and in pathological conditions about the potential dysregulation of cardiac function in newborns, especially in preterm infants.

Cerebral modulation of the autonomic nervous system in term infants

OBJECTIVE

Central topography of autonomic nervous system (ANS) function has yet to be fully deciphered. In adults it has been shown to lateralize sympathetic and parasympathetic influence predominantly to the right and left cerebral hemispheres, respectively. We examined functional topography of central ANS in newborn subjects utilizing spectral analysis of heart rate variability (HRV), an established measure of ANS function.

STUDY DESIGN

We studied newborns with hypoxic-ischemic encephalopathy participating in a prospective study undergoing a therapeutic hypothermia protocol.We included subjects with continuous heart rate data over the first 3 h of normothermia (post rewarming) and brain magnetic resonance imaging, which was reviewed and scored according to a 4 region scheme. HRV was evaluated by spectral analysis in the low-frequency (0.05 to 0.25 Hz) and high-frequency (0.3 to 1 Hz) ranges. The relationship between injured brain regions and HRV was studied using multiple regressions.

RESULTS

Forty eight newborns were included. When examined in isolation, right hemisphere injury had a significant negative effect on HRV (-0.088; 95% CI: -0.225,-0.008). The combination of posterior fossa region injury with right hemispheric injury or left hemispheric injury demonstrated significant positive (0.299; 95% CI: 0.065, 0.518) and negative (-0.475; 95% CI: -0.852, -0.128) influences on HRV, respectively. The association between brain injury location and HRV in the high-frequency range did not reach significance.

CONCLUSION

Our data support the notion that lateralized cerebral modulation of the ANS, specifically of its sympathetic component, is present in the term newborn, and suggest complex modulation of these tracts by components of the posterior fossa.

Novel heart rate parameters for the assessment of autonomic nervous system function in premature infants

Autonomic nervous system (ANS) balance is a key factor in homeostatic control of cardiac activity, breathing and certain reflex reactions such as coughing, sneezing and swallowing and thus plays a crucial role for survival. ANS impairment has been related to many neonatal pathologies, including sudden infant death syndrome (SIDS). Moreover, some conditions have been identified as risk factors for SIDS, such as prone sleep position. There is an urgent need for timely and non-invasive assessment of ANS function in at-risk infants. Systematic measurement of heart rate variability (HRV) offers an optimal approach to access indirectly both sympathetic and parasympathetic influences on ANS functioning. In this paper, data from premature infants collected in a sleep physiology laboratory in the NICU are presented: traditional and novel approaches to HRV analyses are applied and compared in order to evaluate their relative merits in the assessment of ANS activity and the influence of sleep position. Indices from time domain and nonlinear approaches contributed as markers of physiological development in premature infants. Moreover, significant differences were observed as a function of sleep position.

Effect of birth weight on life-course blood pressure levels among children born premature: the Cardiovascular Risk in Young Finns Study

OBJECTIVES

Both fetal growth restriction and prematurity have been associated with elevated blood pressure (BP). However, their combined effects on adult BP are unclear.

METHODS

Our analyses were based on 1756 participants in the population-based Cardiovascular Risk in Young Finns Study who had information on birth weight and gestational age, together with longitudinal data on cardiovascular risk markers from age 3-18 years in 1980 to age 34-49 years in 2011. Three groups were defined by birth data: those born at term (term); those born preterm (<37 weeks) with an appropriate birth weight (>-1 SD z score according to national sex and gestational week-stratified data) for gestational age (preterm appropriate birth weight for gestational age); and those born preterm with low birth weight (≤-1 SD z score) for gestational age [preterm small birth weight for gestational age (SGA)].

RESULTS

There were no differences between the three groups in BP at baseline, but at the 31-year follow-up (mean age 41 years), mean SBP in the preterm SGA group was 7.2 mmHg (95% confidence interval = 2.3-12.1 mmHg, P = 0.004) higher than the preterm appropriate birth weight for gestational age group and 7.3 mmHg (95% confidence interval = 5.2-9.4 mmHg, P < 0.0001) higher than the term group, adjusted for age and sex. In addition, preterm SGA individuals had a higher prevalence of adult hypertension compared with those born at term (36.9 vs. 25.4%; age, sex, and risk factors adjusted P = 0.006).

CONCLUSION

These longitudinal data suggest that elevated BP levels associated with prematurity are more likely to be present in those with fetal growth restriction.

Autonomic Functioning in Young Adults Born at Extremely Low Birth Weight

Autonomic functioning is altered in infants born at extremely low birth weight (ELBW; <1000 g), but we know little about how such alterations manifest in adulthood. We examined associations between birth weight and resting heart rate (R-R interval), high-frequency (HF) and low-frequency (LF) heart rate variability, and systolic (SBP) and diastolic (DBP) blood pressure, in 60 participants (ages 22-26) born at ELBW and free of major neurosensory impairment, and 79 controls born at normal birth weight (NBW; >2500 g). HF in the smallest-born ELBW participants was significantly lower than in NBW controls. In both groups, greater birth weight was associated with higher HF. Among ELBW survivors, lower birth weight predicted faster heart rate and higher DBP, but neither heart rate nor DBP appeared to be well-coordinated with baroreflex activity (LF), the principal mechanism for short-term blood pressure regulation. Adult autonomic regulation may be significantly altered in those born extremely preterm.

Animal models for assessment of infection and inflammation: contributions to elucidating the pathophysiology of sudden infant death syndrome

Sudden infant death syndrome (SIDS) is still not well understood. It is defined as the sudden and unexpected death of an infant without a definitive cause. There are numerous hypotheses about the etiology of SIDS but the exact cause or causes have never been pinpointed. Examination of theoretical pathologies might only be possible in animal models. Development of these models requires consideration of the environmental and/or developmental risk factors often associated with SIDS, as they need to explain how the risk factors could contribute to the cause of death. These models were initially developed in common laboratory animals to test various hypotheses to explain these infant deaths – guinea pig, piglet, mouse, neonatal rabbit, and neonatal rat. Currently, there are growing numbers of researchers using genetically altered animals to examine specific areas of interest. This review describes the different systems and models developed to examine the diverse hypotheses for the cause of SIDS and their potential for defining a causal mechanism or mechanisms.

Gestational age at birth affects maturation of baroreflex control

OBJECTIVES

To assess the effect of prone sleeping, the major risk factor for sudden infant death syndrome, in the control of blood pressure (BP) in preterm infants born across a range of gestational ages.

STUDY DESIGN

Daytime polysomnography was performed at 2-4 weeks, 2-3 months, and 5-6 months postterm age. The participants were 21 very preterm (mean gestation 29.4 ± 0.3 weeks), 14 preterm (mean gestation 33.1 ± 0.3 weeks), and 17 term (mean gestation 40.1 ± 0.3 weeks). BP was measured via a Finometer cuff (Finapres Medical Systems, Amsterdam, The Netherlands) placed around the wrist. Data were recorded both supine and prone. Baroreflex sensitivity (BRS) was calculated via cross-spectral analysis of spontaneous fluctuations in BP.

RESULTS

BRS was lower in the prone position in very preterm infants at 2-4 weeks in active sleep (P < .05). Maturation of BRS was delayed in very preterm compared with both preterm and term infants.

CONCLUSIONS

Maturation of BRS after term-equivalent age is altered in very preterm infants. Reduced BRS may result in an impaired ability of very preterm infants to respond to cardiovascular stress during infancy and may predispose them to cardiovascular disease later in life.

Alterations in viscoelastic properties following premature birth may lead to hypertension and cardiovascular disease development in later life

The aim of this review was to identify the underlying relationship between preterm birth and the development of cardiovascular diseases. Preterm birth significantly affects the elastin content and viscoelastic properties of the vascular extracellular matrix in human arteries. Inadequate elastin synthesis during early development may cause a permanent increase in arterial stiffness in adulthood.

CONCLUSION

Early and permanent alterations in viscoelastic properties may lead to hypertension and cardiovascular disease development in adults born prematurely.

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.

Limitations and vulnerabilities of the neonatal cardiovascular system: considerations for anesthetic management

Development of the cardiovascular system through the last trimester of pregnancy and the subsequent neonatal period is profound. Morphological changes within the myocardium make the heart vulnerable to challenges such as fluid shifts and anesthetic drugs. The sensitivity of the myocardium to metabolic challenges and potential harm of drugs needed to maintain adequate blood pressure and cardiac output are highlighted. Traditional monitoring under anesthesia has focussed on maintaining oxygenation and heart rate in the neonate with less attention paid to blood pressure, cardiac output, and more importantly organ well-being. There is now a better understanding of the limitations of blood pressure homeostasis in the neonate and the potential consequences of marginal hypoperfusion. This article highlights some of these vulnerabilities particularly as they relate to anesthesia and surgery in the very young.

Infrared thermography for detailed registration of thermoregulation in premature infants

OBJECTIVE

To evaluate skin temperature by using different positions with non-contact infrared thermography (IRT) in multiple body areas of preterm infants for detailed information about temperature regulation and distribution.

METHODS

The temperature of ten premature infants (median: 27 weeks; age 36 days; weight 1322 g) was determined via IRT (leg, back, arm, head, upper abdomen; diameter 1 cm, scale 0.00°C), and comparison was made with two conventional sensors. There were measurements of 10 min each: first incubator phase (I1), standardized skin-to-skin care (SSC) at the beginning (SSC1), after 90 min (SSC2), and then there was a second incubator phase (I2).

RESULTS

From I1 to SSC1, patients cooled down (max. 0.62°C; both methods). From SSC1 to SSC2 temperature on central areas (abdomen, back) was maintained but rose distinctively on the head and leg (P<0.05). In the incubator (I2), temperature niveau in all IRT-areas was significantly lower than before SSC.

CONCLUSION

Via IRT, it is possible to detect fluctuations in temperature of premature infants. The cooling in I2 after SSC should be taken into account before routine daily care.

The development of cardiovascular and cerebral vascular control in preterm infants

Over the past three decades there has been a steady increase in the incidence of preterm birth. The worldwide rate of preterm birth is estimated to be 9.6% of all births, a total of almost 13 million births annually. Preterm birth is associated with a range of adverse cardiovascular and central nervous system outcomes, which may be attributed to altered development of these systems following preterm birth. Preterm birth has a considerable impact on cardiovascular parameters with preterm infants displaying higher heart rates and reduced blood pressure when compared to term born infants at matched ages. Furthermore, premature infants have altered autonomic control of cardiovascular parameters which manifests as abnormalities in heart rate variability and baroreflex mediated control of heart rate and blood pressure. As a result, systemic cardiovascular parameters can be unstable following preterm birth which may place stress on the neonatal brain. The brain of a preterm infant is particularly vulnerable to these fluctuations due to immature cerebral haemodynamics. Preterm infants, particularly those who are very preterm or unwell, display fluctuating pressure-passivity between systemic blood pressure and cerebral blood flow representing a considerably increased risk of cerebral haemorrhage or hypoxia. This is further compounded by immaturity of cerebral blood flow-metabolism coupling, which means increased metabolic demand cannot adequately be met by increased cerebral blood flow. It has been suggested that adverse long-term outcomes following preterm birth may occur as a result of exposure to physiological stress either in-utero or early in infancy.

Autonomic cardiovascular control in hypotensive critically ill preterm infants is impaired during the first days of life

BACKGROUND

The first days after preterm birth are a critical period of cardiovascular instability, where hypotension is common. We assessed autonomic cardiovascular function by measuring heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) and hypothesised that these would be impaired in preterm infants born at younger gestational ages. In addition, we speculated that impaired cardiovascular control could be used as a marker of circulatory failure such as is manifest as hypotension.

METHODS

23 preterm infants (11 M/12 F) born between 23 and 35 weeks (mean 27 ± 0.6 weeks) gestational age with indwelling arterial catheters were recruited. Infants were studied over the first 3 days of life with heart rate and blood pressure (BP) analysed beat to beat in the frequency domain in 2 minute epochs of artefact free data during active sleep. Data were compared with one way ANOVA.

RESULTS

Gestational age was correlated with all HRV indices but not BPV or BRS. 9 babies received inotropes. Gestational age between the inotrope group and the non-inotrope group was not different. BP and RR interval were lower in the inotrope group (40.7 ± 1.5 vs 47.1 ± 1.5 mmHg, p<0.05 and 395 ± 14 vs 426 ± 11 ms, p<0.08). BRS was also lower in the inotrope group (3.8 ± 0.9 vs 6.9 ± 1.6 ms/mmHg) as was LF/HF HRV (5.7 ± 1.3 vs 13.6 ± 2.8, p<0.05).

CONCLUSIONS

In the first 3 days after birth, infants receiving inotropes had significantly impaired cardiovascular control compared to those who did not receive treatment, indicating that these infants maybe predisposed to increased vulnerability to circulatory instability.

Preterm birth alters the maturation of baroreflex sensitivity in sleeping infants

OBJECTIVE

Impaired blood pressure (BP) control may underpin the increased incidence of the sudden infant death syndrome (SIDS) in preterm infants. This study aimed to examine the effects of preterm birth, postnatal age, and sleep state on BP control by measuring baroreflex sensitivity (BRS) across the first 6 months of term-corrected age (CA), when SIDS risk is greatest.

METHODS

Preterm (n = 25) and term (n = 31) infants were studied longitudinally at 2 to 4 weeks, 2 to 3 months, and 5 to 6 months CA using daytime polysomnography. BP was recorded during quiet (QS) and active (AS) sleep using a photoplethysmographic cuff placed around the infant's wrist (Finometer [FMS, Finapres Medical Systems, Amsterdam, Netherlands]). BRS (milliseconds/mm Hg) was assessed in 1- to 2-minute epochs using cross-spectral analysis.

RESULTS

In preterm infants, postnatal age had no significant effect on BRS within either QS or AS. This was in contrast to the maturational increase in QS observed in term infants. Compared with term infants, BRS of preterm infants was 38% higher at 2 to 4 weeks CA and 29% lower at 5 to 6 months CA during QS (P <.05). Comparing sleep states, BRS of preterm infants was 26% lower in QS compared with AS at 2 to 3 months CA (P <.05).

CONCLUSIONS

Preterm birth impairs the normal maturational increase in BRS, resulting in a substantial reduction in BRS at 5 to 6 months CA during QS. Lower BRS during QS compared with AS at 2 to 3 months CA may place preterm infants at an increased risk for cardiovascular instability at this age of peak incidence of SIDS.

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.

[Preterm birth as a risk factor for high blood pressure in children: a systematic review]

Epidemiological studies have suggested that arterial hypertension is a chronic disease that begins in childhood, and that prematurity (birth at less than 37 weeks' gestational age) is potentially associated with the development of hypertension in childhood and adulthood. Our objective was to identify the association between prematurity and high blood pressure in children, using a systematic literature review. Original articles related to the theme and published in English, Portuguese, or Spanish from 1998 to 2009 were selected from the MEDLINE, LILACS, and SciELO databases. We excluded articles without abstracts, review articles, and articles not related to prematurity and hypertension in childhood. Nine articles were located and analyzed: 5 case-control studies, 2 cross-sectional studies, and 2 cohort studies. The majority of the studies failed to show an association between prematurity and arterial hypertension in childhood. However, the influence of prematurity should not be ruled out, given the small number of studies on this theme and the diversity of methodological approaches in the literature.

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.

Postnatal development of baroreflex sensitivity in infancy

Baroreflex sensitivity (BRS) using spontaneous sequence analysis in the time domain is not fully applicable in infancy, as the time delay for heart period to change (heart period delay, HPD) after an arterial pressure change is unknown. We estimated and compared HPD and BRS in the frequency (BRS(sp), HPD(sp)) and time domains (BRS(seq), HPD(seq)) from systolic blood pressure (SBP) and heart period fluctuations. Continuous SBP, using photoplethysmography, and heart period measurements were performed on 30 term infants at 2-4 weeks, 2-3 months and 5-6 months postnatal age. Cross-spectral analysis between SBP and heart period fluctuations was used to estimate BRS(sp) and HPD(sp). Spontaneous sequence analysis was used to estimate BRS using a fixed beat delay of 1-12 beats (BRS(seq)) or a variable delay identified by a novel method accounting for epoch-epoch variability in HPD (BRS(seqvar)). HPD(sp) averaged 3.4 s (approximately 7 beats); BRS(sp) averaged 11.4 ms mmHg(1). BRS(seq) and BRS(seqvar) were consistently lower than BRS(sp) (P < 0.05), but the three BRS estimates were strongly correlated using a HPD of approximately 5-6 beats. BRS(seqvar) resulted in the average estimate (8.9 ms mmHg(1)) closest to BRS(sp) and overall had the strongest correlation with BRS(sp) (R(2) = 0.61; P < 0.001). All three BRS estimates increased progressively with postnatal age, with BRS(sp) averaging 6.4, 10.5 and 16.0 ms mmHg(1) at 2-4 weeks, 2-3 months and 5-6 months, respectively (P < 0.05). Accounting for the HPD of infancy provides estimates of BRS in the time domain that closely parallel spectral estimates, and provides a novel analytical tool to assess normal development and dysfunction of the baroreflex in infants.

Extremely low birth weight preterm infants lack vasomotor response in relationship to cold body temperatures at birth

OBJECTIVE

This study evaluated peripheral vasoconstriction in extremely low birth weight (ELBW) infants when body temperature decreased during the first 12 h of life.

STUDY DESIGN

An exploratory, within-subjects design with 10 ELBW infants. Abdominal and foot temperatures were measured every minute. Peripheral vasoconstriction (abdominal>peripheral temperature by 2 degrees C) and abdominal-peripheral temperature difference were also evaluated.

RESULTS

Abdominal and peripheral temperatures were significantly correlated within each infant. One 880 g infant exhibited isolated peripheral vasoconstriction; a 960-g infant had abdominal temperatures >1 degrees C higher than peripheral temperatures. Eight smaller infants exhibited no peripheral vasoconstriction and spent most of their observations with peripheral greater than abdominal temperatures. In eight infants, mean temperature difference was significantly higher when abdominal temperature was <36.5 degrees C.

CONCLUSION

Most ELBW infants did not exhibit peripheral vasoconstriction during their first 12 h of life, despite low temperatures. ELBW infants' vasomotor control may be immature during this period.

Is baroreflex control of sympathetic activity and heart rate active in the preterm fetal sheep?

The arterial baroreflex is a fundamental reflex that buffers rapid changes in arterial blood pressure (BP) via regulation of the heart rate and sympathetic nerve activity to the vasculature. In adults a sigmoidal relationship between BP and both heart rate and sympathetic nerve activity is well documented. Its role in blood pressure control before birth is unclear. Preterm babies have a high incidence of low BP, especially in the first few days of life, which could be related, in part, to immaturity of the baroreflex. In the present study, we investigated the baroreflex control of fetal heart rate and renal sympathetic nerve activity (RSNA) in preterm fetal sheep in utero (102 ± 1 days of gestation; term 140 days). Phenylephrine was associated with a significant increase in BP from 38 ± 2 to 58 ± 3 mmHg and a decrease in heart rate (HR) from 177 ± 4 to 116 ± 8 beats per minute (bpm). Sodium nitroprusside was associated with a significant fall in BP from 38 ± 2 to 26 ± 1 mmHg and an increase in HR from 182 ± 4 to 274 ± 8 bpm. However, the time between the 50% changes in BP and HR was significantly greater after hypotension than hypertension (31 ± 8 s vs. 14 ± 5 s, P < 0.05). No significant changes in RSNA occurred with either stimulus. This suggests that there are different maturational tempos for the components of the central autonomic response to altered blood pressure.

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.

Abnormal circulatory stress responses of preterm graduates

Preterm birth and chronic lung disease may increase the risk of hypertension and cardiovascular disease in infancy and adolescence. Here we looked for evidence of early circulatory dysfunction associated with these perinatal complications. We compared infants born at term (n = 12) with those born preterm with an uncomplicated neonatal course (n = 12) or diagnosed with bronchopulmonary dysplasia (BPD) (n = 10). We measured blood pressure (BP) (Finometer), and heart rate (HR) responses to 4 min of breathing 4% CO2 during quiet sleep. Hypercapnia accelerated HR and increased BP of term infants. Preterm infants either (i) had an exaggerated pressor but little or no HR response to CO2 (healthy or mild-moderate BPD) or (ii) had a diminished pressor response and accompanying decrease in HR (severe BPD). Short-term reflex cardiovascular control was consequently altered by premature birth, with potentially more serious aberrations associated with severe BPD. Most anomalies had not resolved by the time infants born preterm reached term age; some may be early signs of emerging long-term cardiovascular dysfunction.

Characteristics of arterial stiffness in very low birth weight premature infants

Premature birth is a factor of increased blood pressure in adulthood. Little is known about the physiologic characteristics of the arterial bed in neonates. The aim of this study was to characterize in vivo the arterial compliance in neonates and its maturation profile in very low birth weight (VLBW) premature infants. A group of stable, VLBW premature infants was compared with a control group of near term neonates. The abdominal aortic wall distensibility coefficient (DC) and whole-body arterial compliance (WBAC) were determined using specifically designed noninvasive methods, based on ultrasonic measurements in combination with synchronous, beat-to-beat recording of aortic pulse pressure (PP). On the fifth day of life, WBAC and the CD were lower in VLBW premature infants than in controls. Furthermore, WBAC and the DC remained unchanged in VLBW premature infants 7 wk after birth. In conclusion, VLBW premature infants are characterized as early as the fifth day of life by high arterial stiffness, which persists when they reach their theoretical term. It can be speculated that early alteration of arterial elastic properties may pave the way for long-term elevation of arterial pressure in VLBW premature infants.

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.

Evidence for Cardiovascular Autonomic Dysfunction in Neonates With Coarctation of the Aorta

Background— Coarctation of the aorta (CoA) is associated with hypertension and abnormalities of blood pressure control, which persist after late repair. Assumptions that neonatal repair would prevent development of blood pressure abnormalities have not been supported by recent data. We hypothesized that early pathological adjustment of autonomic cardiovascular function may already be established in the neonate with coarctation.

Methods and Results— We studied 8 otherwise well neonates with simple CoA and compared measures of spontaneous baroreflex sensitivity, heart rate variability, and blood pressure variability with 13 healthy newborn babies. Spontaneous baroreflex sensitivity was calculated with sequence methodology from an ECG, and noninvasive blood pressure was recorded with a Portapres. Heart rate variability was determined with time- and frequency-domain measures. Blood pressure variability was measured in the frequency domain. In comparison with normal controls, neonates with CoA had raised blood pressure (78.9±3.8 versus 67.1±2.1 mm Hg), depressed baroreflex sensitivity (8.7±1.5 versus 13.8±1.1 ms/mm Hg), reduced heart rate variability (total power 16.5±3.1 versus 31.5±2.2 ms 2 ), and an increase in the high-frequency component of blood pressure variability (3.1±0.3 versus 2.2±0. 2 mm Hg 2 ). This is not the pattern expected if neonates with CoA simply had subclinical cardiac failure.

Conclusions— These data suggest that infants with CoA already show signs of pathological adjustment of autonomic cardiovascular homeostasis. Further longitudinal studies are required to determine whether these alterations play a role in the increased risk of late hypertension in these patients.

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.

Risk of high blood pressure among young men increases with the degree of immaturity at birth

BACKGROUND

Survivors of preterm birth constitute a new generation of young adults, but little is known about their long-term health. We investigated the association between gestational age (GA) and risk of high blood pressure (HBP) in young Swedish men and whether GA modified the risk of HBP; ie, whether HBP was related to being born small for gestational age (SGA).

METHODS AND RESULTS

This population-based cohort study included 329 495 Swedish men born in 1973 to 1981 who were conscripted for military service in 1993 to 2001. Multivariate linear- and logistic-regression analyses were performed. Main outcome measures were systolic and diastolic BPs at conscription. Linear-regression analyses showed that systolic BP increased with decreasing GA (regression coefficient -0.31 mm Hg/wk, P<0.001). Systolic and diastolic BPs both increased with decreasing birth weight for GA, but the association with systolic BP was most evident (regression coefficient -0.67 mm Hg per SD score in birth weight for GA, P<0.001). Compared with men born at term (GA, 37 to 41 weeks), the adjusted odd ratios (95% confidence intervals [CIs]) for high systolic BP (> or =140 mm Hg) were as follows: moderately preterm (33 to 36 weeks), 1.25 (1.19 to 1.30); very preterm (29 to 32 weeks), 1.48 (1.30 to 1.68); and extremely preterm (24 to 28 weeks), 1.93 (1.34 to 2.76). Being SGA was associated only with an increased risk of high systolic BP among men born at 33 weeks or later. The risk estimates for high diastolic BP (> or =90 mm Hg) increased with decreasing GA, but the risk reached significance only among men born moderately preterm.

CONCLUSIONS

Preterm birth, a common pregnancy complication, is a risk factor for HBP in young men. The risk of high systolic BP associated with birth weight for GA is modified by GA, suggesting that perinatal contributions to BP elevation later in life may be induced by different biological pathways.

Baroreceptor reflex sensitivity in human neonates: the effect of postmenstrual age

We performed a cross-sectional study in human infants to determine if indices of R-R interval variability, systolic blood pressure (SBP) variability, and baroreceptor reflex sensitivity change with postmenstrual age (PMA: gestational age+postnatal age). The electrocardiogram, arterial SBP and respiration were recorded in clinically stable infants (PMA, 28-42 weeks) in the quiet sleep state in the first days after birth. (Cross-)spectral analyses of R-R interval series and SBP series were performed to calculate the power of low-frequency (LF, indicating baroreceptor reflex activity, 0.04-0.15 Hz) and high-frequency (HF, indicating parasympathetic activity, individualized between the p-10 and p-90 values of respiratory frequency) fluctuations, and transfer function phase and gain. The mean R-R interval, and LF and HF spectral powers of R-R interval series increased with PMA. The mean SBP increased with PMA, but not the LF and HF spectral powers of SBP series. In the LF range, cross-spectral analysis showed high coherence values (>0.5) with a consistent negative phase shift between R-R interval and SBP, indicating a approximately 3 s lag in R-R interval changes in relation to SBP. Baroreceptor reflex sensitivity, calculated from LF transfer gain, increased significantly with PMA, from 5 (preterm) to 15 ms mmHg-1 (term). Baroreceptor reflex sensitivity correlated significantly with the (LF and) HF spectral powers of R-R interval series, but not with the LF and HF spectral powers of SBP series. The principal conclusions are that baroreceptor reflex sensitivity and spectral power in R-R interval series increase in parallel with PMA, suggesting a progressive vagal maturation with PMA.

Noninvasive assessment of cardiac output

Improved outcome from shock depends on early detection and correction of circulatory abnormalities. Global cardiac output and oxygen delivery must be adequate and distributed appropriately to meet metabolic demands to prevent the development of multiple organ system dysfunction, prolonged morbidity, and death. Circulatory assessment using standard monitors gives incomplete and sometimes misleading information. This article focuses on the available and emerging technologies that emphasize assessment of blood flow and regional tissue oxygenation.

Cardiovascular autonomic regulation in preterm infants: the effect of atropine

To study cardiovascular autonomic control, we assessed the effect of atropine on heart rate (HR) and blood pressure (BP) variability in 12 preterm infants (range 26-32 wk) before intubation for respiratory insufficiency. Spectral power analysis of R-R interval and systolic BP (SBP) series were estimated in a low-frequency (LF; 0.04-0.15 Hz) and high-frequency (HF; 0.4-1.5 Hz) band and evaluated for a 10-min period before and a 10-min period after atropine sulfate (0.01 mg/kg). Baroreceptor reflex (BR) functioning was estimated using transfer function analysis at LF (coherence, gain, and phase). Atropine resulted in a significant 12% increase in steady-state HR (p < 0.01) and unchanged SBP. For R-R interval series, the total spectral power decreased 6-fold (p < 0.01), which was predominantly due to a reduction in the LF band (16-fold; p < 0.01). In contrast, we observed a significant increase (25%; p < 0.05) in total spectral power of SBP series partly as a result of an increase in HF power. The LF power of SBP series was not altered. The median LF transfer gain (BR sensitivity) between SBP and R-R interval decreased from 4.2 to 1.4 ms/mm Hg (p < 0.01) after atropine. The LF phase relationship (BP leads R-R interval fluctuations by approximately 4 s) was not changed after atropine. In conclusion, even in preterm infants in distress, atropine modulates HR and BP variability, suggesting that BR-mediated parasympathetic control of heart rate is of significance for cardiovascular control at that age.

Developmental patterns of physiological response to a multisensory intervention in extremely premature and high-risk infants

OBJECTIVE

To compare the developmental patterns of heart rate (HR), respiratory rate (RR), and hemoglobin oxygen saturation (SaO2) of premature infants with and without central nervous system (CNS) injury, and evaluate whether a multisensory intervention altered this development.

SAMPLE

Thirty-seven premature infants born at 23-26 weeks with normal head ultrasounds or at 24-32 weeks and diagnosed with periventricular leukomalacia (PVL) and/or intraventricular hemorrhage (IVH) were studied at 33-35 weeks postconceptional age.

DESIGN

Infants were randomly assigned to control and experimental groups. The experimental group infants received auditory, tactile, visual, and vestibular (ATVV) multisensory intervention twice daily from 33 weeks postconceptional age (PCA) until hospital discharge.

MAIN OUTCOME MEASURES

HR, RR, and SaO2 were continuously monitored during baseline, intervention, and the 30-minute postintervention period.

RESULTS

Between 33 and 35 weeks PCA, control group infants with and without CNS injury and experimental group infants without CNS injury had a significant decrease in resting mean HR, whereas RR and SaO2 remained stable. The infants with PVL who received the intervention showed increases in HR even at rest.

CONCLUSIONS

The absence of a weekly decline in HR for experimental group infants with PVL suggests that PVL may affect maturation of the autonomic nervous system and increase risk of decelerative HR changes and associated clinical compromise. Infants diagnosed with PVL should be closely monitored during procedures or interventions that may be stressful or involve handling. Further research is needed to tailor multisensory interventions for infants with PVL.