Development of baroreflex influences on heart rate variability in preterm infants

To investigate developmental changes in autonomic cardiovascular reflexes in preterm infants, we used autoregressive power spectral analysis to analyze the effect of upright tilting on heart rate variability in preterm infants. Twenty-eight infants were studied in a longitudinal fashion beginning at 28-32 weeks postconceptional age (postnatal age 1-5 weeks). Each week, heart rate variability in the supine position and after 45 degrees head-up tilt was analyzed by spectral analysis. With the initial study of each infant, there was no significant change in heart rate following head-up tilt compared with baseline (-0.5+/-0.9 bpm). However, linear regression analysis revealed that with increasing postnatal age, the change in heart rate in response to tilting became more positive (mean slope of regressions 0.45+/-0.12 bpm/week, P<0.005). The power spectral density of R-R interval variability in the low-(LF; 0.02-0.15 Hz) and high-(HF; 0.15-1.5 Hz) frequency ranges were obtained and the values normalized by dividing each component by the total power. For measurements obtained in the supine position, the LF/HF ratio progressively decreased with increasing postnatal age, indicating a maturational change in sympathovagal balance. We used the difference in the LF/HF ratio between tilt and the recumbent position as a measure of the change in autonomic input to the heart in response to unloading of the arterial baroreceptors. No significant change in these ratios were observed when infants were first studied between 28 and 32 weeks postconceptional age, suggesting that the cardiac baroreflex is poorly developed at this stage of development. However, with postnatal maturation, the LF component of the power spectrum became progressively larger with tilt relative to the basal state, such that the difference between LF/HF(tilt) and LF/HF(base) became progressively more positive (P <0.006). These findings suggest that in premature infants, cardiac baroreceptor reflexes become more functional with postnatal development.     

Development of baroreflex control of heart rate in swine

The purpose of this study is to describe the developmental course of arterial baroreflex control of heart rate in swine. Tests of baroreflex function were performed with eight conscious piglets serially over their first 2 mo of life. Systemic blood pressure was raised with phenylephrine (pressor test) and lowered with nitroprusside (depressor test), and stimulus-response curves relating heart rate to mean blood pressure were constructed. Baroreflex sensitivity was determined as the slope of the linear portion of the curve. Baroreflex sensitivity decreased with increasing age. Baroreflex sensitivity was not different between pressor and depressor tests except when the piglets were greater than 52 d old and sensitivity was greater with the depressor test. The heart rates at threshold and saturation, and therefore the heart rate response range, shifted to lower heart rates with increasing age. This shift was more than can be accounted for by the simultaneously decreasing resting heart rate.     

Functional auditory development in preterm and full term infants

Bilateral ABRs were recorded from 452 infants 32–45 weeks conceptional age. Differences in laterality, gender and appropriateness for gestational age were investigated in order to increase our understanding of developmental processes in early life. Rate effects were also studied in a subsample of infants (145 ears). All subjects were free of conditions known to affect ABR parameters. Left/right differences were evident for all ABR measures except the amplitude of wave I. Shorter interwave intervals and larger amplitudes were consistently observed on the right. Females exhibited shorter absolute latencies for waves III and V and larger wave I amplitudes than males. Small for gestational age (SGA) infants displayed shorter wave V latencies and interwave intervals relative to AGA infants. These differences, however, disappeared by term age whereas the contrasts in laterality persisted. Increasing the rate of stimulation reduced wave I amplitude irrespective of conceptional age and increased wave V amplitude prior to term. An increase in wave V latency was more pronounced at the higher rate on the left than the right. There was no interaction between rate and appropriateness for gestational age, although SGA infants had shorter wave V and interwave latencies. Our data indicate a slight but significant right ear advantage in the processing of auditory signals. Gender differences were apparent as well. While research on adults and older children have reported similar findings, no other studies to date have observed these results in neonates. The present work also lends support to the view that accelerated neurological development occurs in growth-retarded infants.     

Factors associated with weaning in full term and preterm infants

BACKGROUND: The optimal age for the introduction of solid foods (weaning) in infants is poorly researched yet may have implications for both short and longer term health. Many parents do not comply with current guidelines. OBJECTIVE: To determine and compare the age at weaning in term appropriate size for gestational age (AGA), small for gestational age (SGA), and preterm infants, and factors associated with weaning age in these groups. DESIGN: Data from > 2000 infants from seven prospective randomised trails conducted between 1990 and 1997 were used to address the objectives. RESULTS: Most infants, term AGA, SGA, or preterm, received solids before 4 months of age. Only 2% of term infants were exclusively breast fed to 6 months of age. Formula fed infants received solids on average two weeks earlier than breast fed infants. Preterm infants were significantly more likely, and term SGA infants less likely, to receive solids at both 6 and 12 weeks after term than term AGA infants. Weight at 6 weeks of age was a stronger predictor of earlier weaning than either birth weight or weight gain from birth to 6 weeks in term infants. In preterm infants, formula feeding and maternal smoking were associated with earlier weaning. CONCLUSIONS: Infants born in the mid 1990s were weaned on average earlier than the 4 months recommended by the Department of Health. Earlier weaning was associated with less positive health behaviours. Further research is required to provide evidence based weaning guidelines, including specific advice for SGA and preterm infants, and to investigate longer term consequences of weaning practices.     

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).     

���� ��������������������� ���������ۺ����ٴ��ȽϷ���

目的 探讨早期、晚期早产儿与足月儿呼吸窘迫综合征(RDS)的发病趋势和临床特征的差异,为临床合理诊治提供依据。方法 2006年1月至2010年12月在郑州大学第三附属医院住院的963例RDS患儿根据胎龄不同分为早期早产儿组(<34周)679例,晚期早产儿组(34～<37周)204例,足月儿组(≥37周)80例,分别对各组患儿的发病率、入院情况、高危因素、临床诊治、预后及并发症进行比较。结果 RDS的发病率逐年增加,均以早期早产儿占多数,晚期早产儿和足月儿RDS比例有增多趋势;RDS患儿男婴超过女婴(P<0.05),且胎龄和体重越大,男婴比例越高;足月儿RDS组产前糖皮质激素使用率明显低于早产儿组;早产儿发生RDS的高危因素主要有胎膜早破、胎盘异常、母亲妊娠高血压疾病,足月儿发生RDS的高危因素主要是择期剖宫产与感染;晚期早产儿与足月儿RDS的临床诊断和应用肺泡表面活性物质(PS)时间均晚于早期早产儿;足月儿RDS应用机械通气比例明显高于早产儿,其临床治愈率高(P<0.05),在死亡率方面与早产儿组无差别;但并发气胸的比例高于早产儿组(P<0.05)。结论 新生儿呼吸窘迫综合征(NRDS)发病率逐年增高,晚期早产儿和足月儿RDS比例有增多趋势;早期、晚期早产儿与足月儿RDS在性别比例、高危因素、起病特点、治疗反应与并发症方面均存在差异,RDS的诊治需要考虑胎龄因素。足月儿RDS多与择期剖宫产、感染有关,发病相对较晚,容易合并气胸,应引起足够重视。     

Perinatal hypoxia and hepatic cell function in preterm and full term newborn infants

Gamma-glutamyl transpeptidase activity and the serum concentration of lipoprotein-x, indirect bilirubin and total bile acids were measured in 28 preterm and 24 full term newborn infants, with or without hypoxia, at the postnatal age 3-4 days. Those preterm and full term babies who suffered from hypoxia had increased mean lipoprotein-x, bilirubin, total bile acid concentration and gamma-glutamyl transpeptidase activity in comparison to that of controls, but the differences were not significant statistically. Clinical implications of the results are briefly discussed.     

Selenium and vitamin E in cord blood from preterm and full term infants.

Selenium was determined in erythrocytes and serum, and vitamin E and beta-lipoprotein in serum from cord blood samples of 31 full term and 20 preterm infants. Venous samples from 21 mothers at birth and 15 normal adult women were also analyzed. No difference for either selenium or vitamin E was found between the preterm and full term infants. The selenium concentration in red blood cells was the same for newborn, mothers at birth, and normal adult women. The serum concentration of selenium was, however, significantly lower in the newborn, the mean level in the children being 64% of that in the mothers. The level in the mothers did not differ from that in non-pregnant women. The vitamin E concentration was found to correlate very well with the beta-lipoprotein concentration. This indicates that differences in the transport capacity account for the large difference in the serum tocopherol levels of mothers at birth and newborn.     

Resting heart rate does not predict growth in preterm infants

Background

Previous reports indicate that preterm infants with higher baseline heart rate (HR) have greater weight gain than preterm infants with lower baseline HR. To verify this correlation and the potential utility of resting HR as a bench mark for risk of extrauterine growth restriction (EUGR), we studied preterm infants born between 32 and 36 weeks gestation. Earlier gestation infants (27 to 31 weeks) were included.

Methods

In retrospective chart review we collected heart rate (HR) and growth data on 156 infants between 27.0 and 34.0 weeks gestation from birth to hospital discharge.

Results

There was a significant increase in weight gain from day 10 of life in infants with higher resting HR compared to infants with lower resting HR. However, upon controlling for birth weight and gestational age, there was no significant relationship between HR and weight gain for any gestational age group of premature infants.

Conclusions

Contrary to previous reports, there was no significant relationship between HR and growth at any gestational age after controlling for birth weight and gestational age. It is important to continue to search for a clinical marker of risk for poor growth in preterm infants and to give an opportunity for nutritional interventions which may support better growth and developmental outcomes.     

Serum ferritin in term and preterm infants

Serum ferritin levels were examined in maternal serum, In cord sera and at one, four, eight and twelve weeks in 19 term and 28 preterm infants. There was no correlation between maternal and cord ferritin levels. Mean serum ferritin concentration was lower in preterm infants, and both term and preterm Infants exhibited' an initial rise in serum ferritin concentration followed by a steady fall. Serum ferritin concentration showed a good correlation with calculated iron stores at twelve weeks of age suggesting that serum ferritin estimation is the method of choice for monitoring body iron stores in infants. No correlation was found between serum ferritin concentration and calculated iron intake at any age in either term or preterm infants. It is suggested that iron supplementation additional to that present in modified cow's milk is not necessary for the first twelve weeks of life in either term or preterm infants.     

Circulating blood volume in appropriate and small for gestational age full term and preterm polycythaemic infants

Relative circulating volume (CV) was determined in 31 polycythaemic newborn infants who underwent a partial plasma exchange transfusion (PPET). The infants were divided in four sub-groups: appropriate for gestational age (AGA) term and preterm infants, and small for gestational age (SGA) term and preterm infants. CV was calculated using a regression line between the number of exchange steps and central venous haematocrit values obtained before the procedure and after every exchange step. The median relative CV in all polycythaemic newborn infants was 94.0 (range 69-143) ml/kg. Irrespective of gestational age and birthweight the median relative CV in AGA infants was 86.5 (range 69-107) ml/kg, which differed significantly from the value of 106 (range 85-143) ml/kg found in SGA infants. If a PPET is indicated we recommend to calculate the exchange volume in AGA infants using a relative CV of 86 ml/kg and in SGA infants using a relative CV of 106 ml/kg.     

Macromolecular absorption in preterm and term infants

Human alpha-lactalbumin (alpha-LA) has been used as a marker for measuring macromolecular absorption. The serum concentration of human alpha-LA after a human milk feed has been studied in 32 healthy very low birthweight infants (VLBW), fed human milk (gestational age 26-32 weeks) and in 56 term, breast-fed infants, age 3-140 days. At 31 weeks of gestation the serum concentration of human alpha-LA was more than 10 times higher (mean value 3,000 and median value 2,101 micrograms/l serum/l human milk/kg body weight, n = 11) than in the term infants aged 3-30 days (mean value 257 and median value 152, n = 29). The serum concentration of alpha-LA decreased with increasing maturity in the VLBW-infants. At a postconceptional age of 37 weeks the values were similar (mean value 200 and median value 99, n = 8) to those found for term infants during the first month. In the term infants a decreasing absorption of alpha-LA was found with increasing postnatal age.     

Breath amplitude modulation of heart rate variability in normal full term neonates

The relationship between heart rate variability and respiration patterns was investigated using spectral analysis techniques in nine full-term infants whose ages ranged from 39-75 h. All the infants were studied during sleep, although no attempt was made to classify rapid eye movement or nonrapid eye movement states prospectively. The data obtained were examined to determine which aspects of neonatal breathing patterns are correlated with heart rate variability. Three spectral regions of heart rate variability could be identified: a very low frequency region below 0.02 Hz; a low frequency region from 0.02-0.20 Hz; and a high frequency region above 0.20 Hz. The dominant heart rate variability activity in these neonates was seen in the very low and low frequency regions, with little activity in the high frequency regions. In contrast to older infants and adults, respiration and heart rate variability were not strongly related through a high frequency region respiratory sinus arrhythmia but rather through a breath amplitude sinus arrhythmia which occurs in the low frequency region of the spectrum. The prominent very low frequency activity and the low frequency activity ascribed to breath amplitude modulation may result from autonomic nervous system mediation of chemoregulation.     

Muscle tendon unit comparisons between infants born preterm and infants born full term: a pilot study.

PURPOSE: This study assessed differences in measures of the muscle tendon unit between infants born preterm and infants born full-term. METHODS: Twenty infants born between 26 and 36 weeks of gestation comprised the preterm group and 21 infants born between 38 and 42 weeks of gestation comprised the full-term group. Gastrocnemius-soleus measurements were obtained with a taut tendon and relaxed muscle belly (Ao), and with a taut tendon and elongated muscle belly (Amax). Muscle extensibility measurements were obtained with a goniometer. Ao to Amax was the difference between Ao and Amax measurements. RESULTS: Statistically significant differences were found for both measures of muscle extensibility, but not for the difference between these measures. The preterm group demonstrated measures of Ao and Amax in more extended ankle positions. CONCLUSION: Muscle length differences are present between infants born full-term and infants born preterm. These differences are most likely due to differences in tendon length.