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

Aim: Newborn infants produce significant heart rate responses to both head-up and head-down tilting: heart rate increases with head-up tilting and decreases with head-down tilting. However, previously we found that, at 2-4 mo of age, heart rate increases were no longer significant following slow head-up tilting. This study was designed to determine if 2-4-mo-old infants have significant increases in heart rate when tilted rapidly. Methods: Fifty-four infants were tested as newborns or at 2-4 mo of age. Heart rate was measured while infants were tilted to a 30° head-up angle either slowly over a period of 30 s or rapidly in 5 s. Results: Newborns exhibited increases in heart rate using both tilt speeds; however, at 2-4 mo of age, heart rate did not change significantly using either speed of tilting.

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

Capturing postoperative pain responses in critically ill infants aged 0 to 9 months.

OBJECTIVES: The purpose of this study was to describe physiologic and behavioral pain behaviors in postoperative critically ill infants. A secondary aim was to identify how these pain responses vary over time. DESIGN: This observational study was conducted in the pediatric intensive care unit at two tertiary referral hospitals. Using ethological methods of observation, video recordings of postoperative infants were viewed to depict different situations of pain and no pain and were then coded using a reliable checklist. PATIENTS: A total of 803 recorded segments were generated from recordings of five critically ill infants aged between 0 and 9 months who had undergone major surgery. MEASUREMENTS AND MAIN RESULTS: There was an 82% agreement between the two coders. Multivariate analyses showed that physiologic responses differed only when adjusted for time. Significant decreases in systolic and diastolic arterial pressure (p < .001 and p = .036, respectively) were associated with postoperative pain exacerbated by painful procedures on day 2. On day 3, however, heart rate, arterial pressure (systolic, diastolic, and mean), and central venous pressure significantly increased (p < .05) in response to postoperative pain. Indicators included vertical stretch of the mouth, hand twitching, and jerky leg movements for postoperative pain and increase in respiratory distress, frown, eyes tightly closed, angular stretch of the mouth, silent or weak cry, jerky head movements, fist, pulling knees up, and spreading feet for postoperative pain exacerbated by painful stimuli. CONCLUSIONS: Findings support the ability to capture different intensities of postoperative pain in critically ill infants beyond neonatal age. These pain indicators can be used for the development of a pain assessment tool for this group of infants.     

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.     

Influences on heart rate variability in spontaneously breathing preterm infants.

To investigate the influence of maturational and physiological factors on heart rate variability in spontaneously breathing very preterm infants (n = 29) a multiparametric study was performed during the first 3 days of life in infants born at a gestational age below 33 weeks. Four times a day, RR-intervals, respiration curve and rate, transcutaneously measured blood gases and observed body movements were recorded while the infants were asleep. All data were stored simultaneously in a micro-computer. Non-invasively measured blood pressure and patency of the ductus arteriosus were documented as well. Four sets of short- (STV) and long term variability (LTV) indices were calculated. Both STV and LTV appeared to be significantly influenced by conceptional and postnatal age in the appropriate for gestational age infants. LTV was influenced by the behavioural state and body movements. During state coincidence 2 ('active sleep') LTV was influenced by respiratory rate and the variations in transcutaneous PO2. An effect of blood pressure or ductus patency could not be demonstrated.     

Spectral analysis of heart rate variability in premature infants with feeding bradycardia

An elevated level of baseline parasympathetic activity was noted in a group of premature infants suffering from bradycardia during feeding. At approximately 34 wk post-conceptional age, the heart rates of 12 infants with feeding bradycardia (birth weight = 1539 +/- 279 g; gestational age = 31.0 +/- 1.6 wk) and 10 controls (birth weight = 1710 +/- 304 g; gestational age = 32.0 +/- 1.4 wk) were recorded 1 h before and 1 h after feeding. EKG data were digitized and 3.2-min segments of data were analyzed to determine the spectral power at very low (VLF = 0.003-0.03 Hz), low (LF = 0.03-0.39 Hz), and high (HF = 0.40-1.00 Hz) frequencies. In preterm infants with feeding bradycardia, an elevation in baseline parasympathetic activity was evident before feeding, as indicated by significantly higher HF power and a lower LF/HF ratio. This elevation in baseline parasympathetic activity may contribute to the observed bradycardia during feeding.     

Spectral analysis of heart rate variability in spontaneously breathing very preterm infants

Van Ravenswaaij-Arts C, Hopman J, Kollée L, Sloelinga G, Van Geijn H. Spectral analysis of heart rate variability in spontaneously breathing very preterm infants. Acta Pædiatr 1994;83:473–80. Stockholm. ISSN 0803–5253
The influence of maturation, sleep state and respiration on heart rate variability was studied in 16 spontaneously breathing preterm infants (<33 weeks). ECG, respiratory impedance curve and movements were recorded four times a day, during the first three days of life. The power content of selected frequency bands of the R-R interval power spectrum, as well as respiratory frequency and breath amplitude oscillation frequency, were calculated for 3–min periods. An increase in low-frequency heart rate variability with gestational age was found. High-frequency variability increased during early postnatal life. Sleep state influenced very low-frequency heart rate variability. The amount of respiratory sinus arrhythmia and breath amplitude sinus arrhythmia was determined mainly by respiratory rate and breath amplitude oscillation frequency, respectively. The influences of gestational and postnatal age on heart rate variability might be due to an increase in sympathetic tone before birth and a change in parasympathetic-sympathetic balance after birth. Respiration has an important influence on heart rate variability, even in very preterm infants.     

Oral rotavirus vaccination in breast- and bottle-fed infants aged 6 to 12 months

Oral bovine rotavirus vaccine RIT 4237 was tested at two dose levels in 217 children between 6 and 12 months of age who received either breast milk or bottle milk (cow's milk or infant formula) before vaccination. Of the children 65% were initially seronegative for rotavirus ELISA IgG and IgM antibody. The full vaccine dose (10(8.3) 50% tissue culture infective doses, TCID50) induced seroconversion rates 81% and 86% and booster response rates 69% and 64% in breast and bottle-fed children, respectively. There was no difference in the vaccine response of infants receiving cow's milk or infant formula either. It is concluded that the RIT 4237 rotavirus vaccine at the dose level 10(8.3) TCID50 gives a satisfactory response in both breast- and bottle-fed children in this age group, but multiple vaccinations may be needed for maximal efficacy.     

Circadian rhythm of heart rate and heart rate variability

BACKGROUND—Measurements of heart rate variability (HRV) are increasingly used as markers of cardiac autonomic activity.AIM—To examine circadian variation in heart rate and HRV in children.SUBJECTS—A total of 57 healthy infants and children, aged 2 months to 15 years, underwent ambulatory 24 hour Holter recording. Monitoring was also performed on five teenagers with diabetes mellitus and subclinical vagal neuropathy in order to identify the origin of the circadian variation in HRV.METHODS—The following variables were determined hourly: mean RR interval, four time domain (SDNN, SDNNi, rMSSD, and pNN50) and four frequency domain indices (very low, low and high frequency indices, low to high frequency ratio). A chronobiological analysis was made by cosinor method for each variable.RESULTS—A significant circadian variation in heart rate and HRV was present from late infancy or early childhood, characterised by a rise during sleep, except for the low to high frequency ratio that increased during daytime. The appearance of these circadian rhythms was associated with sleep maturation. Time of peak variability did not depend on age. Circadian variation was normal in patients with diabetes mellitus.CONCLUSION—We have identified a circadian rhythm of heart rate and HRV in infants and children. Our data confirm a progressive maturation of the autonomic nervous system and support the hypothesis that the organisation of sleep, associated with sympathetic withdrawal, is responsible for these rhythms.     

1~3月龄婴儿下呼吸道感染痰检病原菌分布及耐药分析

目的 了解1~3月龄婴儿下呼吸道感染(LRTI)病原菌的分布及耐药情况,为临床合理选用抗生素提供依据.方法 选取2013年1~12月本院收治的患LRTI的1~3月龄婴儿622例,取痰标本送细菌培养.采用琼脂扩散敏感试验行药敏试验.结果 622份痰标本中共分离到菌株379株,检出率为60.9%,其中革兰阴性菌325株(85.8%),革兰阳性菌50株(13.2%),真菌4株(1.1%).革兰阴性菌主要为大肠埃希菌(31.1%)和肺炎克雷伯菌(18.2%),产超广谱β内酰胺酶(ESBLs)菌的检出率分别为48.3%和52.2%,且上述两种产ESBLs菌的平均耐药率为53%,对氨苄西林、头孢噻肟耐药率达100%,对碳青霉烯类抗生素均敏感.革兰阳性菌主要为金黄色葡萄球菌(10.0%),其中耐甲氧西林金黄色葡萄球菌检出比例较低(1.8%),但对β内酰胺类抗生素100%耐药.结论 1~3月龄婴儿LRTI的病原菌以革兰阴性菌:大肠埃希菌和肺炎克雷伯菌为主,产ESBLs菌检出率达48%以上,平均耐药率达53%以上,可指导临床首次经验性选药,以提高低龄婴儿的治疗有效率和生存率.     

正常儿童动态心电图窦性心率及心率变异分析

目的探讨正常儿童心率及心率变异性(HRV)特点。方法对804例正常儿童进行24h全程动态心电图检查,分析心率及HRV。结果不同年龄儿童窦性心率范围不同,年龄越小心率越快;儿童不同性别间HRV中24h内全部正常心动周期的标准差(SDNN)、24h内每5minNN间期标准差的平均值(SDNNindex)、NN50占所有N-N间期个数的百分数(PNN50)、极低频率(VLF)、低频(LF)差异有显著性;儿童不同年龄组间24h内5min节段平均心动周期的标准差(SDANN)、VLF、LF、全程相邻NN间期之间的均方根值(rMSSD)差异有显著性;儿童组与成人正常参考值中SDNN、SDANN、rMSSD差异有显著性,rMSSD儿童组中明显高于成人组。结论HRV是一种反映自主神经活性及其平衡的能定量、可重复的非侵入性的检测方法,是自主神经系统与心血管系统相互制约的结果。不同年龄、不同性别间儿童HRV存在显著差异;儿童组与成人参考值存在显著差异,尤其rMSSD儿童明显高于成人,提示儿童的自主神经功能较成人活跃,而随着年龄增长自主神经功能减退,尤其是迷走神经的紧张抑制功能明显减退。     

Developmental patterns of heart rate and variability in prematurely-born infants with apnea of prematurity

At equivalent post-conceptional ages, prematurely-born infants have higher heart rates and reduced heart rate variability, relative to full-term neonates. Premature birth might exert long-lasting effects on central and peripheral mechanisms that control cardiovascular activity. We assessed development of heart rate and heart rate variability in symptomatic preterm infants up to 6 months of age. Fifty 6.5-h evening recordings of EKG and breathing were obtained from prematurely-born infants (gestational ages: 24–35 weeks). Cardiac R-R intervals were captured with a resolution of ±0.5 msec. One-min epochs were selected from three periods of regular respiration in recordings from premature infants and 72 recordings of full-term infants at comparable post-conceptional ages. Mean heart rate and heart rate variability were determined for each recording. At 40 weeks post-conception, prematurely-born infants with apnea of prematurity showed higher heart rates and reduced heart rate variability than did full-term neonates. These differences between premature and full-term infants persisted throughout the next 6 months in those infants born prior to 30 weeks gestation, and in those infants born at 30–35 weeks who experienced respiratory distress syndrome (RDS) during the neonatal period. The findings suggest that premature delivery, or complications thereof, exerts long-lasting effects on cardiac control.     

Developmental patterns of heart rate and variability in infants with persistent apnea of infancy

During periods of regular breathing, heart rate is slower and more variable in healthy (no history of respiratory distress syndrome) prematurely born infants with persistent apnea, relative to full-term control infants of comparable post-conceptional ages. We tested the hypothesis that the cardiovascular differences may be linked to the persistent apnea, rather than premature birth, by assessing heart rate and variability in full-term infants with persistent apnea. Thus, resting heart rate and variability were compared in full-term infants with apnea of infancy, prematurely born infants with persistent apnea, and full-term control infants. Full-term infants with persisting apnea showed slower heart rates than control infants, beginning at 4 months after birth, and enhanced heart rate variability beginning at 6 months. Healthy prematurely born infants with persistent apnea showed cardiovascular alterations similar to those of full-term infants with apnea; these alterations differed from those observed in very premature infants with histories of respiratory distress. The postnatal development of cardiovascular aberrations in infants with persistent apnea suggests that mechanisms accompanying apneic events may contribute to long-term alterations in autonomic control.     

Circadian rhythm of heart rate and heart rate variability.

BACKGROUND: Measurements of heart rate variability (HRV) are increasingly used as markers of cardiac autonomic activity. AIM: To examine circadian variation in heart rate and HRV in children. SUBJECTS: A total of 57 healthy infants and children, aged 2 months to 15 years, underwent ambulatory 24 hour Holter recording. Monitoring was also performed on five teenagers with diabetes mellitus and subclinical vagal neuropathy in order to identify the origin of the circadian variation in HRV. METHODS: The following variables were determined hourly: mean RR interval, four time domain (SDNN, SDNNi, rMSSD, and pNN50) and four frequency domain indices (very low, low and high frequency indices, low to high frequency ratio). A chronobiological analysis was made by cosinor method for each variable. RESULTS: A significant circadian variation in heart rate and HRV was present from late infancy or early childhood, characterised by a rise during sleep, except for the low to high frequency ratio that increased during daytime. The appearance of these circadian rhythms was associated with sleep maturation. Time of peak variability did not depend on age. Circadian variation was normal in patients with diabetes mellitus. CONCLUSION: We have identified a circadian rhythm of heart rate and HRV in infants and children. Our data confirm a progressive maturation of the autonomic nervous system and support the hypothesis that the organisation of sleep, associated with sympathetic withdrawal, is responsible for these rhythms.     

Development of heart rate variation over the first 6 months of life in normal infants

Development of heart rate variation in three frequency ranges was examined during sleep-walking states in normal infants over the first 6 mo of life. Extent of all three types of heart rate variation decreased from 1 wk to 1 mo of age. Extent of respiratory sinus arrhythmia increased from 1 mo to 6 mo during all sleep-waking states, with the increase most pronounced during quiet sleep. Variation in two bands of lower frequencies showed increases in extent from 1 to 3 mo, then a slowing or reversal of the increase between 3 and 4 mo of age. During rapid eye movement sleep, the two types of lower frequency heart rate variation decreased in extent from 3 through 6 mo of age. These results suggest that alterations in autonomic control of heart rate occur at several time periods over the first 6 mo of life and that these alterations may have an effect only on particular types of heart rate variation and only during particular sleep-waking states. The diminution of all three types of heart rate variation at 1 mo may indicate a reduction in vagal tone at this age.     

Fetal responses to acoustic stimulation depend on heart rate variability pattern, stimulus intensity and repetition

Fetuses (37-40 wks DA) were exposed to three successive presentations of a 5-s high-pass filtered (800 Hz) pink noise either at 105 dB or at 110 dB SPL. Stimulations were given during high or low variability heart rate (HR) patterns (HV or LV) which presumably correspond mostly to active and quiet sleep episodes, respectively. The proportion of fetuses showing cardiac response (CR) was always greater than the proportion showing leg movement (LM) but the presence of an accompanying leg movement always increased the amplitude of CR, independent of HR pattern, stimulus repetition and intensity. Fetal reactiveness always diminished with stimulus repetition but diminished more on the three examined dimensions (CR ratio, LM ratio and CR amplitude) with LV infants than with HV infants, and more with the 105 dB stimulus than with the 110 dB stimulus. More importantly, stimulus parameters and HR patterns interacted. At 110 dB in HV, neither the median amplitude of the CRs nor the probability of a CR changed over trials but the probability of a concommittant LM decreased. At 110 dB in LV, repetition induced a decrement on all three response dimensions from the second trial onwards. At 105 dB in HV, LM decreased rapidly, as much as at 110 dB in LV. Thus, state, as reflected by HR pattern, plays a significant role in determining the occurrence and the amplitude of the CR and the occurrence of a LM which, in turn, will enhance the CR amplitude.     

Hepatitis A seroprevalence among infants aged 12 months in Ankara

Seroprevalence studies in various age groups contribute to a better understanding of hepatitis A infection and response to hepatitis A immunization. Hepatitis A seroprevalence in 12-month-old infants from Ankara was studied. Among 601 healthy infants, overall hepatitis A seropositivity was found to be 23.5%. There were no gender differences in seropositivity (22.6% for male and 24.5% for female infants). Although vaccination of infants would be an ideal prevention strategy, presence of maternal anti-hepatitis A virus (HAV) antibody interferes with the immune response to hepatitis A vaccine in infants and young children. Therefore, further knowledge about decay of maternal antibody in infants is important in determining the optimal age for vaccination against hepatitis A. There is no recommendation for routine hepatitis A vaccination in Turkey. However, we need more seroprevalence studies in different age groups to decide the appropriate timing/age of vaccination.