Neonatal Heart Rate Variability Research Articles

Early neonatal heart rate variability patterns in different subtypes of perinatal hypoxic-ischemic brain injury.

This study aims to compare the longitudinal changes in heartrate variability (HRV) during therapeutic hypothermia in neonates with different subtypes of hypoxic-ischemic brain injury. HRV was computed from 1 hour time-epochs q6 hours for the first 48 hours. Primary outcome was brain-injury pattern on MRI at 4(3-5) days. We fitted linear mixed-effect regression models with HRV metric, brain injury subtype and postnatal age. Among 89 term neonates, 40 neonates had abnormal brain MRI (focal infarct 15 (38%), basal-ganglia predominant 8 (20%), watershed-predominant 5 (13%), and mixed pattern 12 (30%)). There was no significant difference in the HRV metrics between neonates with normal MRI, focal infarcts and basal ganglia pattern. At any given postnatal age, the degree of HRV suppression(HRV measure in the brain-injury subtype group/HRV measure in Normal MRI group) was significant in neonates with watershed pattern (SDNN(0.63, p = 0.08), RMSSD(0.74, p = 0.04)) and mixed pattern injury (SDNN (0.64, p < 0.001), RMSSD (0.75, p = 0.02)). HRV suppression was most profound at the postnatal age of 24-30 h in all brain injury subtypes. Neonates with underlying watershed injury with or without basal-ganglia injury demonstrates significant HRV suppression during first 48 hour of hypothermia therapy. Our study suggests that suppression of heartrate variability in neonates during therapeutic hypothermia varies according to the pattern of underlying hypoxic-ischemic brain injury. Neonates with watershed predominant pattern and mixed pattern of brain injury have the most severe suppression of heartrate variability measures. Heartrate variability monitoring may provide early insights into the pattern of hypoxic-ischemic brain injury in neonates undergoing therapeutic hypothermia earlier than routine clinical MRI.

In infants with congenital heart disease autonomic dysfunction is associated with pre-operative brain injury.

Background:Brain injury is a serious and common complication of critical congenital heart disease (CHD). Impaired autonomic development (assessed by heart rate variability; HRV) is associated with brain injury in other high-risk neonatal populations.Objective:To determine whether impaired early neonatal HRV is associated with pre-operative brain injury in CHD.Methods:In infants with critical CHD, we evaluated HRV during the first 24 hours of cardiac ICU (CICU) admission using time-domain (RMS1, RMS2, and alpha 1) and frequency-domain metrics (LF, nLF, HF, nHF). Pre-operative brain MRI was scored for injury using an established system. Spearman’s correlation coefficient was used to determine the association between HRV and pre-operative brain injury.Results:We enrolled 34 infants with median birth gestational age (GA) of 38.8 weeks (IQR 38.1-39.1). Median postnatal age (PNA) at pre-operative brain MRI was 2 days (IQR 1-3 days). Thirteen infants had MRI evidence of brain injury. RMS 1 and RMS 2 were inversely correlated with pre-operative brain injury.Conclusions:Time-domain metrics of autonomic function measured within the first 24 hours of admission to the CICU are associated with pre-operative brain injury, and may perform better than frequency domain metrics under non-stationary conditions such as critical illness.

Neonatal heart rate variability: a contemporary scoping review of analysis methods and clinical applications

BackgroundNeonatal heart rate variability (HRV) is widely used as a research tool. However, HRV calculation methods are highly variable making it difficult for comparisons between studies.ObjectivesTo describe the different types...

A method to assess heart rate variability in neonate rats: validation in normotensive and hypertensive animals.

Several studies have focused on the heart rate variability (HRV) of murine species, while studies discussing HRV in murine neonates and infants remain scarce, since recording hemodynamic signals through invasive methods in small animals has been found to be quite challenging. Thus, this study aimed at describing and validating a novel method to assess HRV in newborn rats. An electrocardiogram (ECG) system was used to determine RR intervals in awake newborns and evaluate HRV in normotensive (Wistar) and hypertensive (SHR) neonate rats. After birth, ECG was recorded in the awake newborns, and they were allowed to rest on a heated surface, restricted only by the weight of the adhesive ECG electrodes. The electrodes were cut and adapted to provide more comfort to the animal, and gently placed on the newborn's skin. RR intervals were recorded over a 30-min period using an ECG system together with LabChart software (4 KHz). Three sequences of 5 min each from the ECG recording period were analyzed in time and frequency domains, using CardioSeries software. ECG data resulted in a clearly interpretable signal that was used to generate an RR interval sequence through time for the analysis of HRV. SHR neonates presented increased cardiac sympathovagal balance compared to Wistar neonates (low frequency/high frequency: 3.85±0.71 vs 0.90±0.09). In conclusion, the ECG setup here described may be used to record RR intervals to assess HRV in neonate rats, thus detecting early impairment of HRV in hypertensive newborns.

Early Postnatal Heart Rate Variability in Healthy Newborn Infants.

BackgroundDespite the increasing interest in fetal and neonatal heart rate variability (HRV) analysis and its potential use as a tool for early disease stratification, no studies have previously described the normal trends of HRV in healthy babies during the first hours of postnatal life.MethodsWe prospectively recruited 150 healthy babies from the postnatal ward and continuously recorded their electrocardiogram during the first 24 h after birth. Babies were included if born in good condition and stayed with their mother. Babies requiring any medication or treatment were excluded. Five-minute segments of the electrocardiogram (non-overlapping time-windows) with more than 90% consecutive good quality beats were included in the calculation of hourly medians and interquartile ranges to describe HRV trends over the first 24 h. We used multilevel mixed effects regression with auto-regressive covariance structure for all repeated measures analysis and t-tests to compare group differences. Non-normally distributed variables were log-transformed.ResultsNine out of 16 HRV metrics (including heart rate) changed significantly over the 24 h [Heart rate p < 0.01; Standard deviation of the NN intervals p = 0.01; Standard deviation of the Poincaré plot lengthwise p < 0.01; Cardiac sympathetic index (CSI) p < 0.01; Normalized high frequency power p = 0.03; Normalized low frequency power p < 0.01; Total power p < 0.01; HRV index p = 0.01; Parseval index p = 0.03], adjusted for relevant clinical variables. We observed an increase in several HRV metrics during the first 6 h followed by a gradual normalization by approximately 12 h of age. Between 6 and 12 h of age, only heart rate and the normalized low frequency power changed significantly, while between 12 and 18 h no metric, other than heart rate, changed significantly. Analysis with multilevel mixed effects regression analysis (multivariable) revealed that gestational age, reduced fetal movements, cardiotocography and maternal chronic or pregnancy induced illness were significant predictors of several HRV metrics.ConclusionHeart rate variability changes significantly during the first day of life, particularly during the first 6 h. The significant correlations between HRV and clinical risk variables support the hypothesis that HRV is a good indicator of overall wellbeing of a baby and is sensitive to detect birth-related stress and monitor its resolution over time.

Heart rate variability and inflammatory markers in neonates with hypoxic-ischemic encephalopathy.

To examine heart rate variability (HRV) and inflammatory markers as predictors for neurological injury in neonates undergoing therapeutic hypothermia for hypoxic‐ischemic encephalopathy (HIE). We hypothesized that HRV would differentiate between infants with no/mild injury and infants with moderate/severe injury observed on MRI. Because HRV can be associated with the inflammatory cascade, cytokine concentrations were compared with the severity of brain injury indicated by MRI. Further, we studied the effect of temperature, sex, and mechanical ventilation on HRV. HRV was prospectively collected on neonates with HIE using spectral analysis for low and high frequency components (n = 16). A subset (n = 10) of neonates had serum available for inflammatory cytokine analysis obtained during cooling. Neonates were stratified into no/mild or moderate/severe injury based on MRI obtained after rewarming. Differences in HRV were identified; lower low frequency power predicted more injury on MRI. Additionally, in neonates with HIE after cooling procedure, HRV differed by gender. Elevated RANTES (CCL5) and decreased GM‐CSF (Granulocyte‐macrophage colony‐stimulating factor) at 96 hours predicted less severe injury. In this small study, HRV differs between no/mild and moderate/severe injury in neonates with HIE. With further study, this may aid the clinician in real‐time decision making. HRV differs by gender. Finally, inflammatory biomarkers may help elucidate the pathophysiology of HIE.

Maternal, fetal and neonatal heart rate and heart rate variability in Holstein cattle

ABSTRACT: The aim of this study was to describe the normal values for maternal, fetal and neonatal heart rate (HR) and heart rate variability (HRV) indexes in the time domain (standard deviation of beat-to-beat interval - SDNN; root mean square of successive beat-to-beat differences - RMSSD) and the frequency domain (low frequency - LF; high frequency - HF; relationship between low and high frequency - LF/HF) in 23 Holstein cows, 23 fetuses and 18 neonates during the perinatal period. HR and HRV were calculated by fetomaternal electrocardiography (ECG). Fetomaternal measurements were taken six times prepartum (between days 234 and 279 of pregnancy) and measurements were taken in neonates six times after calving (after birth and five times weekly). HR, time and frequency domain were analyzed. No significant changes in maternal, fetal beat-to-beat interval (RR interval) or HR were found. In maternal variables, SDNN decreased significantly from 38.08±2.6ms (day 14 before calving) to 23.7±2.5ms (day 1 after calving) (p&lt;0.05), but the RMSSD did not change significantly. HR and RR interval of calf differed statistically from the day before delivery (163±7.5bpm; 381±24.2ms) to the day after calving (131±5bpm; 472±16.2ms). Time variables (SDNN and RMSSD) and the frequency-domain variables (LF and HF) were significantly different (p&lt;0.05) between fetal and neonatal stages. Reductions in the values of SDNN and RMSSD can reflect a sympathetic dominance. After calving, the increase in HF and decrease in LF variables can indicate activation of the vagal nerve followed by heart and respiratory modulation.

Unlike Kangaroo care, mechanically simulated Kangaroo care does not change heart rate variability in preterm neonates

BackgroundWhile numerous positive effects of Kangaroo care (KC) have been reported, the duration that parents can spend kangarooing is often limited. AimTo investigate whether a mattress that aims to mimic breathing motion and the sounds of heartbeats (BabyBe GMBH, Stuttgart, Germany) can simulate aspects of KC in preterm infants as measured by features of heart rate variability (HRV). MethodsA within-subject study design was employed in which every routine KC session was followed by a BabyBe (BB) session, with a washout period of at least 2 h in between. Nurses annotated the start and end times of KC and BB sessions. Data from the pre-KC, KC, post-KC, pre-BB, BB and post-BB were retrieved from the patient monitor via a data warehouse. Five time-domain features of HRV were used to compare both types of intervention. Two of these features, the percentage of decelerations (pDec) and the standard deviation of decelerations (SDDec), were developed in a previous study to capture the contribution of transient heart rate decelerations to HRV, a measure of regulatory instability. ResultsA total of 182 KC and 180 BabyBe sessions were analyzed in 20 preterm infants. Overall, HRV decreased during KC and after KC. Two of the five features showed a decrease during KC, and all features decreased in the post-KC period (p ≤ 0.01). The BB mattress as employed in this study did not affect HRV. ConclusionUnlike KC, a mattress that attempts to mimic breathing motion and heartbeat sounds does not affect HRV of preterm infants.

The Use of Hemodynamic and Cerebral Monitoring to Study Pharmacodynamics in Neonates.

Drugs acting on the cardiovascular and central nervous system often display relatively fast clinical responses, which may differ in neonates compared to children and adults. Introduction of bedside monitoring tools might be of additional value in the pharmacodynamic (PD) assessment of such drugs in neonates. We aim to provide an overview of the frequently used monitoring tools to assess drug effects on the hemodynamic status as well as the cerebral circulation, oxygenation and cerebral metabolism in neonates. The use of blood pressure measurements, heart rate variability, functional echocardiography, nearinfrared spectroscopy and (amplitude-integrated) electroencephalography in neonates is discussed, as well as new parameters introduced by these tools. Based on the 'brain circulation model', the hemodynamic effects on the brain and their interplay are summarized. In this model, 3 processes (i.e. blood processes, vascular smooth muscle processes and tissue processes) and 3 mechanisms (i.e. autoregulation, blood flow metabolism coupling and cerebral oxygen balance) are distinguished, which all may be influenced by drug administration. Finally, propofol, sevoflurane, midazolam and inotropes are used as examples of which PD has been studied using the available hemodynamic and/or cerebral monitoring tools. The implementation of (non-)invasive monitoring tools to document hemodynamic and cerebral PD effects in neonates is of relevance both in a neonatal research and intensive clinical care setting. We highlight the need to integrate these tools in future PD research. Furthermore, besides short-term drug effects, long-term outcome of drug therapy in neonates also warrants further attention.

Surface electromyography for analysis of heart rate variability in preterm infants

Objective: Characterizing heart rate variability (HRV) in neonates has gained increased attention and is helpful in quantifying maturation and risk of sepsis in preterm infants. Raw data used to derive HRV in a clinical setting commonly contain noise from motion artifacts. Thoracic surface electromyography (sEMG) potentially allows for pre-emptive removal of motion artifacts and subsequent detection of interbeat interval (IBI) of heart rate to calculate HRV. We tested the feasibility of sEMG in preterm infants to exclude noisy raw data and to derive IBI for HRV analysis. We hypothesized that a stepwise quality control algorithm can identify motion artifacts which influence IBI values, their distribution in the time domain, and outcomes of nonlinear time series analysis. Approach: This is a prospective observational study in preterm infants <6 days of age. We used 100 sEMG measurements from 24 infants to develop a semi-automatic quality control algorithm including synchronized video recording, threshold-based sEMG envelope curve, optimized QRS-complex detection, and final targeted visual inspection of raw data. Main results: Analysis of HRV from sEMG data in preterm infants is feasible. A stepwise algorithm to exclude motion artifacts and improve QRS detection significantly influenced data quality (34% of raw data excluded), distribution of IBI values in the time domain, and nonlinear time series analysis. The majority of unsuitable data (94%) were excluded by automated steps of the algorithm. Significance: Thoracic sEMG is a promising method to assess motion artifacts and calculate HRV in preterm neonates.

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.

Heart rate variability in neonates of type 1 diabetic pregnancy

BackgroundCardiomyopathy is a common finding in offspring of pre-gestational type 1 diabetic pregnancy. Echocardiographic and biochemical evidence of fetal cardiac dysfunction have also been reported. Studies suggest that offspring of diabetic mothers (ODM) undergo a fetal programming effect due to the hyperglycaemic intrauterine milieu which increases their risk of cardiovascular morbidity in adult life. Decreased neonatal heart rate variability (HRV) has been described in association with in-utero growth restriction, prematurity, sudden infant death syndrome and congenital heart disease. The effect of in-utero exposure to hyperglycaemia in diabetic pregnancy on neonatal HRV is unknown. AimsOur aim was to determine if neonatal HRV differs between normal and diabetic pregnancy. Study design and subjectsThis was a prospective observational study of 38 patients with pregestational type 1 diabetes and 26 controls. HRV assessment was performed using Powerlab (ADI Instruments Ltd). Outcome measuresHeart rate variability assessment and cord blood sampling for pH and glucose were performed for all neonates. Maternal glycaemic control was assessed via measurement of glycosylated haemoglobin in each trimester in the diabetic cohort. ResultsNeonates of diabetic mothers had evidence of altered heart rate variability, with increased low frequency to high frequency ratio (LF: HF), suggestive of a shift towards sympathetic predominance (p<0.05). This altered HRV was significantly related to fetal acidaemia, cord blood glucose values and maternal glycaemic control during pregnancy (p<0.05). ConclusionNeonates of pregestational diabetic pregnancy have altered HRV which is related to maternal hyperglycaemia, fetal acidaemia and fetal glycaemia. Exposure of the developing heart to fluctuations in maternal glycaemia with subsequent alterations in HRV may explain why infants of diabetic mothers are at greater risk of cardiovascular disease in later life.

Development of a pain monitoring device focused on newborn infant applications: The NeoDoloris project

Heart rate variability (HRV) reflects the autonomic nervous system activity on the organism. Sympathetic and parasympathetic influences in response to painful or stressful stimulus can be measured by the variations of RR intervals. After the elaboration of an automated index evaluating parasympathetic tone in adults (Analgesia Nociception Index, ANI), we choose to adapt this technology to neonates. A work system analysis of the maternity and the neonatal intensive care unit has established the needs for such an application and users' requirements the application should meet. Based on these observations, neonatal applications have been developed for an automated analysis of neonatal HRV in high frequencies only (<0.15Hz) which is representative of parasympathetic activity. Technical developments have resulted in two specific devices (one ambulatory and one monitor) displaying a unique index: the Newborn Infant Parasympathetic Evaluation (NIPE). Several clinical studies have been carried out and they have shown that the NIPE index is able to evaluate prolonged pain, acute pain, discomfort, and comfortable stimulations. The NIPE index assesses the parasympathetic tone and could be a good decision support for medical staff. Long term studies are needed in order to evaluate the neuro-developmental benefits of continuously parasympathetic evaluation on neonates.

Nonreassuring fetal heart rate decreases heart rate variability in newborn infants.

Nonreassuring fetal status (NRFS) refers to a compromised fetal condition which implies hypoxia. The influence of intrapartum hypoxia on autonomic nervous system function in early postnatal life is unknown. This study explored the influence of NRFS on the heart rate variability (HRV) of newborn infants. Singleton newborn infants delivered through Cesarean delivery (CD) with indications of elective purpose (n = 32), dystocia (n = 29), or NRFS (n = 22), and through vaginal birth (VB) (n = 80) were consecutively collected. HRV parameters including standard deviation of average NN intervals (SDANN), low frequency (LF), high frequency (HF), LF%, HF%, and total power (TP), were obtained for analysis in 3 days postpartum. An independent t-test or one-way ANOVA was used to compare differences in numeric data. SDANN, HF, HF%, and TP of newborn infants in the VB group were significantly higher than those in the CD group. The NRFS group had significantly lower SDANN, HF, and TP than those of the elective group, and significantly lower HF, HF%, and TP than those of the dystocia group. Newborn infants delivered through Cesarean section had lower HRV, especially those who experienced NRFS during labor. The long-term effects of changes of HRV in neonates require further evaluation.

Cortisol and progestin release, heart rate and heart rate variability in the pregnant and postpartum mare, fetus and newborn foal

The mechanisms leading to parturition in the horse in many aspects differ from those in other species. Pregnancy is maintained not by progesterone but by 5α-pregnanes and the progestin precursor pregnenolone originates from the fetus. As parturition approaches, the fetal adrenal switches from pregnenolone to cortisol synthesis but it is not known whether cortisol crosses the placenta. We hypothesized that in parallel to fetal cortisol release, cortisol in the maternal circulation increases before foaling and this increase can be determined in both saliva and plasma. In addition, maternal, fetal and neonatal heart rate and heart rate variability were measured. In 25 pregnant mares, saliva for cortisol analysis was collected 4 times daily from 15 days before to 5 days after foaling. In 13 mares, in addition, fetomaternal electrocardiogram (ECG) recordings were made and blood samples for progestin and cortisol analysis were collected once daily. Heart rate (HR) was recorded until 5 days after foaling. The heart rate variability (HRV) variables standard deviation of the beat-to-beat (RR) interval (SDRR) and root mean square of successive RR differences (RMSSD) were calculated. From Days 15 to 4 before parturition, progestin concentration increased (peak 267 ± 42 ng/mL) and decreased thereafter (P < 0.05, day of foaling 113 ± 18 ng/mL). A prepartum increase in maternal cortisol concentrations was evident in blood (P < 0.05) and saliva (P < 0.05) and paralleled the decrease in progestin concentrations. In mares, HR remained constant during the last days of pregnancy but decreased within one day after parturition (P < 0.05) while maternal HRV did not change. In the fetus and neonate, HR increased from before to after birth (P < 0.05) indicating increasing demands on the cardiovascular system with adaptation to extrauterine life.

Heart Rate Variability in Neonates with Hypoxic Ischemic Encephalopathy

To evaluate the changes in heart rate variability (HRV) in newborns with hypoxic-ischemic encephalopathy (HIE). Twenty-two newborns (14 boys, 8 girls) with moderate or severe HIE and 24 term neonates with similar gestational and postnatal age for control were included in this study. Normalized low and high frequency components of HRV and their ratio were evaluated for 24-h in newborns with HIE and control subjects. The newborns with hypoxic-ischemic encephalopathy had significantly lower normalized low frequency (LFn) and low frequency (LF) / high frequency (HF) values and higher normalized high frequency (HFn) values when compared with the control babies. In addition, when the cases with severe HIE are compared with those of moderate HIE, decreased LFn, LF/HF values and also increased HFn values were present in the severe cases. HIE is associated with reduced sympathetic nervous system activity, and increased parasympathetic nervous system activity and these activities also correlate with the severity of the disease.

Relation between neonatal behavioral states and heart rate variability

Article Relation between neonatal behavioral states and heart rate variability was published on August 30, 2012 in the journal Biomedical Engineering / Biomedizinische Technik (volume 57, issue SI-1-Track-F).

Neonatal heart rate variability in type 1 diabetic pregnancy

IntroductionIn adult diabetic patients, abnormalities in heart rate variability can predict mortality post myocardial infarction. Fetuses of diabetic mothers are at increased risk of unexplained death in utero and it...

Normalization of Autonomic Function in Children With Coarctation of the Aorta After Surgical Correction in Infancy

To the Editor: Systemic hypertension affects ≥20% of patients with coarctation of the aorta (CoA) by adolescence, despite early surgical repair.1 This leads to premature death and is arguably the most important outcome variable in these patients. We have previously demonstrated reduced spontaneous baroreceptor reflex sensitivity (BRS) and heart rate variability (HRV) in preoperative neonates with CoA compared with age-matched controls, suggesting early autonomic dysfunction.2 Altered BRS has also been demonstrated in older children after late surgical repair,3 however, little is known about BRS and autonomic function in younger patients after successful neonatal repair. In the current study, we re-evaluated spontaneous BRS, HRV, and blood pressure (BP) variability (BPV) from our initial cohort at 5 years on to determine whether there was persisting abnormality of cardiovascular autonomic variables as a precursor to arterial hypertension. We re-examined 6 of the 7 living CoA patients and 7 of the 12 living age- and sex-matched control patients from the initial cohort. The remaining 5 controls could no longer be traced, and 1 CoA patient was not included because of severe developmental delay. None of the subjects were taking medications. …

Effect of Phototherapy on Neonatal Heart Rate Variability and Complexity

Background: Phototherapy is a common mode of treatment for neonatal hyperbilirubinemia. However, phototherapy has been reported to alter cardiovascular function by causing increased peripheral blood flow, diminished cardiac output and increased sympathetic activity that may be of concern particularly in sick or premature newborns. The effects of phototherapy on the autonomic nervous system modulation of heart rate in term neonates have not yet been investigated. Objectives: The aim of the present study was to investigate the effects of phototherapy on the autonomic nervous system modulation of heart rate in healthy full-term jaundiced neonates. Methods: 30 full-term jaundiced infants were prospectively studied before and during phototherapy. Heart rate variability was analyzed with conventional time-domain, spectral, and time-dynamic techniques by using Poincaré plots. Results: Phototherapy was found to cause significant diminution in the short- and long-term variability of heart rate in newborns as documented by time-domain analysis of heart rate variability, and visually demonstrated by using Poincaré plots. Spectral indices and heart rate were unchanged during phototherapy. Conclusions: A significant diminution in heart rate variability was documented during phototherapy, a phenomenon assumed to be centrally mediated. The reasons for this decrease are yet unknown. The use of time-dynamic analysis methods may offer important details on the newborn’s physiology that cannot be revealed by traditional methods.