The influence of artificial ventilation on heart rate variability in very preterm infants

Cardiorespiratory signature of neonatal sepsis: development and validation of prediction models in 3 NICUs

BACKGROUND

Heart rate characteristics aid early detection of late-onset sepsis (LOS), but respiratory data contain additional signatures of illness due to infection. Predictive models using cardiorespiratory data may improve early sepsis detection. We hypothesized that heart rate (HR) and oxygenation (SpO₂) data contain signatures that improve sepsis risk prediction over HR or demographics alone.

METHODS

We analyzed cardiorespiratory data from very low birth weight (VLBW, <1500 g) infants admitted to three NICUs. We developed and externally validated four machine learning models to predict LOS using features calculated every 10 m: mean, standard deviation, skewness, kurtosis of HR and SpO₂, and cross-correlation. We compared feature importance, discrimination, calibration, and dynamic prediction across models and cohorts. We built models of demographics and HR or SpO₂ features alone for comparison with HR-SpO₂ models.

RESULTS

Performance, feature importance, and calibration were similar among modeling methods. All models had favorable external validation performance. The HR-SpO₂ model performed better than models using either HR or SpO₂ alone. Demographics improved the discrimination of all physiologic data models but dampened dynamic performance.

CONCLUSIONS

Cardiorespiratory signatures detect LOS in VLBW infants at 3 NICUs. Demographics risk-stratify, but predictive modeling with both HR and SpO₂ features provides the best dynamic risk prediction.

IMPACT

Heart rate characteristics aid early detection of late-onset sepsis, but respiratory data contain signatures of illness due to infection. Predictive models using both heart rate and respiratory data may improve early sepsis detection. A cardiorespiratory early warning score, analyzing heart rate from electrocardiogram or pulse oximetry with SpO₂, predicts late-onset sepsis within 24 h across multiple NICUs and detects sepsis better than heart rate characteristics or demographics alone. Demographics risk-stratify, but predictive modeling with both HR and SpO₂ features provides the best dynamic risk prediction. The results increase understanding of physiologic signatures of neonatal sepsis.

Experimental study on the effects of isoflurane with and without remifentanil or dexmedetomidine on heart rate variability before and after nociceptive stimulation at different MAC multiples in cats

BACKGROUND

Heart rate variability (HRV) provides information about autonomic nervous system (ANS) activity and is therefore a possible tool with which to assess anaesthetic depth. The aim of the present study was to evaluate the effects of isoflurane, remifentanil and dexmedetomidine on HRV before and after nociceptive stimulation at different anaesthetic depths. Seven healthy domestic short-hair cats were used, and each cat was anaesthetized three times - group I with isoflurane alone, group IR with isoflurane and a constant rate infusion (CRI) of remifentanil (18 μg/kg/h), and group ID with isoflurane and a CRI of dexmedetomidine (3 μg/kg/h). Minimum alveolar concentration (MAC) values were determined via electrical supramaximal nociceptive stimulation for each treatment group. Nociceptive stimulation was repeated at 3 different MAC multiples (0.75, 1.0 and 1.5 MAC), and electrocardiographic recordings were performed for 3 min before and after stimulation. Only the 1 min epochs were used for further statistical analysis. Electrocardiographic data were exported for offline HRV analysis.

RESULTS

The mean isoflurane MAC ± standard deviation (SD) was 1.83 ± 0.22 vol% in group I, 1.65 ± 0.13 vol% in group IR and 0.82 ± 0.20 vol% in group ID. Nociception was indicated by several HRV parameters, however, with high variability between treatments. The best correlation with MAC was found for the SD of heart rate (STD HR) in group I (r_s = - 0.76, p = 0.0001, r² = 0.46). STD HR was also able to distinguish 0.75 MAC from 1.5 MAC and 1.0 MAC from 1.5 MAC in group I, as well as 0.75 MAC from 1.5 MAC in group ID.

CONCLUSIONS

The choice of anaesthetic protocol influences the HRV parameters in cats. Frequency domain parameters respond to nociception at lower MAC levels. The STD HR has the potential to provide additional information for the assessment of anaesthetic depth in isoflurane-anaesthetized cats. The utility of HRV analysis for the assessment of anaesthetic depth in cats is still questionable.

Linear and Nonlinear Analyses of the Cardiac Autonomic Control in Children With Developmental Coordination Disorder: A Case-Control Study

Children with Developmental Coordination Disorder (DCD) and children at risk for DCD (r-DCD) present motor impairments interfering in their school, leisure and daily activities. In addition, these children may have abnormalities in their cardiac autonomic control, which together with their motor impairments, restrict their health and functionality. Therefore, this study aimed to assess the cardiac autonomic control, by linear and nonlinear analysis, at supine and during an orthostatic stimulus in DCD, r-DCD and typically developed children. Thirteen DCD children (11 boys and 2 girls, aged 8.08 ± 0.79 years), 19 children at risk for DCD (13 boys and 6 girls, aged 8.10 ± 0.96 years) and 18 typically developed children, who constituted the control group (CG) (10 boys and 8 girls, aged 8.50 ± 0.96 years) underwent a heart rate variability (HRV) examination. R-R intervals were recorded in order to assess the cardiac autonomic control using a validated HR monitor. HRV was analyzed by linear and nonlinear methods and compared between r-DCD, DCD, and CG. The DCD group presented blunted cardiac autonomic adjustment to the orthostatic stimulus, which was not observed in r-DCD and CG. Regarding nonlinear analysis of HRV, the DCD group presented lower parasympathetic modulation in the supine position compared to the r-DCD and CG groups. In the within group analysis, only the DCD group did not increase HR from supine to standing posture. Symbolic analysis revealed a significant decrease in 2LV (p < 0.0001) and 2UV (p < 0.0001) indices from supine to orthostatic posture only in the CG. In conclusion, r-DCD and DCD children present cardiac autonomic dysfunction characterized by higher sympathetic, lower parasympathetic and lower complexity of cardiac autonomic control in the supine position, as well as a blunted autonomic adjustment to the orthostatic stimulus. Therefore, cardiovascular health improvement should be part of DCD children's management, even in cases of less severe motor impairment.

Heart rate variability of transported critically ill neonates

Determining heart rate variability (HRV) in infants is a useful measure of physiological stability. Transport of ill neonates imposes a measurable degree of stress. A prospective observational study on 58 critically ill neonates, transported to an intensive care unit (ICU) was performed. HRV during the 24-h period before, during and after transport, heart rate (HR), mean arterial pressure and transport risk index of physiologic stability (TRIPS) score were observed. The median HRV total power value of 40.80 ms(2) was set as the cutoff value, and neonates with values below this were designated as the low-HRV group (l-HRV; n=29), and those above this as the high-HRV group (h-HRV; n=29). The h-HRV group had a significantly lower HR at retrieval and 1 h after admission and a significant 2- and 4-day shorter duration of mechanical ventilation and ICU treatment compared to the l-HRV group. Spearman's correlations between total power and duration of mechanical ventilation (ρ=-0.346; P<0.01) and ICU treatment (ρ=-0.346; P<0.01) were significant. Transported neonates were also tested for differences in HRV and other physiological and demographic parameters between the transport mode and time. No differences were found, except that the nighttime ambulance group had a statistically higher HRV compared to the daytime ambulance group.

CONCLUSION

Higher HRV of group of neonates, who did not differ in illness severity TRIPS score from the lower HRV group, is associated with a faster and significant decrease in HR after transport and a 2- and 4-day shorter duration of mechanical ventilation and ICU treatment.

Heart rate variability and extubation readiness in extremely preterm infants

BACKGROUND

Mechanical ventilation (MV) is associated with changes in autonomic nervous system activity in preterm infants, which can be assessed by measurements of heart rate variability (HRV). Decreased HRV has been described in adults undergoing disconnection from MV; such information is not available in preterm infants.

OBJECTIVE

To compare differences in HRV between infants successfully extubated and those who failed, and to evaluate the accuracy of HRV as a predictor of extubation readiness.

METHODS

This is a prospective, observational study of infants with a birth weight ≤1,250 g undergoing their first extubation attempt. Heart rate was measured during a 60-min period immediately prior to extubation and HRV was calculated using the frequency domain analysis.

RESULTS

A total of 47 infants were studied; 36 were successfully extubated and 11 reintubated. There were no differences in patient demographics, ventilator settings, blood gases or postextubation management between the groups. All components of the HRV analysis were significantly decreased in infants who failed, generating high areas under the receiver operating characteristic curve. The specificity and positive predictive values were 100, but with limited sensitivity and negative predictive values.

CONCLUSIONS

Infants considered 'ready to be extubated' but who subsequently failed their first extubation attempt had decreased HRV prior to extubation. Though promising, the value of HRV as a predictor of extubation readiness requires further evaluation.

Sound and vibration: effects on infants' heart rate and heart rate variability during neonatal transport

AIM

To measure the effect of sound and whole-body vibration on infants' heart rate and heart rate variability during ground and air ambulance transport.

METHODS

Sixteen infants were transported by air ambulance with ground ambulance transport to and from the airports. Whole-body vibration and sound levels were recorded and heart parameters were obtained by ECG signal.

RESULTS

Sound and whole-body vibration levels exceeded the recommended limits. Mean whole-body vibration and sound levels were 0.19 m/s(2) and 73 dBA, respectively. Higher whole-body vibration was associated with a lower heart rate (p < 0.05), and higher sound level was linked to a higher heart rate (p = 0.05). The heart rate variability was significantly higher at the end of the transport than at the beginning (p < 0.01). Poorer physiological status was associated with lower heart rate variability (p < 0.001) and a lower heart rate (p < 0.01). Infants wearing earmuffs had a lower heart rate (p < 0.05).

CONCLUSIONS

Sound and whole-body vibration during neonatal transport exceed recommended levels for adults, and sound seem to have a more stressful effect on the infant than vibrations. Infants should wear earmuffs during neonatal transport because of the stress-reducing effect.

Heart rate variability in response to pain stimulus in VLBW infants followed longitudinally during NICU stay

The objective of this longitudinal study, conducted in a neonatal intensive care unit, was to characterize the response to pain of high-risk very low birth weight infants (<1,500 g) from 23 to 38 weeks post-menstrual age (PMA) by measuring heart rate variability (HRV). Heart period data were recorded before, during, and after a heel lanced or wrist venipunctured blood draw for routine clinical evaluation. Pain response to the blood draw procedure and age-related changes of HRV in low-frequency and high-frequency bands were modeled with linear mixed-effects models. HRV in both bands decreased during pain, followed by a recovery to near-baseline levels. Venipuncture and mechanical ventilation were factors that attenuated the HRV response to pain. HRV at the baseline increased with post-menstrual age but the growth rate of high-frequency power was reduced in mechanically ventilated infants. There was some evidence that low-frequency HRV response to pain improved with advancing PMA.

Heart rate variability responses of a preterm infant to kangaroo care

OBJECTIVE

To examine the effect of kangaroo care on heart rate variability in a healthy preterm infant.

DESIGN

Case study.

SETTING

Private room on a postpartum unit.

PARTICIPANT

A mother-preterm infant dyad.

INTERVENTION

Kangaroo (skin-to-skin) care.

MAIN OUTCOME MEASURE

Heart rate variability, a noninvasive measurement of the sympathetic and parasympathetic components of the autonomic nervous system's influence on heart rate.

RESULTS

Heart rate variability, especially the parasympathetic component, was high when the infant was fussy in the open crib, indicating increased autonomic nervous system activity. With kangaroo care, the infant fell asleep, and both sympathetic and parasympathetic components of heart rate variability decreased.

CONCLUSIONS

The wide fluctuations in the parasympathetic component of heart rate variability suggest immaturity of the sympathovagal response. Overall, kangaroo care produced changes in heart rate variability that illustrate decreasing stress.

A Scottish study of heel-prick blood sampling in newborn babies

OBJECTIVE

to conduct a randomised-controlled trial to investigate the effectiveness of two heel-prick devices (Tenderfoot and Genie Lancet) used in the newborn-baby screening test.

DESIGN

a randomised-controlled trial.

PARTICIPANTS AND SETTING

the homes of 340 healthy term newborn babies discharged from the maternity unit of Stirling Royal Infirmary, Scotland. Data were collected between April and November 2003.

INTERVENTIONS

babies were randomly allocated to be tested with either the Tenderfoot or Genie Lancet heel-prick device.

MEASUREMENTS

primary study outcomes include (1) quality of the blood sample; (2) time taken to collect the sample; (3) number of heel pricks required to take the sample; (4) whether squeezing of heel was required; (5) pain expressed by the baby; and (6) presence of bruising. A potential intervening variable was the experience of the midwife.

FINDINGS

on all outcomes, the Tenderfoot device was more effective than the Genie Lancet. Experienced midwives were more efficient in sample collection.

KEY CONCLUSIONS

this study shows that the Tenderfoot device saves significant time for midwifery staff, improves baby care and reduces the need for more than one heel prick at each test, making it superior to the Genie Lancet device.

IMPLICATIONS FOR PRACTICE

there is a case to be made for midwives to be issued with the Tenderfoot device for neonatal screening.

Birth prematurity determines prolonged autonomic nervous system immaturity

Because of its multiple involvement in physiological processes, autonomic nervous system (ANS) activity, a key regulator of homeostatic control, demonstrates a progressive increase during pregnancy. The profile of its maturation, mainly in the parasympathetic arm, in premature or full term infants, may help us to better understand its pathophysiological role. We prospectively evaluated ANS maturity in a group of 23 premature (PREM) infants at their theoretical term age and in 8 full term (FT) newborns. All recordings were registered close to the theoretical full term period (from 38 to 41 weeks) for the PREM group and during the first week of life for the FT newborns. Polygraphic recordings, EEG monitoring associated with visual clinical control, and Holter ECG, were performed simultaneously. ANS indices were then calculated during quiet sleep periods, using Wavelet transform of RR (beat to beat) intervals. High frequency components were found to be significantly lower in the PREM than in the FT group (p<0.05). Furthermore, at theoretical full term age, the greater the prematurity, the lower was parasympathetic activity. Because it is easy, monitoring of parasympathetic activity may help us to understand autonomic maturation and its clinical prognostic implications.

Heart Period Variability of Intubated Very-Low-Birth-Weight Infants During Incubator Care and Maternal Holding

• Background Heart rate has been used to measure infants’ physiological stability during skin-to-skin holding. Variability in heart period (interbeat interval), a more sensitive measure of autonomic nervous system tone, has not.

• Objective To describe heart period variability in intubated very-low-birth-weight infants during incubator care and during maternal skin-to-skin holding.

• Design/Methods An experimental, interrupted time series, crossover design was used; infants served as their own controls. Infants were randomly assigned to treatment order: 2 hours of intermittent skin-to-skin holding for 2 consecutive days followed by 2 days of incubator care or vice versa. The analog signal representing heart period was sampled and quantized at 5 Hz via a dedicated computer system in multiple 300-second epochs each day.

• Results Fourteen infants with similar characteristics completed the protocol. The mean interbeat interval was 332 ms during skin-to-skin care and 368 ms during incubator care. Power within the low-and high-frequency regions of heart period was not significantly different between skin-to-skin holding and incubator care. Mean low-frequency power was 124.6 ms2 during skin-to-skin holding and ranged from 51.9 ms2 to 71.4 ms2 during all periods of incubator care. Mean high-frequency power was similar during skin-to-skin holding and incubator care (8.8 ms2 and 6.1 ms2). Infants of 32 to 34 weeks’ corrected gestational age had increased power in the low- and high-frequency regions.

• Conclusions Heart period variability did not improve during skin-to-skin holding. Gestationally older infants had increased power in the low- and high-frequency regions, suggesting a maturing autonomic nervous system.

Methodological considerations for the use of heart rate variability as a measure of pain reactivity in vulnerable infants

Measures of HR and HRV offer multiple indices of reactivity to painful events. These measures are particularly helpful in preterm and ill infants where distress signals are often nonspecific and ambiguous. HR is easy to acquire, and a variety of widely used techniques are available for processing it. In general, the neuroanatomic and neurophysiologic bases for pain perception are in place even in the most preterm infant and produce patterns of HR and HRV responses that are similar across multiple settings. Developmental and experiential factors related to preterm birth, however, may affect these HR responses. Furthermore, evaluation of ill infants in an NICU setting adds multiple contextual factors that potentially influence HR and HRV and alter their specificity as measures of pain. In some cases, it may appear that pain reactivity is reduced when, in fact, HR reactivity is only an expression of the biologic capacity to produce a response, not the presence of a response itself. The nature of the setting and the infant's health, developmental stage, and behavioral state all contribute to potentially altering HR responses to painful events in this setting. Thus, the methodology used and its application must be flexible. A variety of HRV analysis techniques may be needed to identify a variety of response patterns and mechanisms that influence pain reactivity. Furthermore, careful selection of HR epochs for stationarity, an understanding of the potential discordance between biologic and behavioral measures, the effects of medication, and an accounting for developmental differences that occur during a typical NICU course are all critical factors for investigators to be aware of. Understanding cardiovascular reactivity as a measure of response to painful events in vulnerable infants requires ongoing work.

Erythromycin as a prokinetic agent in preterm infants

BACKGROUND

The macrolide antibiotic erythromycin is a prokinetic agent that stimulates gastrointestinal motility. The aim of the study was to determine the effect of erythromycin on the gastrointestinal motility of preterm infants.

METHODS

Erythromycin 10 mg/kg, 8 hourly or a placebo, was given orally for 7 days in a double-blind randomized, crossover study of 20 preterm infants with a median gestational age of 32 weeks (range, 26-34 weeks). Antral contractility was determined by using ultrasonography to measure the decrease in the gastric antral cross-sectional area after a feed. The whole gut transit time was assessed by timing the transit of carmine red through the gut.

RESULTS

Antral contractility lasted for a shorter period of time during erythromycin treatment than during placebo treatment (mean [standard deviation], 31 minutes [9.9 minutes] vs. 70 minutes [13 minutes]; P < 0.01). Whole gut transit time was also shorter during erythromycin treatment (mean, 23.1 hours [12.9 hours] vs. 49.3 hours [29 hours]; P < 0.01). All infants tolerated the drug well.

CONCLUSIONS

Oral erythromycin in food-intolerant preterm infants enhances both antral contractility and whole gut transit time.

Assessment of the effect of EMLA during venipuncture in the newborn by analysis of heart rate variability

The objective of this study was to investigate the effect of EMLA on the pain response when venipuncture was performed in 60 3-day-old healthy newborns. EMLA/placebo was applied to the back of the baby's hand, following a randomized, double-blind procedure. ECG and crying were recorded during the test. The incidence of crying, heart rate (HR) and spectral analysis of heart rate variability were used to characterize the reaction of the baby to the venipuncture procedure. The occurrence of crying during venipuncture did not differ significantly between the EMLA and the placebo groups. The placebo-treated group showed a statistically significant higher HR, and a decrease in variance (total power) and power in the low-frequency band (0.02-0.15 Hz) when compared with the EMLA group. We conclude that EMLA decreases the stress response during venipuncture in newborn infants.

Heart rate variability of preterm neonates quantified by energy entropy

Identifying variables predictive of neurobehavioural sequelae is a key objective in the study of high-risk neonates. Examination of heart rate variability (HRV) characteristics may be a finer discriminator of the neonate's response to physiologic stressors than the mean heart rate. The energy entropy of the heart beat tachogram, computed in four different domains, was used to quantify the HRV in 13 preterm neonates. The entropies of energies were computed from 1024 interbeat time intervals obtained once per week from 26 to 35 weeks postconceptional age (PCA). The energy entropy computed in three of the domains, like the standard deviation of intervals, distinguished between the 10 neonates that were measured at 35 weeks PCA with 100% specificity and 67% sensitivity, but did not distinguish between healthy and unhealthy neonates at earlier ages. The findings suggest that energy entropy may be a discerning measure of physiologic stress in the preterm infant, although future research is needed to refine the test and determine statistical significance.

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.

Assessment of acute pain in preterm infants by evaluation of facial expression and frequency domain analysis of heart rate variability

In ten preterm infants (postconceptional age 27-35 weeks) facial expression and heart rate variability (HRV) were investigated during three situations: (a) the infant at rest in its crib or incubator, (b) provocation of the withdrawal flexor reflex by application of von Frey's hairs, and (c) lancing and squeezing for blood sampling. Video recordings of facial expressions, mixed at random, were categorised as the baby being either undisturbed, disturbed or in pain and a detailed scoring for each situation was performed. Mean heart rate (HR) was calculated and power spectral analysis was assessed on data from segments of 45-s duration from the three procedures. Flexor withdrawal did not evoke visual signs of pain or influence HRV, but caused a slight increase in HR. The lancing and squeezing of the heel evoked a facial expression of pain in all infants. The HR increased and a reduction in both total HRV and power in the low frequency band of the HRV spectrum was seen during blood sampling. The differentiation between painful and non-painful procedures was more apparent when principal component analysis of HRV was applied.

Developments in CTG analysis

FHR monitoring has been the subject of many debates. The technique, in itself, can be considered to be accurate and reliable both in the antenatal period, when using the Doppler signal in combination with autocorrelation techniques, and during the intrapartum period, in particular when the FHR signal can be obtained from a fetal ECG electrode placed on the presenting part. The major problems with FHR monitoring relate to the reading and interpretation of the CTG tracings. Since the FHR pattern is primarily an expression of the activity of the control by the central and peripheral nervous system over cardiovascular haemodynamics, it is possibly too indirect a signal. In other specialities such as neonatology, anaesthesiology and cardiology, monitoring and graphic display of heart rate patterns have not gained wide acceptance among clinicians. Digitized archiving, numerical analysis and even more advanced techniques, as described in this chapter, have primarily found a place in obstetrics. This can be easily explained, since the obstetrician is fully dependent on indirectly collected information regarding the fetal condition, such as (a) movements experienced by the mother, observed with ultrasound or recorded with kinetocardiotocography (Schmidt, 1994), (b) perfusion of various vessels, as assessed by Doppler velocimetry, (c) the amount of amniotic fluid or (d) changes reflected in the condition of the mother, such as the development of gestation-induced hypertension and (e) the easily, continuously obtainable FHR signal. It is of particular comfort to the obstetrician that a normal FHR tracing reliably predicts the birth of the infant in a good condition, which makes cardiotocography so attractive for widespread application. However, in the intrapartum period, many traces cannot fulfil the criteria of normality, especially in the second stage. In this respect, cardiotocography remains primarily a screening and not so much a diagnostic method. As long as continuous monitoring of fetal acid-base balance has not been extensively tested in clinical practice, microblood sampling of the fetal presenting part (Saling, 1994) is a useful adjunct. The problem with non-normal tracings is that their significance is very often unclear. They may indicate serious fetal distress, finally resulting in preventable destruction of critical areas in the fetal brain and damage to various organs; or, on the contrary, they may indicate temporary changes in cardiovascular control as a reaction to the intermittent effects on fetal haemodynamics of, for example, uterine contractions, whether or not in combination with partial or complete compression of umbilical cord vessels or the vessels on the chorionic plate (van Geijn, 1994). Many factors influence the FHR and its variability, which further complicates the interpretation of FHR patterns; some have been discussed here in some detail. Undoubtedly, there is a need for quantitative and objective FHR analysis, as long as it does not lead to erroneous results. Close collaboration between engineers and clinicians is a prerequisite for further advances in this field. Decision support systems certainly have a future but only if they are able to take into account a large set of clinical data and can combine it with data obtained from FHR signals and other parameters referring to the fetal condition, such as fetal growth, Doppler velocimetry, amniotic fluid volume and biochemical and biophysical data obtained from the mother. Basic technical concepts inherent in computerized CTG analysis, such as sampling rate (Chang et al, 1995), signal loss, artefact detection (van Geijn et al, 1980), further processing of intervals, archiving in digitized format and monitor display, should receive considerable attention. There is still a long way to go until decision support systems find their way into obstetric practice. Further developments can only be achieved thanks to efforts of many basic and clinical researchers, wo

Ventilator-associated sinus arrhythmia in a preterm neonate--an indicator for a mature autonomic nervous system?

According to control theory, the interactions between respiration and heart rate (i.e. respiratory sinus arrhythmia, RSA, and breath amplitude sinus arrhythmia, BASA) reflect the inner workings of the physiological control systems of respiration and circulation. This paper reports on a preterm neonate (28.5 weeks old, 940 g) who showed the presence of ventilation-associated sinus arrhythmia (VASA) under moderate artificial ventilation. His heart rate variability was entrained to the ventilatory stimulus. VASA and entrainment suggest that the parasympathetic part of the autonomic nervous system might be more mature than expected in some preterm neonates.