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.     

Cardiovascular autonomic regulation in preterm infants: the effect of atropine

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

Power spectral analysis of heart rate in relation to sleep position

We used spectral analysis of heart rate variability, as a measure of autonomic tone, to determine spectral power differences in infants sleeping supine and prone. We studied 29 infants with a birth weight of 1,915 +/- 939 g, at the postconceptional age of 36 +/- 2 weeks. We then calculated total power (TP), low-frequency power (LF, 0.03-0.15 Hz), and high-frequency power (HF, 0.5-1.0 Hz). TP corresponds to overall heart rate variability, LF to both sympathetic and parasympathetic activity, and HF to parasympathetic activity only. Median (25th, 75th percentile) TP (beats/min2) in the supine position was 32.60 (23.12, 59.90), which was significantly higher than the prone position of 25.87 (14.94, 35.57). Similarly, LF (beats/min2) in the supine position of 13.82 (8.63, 23.31) was significantly higher than the prone position of 9.79 (5.46, 14.33). No significant difference was seen in the HF. We conclude that the prone position is associated with decreased heart rate variability and probably decreased sympathetic tone, which imply decreased autonomic stability in this position.     

甲状腺功能亢进症儿童的甲状腺激素与心率减速力及心率变异性的相关性

目的 对甲状腺功能亢进症（简称“甲亢”）儿童的心率减速力（DC）、心率加速力（AC）、心率变异性（HRV）进行分析,并探讨甲亢儿童的血清甲状腺激素水平与DC、AC及HRV的关系。方法 选取甲亢儿童47例,另选取50例健康儿童为对照组,对所有受试者行24 h动态心电图检查,将甲亢组与对照组的DC、AC、心率（HR）及HRV各指标[RR间期总体标准差（SDNN）、RR间期平均值的标准差（SDANN）、相邻RR间期差值的均方根（RMSSD）、低频功率（LF）、高频功率（HF）]进行比较,并将甲亢儿童的甲状腺激素指标[游离三碘甲状腺原氨酸（FT3）、游离甲状腺素（FT4）]与DC、AC及HRV各指标进行相关性分析。结果 甲亢组的DC、SDNN、SDANN、RMSSD、LF、HF均低于对照组;AC和HR均高于对照组（P < 0.05）。甲亢儿童的血清FT3、FT4与DC、SDNN、SDANN、RMSSD、LF、HF均呈负相关（P < 0.05）;与AC和HR呈正相关（P < 0.05）。结论 甲亢儿童的心脏自主神经功能受损,表现为迷走神经张力降低。血清甲状腺激素水平越高,迷走神经张力越低,提示发生心血管疾病的危险性越大。     

Normal Ranges of Heart Rate Variability During Infancy and Childhood

Heart rate variability is a noninvasive index of the neural activity of the heart. The present study examined heart rate variability indices in 210 infants and children aged 3 days to 14 years to obtain normal ranges for all age classes. Heart rate variability was measured by calculating mean RR interval over the length of the analysis, mean RR interval during quiet sleep, 5 time-domain (SDNN, SDNN-i, SDANN-i, r-MSSD, pNN50), and 4 frequency-domain (VLF, LF, HF, LF/HF ratio) indices. Our data show a significant positive correlation between all indices and the mean RR interval over the length of the analysis, except for the LF/HF ratio for which the correlation was binomial. A positive power correlation was also found between all parameters and age. The multiple correlation analysis confirmed the independent effect of age and mean RR interval on the heart rate variability. These data in a healthy pediatric population confirm a progressive maturation of the autonomic nervous system during childhood and may be utilized to examine the effects of underlying disease processes or therapeutic interventions on cardiac autonomic tone during infancy and childhood.     

小儿扩张型心肌病心率变异性分析

目的分析扩张型心肌病(DCM)儿童的心率变异性(HRV)。方法DCM儿童23例(研究组),匹配健康儿童23例为对照(对照组)。采用康泰TLC3000A12通道动态心电图(EKG)分析系统描记24hEKG,分析心率、HRV的时域指标和频域指标。应用SPSS11.0软件进行统计学处理。结果与对照组比较,研究组最低心率明显增高(P<0.05),最高心率稍增高(P>0.05);HRV时域指标SDNN、SDANN、pNN50明显降低(P<0.05),rMSSD稍降低(P>0.05);HRV频域指标TP、ULF明显降低(P<0.05),VLF、LF、HF、LF/HF稍增高(P>0.05)。结论DCM儿童自主神经功能明显受损。     

Effects of Gender and Aerobic Fitness on Cardiac Autonomic Responses to Head-Up Tilt in Healthy Adolescents

Cardiovascular autonomic responses to orthostatic challenges are affected by gender and cardiorespiratory fitness in adults. However, little is know about the effects of these factors in healthy adolescents. We studied 41 adolescents (20 boys and 21 girls) aged 12-17 years, divided into aerobic fitness tertiles based on the results of a maximal treadmill exercise test. Cardiac autonomic modulation was assessed by heart rate variability (HRV) analysis of 5-minute RR interval recordings before and after 70° head-up tilt maneuver. HRV was analyzed by time (TD) and frequency domain (FD) methods. TD was analyzed by standard deviation of the RR intervals and the root mean square of successive differences of RR intervals. The power spectral components were studied at low (LF) and high (HF) frequencies and as the LF/HF ratio. We did not find any differences in TD and FD measures before and after tilt in either gender or fitness groups, except for a higher heart rate response for boys. These results suggests that cardiac autonomic responses to head-up tilt in healthy adolescents are not affected by gender or aerobic fitness.     

The development of autonomic cardiovascular control is altered by preterm birth

Objectives

Autonomic dysfunction, either sympathetic or parasympathetic, may explain the increased incidence of Sudden Infant Death Syndrome (SIDS) among preterm infants, as well as their subsequent heightened risk of hypertension in adulthood. As little is known about the development of autonomic function in preterm infants, we contrasted autonomic cardiovascular control across the first 6 months after term-corrected age (CA) in preterm and term infants.

Study design

Preterm (n = 25) and age matched term infants (n = 31) were studied at 2–4 weeks, 2–3 months and 5–6 months CA using daytime polysomnography. Blood pressure and heart rate were measured during quiet (QS) and active (AS) sleep. Autonomic control was assessed using spectral indices of blood pressure and heart rate variability (BPV and HRV) in ranges of low frequency (LF, reflecting sympathetic + parasympathetic activity), high frequency (HF, respiratory-mediated changes + parasympathetic activity), and LF/HF ratio (sympatho-vagal balance).

Results

In preterm infants, HF HRV increased, LF/HF HRV decreased and LF BPV decreased with age (p < 0.05); these changes were most evident in AS. Compared to term infants, preterm infants in QS exhibited lower LF, HF and total HRV at 5–6 months; higher HF BPV at all ages; and lower LF BPV at 2–4 weeks (p < 0.05).

Conclusions

With maturation, in preterm infants, parasympathetic modulation of the heart increases while sympathetic modulation of blood pressure decreases. Compared to term infants, preterm infants exhibit lesser parasympathetic modulation of the heart along with greater respiratory-mediated changes and lower sympathetic modulation of blood pressure. Impaired autonomic control in preterm infants may increase their risk of cardiovascular dysfunction later in life.     

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。     

Heart rate variability in diabetic children: Sensitivity of the time- and frequency-domain methods

Summary Heart rate variability (HRV) is a noninvasive index of the neural activity of the heart. Although also influenced by the sympathetic activity of the heart, HRV is essentially determined by the vagal stimulation of the heart. Several HRV abnormalities have been described in adults with diabetes mellitus. However, there are few data on HRV in children with diabetes mellitus. In the present study, HRV was assessed in seven healthy children, 10 diabetic children with good glycemic control and 11 diabetic children with poor glycemic control. All had normal standard cardiac autonomic function tests, obtained from 24-h Holter tapes. HRV was measured by calculating six time-domain (mean R-R interval (RR), standard deviation of the R-R interval [SDRR], standard deviation of the mean of 288 R-R intervals [SDANN], the mean of the 288 standard deviations computed for each 5-min period [SD], percentage of differences of adjacent R-R intervals of >50 msec for the entire 24 h [pNN50], and the root mean square of successive differences [rMSSD]) and four frequency-domain (low frequency [LF], high frequency [HF], total heart rate power spectra, and LF/HF ratio) indexes. SD, pNN50, rMSSD, LF, HF and total heart rate power spectra were markedly and significantly reduced in diabetic children with poor metabolic control. The 24-h variation of low- and high-frequency components of heart rate power spectra of the latter children had a differet shape. Thus, diabetic children with poor metabolic control (elevated HbA₁c and B₂M levels) have a low HRV compared to those diabetic children with good control and healthy chidren. These results can be interpreted as evidence of cardiac autonomic neuropathy in diabetic children with asymptomatic diabetic autonomic neuropathy.     

Influence of maternal smoking on autonomic nervous system in healthy infants

To determine the influence of maternal smoking on autonomic nervous system in healthy infants, 36 infants were recorded polygraphically for one night. Their mothers were defined, according to their smoking frequency during pregnancy, as "nonsmokers" (no cigarettes smoked during pregnancy) or "smokers" (10 or more cigarettes per day). The infants had a median postnatal age of 10.5 wk (range 6 to 16 wk); 18 were born to nonsmokers, and 18 to smokers. During the whole night, spectral analyses of heart rate (HR) were evaluated as a function of sleep stages. Two major peaks were recognizable: a low-frequency component (LF) related to sympathetic and parasympathetic activities and a high-frequency component (HF) reflecting parasympathetic tonus. The ratio of LF/HF powers was calculated as an index of sympathovagal interaction. In REM sleep, "smokers" infants were characterized by significantly lower HF powers and normalized HF powers, and higher LF/HF ratios than "nonsmokers." The finding did not reach statistical significance in NREM sleep. In conclusion, maternal smoking induced changes in autonomic control and maturation in infants. These effects of cigarette smoke exposure can be added to those already reported and offer additional evidence for counseling mothers to stop smoking.     

Evolution of Heart Rate Control After Transplantation: Conduction Versus Autonomic Innervation

In cardiac transplantation, the donor organ is not initially innervated and demonstrates decreased heart rate variability (HRV). However, HRV may improve after several months. The mechanism for HRV improvement has not been elucidated; autonomic reinnervation of the donor heart has been proposed. The role of atrioatrial conduction from recipient to donor organ has not been evaluated. We prospectively evaluated cardiac transplant patients with a limited electrophysiology study at the time of their surveillance biopsies. Recordings were made of recipient and donor signals, observing conduction properties between recipient and donor atria. Holter recordings were analyzed and HRV was determined using spectral analysis techniques, recording mean RR interval, low-frequency power (LF), high-frequency power (HF), and the LF/HF ratio. These were compared to published norms. From November 1999 to May 2000, 21 patients (6 female) who underwent cardiac transplantation participated at a median age of 101 months (range, 4.1–217 months). Time posttransplant ranged from 26 days to 71 months. Holter data were available for 20 patients and demonstrated dissociated P waves in 13 (65%). The mean heart rate on Holter was 111 beats per minute (bpm) (range, 85–161 bpm). We were able to record distinct recipient atrial signals in 16 of 21 (76%) patients. The average recipient tissue heart rate was 55% that of the donor heart rate. We documented atrioatrial association in only 1 patient. HRV did not reach normal values for most patients and did not increase with time posttransplantation. The LF values were in the normal range for most patients, whereas 3 patients had normal HF values and 2 patients had values just below normal. Recipients of heart transplantation have a predominantly sympathetic influence of HRV. These preliminary data suggest that atrioatrial conduction does not play a role in reestablishing normal heart rate control following pediatric cardiac transplantation.     

Characteristics of heart period variability in intubated very low birth weight infants with respiratory disease

BACKGROUND: Heart period variability provides a measure of balance between the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS). Since the PNS develops during the final weeks of gestation, premature infants have an overriding SNS. Spectral power analysis of heart period variability reveals two main frequency regions, the low frequency region (LF) representing primarily SNS activity and the high frequency region (HF) representing PNS activity. OBJECTIVES: To identify the characteristics of heart period power in the LF and HF regions in very low birth weight (VLBW) infants in the neonatal intensive care unit across gestational age groups and between sleep and awake states. METHODS: Data were collected from 16 intubated and mechanically ventilated VLBW infants with respiratory disease. Using spectral analysis techniques, heart period power in the two main frequency regions was extracted. RESULTS: HF power did not improve with gestational age as expected. LF power did increase with age, albeit nonsignificantly. LF and HF power were not significantly different between awake and sleep states. CONCLUSIONS: The results of this preliminary study suggest that PNS tone does not improve with gestational age in VLBW infants with respiratory disease. The intensive care environment may stimulate a sympathetic response in these infants and disrupt normal PNS development.     

Heart rate variability in infants with apparent life-threatening events

Heart rate variability (HRV) is often used as an index of sympatho-vagal balance. A decreased HRV has been observed in patients with central hypoventilation and in infants who have later succumbed to sudden infant death syndrome (SIDS). The aim of the present study was to investigate whether HRV is altered in infants with apparent life-threatening events (ALTE), a group with an increased risk of SIDS. Fifty infants with ALTE were compared with 50 age- and sex-matched controls. ECG was recorded overnight in all infants. Two sequences of RR intervals free of artefacts were selected from each sleep state and spectral analysis of RR variability was performed. The mean and SD of RR and the low (LFPow) and high (HFPow) frequency power were analysed. In active sleep (AS) the LF/HF ratio was lower in ALTE infants, but no differences were seen in either the LFPow or the HFPow. In quiet sleep (QS), however, ALTE infants had higher SD-RR (p = 0.006), greater HFPow (p = 0.02) and VLFPow (very low frequency power, p = 0.02) than the control infants. The same results were seen when the two sleep states were combined for analysis, ALTE infants had higher SD-RR (p = 0.004), HFPow (p = 0.006) and VLFPow (p = 0.04). Conclusion: The different HRV pattern in ALTE infants compared to healthy controls suggests an altered autonomic control.     

Dynamic analysis of beat-to-beat fetal heart rate variability recorded by SQUID magnetometer: quantification of sympatho-vagal balance

BACKGROUND: Quantitative analysis of fetal heart rate variability (HRV) can be used to investigate the neural control mechanisms of fetal cardiac activity. However, conventional power spectrum methods do not reveal the full complexity of the time-varying sympatho-vagal balance in the fetus. AIM: This study was carried out to explore alternative digital signal processing methods of analysing fetal HRV in time domain (rather than frequency domain), in line with most types of physiological monitoring. METHODS: The beat-to-beat fetal heart rate was obtained by Superconducting Quantum Interference Device (SQUID) magnetocardiographic recording. These data were filtered within appropriately selected frequency bands: high frequency (HF) f>0.2 Hz, low frequency (LF) 0.05相似文献   

Time domain correlation analysis of heart rate variability in preterm neonates

BACKGROUND AND AIM: A fuller understanding of the neural control mechanisms of heart rate during the early stages of human development would be of great value to obstetric and neonatal management. In this paper, we investigate the correlation between heart rate variability (HRV) and other physiological parameters such as blood pressure and respiration in preterm neonates with the aim of developing a numerical model to explain and predict heart rate variability. STUDY DESIGN AND SUBJECTS: All the required data are readily available for premature babies who are routinely monitored while being nursed in intensive care, and we have collected large data sets for a random group of such neonates. For the quantitative analysis of the data, we have developed a time domain correlation method, which has a number of advantages over the more commonly used power spectral analysis. We have been able to study the dynamics of the different frequency components of HRV by this method. RESULTS: Highly correlated behaviour of the different HRV components, previously observed in our work on fetal HRV, is also present in the neonate, with similar characteristic time constants. Furthermore, the correlation of high-frequency (HF) oscillations of HRV with respiration and that of low-frequency (LF) oscillations of HRV with blood pressure are demonstrated on timescales of a single oscillation. In neonates receiving artificial ventilation, the correlation between HRV and respiration depends on the type of ventilation involved and assumes opposite polarities for the two main types of equipment currently in use. CONCLUSION: We demonstrate that it is possible to analyse HRV quantitatively by calculating the relative gains and characteristic time constants for the correlated parameters and components.     

重型β-地中海贫血患儿心率变异性的分析

目的：该研究通过对重型β-地中海贫血（β-TM）患儿心率变异性（HRV）的变化特点的研究,探讨HRV对β-TM患儿心功能异常的诊断价值。方法：对21例β-TM患儿（地贫组）和15例正常儿童（对照组）分别进行24 h动态心电图（Holter）检查,比较分析两组HRV时域和频域指标的变化及β-TM患儿血清铁蛋白水平与HRV的相关性。结果：地贫组患儿HRV时域指标SDNN、rMSSD、pNN50 和频域指标极低频谱（VLF）、低频谱（LF）、高频谱（HF）均降低,与对照组比较差异有统计学意义（P<0.05）;血清铁蛋白水平与HRV的变化无相关性。结论：β-TM患儿自主神经功能异常;HRV对β-TM患儿早期心功能异常有预测价值。     

Heart rate variability during caregiving and sleep after massage therapy in preterm infants

Background

Preterm birth impairs the infant's stress response due to interruption of autonomic nervous system (ANS) development. Preterm infants demonstrate a prolonged and aberrant sympathetic response to stressors. ANS development may be promoted by massage therapy (MT), which has been shown to improve stress response in preterm infants.

Aims

The aim of this study was to compare preterm infant ANS function and stress response during sleep and caregiving epochs, as measured by heart rate variability (HRV), after two weeks of twice-daily MT.

Study design

A subset of participants from a larger randomized, masked, controlled trial was used.

Subjects

Twenty-one infants (8 males and 13 females) from a larger study of 37 medically stable preterm infants were studied. The infants were receiving full volume enteral feedings with a mean post-menstrual age of 31.4 (MT) and 30.9 (control) weeks.

Outcome measures

Low to high frequency (LF:HF) ratio of HRV was the outcome of interest.

Results

There was a significant group × time × sex interaction effect (p < .05). Male control infants demonstrated a significant decline in LF:HF ratio from baseline to the second caregiving epoch, suggesting decreased mobilization of sympathetic nervous system response when exposed to stressors. Male MT infants demonstrated increased LF:HF ratio during caregiving and decreased LF:HF ratio during sleep epochs, suggesting improved ANS function, although this was not statistically significant. LF:HF ratio was similar in female MT and female control infants during caregiving and sleep.

Conclusions

Control males had decreased HRV compared to MT males. There was no difference in HRV between MT and control females.     

Heart rate variability analysis in full-term infants: spectral indices for study of neonatal cardiorespiratory control

The heart rate and respirations of twenty healthy full-term infants between 30 and 60 h postnatal age were studied during quiet sleep with the objective of defining spectral indices which represent normal neonatal heart rate variability (HRV) characteristics. Total HRV power and the distribution of power across different frequency bands varied considerably among infants. Cluster analysis on the measured variables indicated that the population divided into two groups that represented significantly different patterns of HRV behavior. In one group (11 subjects), infants had lower breathing rates and HRV power in a band about the respiration frequency [respiratory sinus arrhythmia (RSA) band] was more than 20% of the total power (TP). Additionally, the ratio of low frequency band power to RSA band power was less than 4. The other group of neonates (nine subjects) had relatively higher breathing rates, RSA power less than 20% of total power, and low frequency to RSA power ratio greater than 4. Regression analysis of low frequency versus TP and RSA versus TP graphs gave strong support to the hypothesis that there were indeed two distinct patterns of HRV behavior. Separation of apparently normal neonates into two groups may be attributed partially to differences in respiratory rates and breathing patterns. However, it is possible that differences in the balance between sympathetic and parasympathetic nervous system control, perhaps related to autonomic maturation, also contribute to group separation. The indices developed from HRV spectral analysis in this investigation may be of value in the study of cardiorespiratory control in neonates.     

Increased amplitude modulation of continuous respiration precedes sudden infant death syndrome -detection by spectral estimation of respirogram

The immaturity of the control of the autonomic nervous system has been suggested as one of the key factors in the pathophysiology of sudden infant death syndrome (SIDS). Therefore, the attenuated control of respiration may also cause more slow oscillatory breathing among infants at risk of SIDS. In this study, patterns of respiratory activity (RAV) and heart rate variability (HRV) were examined in Medilog-records prospectively obtained from 22 tape recordings made on 16 babies subsequently suffering from SIDS and from 22 matched control babies. A total of 248 signal segments, 120 s in duration, representing the state of regular breathing were visually selected for further analysis. The digitised signal sets were detrended, Fast-Fourier-transformed and autospectra as well as cross-spectra for the HRV and HRV were computed. The RAV and HRV were examined at two spectral bands: (1) a low frequency (LF) band 0.03-0.17 Hz (1.8-10 cycles/min) and (2) a high frequency (HF) band 0.3-1.3 Hz (18-90 cycles/min). Different parameters of each band were tested in the spectral analysis of cardiorespiratory control. The LF/HF-ratio of the spectral peak area of the respiratory activity and the LF/HF-ratio of the spectral band area of the respiratory activity were greater in the SIDS group when compared to the controls. No significant intergroup differences were found in the parameters of HRV, or the cross-spectral parameters. Interestingly, the technique appeared helpful in displaying that the victims of SIDS had a significantly greater amount of slow oscillation in the continuous respiratory signal (1.05+/-1.89 vs. 0.41+/-0.57, P=0.02). In the victims of SIDS the respiratory control system seems to be less stable and cause more slow oscillatory breathing and this can be detected using spectral analysis of respiratory activity even during breathing that visually seems to be regular.