胎儿心率变异功率谱与胎儿宫内窘迫关系探讨

作者利用自行设计的胎儿心率变异检测分析系统采集的248例临床监护数据，研究胎儿心率变异（FHRV）功率谱的特征，对其中距分离时间1周以内的150例数据（睡眠期52例和活跃期98例），以谱参数为特征变量，窘迫值为分类变量，建立判别函数，作判别统计分析，通过跟踪病历对结果作回顾性考核，其判别准确率分别达88.5%(睡眠期）和83.3%(活跃期），显示FHRV功率谱特征与胎儿宫内窘迫有密切的关系。     

Sleep‐disordered breathing in children is associated with impairment of sleep stage‐specific shift of cardiac autonomic modulation

We examined the effects of sleep stages and sleep‐disordered breathing (SDB) on autonomic modulation in 700 children. Apnea hypopnea index (AHI) during one 9 h night‐time polysomnography was used to define SDB. Sleep stage‐specific autonomic modulation was measured by heart rate variability (HRV) analysis of the first available 5 min RR intervals from each sleep stage. The mean [standard deviation (SD)] age was 112 (21) months (49% male and 25% non‐Caucasian). The average AHI was 0.79 (SD = 1.03) h^?1, while 73.0%, 25.8% and 1.2% of children had AHI <1 (no SDB), 1–5 (mild SDB) and ≥5 (moderate SDB), respectively. In the no SDB group, the high frequency (HF) and root mean square SD (RMSSD) increased significantly from wake to Stage 2 and slow wave sleep (SWS), and then decreased dramatically when shifting into rapid eye movement (REM) sleep. In the moderate SDB group, the pattern of HRV shift was similar to that of no SDB. However, the decreases in HF and RMSSD from SWS to REM were more pronounced in moderate SDB children [between‐group differences in HF (?24% in moderate SDB versus ?10% in no SDB) and RMSSD (?27% versus ?12%) were significant (P < 0.05)]. The REM stage HF is significantly lower in the moderate SDB group compared to the no SDB group [mean (standard error): 4.49 (0.43) versus 5.80 (0.05) ms², respectively, P < 0.05]. Conclusions are that autonomic modulation shifts significantly towards higher parasympathetic modulation from wake to non‐rapid eye movement sleep, and reverses to a less parasympathetic modulation during REM sleep. However, the autonomic modulation is impaired among children with moderate SDB in the directions of more reduction in parasympathetic modulation from SWS to REM sleep and significantly weaker parasympathetic modulation in REM sleep, which may lead to higher arrhythmia vulnerability, especially during REM sleep.     

Fetal neurobehavioral development: Associations with socioeconomic class and fetal sex

This longitudinal study investigated neurobehavioral development in the human fetus from 24 to 36 weeks gestation. Subject (N = 103) were stratified by socioeconomic class. Fetal data were collected for 50 min at three intervals, and included measures of heart rate, movement, and biobehavioral patterns. Repeated measures analysis of variance by fetal sex and maternal socioeconomic status was used to detect maturation effects and group differences. With advancing gestation, fetuses exhibited reduced heart rate, increased heart rate variability and coupling between movement and heart rate, increased movement vigor, and more biobehavioral concordance. Male fetuses displayed higher heart rate variability throughout gestation and somewhat earlier emergence of biobehavioral organization than females. Fetuses of women of lower socioeconomic status had reduced heart rate variability, moved less often and with less vigor, showed less coupling between movement and heart rate, and had fewer episodes of synchronous quiescence/activity. Results are discussed in terms of development of the central nervous system. © 1998 John Wiley & Sons, Inc. Dev Psychobiol 33: 79–91, 1998     

急性饮酒对青年心率变异的影响及性别差异研究

目的通过检测轻度急性饮酒前后心率变异性指标,评价酒精对于自主神经活动影响的性别差异。方法20例健康志愿者．其中男性10例．年龄（20．1±0．6）岁：女性10例．年龄（19．6±0．8）岁。根据受试者体质量计算乙醇溶液饮用量（0．27g／kg）。分别在饮酒前和饮酒后15min、45min共3次记录心电信号．提取RR间期时间序列,计算心率变异性（HRV）评价指标,包括时域参数RR间期的平均值（RRI）、全部RR间期标准差（SDRR）、全程相邻RR间期之差的均方根（RMSSD）、相邻RR间期之差大于50ms的心搏动数占总心搏动数的比例（pNN50）,频域参数低频频段（LF）、高频频段（HF）和LF／HF,Poincar6图参数宽度（短轴,SDl）、长度（长轴,SD2）和SDl／SD2。结果时域参数、频域参数和P0inca诺参数存急性饮酒后降低。对于RMSSD和SDRR参数．仅在女性受试者中观测到饮酒45min后降低．差异均具有统计学意义（P〈0．05）。对于LF和SDl参数在饮酒后15min即观测到在男性受试者中降低,差异均具有统计学意义（P〈0．05）。结论少量的急性饮酒降低了心率变异程度．酒精抑制了副交感神经的活动度．女性比男性对酒精的敏感程度更高．男性自主种经活动对酒精影响的响应时间更短。     

胎儿心率变异性的近似熵分析在胎儿窘迫诊断中的应用

介绍一种近似熵分析方法,并将其应用于胎心率变异性的研究中,探讨近似熵分析结果与临床胎儿窘迫的相关性。对67例次胎心电子监护(CTG)结果经胎心率变异性的近似熵分析及时域分析。新生儿出生后记录Apgar评分,取脐动脉血行血气分析。结果显示胎心率变异性的近似熵值ApEn与脐血血气分析指标pH、Pco2、Po2、HCO3-、ABE、SO2及新生儿评分Apgar有显著相关性(r=0.51、-0.29、0.49、0.29、0.45、0.56、0.28,P值均<0.05);酸中毒组(pH≤7.2)胎心率变异性的ApEn值显著低于正常组(pH>7.2)(P<0.01),而常规时域分析指标平均胎心率(BHR)、胎心率标准差(SD)、胎心率变异系数(CV)则无显著性差别。提示胎心率变异性的近似熵值是一较敏感的反映胎儿缺氧酸中毒的指标,近似熵分析方法可为胎儿窘迫早期诊断的准确性提供新的思路。     

Heart rate variability during sleep in children with partial epilepsy

Alterations in autonomic control of cardiac activity in epileptic patients have been reported by several studies in the past, and both ictal and interictal modifications of heart rate regulation have been described. Alterations of autonomic control of cardiac activity can play an important role in sudden unexplained death in patients with epilepsy (SUDEP). However, the presence of specific changes in heart rate variability (HRV) during sleep, not correlated with seizures, has not been assessed in children with epilepsy; for this reason, we evaluated features of cardiac autonomic function during sleep without ictal epileptiform electroencephalogram (EEG) activity in a group of children with partial epilepsy. Eleven patients (five males and six females; mean age 11.5 years, SD: 3.65 years) affected by partial epilepsy were admitted to this study; 11 normal subjects (five males and six females; mean age 12.9 years, SD: 2.72 years) served as a control group. All subjects slept in the laboratory for two consecutive nights. The data were analyzed during the second night. Sleep was polygraphically recorded [including one electrocardiography (ECG) channel] and signals were digitally stored. A series of 5-min ECG epochs were chosen from each sleep stage, during periods without evident ictal epileptiform activity in the EEG. Electrocardiography signals were analyzed for automatic detection of R-waves and, subsequently, a series of time- and frequency-domain measures were calculated. Epileptic subjects tended to show an overall lower HRV in both time- and frequency-domain parameters, principally during rapid eye movement (REM) sleep and, to a lesser extent, during sleep stage 2. Among the different bands, this decrease was most evident for the high-frequency band (HF) absolute power. For this reason, the ratio between the low-frequency band (LF) and HF was always higher in epileptic patients than in normal controls and the difference was statistically significant during sleep stages 3 and/or 4 and REM sleep. Our results indicate that during sleep, a particular condition of basal modification in autonomic characteristics occurs (mostly during REM sleep) in partial epilepsy patients. This finding might represent an important factor contributing to the complex mechanism of SUDEP which takes place most often during sleep and supports the need of studying HRV specifically during this state in subjects with seizures.     

The influence of coincidence of fetal and maternal QRS complexes on fetal heart rate reliability

Bioelectrical fetal heart activity being recorded from maternal abdominal surface contains more information than mechanical heart activity measurement based on the Doppler ultrasound signals. However, it requires extraction of fetal electrocardiogram from abdominal signals where the maternal electrocardiogram is dominant. The simplest technique for maternal component suppression is a blanking procedure, which relies upon the replacement of maternal QRS complexes by isoline values. Although, in case of coincidence of fetal and maternal QRS complexes, it causes a loss of information on fetal heart activity. Its influence on determination of fetal heart rate and the variability analysis depends on the sensitivity of the heart-beat detector used. The sensitivity is defined as an ability to detect the incomplete fetal QRS complex. The aim of this work was to evaluate the influence of the maternal electrocardiogram suppression method used on the reliability of FHR signal being calculated.     

Comparison of short term variability indexes in cardiotocographic foetal monitoring

Concise indexes related to variability of foetal heart rate (FHR) are usually utilised for foetal monitoring; they enrich information provided by cardiotocography (CTG). Most attention is paid to the short term variability (STV), which relates to activity and reaction of autonomic nervous control of foetal heart. There is not a unique method to compute short term variability of the FHR but different formulas have been proposed and are employed in clinical and scientific environments: this leads to different evaluations and makes difficult comparative studies. Nine short term variability indexes: Arduini, Dalton, Organ, Sonicaid 8000, Van Geijn, Yeh, Zugaib a modified version of Arduini index and Standard Deviation were considered and compared to test their robustness in CTG applications. A large set of synthetic foetal heart rate series with known features were used to compare indexes performances. Different amounts of variability, mean foetal heart rate, storage rates, baseline variations were considered. The different indexes were in particular tested for their capability to recognise short term heart rate variability variation, their dependence on heart rate signal storage rate (as those provided by commercial cardiotocographic devices), on mean value of the foetal heart rate and on modifications of the floatingline, such in case of accelerations or decelerations.Concise statistical parameters relative to indexes scores were presented in comparative tables.Results indicate that although the indexes are able to recognise STV variation, they show substantial differences in magnitude and some in sensibility. Results depend on the frequency used to acquire and store FHR data (depending on devices); in general, the lower is data rate the more degraded are the results. Furthermore, results differently depend on FHR mean, some for their intrinsic definition; differences arise also in correspondences of accelerations and decelerations. Our results demonstrate that only indexes which refer directly to differences in FHR values, such as Organ and SD indexes, not show dependence on FHR mean.The use of the Standard Deviation index may provide efficient information while showing independence from the considered variables.Indexes performance in case of real cardiotocographic signals were also presented as examples.     

Fetal responses to induced maternal relaxation during pregnancy

Fetal responses to induced maternal relaxation during the 32nd week of pregnancy were recorded in 100 maternal-fetal pairs using a digitized data collection system. The 18-min guided imagery relaxation manipulation generated significant changes in maternal heart rate, skin conductance, respiration period, and respiratory sinus arrhythmia. Significant alterations in fetal neurobehavior were observed, including decreased fetal heart rate (FHR), increased FHR variability, suppression of fetal motor activity (FM), and increased FM-FHR coupling. Attribution of the two fetal cardiac responses to the guided imagery procedure itself, as opposed to simple rest or recumbency, is tempered by the observed pattern of response. Evaluation of correspondence between changes within individual maternal-fetal pairs revealed significant associations between maternal autonomic measures and fetal cardiac patterns, lower umbilical and uterine artery resistance and increased FHR variability, and declining salivary cortisol and FM activity. Potential mechanisms that may mediate the observed results are discussed.     

Heart rate variability during waking and sleep in healthy males and females

STUDY OBJECTIVES: The study goal was to investigate autonomic activity with heart rate variability analysis during different sleep stages in males and females. DESIGN: The study utilized a 2 Groups (males, females) x 4 States (waking, stage 2 sleep, stage 4 sleep, rapid-eye movement sleep) mixed design with one repeated, within-subjects factor (i.e., state). SETTING: The study was carried out in the sleep laboratory of the Thomas N. Lynn Institute for Healthcare Research. PARTICIPANTS: Twenty-four healthy adults (fourteen females and ten males). INTERVENTIONS: NA. MEASUREMENTS AND RESULTS: All participants underwent polysomnographic monitoring and electrocardiogram recordings during pre-sleep waking and one night of sleep. Fifteen-minute segments of beat-to-beat heart rate intervals during waking, stage 2 sleep, stage 4 sleep, and REM sleep were subjected to spectral analysis. Compared to NREM sleep, REM sleep was associated with decreased high frequency (HF) band power, and significantly increased low frequency (LF) to (HF) ratio. Compared to females, males showed significantly elevated LF/HF ratio during REM sleep. Males also demonstrated significantly decreased HF band power during waking when compared to females. No significant sleep- or gender-related changes in LF band power were found. CONCLUSIONS: The results confirmed changes in autonomic activity from waking to sleep, with marked differences between NREM and REM sleep. These changes were primarily due to stage-related alterations in vagal tone. REM sleep was characterized by increased sympathetic dominance, secondary to vagal withdrawal. The data also suggested gender differences in autonomic functioning during waking and sleep, with decreased vagal tone during waking and increased sympathetic dominance during REM sleep in the males.     

Cardiac autonomic activity during daytime nap in young adults

The current study investigated both sympathetic and vagal autonomic patterns during a daytime sleep in 25 healthy adults (23.2 ± 2.4 years). Pre‐ejection period (PEP; related inversely to beta‐adrenergic sympathetic activity), the interval between consecutive R‐waves (RR) and frequency‐domain heart rate variability (HRV) were computed during pre‐nap wakefulness and undisturbed sleep stages. Results showed sleep‐related changes in RR and HRV measures, whereas PEP decreased significantly from pre‐nap to sleep, showing no differences across sleep stages. Moreover, pre‐nap PEP and HFnu (the normalized unit of the high‐frequency component of HRV) were associated negatively with sleep latency and wake after sleep onset. These results indicate a marked autonomic output reduction during daytime sleep, with different stage‐dependent fluctuations for sympathetic and vagal activity. Importantly, pre‐nap autonomic activity seems to modulate subsequent sleep quality.     

Foetal heart rate power spectrum response to uterine contraction

Cardiotocography is the most diffused prenatal diagnostic technique in clinical routine. The simultaneous recording of foetal heart rate (FHR) and uterine contractions (UC) provides useful information about foetal well-being during pregnancy and labour. However, foetal electronic monitoring interpretation still lacks reproducibility and objectivity. New methods of interpretation and new parameters can further support physicians’ decisions. Besides common time-domain analysis, study of the variability of FHR can potentially reveal autonomic nervous system activity of the foetus. In particular, it is clinically relevant to investigate foetal reactions to UC to diagnose foetal distress early. Uterine contraction being a strong stimulus for the foetus and its autonomic nervous system, it is worth exploring the FHR variability response. This study aims to analyse modifications of the power spectrum of FHR variability corresponding to UC. Cardiotocographic signal tracts corresponding to 127 UC relative to 30 healthy foetuses were analysed. Results mainly show a general, statistically significant (t test, p<0.01) power increase of the FHR variability in the LF 0.03–0.2 Hz and HF 0.2–1 in correspondence of the contraction with respect to a reference tract set before contraction onset. Time evolution of the power within these bands was computed by means of time-varying spectral estimation to concisely show the FHR response along a uterine contraction. A synchronised grand average of these responses was also computed to verify repeatability, using the contraction apex as time reference. Such modifications of the foetal HRV that follow a contraction can be a sign of ANS reaction and, therefore, additional, objective information about foetal reactivity during labour.     

Prenatal predictors of infant temperament

Emerging data suggest that prenatal factors influence children's temperament. In 50 dyads, we examined fetal heart rate (FHR) activity and women's antenatal psychiatric illness as predictors of infant temperament at 4 months (response to novelty and the Infant Behavior Checklist). FHR change during maternal challenge was positively associated with observed infant motor reactivity to novelty (p = .02). The odds of being classified as high versus low motor among fetuses who had an increase in FHR during maternal stress was 11 times those who had a decrease in FHR (p = .0006). Antenatal psychiatric diagnosis was associated with an almost fourfold greater odds of having a high cry reactivity classification (p = .03). There also were modest associations between baseline FHR and maternal reports of infant temperament and between observed temperament and that based on mothers' reports. All of the infant results were found independent of the influence of women's postnatal anxiety. These data indicate that physiological markers of individual differences in infant temperament are identifiable in the fetal period, and possibly shaped by the prenatal environment.     

冠心病患者心率变异性指标与冠状动脉病变程度的关系

目的:探讨心率变异性指标与冠心病患者冠脉病变程度的关系。方法:选取冠心病患者84例（观察组）,同时选取健康志愿者90例作为对照组,均给予24 h动态心电图监测。结果:观察组NN间期的标准差（SDNN）、RR间期的均值标准差（SDANN）、相邻RR间期差值的均方根（RMSSD）、相邻RR间期差值>50 ms的心搏数所占百分比（PMN50）和高频功率（HF）分别为（95.54±20.12） ms、（94.48±21.15） ms、（29.84±10.06） ms、（7.46±2.31）%和（0.85±0.20） Hz,明显低于对照组（P<0.05）,而低频功率（LF）为（137.74±21.16） Hz,明显高于对照组（P<0.05）;冠状动脉病变≥3支患者SDNN、SDANN、RMSSD、PMN50和HF分别为（84.31±19.64） ms、（89.42±18.82） ms、（23.38±7.15） ms、（5.40±1.90）%和（0.70±0.21） Hz,明显低于冠状动脉病变数为1支和2支患者（P<0.05）,而LF为（150.54±21.15） Hz,明显高于冠状动脉病变数为1支和2支患者（P<0.05）;观察组男女患者SDNN、SDANN、RMSSD、PMN50、HF和LF比较差异无统计学意义（P>0.05）;Gensini评分与SDNN、SDANN、RMSSD、PMN50、HF呈负相关（r=-0.511、-0.487、-0.543、-0.512和-0.507, P<0.05）,与LF呈正相关（r=0.577, P<0.05）。结论:动态心电图在冠心病患者冠脉病变程度评价中有一定应用价值,其心率变异性指标与冠状动脉病变程度有一定关系。     

Rapid eye movement sleep parasympathetic activity predicts wake hyperarousal symptoms following a traumatic event

Heart rate variability (HRV) can be used to assess changes in output of the parasympathetic nervous system (PNS). Considering that patients with post-traumatic stress disorder (PTSD) often experience disturbances in sleep, arousal, and autonomic functioning, we sought to explore the association of PNS activity during sleep with hyperarousal symptoms of PTSD. Because a broad literature supports the importance of rapid eye movement (REM) sleep in PTSD, REM-sleep features were specifically examined as predictors of PTSD symptom severity. A total of 90 participants, primarily civilian and female, aged 18–40 years who had experienced a traumatic event in the last 2 years, underwent an ambulatory polysomnography (PSG) acclimation night followed by a second PSG night from which sleep physiological measures were computed. Participants underwent an ambulatory polysomnography (PSG) acclimation night followed by a second PSG night from which sleep physiological measures were computed. PTSD severity was measured using the PTSD Checklist for the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (PCL-5). Dependent variables were total PCL-5 score as well as its hyperarousal symptom subscore. Predictors included REM latency, percentage, density, segment length, and an index of parasympathetic tone (root mean square of the successive differences in the R–R interval or RMSSD). Hierarchical regression models were conducted to analyse the association of REM features with PCL-5 total and hyperarousal subscales. Using hierarchical regression, REM-sleep RMSSD accounted for a significant proportion of the variation in outcome variables, even when accounting for other REM-sleep features. The present findings support hypothesised relationships between PTSD symptomatology and REM-sleep physiology and, specifically, that lowered parasympathetic tone in REM may be an important associate of the hyperarousal symptom cluster in PTSD.     

Variability of QT interval duration in obstructive sleep apnea: an indicator of disease severity

STUDY OBJECTIVE: To determine OSA-related changes in variability of QT interval duration and in heart rate variability (HRV), and to evaluate the relationship of these parameters to disease severity. DESIGN: Retrospective analysis of diagnostic sleep records. SETTINGS: Clinical sleep laboratory in a hospital setting. PATIENTS: Twenty patients (12 males and 8 females) without significant comorbidities who were undergoing polysomnography were studied. MEASUREMENTS AND RESULTS: Standard heart rate variability measures and QT variability (Berger algorithm) were computed over consecutive 5-minute ECG epochs throughout the night. The effect of sleep stage and the relationship between these parameters and the severity of OSA as determined by the respiratory disturbance index (RDI) were explored. Further, a linear regression model of QT variability was developed. Severity of OSA (RDI) was 49 +/- 28 (range from 17-107) events/ hr. QT variability was the only ECG measure significantly correlated with RDI (both log-transformed; r = 0.6, P = 0.006). Further, QT variability was correlated with the minimum oxygen saturation (r = -0.55, P = 0.01). Sleep stage showed a significant effect on HRV, but not on QT variability. In the regression model, RDI was the strongest predictor of QT variability (R2 increase 38%), followed by high and low frequency power of HRV (R2 increase 10% each). CONCLUSION: Obstructive sleep apnea is associated with changes in QT interval variability during sleep. The variance of beat-to-beat QT intervals correlates more strongly with the severity of OSA (as determined by RDI) than standard measures of heart rate variability, and is correlated with blood oxygenation, but not sleep stage.     

Sex differences in empathy for pain: What is the role of autonomic regulation?

Empathy involves both affective and cognitive components whereby we understand, and express concerns for, the experiences of others. Women typically have superior trait empathy compared with men, which seems to have a neurological basis with sex differences in the structure and function of neural networks involved in empathy. This study investigated sex differences in empathy for pain using the Empathy for Pain Scale, and examined whether these trait differences were associated with disruptions in autonomic regulation, specifically via the parasympathetic nervous system (measured through the square root of the mean squared differences of successive R‐R intervals; RMSSD) both at rest and during a socioevaluative stress task (i.e., the serial sevens task). Compared with men, women reported higher empathic concern (Cohen's r = .25) and affective distress (Cohen's d = 0.65) toward another in pain. In both men and women, there was a decrease in lnRMSSD in the stress task compared to rest. Sex moderated the relationship between resting lnRMSSD and self‐reported empathic concern. Specifically, there was no clear association between empathic concern and lnRMSSD in men whereas in women there was a negative relationship, with lower resting lnRMSSD associated with higher empathic concern, and higher lnRMSSD associated with lower levels of empathic concern that were similar to men. These findings suggest that empathic feelings may result from poorer psychophysiological regulation, and concur with previous research displaying sex‐specific relationships between resting heart rate variability and emotion regulation abilities.     

Differential Association of Adiposity Measures with Heart Rate Variability Measures in Koreans

Purpose

Although obesity has been associated with imbalances in cardiac autonomic nervous system, it is unclear whether there are differential relationships between adiposity measures and heart rate variability (HRV) measures. We aimed to examine differences in the relationship between adiposity measures and HRV indices in a healthy Korean population.

Materials and Methods

In all, 1409 non-smokers (811 males, 598 females) without known histories of cardiovascular (CV), endocrine, or neurological diseases underwent adiposity measurements [(body mass index (BMI), percentage of body fat mass (PBF), and waist-to-hip ratio (WHR)], the HRV assessment (SDNN, RMSSD, LF, HF, LF/HF, and pNN50), and examination for CV risk factors (fasting glucose, LDL-cholesterol, HDL-cholesterol, triglycerides, hs-CRP, and blood pressure).

Results

Compared with BMI and PBF, WHR was more strongly correlated with each HRV index and more likely to predict decreased HRV (<15 percentile vs. ≥15 percentile of each HRV index) in ROC curves analysis. In linear regression analysis, all adiposity measures were inversely associated with each HRV measure before adjusting for age, gender, and CV risk factors (p<0.05). After adjusting for the covariates, WHR was inversely related to RMSSD, LF, and pNN50; PBF with RMSSD, HF, and pNN50; BMI with RMSSD (p<0.05). The inversed association between HRV indices and the gender-specific WHR tertile was significant for subjects with BMI ≥25 kg/m², but not for those with BMI <25 kg/m².

Conclusion

WHR and PBF appear to be better indicators for low HRV than BMI, and the association between abdominal adiposity and HRV may be stronger in overweight subjects.     

An algorithm for the recovery of fetal heart rate series from CTG data

Cardiotocography (simultaneous recording of fetal heart rate (FHR) and uterine contractions) is one of the most used diagnostic techniques to evaluate fetal well-being and to investigate the functional state of the fetal autonomic nervous system. Recently, great interest has been paid to the variability of the FHR, and its frequency analysis, as a base for a more objective analysis of the cardiotocographic (CTG) tracings. FHR signals are unevenly sampled series. To obtain evenly sampled series, cardiotocographs often use zero-order interpolation. Such process is simple and fast but results unsuitable for frequency analyses because it introduces alterations in the FHR power spectrum. An algorithm for the recovery of the true FHR series out of the zero-order interpolated CTG data was developed and evaluated.