Long-term Irregularity Research Articles

Computerised analysis of antepartum foetal heart parameters: New reference ranges

We selected 4012 cCTG records (one trace for each patient) performed in healthy pregnancies from 30th to 42nd gestational week using foetal heart rate (FHR), short-term variability (STV), long-term irregularity (LTI), Delta, approximate entropy (ApEn), spectral components as low frequency (LF), median frequency (MF), high frequency (HF) and LF/(HF + MF) ratio were analysed. Reference nomograms were created and sensitivity and specificity for the prediction of foetal compromise were calculated which were 90% and 89%, respectively. Changes of cCTG parameters according to gestational week were evaluated: FHR (r = −.65) and LF (r = −.87) showed a statistically significant reduction (p < .05) with gestational age. STV (r = .59), LTI (r = .69), Delta (r = .67), and MF (r = .88) showed a statistically significant increase (p < .05) with gestational age. In contrast, for ApEn (r = −.098), HF (r = .14) and LF/(HF + MF) ratio (r = −.47) a non-statistically significant change was found (p > .05). The identification of reference ranges for cCTG indexes in according to gestational age could provide a more objective examination of cCTG trace.

Fetal Vibroacoustic Stimulation in Computerized Cardiotocographic Analysis: The Role of Short-Term Variability and Approximate Entropy

The aim of this study was to evaluate the impact of vibroacoustic stimulation (VAS) on computerized cardiotocography short-term variability (STV) and approximate entropy (ApEn) in both low- and high-risk pregnancies. VAS was performed on 121 high- and 95 low-risk pregnancies after 10 minutes of continuous quiet, while their FHR parameters were monitored and recorded by cCTG analysis. Fetal heart rate was recorded using a computer-assisted equipment. Baseline FHR, accelerations, decelerations, STV, long-term irregularity (LTI), ApEn, and fetal movements (FMs) were calculated for defined observational periods before VAS and after 10 minutes. Data were also investigated in relationship with the perinatal outcome. In each group of patients, FHR after VAS remained almost unmodified. Fetal movements significantly increased after VAS in both groups. Results show that only in the high-risk pregnancies, the increase of STV and the decrease of ApEn after VAS were significantly associated with favorable perinatal outcomes.

Linear and nonlinear heart-rate analysis in a rat model of acute anoxia

The objective of this study was the assessment of heart-rate (HR) dynamics with linear and nonlinear methods during episodes of mechanical ventilation and acute anoxia in rats. Namely, to assess whether linear and nonlinear HR analysis was able to discriminate acute anoxia from baseline in rats and if this was consistent with human foetal and adult studies. Five HR segments of 1 min duration, during baseline recording, mechanical ventilation and first, second and third minutes of induced acute anoxia, were analysed in ten adult Wistar rats. Linear time and frequency domain and nonlinear methods were used, namely mean HR (mHR), long-term irregularity (LTI), interval index (II), low frequency (LF) and high frequency (HF), approximate entropy (ApEn) and sample entropy (SampEn). New parameters for the entropy indices are proposed for the analysis of rats' HR. Bootstrap percentile confidence intervals and nonparametric statistical tests were used in the evaluation of the differences between segments. During mechanical ventilation a clear spectral band was detectable at the ventilation rate, but mHR, II and the ‘new’ entropy indices were the only significantly changed indices. In the transition from baseline–mechanical-ventilation to mechanical-ventilation–induced anoxia, a statistically significant decrease of mHR, II and entropy indices was observed, clearly discriminating these two instances, whereas most linear indices increased. With continued anoxia, most linear indices decreased significantly, whereas entropy remained stably low. These results are consistent with other foetal human and non-human studies and evidence that the rat model may be used for further research on linear and nonlinear analysis of heart-rate dynamics. The transition from baseline to acute anoxia was encompassed by signs of increased activation of the autonomic nervous system sympathetic branch, and decreased or blunted activity of the HR complexity regulatory centres.