Internal versus external intrapartum foetal heart rate monitoring: the effect on linear and nonlinear parameters

Abstract

The effect of foetal heart rate (FHR) acquisition mode on linear and nonlinear parameters is still largely unknown. In 33 normal labouring women, FHR signals were acquired simultaneously by an external ultrasound sensor applied to the maternal abdomen and an internal scalp electrode, in the minutes preceding delivery. For each case, the initial and final 5, 10 and 20 min segments were analysed, considering FHR signals at a frequency of 4 Hz (the frequency at which they are transmitted by the majority of commercialized foetal monitors). Several time and frequency domain linear and nonlinear FHR indices were computed in these segments, namely mean FHR, very low frequency (VLF), low frequency (LF), high frequency (HF), approximate entropy (ApEn) and sample entropy (SampEn). Parametric confidence intervals, statistical tests and correlation coefficients were calculated in order to evaluate the effect of internal versus external FHR monitoring modes on the considered indices. The whole evaluation was repeated using FHR signals at a frequency of 2 Hz. Most time domain linear indices were similar with external and internal monitoring in the initial and final segments of the tracings. However, linear frequency domain indices were poorly correlated in the final segments and had significantly different mean values in the initial segments. Nonlinear indices were significantly different in both initial and final segments. The correlation between 4 and 2 Hz sampled parameters was high for both linear and nonlinear indices (most correlation coefficient values ranging between 0.95 and 1) but nonlinear index values were significantly higher at 2 Hz. In conclusion, the mode used to acquire FHR signals and the sampling rate employed can significantly affect most FHR indices.

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“…This denotes increased activation of the autonomic nervous with sympathetic imbalance and decreased or blunted activity of the HR complexity regulatory centres (Gonçalves et al 2006a, Moraru et al 2004, Beckers et al 2006b. With continued agonizing anoxia, linear indices decreased, whereas entropy remained stably low, denoting an overall decrease of the activity of all HR dynamics regulatory centres (Gonçalves et al 2006a, Moraru et al 2004, Beckers et al 2006b.…”

“…This denotes increased activation of the autonomic nervous with sympathetic imbalance and decreased or blunted activity of the HR complexity regulatory centres (Gonçalves et al 2006a, Moraru et al 2004, Beckers et al 2006b. With continued agonizing anoxia, linear indices decreased, whereas entropy remained stably low, denoting an overall decrease of the activity of all HR dynamics regulatory centres (Gonçalves et al 2006a, Moraru et al 2004, Beckers et al 2006b. All this evidence is consistent with human foetal studies performed in the final minutes of labour (Gonçalves et al 2006b, Siira et al 2005, as well as with non-human foetal studies developed during episodes of acute hypoxia or anoxia (Li et al 2004, Chaffin et al 1998.…”

“…The analysis included common time-and frequency-domain measures, as previously described in detail (Gonçalves et al 2006a). The time-domain measures included mean HR (mHR), HR standard deviation (sdHR), long-term irregularity (LTI), the mean amplitude between the maximum and minimum for each minute ( ), short-term variability (STV) and interval index (II).…”

“…However, many questions remain to be answered before the use of these HR indices can be advised in clinical practice. It is already known that these indices are influenced by equipment, signal acquisition mode, sampling rate and pre-processing, but studies about these issues are still limited (Task Force 1996, Gonçalves et al 2006a. In the same way, some studies have contributed to elucidate the mathematical and pathophysiological meaning of these indices, as well as their clinical validity, but many doubts still persist about these matters (Gonçalves et al 2006b, Gonçalves et al 2007.…”

“…In the same way, some studies have contributed to elucidate the mathematical and pathophysiological meaning of these indices, as well as their clinical validity, but many doubts still persist about these matters (Gonçalves et al 2006b, Gonçalves et al 2007. We have performed some studies using linear and nonlinear HR analysis in human foetuses, both before and during labour (Gonçalves et al 2006a(Gonçalves et al , 2006b(Gonçalves et al , 2007. However, studies on human subjects have always inherent difficulties, particularly during foetal life.…”