A Linear Time Series Analysis of Fetal Heart Rate to Detect the Variability: Measures Using Cardiotocography

A Linear Time Series Analysis of Fetal Heart Rate to Detect the Variability: Measures Using Cardiotocography

Sahana Das (Narula Institute of Technology, India), Kaushik Roy (West Bengal State University, India) and Chanchal Kumar Saha (Biraj Mohini Matrisadan and Hospital, India)
DOI: 10.4018/978-1-5225-1785-6.ch018
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Abstract

Real time analysis and interpretation of fetal heart rate (FHR) is the challenge posed to every clinician. Different algorithms had been developed, tried and subsequently incorporated into Cardiotocograph (CTG) machines for automated diagnosis. Feature extraction and accurate detection of baseline and its variability has been the focus of this chapter. Algorithms by Dawes and Redman and Ayres-de-Campos have been discussed in this chapter. The authors are pleased to propose an algorithm for extracting the variability of fetal heart. The algorithm's accuracy and degree of agreement with clinician's diagnosis had been established by various statistical methods. This algorithm has been compared with an algorithm proposed by Nidhal and the new algorithm is found to be better at detecting variability in both ante-partum and intra-partum period.
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Physiology Of Fetus

Placenta exchanges oxygen and carbon dioxide between the mother and the fetus. There are two types of metabolism: anaerobic and aerobic. Waste products of aerobic metabolism are carbon dioxide and water. The energy produced controls the fetal growth and activity. Aerobic metabolism is dependent on the oxygen.

In anaerobic metabolism oxygen is not available. The waste product is lactic acid and the energy produced controls the basal/ vital activity. Since anaerobic metabolism only provides energy for vital activity, the fetal growth is inhibited. Anaerobic metabolism thus should not last long. If the supply of oxygen is not restored on time oxygen saturation in the fetal blood gets reduced and gradually hypoxemia, hypoxia and finally the most dangerous stage, the asphyxia sets in. This relationship is depicted in Figure 1.

Key Terms in this Chapter

Kappa Statistics (?): It is a measure of agreement between categorical variables X and Y. Kappa can be used to compare the ability of different raters to classify subjects into one of different groups.

Fetal Heart Rate Variability: It is defined as the fluctuations in fetal heart rate of more than 2 cycles/ minute in the absence of acceleration and deceleration.

Baseline of Fetal Heart Rate: Baseline of fetal heart is the mean fetal heart rate rounded to 5 beats per minute in the absence of acceleration and deceleration. It is measured over a period of 10 minutes.

Long Term Variability (LTV): It is the fluctuation range of the heart beat interval period in analyzable one minute sections. The fluctuation range is calculated as a sum between maximal deviation above and below the baseline.

Short Term Variability (STV): It is the beat-to-beat variation in fetal heart rate. STV is computed as mean difference between successive heart beat interval epochs in all analyzable one minute sections.

Cardiotocography: Cardiotocography is the electronic recording of fetal heart beat and mother’s uterine contraction pressure simultaneously.

Bland-Altman Plot: In medical statistics is a method of data plotting used to analyze the agreement between two different methods.

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