Ανάλυση βιολογικών ιστών με χρήση βιοσημάτων: περίπτωση εμβρυϊκού ηλεκτροκαρδιογραφήματος

Abstract

During pregnancy, the flow of oxygen and nutrients to the fetus and the removal of carbon dioxide and other waste gases from it is achieved through the placenta. Adequate blood flow to and from the placenta, and in both the maternal and fetal circulations, is necessary in order for the baby to receive enough oxygen and for it to be able to expel carbon dioxide and other waste gases. Any alteration in placental function can lead to decreases in the delivery of oxygen to the baby, a condition known as fetal hypoxia. The motivation for monitoring the fetus during pregnancy is to recognize pathologic conditions, typically decreased oxygen saturation, accompanied with sufficient warning to enable intervention by the clinician before irreversible changes take place. Scientists are working for the last decades to develop new technologies for the continuous intrapartum fetal monitoring. Early approaches are used for monitoring of the fetal heart rate (fHR) and the mother's uterine contractions (cardiotocography- CTG). In CTG, fHR is monitored using an ultrasound transducer strapped to the mother's abdomen, while uterine activity is recorded from an external toco sensor. Monitoring using CTG mainly identifies fetuses affected by intrapartum asphyxia, resulting in early intervention and a reduction in cerebral palsy. Unfortunately, a large number of fetuses affect fHR without being asphyxiated. Thus, electronic fHR monitoring based on CTG provides with poor specificity in detecting fetal hypoxia and cannot provide all information which is required. This has created an increased rate of intervention and uncertainty about the clinical value of CTG. Doppler ultrasound is a widely used technique by medical doctors to monitor fHR. However, except some specific disadvantages (e.g. need for experienced personnel, specialized equipment and use in hospital environments), the major limitation of the Doppler ultrasound is its sensitivity to any movement. The movement of the mother can result in Doppler-shifted reflected waves, which are stronger than the cardiac signal. Thus this technique is not suitable for long-term monitoring of the fHR as it requires the patients to be bed-rested. In addition, there have been a number of publications linking diagnostic ultrasound to an increase in Intrauterine Growth Restriction (IUGR) and the stimulation of endothelial cell growth and the release of adenosine triphosphate (A-tp). However, the effect of ultrasound on the fetus is not completely clear. Important clinical studies support the incorporation of ST waveform analysis into fHR analysis for intrapartum monitoring, with reduction in the rates of neonatal metabolic acidosis as well as neonatal encephalopathy. ST waveform analysis is mainly performed in the fetal ECG (fECG) signal, recorded using a fetal scalp electrode. Repolarisation of myocardial (heart muscle) cells is very sensitive to metabolic dysfunction, and might be reflected in changes of the ST waveform. The changes in fECG associated with fetal hypoxia are either an increase in T-wave, quantified by the ratio of the T-wave to the QRS amplitude (T/QRS ratio), or biphasic ST-pattern: the combination of these features with fHR pattern analysis and additional clinical information can lead to accurate identification of hypoxia cases and to the avoidance of unnecessary interventions. However, application of a fetal scalp electrode has the risk of maternal to fetal infection, which contraindicates any invasive monitoring technique. In addition, as an invasive technique, this type of fetal monitoring is less acceptable than external monitoring from pregnant women and midwives. Also, as the system responds primarily to changes in the ST segment, if it is applied when such changes have already occurred, there is the possibility of a false-negative result (inappropriate reassurance about a fetal condition). Thus, automated assessment of fetal cardiac health status based on non-invasive monitoring techniques is an important issue which must be investigated.