Điện thai cơ bản là một bản đồ tiềm năng hành động tạo ra trong suốt chu kỳ tim. Như đã thảo luận trong chương 4, chu kỳ bắt đầu với depolarisation của nút Trung-tâm nhĩ là một kết quả các tiềm năng màng của các tế bào máy điều hòa nhịp tim và điều này có liên quan với một làn sóng mạnh mẽ của Na + | 90 Fetal Electrocardiography The fetal electrocardiogram is essentially a map of the action potentials generated throughout the cardiac cycle. As discussed in Chapter 4 the cycle starts with the depolarisation of the sino-atrial node as a result of membrane potentials of pacemaker cells and this is associated with a dramatic influx of Na and an efflux of K ions. At the same time an influx of Ca44- results in upstroke of the action potential in the SA node. Subsequently the upstroke of the action potential in the atrioventricular node depends on both slow Ca channels and on the relatively fast oxygen insensitive Na channels. The PR interval reflects the conduction time in the AV node and the QRS complex represents ventricular depolarisation whilst atrial repolarisation is buried within the QRS complex. The ST segment and T wave reflect ventricular repolarisation. Analysis of the FECG The real difficulty about the analysis of the FECG is that the signal is often distorted by electrical noise in particular 50 Hz interference but also extraneous noise from other maternal and fetal sources. These issues have been addressed in detail in Chapter 4 but are rehearsed briefly here in the context of their importance to this chapter. Part of this noise and the need for signal modification can be minimised by the use of appropriate scalp electrodes. The single spiral electrodes manufactured by Corometrics Medical Systems USA have a high signal amplitude and a good frequency response and low signal-to-noise ratio Westgate et al. 1990 but the Copeland electrode has also been shown to have characteristics that are adequate for the measurement of the time intervals of the FECG. Development of an Analyser of the FECG The development of a system that could provide real-time analysis has been the subject of continuing research at the Department of Electrical and Electronic Engineering at the University of Nottingham and reference has already been made in previous chapters to the .
