Tham khảo tài liệu 'biomedical engineering trends in electronics communications and software part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 350 Biomedical Engineering Trends in Electronics Communications and Software Even though the heart it is not fully developed in a foetus it is still divided into two pairs of chambers and has four valves. During the foetal cardiac cycle when the ventricles begin to contract the blood attempts to flow back into the atrial chambers where the pressure is lower this reverse flow is arrested by the closing of the valves mitral and tricuspid which produces the first heart sound S1 . After the pressure in the ventricular chambers increases until the pulmonary valves open and the pressurized blood is rapidly ejected into the arteries. The pressure of the remaining blood in the ventricles decreases with respect to that in the arteries and this pressure gradient causes the arterial blood to flow back into the ventricles. The closing of the pulmonary valves arrest this reverse flow and this gives rise to the second heart sound S2 McDonnell 1990 . A disadvantage of FPCG is that it is not possible to fully automate the signal processing for detecting the hear sounds because the signal characteristics depend on the relative positioning of the foetus with respect to the sensor. This results in a variable signal intensity and spectrum. Moreover recordings are heavily affected by a number of acoustic noise sources such as foetal movements maternal digestive and breathing movements maternal heart activity and external noise Mittra et al. 2008 Ruffo et al. 2010 . Despite the disadvantages mentioned above FPCG provides valuable information about the physical state of the foetus during pregnancy and has the potential for detection of cardiac functionality anomalies such as murmur split effect extra systole bigeminal trigeminal atrial. Such phenomena are not obtainable with the traditional CTG monitoring or other methods Chen et al 1997 Moghavvemi Tan 2003 Mittra et al. 2008 . Foetal electrocardiography FECG Echeverria et al. 1998 Pieri et al. 2001 has also been extensively studied
