| Summary: | Fetal Heart Rate (FHR) monitoring using Doppler Ultrasound (DUS) is a noninvasive technique that is in widespread use to assess fetal well-being both during pregnancy (antepartum) and labour (intrapartum) However, despite the routine use of FHR monitoring for several decades, the DUS method can under certain conditions provides estimates of FHR of insufficient accuracy. Well-known problems are doubling of the FHR and calculating the FHR from signals arising from maternal blood flow.
The aim of the research described in this thesis is to contribute to the development of both more robust FHR monitors and the extraction of other information, such as cardiac timing intervals. The main objective is focussed on developing a new approach to monitoring the mechanical activities of fetal heart, including calculation of the beat-to-beat FHR using DUS. Direct sampling quadrature demodulation is used to directly sample and demodulate the received DUS signal using a sampling rate of four times the centre frequency of the ultrasound used. This process is entirely digital, with no analogue mixing required. Selecting two consecutive samples allows the in-phase and quadrature signals to be produced, with the Hilbert transform then used to both produce forward and reverse motion signals and subsequently extract instantaneous amplitude and frequency information.
The second objective was to develop a novel mechanical fetal heart motion simulator that would be used to test the performance of the proposed new processing system and commercial monitoring systems. An initial approach employing servomotors was not ideal, which led to a better soft actuator based design. The second simulator was based on soft actuators. This simulator consists of two reflectors to represent one wall and one valve. The velocity of the actuator covers the timing requirement of the fetal heart and avoided mechanical friction by using the pneumatic system to drive it.
Following the successful demonstration of the proposed new processing method using commercially available hardware and software, and the fetal heart simulator, the final phase of the research was to design, produce and test a design based on bespoke electronics. This is essentially a novel FHR monitor that produces raw information that could be processed to extract information regarding fetal heart valve and wall motion.
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