Abstract
A portable fetal heart tone monitor has been developed using an array of PVF2 surface pressure sensors. The sensor array, mounted on a belt worn by the mother, detects pressure pulses from the fetal heart incident upon the maternal abdominal surface. Each sensor is constructed of components to fulfill five functions: signal detection, acceleration cancellation, acoustical isolation, electrical shielding, and electrical isolation of the mother. An analysis based on an acoustical model of the sensor yields the open-circuit sensitivity, which permits determination of the surface pressure levels. The sensor behaves like a low-pass filter having a cutoff frequency proportional to the stiffness of the belt material. Peak-to-peak surface pressures of the first (mitral–tricuspid) and second (aortic–pulmonary) heart sounds were determined to be 12.0±3.6 Pa and 9.4±2.8 Pa for a fetus of 34.5 weeks gestational age; and 47.0±6.8 Pa and 27.9±9.4 Pa for one of 39 weeks gestational age (full term).
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