Principle study on the signal connection at transabdominal fetal pulse oximetry

Abstract

Transabdominal fetal pulse oximetry is an approach to measure oxygen saturation of the unborn child non-invasively. The principle of pulse oximetry is applied to the abdomen of a pregnant woman, such that the measured signal includes both, the maternal and the fetal pulse curve. One of the major challenges is to extract the shape of the fetal pulse curve from the mixed signal for computation of the oxygen saturation. In this paper we analyze the principle kind of connection of the fetal and maternal pulse curves in the measured signal. A time varying finite element model is used to rebuild the basic measurement environment, including a bulk tissue and two independently pulsing arteries to model the fetal and maternal blood circuit. The distribution of the light fluence rate in the model is computed by applying diffusion equation. From the detectors we extracted the time dependent fluence rate and analyzed the signal regarding its components. The frequency spectra of the signals show peaks at the fetal and maternal basic frequencies. Additional signal components are visible in the spectra, indicating multiplicative coupling of the fetal and maternal pulse curves. We conclude that the underlying signal model of algorithms for robust extraction of the shape of the fetal pulse curve, have to consider additive and multiplicative signal coupling.

Estimating the Shape of the Fetal Pulse Curve for Transabdominal Pulse Oximetry using Synchronous Averaging

“…It can be seen that the signals in Setup 1 are disturbed by cross terms, represented by small peaks between the fetal and maternal component. They are analyzed more in detail in our former works in [10], [8]. Due to the heart rate variability, the maternal and fetal component are not separable in the overall frequency spectrum of the artificial signal (upper left plot of Fig.…”

“…Light sources and detectors are placed on the belly of the pregnant woman to measure the photoplethysmogram (PPG) as shown is several previous works [4], [5], [2], [3], [6]. The measured signal consists of a mixture of the maternal and fetal pulse curves [4], [5], [10], [6]. One major challenge of the method is the extraction of the fetal pulse curve [5], [10], [8].…”

“…The measured signal consists of a mixture of the maternal and fetal pulse curves [4], [5], [10], [6]. One major challenge of the method is the extraction of the fetal pulse curve [5], [10], [8]. Following the principle of pulse oximetry, the resulting fetal PPG needs to be of high quality to clearly identify the signal level during systole and diastole of the fetus to conclude about the oxygen saturation.…”