Development of a phantom to modulate the maternal and fetal pulse curve for pulse oximetry measurements

For getting reliable information about the state of health from the fetus and the mother during labor and delivery, a fetal pulse oximeter is being developed. This paper describes the development of a special phantom to verify the algorithms for separating the weak fetal from the dominant maternal optical signal. To reach a realistic behavior it is necessary for two circulations to be controlled independently. Inspired by the natural blood circulation behavior, a RC-System with fixed resistance and capacity was created. Pumping a liquid with a roller pump into the tubes widens them. The digital signal processor (DSP) controls the expansion of the tube diameter by modifying the rotation velocity of the pump for active regulation. Therefore a soft and good enlargeable material was used. The measured values of the pressure sensor enabled active feedback for motor control The determined system characteristics are used to adapt the given pulse curve to the real system behavior. Via a LabView interface it is possible to change curve parameters like amplitude and frequency. The goal was to replicate the pulsation of the blood vessels like in the abdomen of a pregnant woman. Changing the parameters influences the modulation of the signal under consideration of the transfer function. With this phantom it is possible to simulate different scenarios, for example different states of pregnancy or pathogen indications.