NEW IMPLANTED DOPPLER SENSORS FOR THE ASSESSMENT OF THE MAIN FETAL HEMODYNAMICS

If the fetal Doppler examination during human pregnancies provides useful information to the obstetrician, it does not allow us to collect all the biological and haemodynamic data required to understand the physiopathological mechanisms involved in the development of intrauterine growth retardation (IUGR) and hypoxia. With the animal model, it is possible to have access to the blood pressure, the blood velocity and volume, to collect blood sampling and to perform pharmacological tests, or to simulate some human pathology. Several studies have been already carried out on lamb fetuses using electromagnetic flowmeters placed around the cord and catheters, with pressure sensors placed inside the fetal aorta. Most of the time only the umbilical flow was assessed on the fetal side. The aim of the present work was to develoly a new Doppler system able to monitor in real time and simultaneously, the fetal cerebral and the umbilical arterial flows as well as the uterine circulation. New flat Doppler probes have been designed, to be implanted on the fetus and on the mother, which inakes possible the atraumatic assessment of fetal and maternal flows during approximately 20 days. The 4-MHz CW Doppler probe consists of two rectangular piezoelectric transducers of 13-mm wide, preoriented at 45-degrees from the surface of the probe, placed in a 6-mm-high plastic case in which small holes are made to sew the probe on the fetal skin. The sensors are fixed on the fetal skin, facing the umbilical cord, the fetal cerebral arteries and in front of the uterine arteries. The output wires and the fetal catheter connectors are stowed in a pocket fixed on the back of the ewe, and at each measurement session the fetus is connected during one or two hours (without any anesthesia) to the Doppler and pressure system. From the Doppler waveforms we can calculate the blood flow volume and the vascular resistance changes in the area supplied by the vessel (placenta, brain) and the fetal heart rate. This system has been tested on normal gestation, during simulated fetal hypoxia and pharmacological treatments.