E.E. Gomov, A.P. Kazantsev, E.O. Putilin

Ultrasonic dopplerometry is chosen for outpatient FHR monitoring because it meets the requirements of cardiotocography. Ultrasonic waves of 2 MHz frequency and of 10 mW/cm2 power density are applied to a fetus heart to detect the heart beat. The Doppler effect occurs at the response driving the carrier angle modulation that is recorded as a dopplerogram after a frequency downshift. Demodulation is carried out by the quadrature processing of the dopplerogram to get the complex envelope and the intact rhythm signal as a result. The computation of instant FHR and rhythmogram building are executed in a loop with 0.1 s step while the dopplerogram is recorded/played-back in background. The rhythm signal of the 2/5/10 s length is processed in each loop. The experimental instrument for FHR measurement based upon the LabVIEW 10.0 platform has been developed. The instrument inherits the Storage Scope pattern and contains the following objects: Gauge - an ultrasonic probe with a program interface; Recorder - a VI for recording/playing-back and quadrature processing of dopplerograms; Display - a VI for the FHR adaptive prediction and rhythmogram indication. The results obtained: a robust method of FHR measurement based on the ultrasonic dopplerogram complex envelope extraction; a LabVIEW based instrument of robust architecture for FHR measurement; residual standard uncertainty of FHR measurement is of 0.01÷0.1 beat/minute for noise wise basal heart rate variability and 0.1÷1 beat/minute for accelerations and decelerations.