Robust estimation of fetal heart rate variability using Doppler ultrasound

Heart rate variability (HRV) provides important information about the development of the cardiovascular system in fetuses. The paper presents a new measure of fetal HRV that can be estimated using Doppler ultrasound techniques. This measure employs the multiple signal characterization (MUSIC) algorithm which is a high-resolution method for estimating the frequencies of sinusoidal signals embedded in white noise from short-duration measurements. We show that the product of the square-root of the estimated signal-to-noise ratio (SNR) and the variance of the frequency estimates is independent of the noise level in the signal. Since variations in the angle of incidence of the Doppler ultrasound beam effectively changes the input SNR, this measure of HRV is robust to the input noise as well as the angle of incidence. Presented analysis results validate the robustness properties and the usefulness of the HRV measure.