Modified MUSIC pseudospectral analysis reveals common uterus and fetal heart resonances during labour contractions

A potentially successful non-invasive on-line labor contraction and fetal monitoring technique is proposed. The authors present the high resolution spectral signatures of the uterus and fetal during normal labor contraction episodes and their intermittent periods. Also, they discuss some abnormal labor cases. Two surface electrodes aligned transversally with the umbilicus, each spaced about 10 cm away from it, have been used together with a reference limb electrode to transabdominal electromyography (TEMG). The fetal heart electrocardiogram (ECG) signals have been recorded, simultaneously, both using the surface electrode pair (intermittent periods) and a scalp electrode (deemed essential in some high-risk labor cases). Both signals have been digitized at 512 Hz and processed using a SONICAID monitor, an interface card, and a host computer. The spectral estimator uses the super-resolution MUltiple SIgnal Classification (MUSIC) algorithm which performs the singular value decomposition (SVD) of the orthogonal signal and white noise subspaces, and subsequent choice of a suitable frequency estimation function. The modification to the MUSIC algorithm conforms to a customized FIR Kaiser-based filter to pre-emphasize the data in the selected and known, a priori, signal frequency bins. This results in a significant improvement in the resolution and variance of the frequency estimates