Two-dimensional estimation of the electrohysterographic conduction velocity

Abstract

Abstract-Propagation of action potentials (APs) through an adequate number of uterine muscle cells induces contraction of the uterus. Monitoring uterine contractions, as the first sign of labor, can provide important information on the course of pregnancy and delivery. Unfortunately, current monitoring methods are affected by serious limitations. The electrohysterogram (EHG), which is the noninvasive recording of the APs propagating through the uterine smooth muscle cells, is here analyzed as a potential alternative to current methods. We focus on estimating the conduction velocity (CV) of surface APs extracted from an EHG recorded in a multielectrode configuration. In this work, a two-dimensional, 64-channel, high density electrode grid is used. Maximum likelihood methods are employed for analyzing the EHG AP propagation in two dimensions. The use of different weighting strategies of the derived cost function is introduced to deal with poor interchannel signal similarity. The presented methods were evaluated by specific simulations proving the best weighting strategy to lead to an accuracy improvement of 58%. EHG measurements on women with uterine contractions confirmed the feasibility of the method by leading to values of conduction velocity within the expected physiological range.

Biomathematical pattern of EMG signal propagation in smooth muscle of the non-pregnant porcine uterus

“…This could be an explanation for significantly higher similarity rates in the frequency vs. time domain for burst similarity parameters. Variation in number of spikes can be caused by the progressive and reverse recruitment phenomenon where the muscle area affected by spike within burst enlarges progressively [20]. Moreover, contractions demonstrate different propagation parameters, so within the same burst, analysis of single spike can lead to more extensive information compared to the whole burst analysis [7, 20].…”

“…Variation in number of spikes can be caused by the progressive and reverse recruitment phenomenon where the muscle area affected by spike within burst enlarges progressively [20]. Moreover, contractions demonstrate different propagation parameters, so within the same burst, analysis of single spike can lead to more extensive information compared to the whole burst analysis [7, 20]. Consequently, the combination of simultaneous single spike and burst analyses used in this study significantly reduce inherent variability in the EMG sensitivity in the porcine myometrium.…”

“…All authors recorded myometrial activity directly within the myometrium (EMG) [22, 28, 29, 30, 31] or used intrauterine pressure (IUP) [27]. An alternative method for monitoring the uterine activity based on surface EMG—EHG (electrohysterogram) allowed to application from 3 [32] to 16 [33] and 64 [20] active electrodes located on abdomen skin. The needle EMG picked up the bioelectrical signal directly associated with the muscular activity of myometrium, while EHG collected signal abundant in noise generated between cells and electrodes.…”

“…The speed at which an action potential propagates along a muscle fiber or tissue is referred to as propagation (or conduction) speed [17, 37]. Recent studies described the speed of action potential propagation in the muscular layer of isolated uterine strips in animals [18, 36, 38] and whole uterus in women [20]. Once again the analysis method may be generalized to pig, guinea pig, rabbit, cat and human data obtained during in vivo and in vitro experiments.…”

“…In contrast to skeletal muscle, in which the propagation of action potentials that progresses in muscle fibers is highly predictable, the direction and speed of electrical activation in myometrial cells remain to be elucidated [17]. Most of previously published studies were devoted to the analysis of entire bursts or single spikes in pregnant uterus [8, 18, 19, 20], and only few studies dealt with non-pregnant state [4, 21]. Hence, the main goal of the present study was to determine the biomathematical pattern describing EMG signal propagation in the non-gravid porcine uterus in vivo .…”