Patterns of electrical propagation in the intact pregnant guinea pig uterus

Abstract

Previous studies have reported on propagation of individual spikes in isolated segments of the pregnant uterus, but there is no information on patterns of spike propagation in the intact organ. There is also no information on propagation of myometrial burst. The aim of this study was to record, at high resolution, patterns of propagation of electrical activities in the pregnant uterus. Sixteen timed-pregnant guinea pigs were euthanized at term, and their uteruses isolated. Fetuses were removed and replaced by an equal amount of Tyrode. A 240-electrode array was positioned at various locations along the organ, all signals were recorded simultaneously, and the electrical propagations were reconstructed. In the intact pregnant uterus at term, spikes propagated with high velocity in longitudinal (6.8 Ϯ 2.4 cm/s) and slower velocity in circular direction (2.8 Ϯ 1.0 cm/s; P Ͻ 0.01). Direction of propagation and frequency of activity were highly variable but showed similar patterns at the ovary or cervical end and along the anterior, posterior, and antimesometrial borders. Along mesometrium, spike propagation was sparse and fractionated. Migration of burst (0.6 Ϯ 0.4 cm/s) was significantly much slower than that of individual spikes (P Ͻ 0.001). Initial burst activity was located at variable locations along the ovarial end of the antimesometrial border, while the latest excitation occurred at the cervical end (1.2 Ϯ 0.9 min). In conclusion, high resolution electrical mapping of the intact pregnant uterus reveals fundamental properties in spatial and temporal patterns of spike and burst propagation that determine the contraction of the organ. spikes; myometrial burst migration ELECTRICAL ACTIVITY in the pregnant myometrium is characterized by phasic bursts of action potentials (spikes), which could be based on cyclic changes in transmembrane potential (24). Cyclic changes in potential resemble in some respects slow waves in the intestines and presumably propagate through the myometrium, similar to the propagation of the intestinal slow waves. In both cases, the depolarization induced by the (slow) waves initiate the opening of L-calcium channels leading to the occurrence of spikes. In the intestines, it is possible to record both slow waves and spikes with extracellular electrodes, and this made it possible to reconstruct the pattern of propagation of both signals and to study the complex interaction between these two electrical waveforms (22).In the myometrium, the basic electrical wave is too slow or its magnitude too small to be recorded extracellularly (9). The spikes, however, are visible in extracellular recordings and this led to several studies on their behavior. Miller et al. (25) analyzed spike propagation in pregnant uterine segments that were 3 ϫ 1 cm in size and showed that velocity in the longitudinal direction was much faster than in the circumferential direction. Lammers et al. (20) found similar results in equally small segments (8 ϫ 2 cm). Most of these studies were performed on isolated segments of...

Modeling and Identification of the Electrohysterographic Volume Conductor by High-Density Electrodes

“…Further investigation might be dedicated to the advantages of integrating our volume conductor model with more complex descriptions of the myometrial cell AP generation [13], [14]. In view of the recent investigations on the guinea pig myometrium [12], possible limitations of the proposed model are the assumption that the myometrial tissue is isotropic and the hypothesis that APs propagate exclusively either along the longitudinal or the circumferential axis of the uterus. Therefore, in the future, the role played by the complex 3-D geometrical and anatomical structures of the myometrium in the conduction of electrical activity needs to be understood and possibly integrated in the source model.…”

“…Many studies demonstrated that the analysis of the EHG signal may play a key role for accurate monitoring of the uterine contractions, prediction of labor, and improvement of perinatal outcome [7]- [11]. However, many issues related to the conduction pattern of electrical activation are still unsolved [12].…”

“…Due to a lack of evidence [19], many authors concluded that no classical linear propagation of single APs, similar to the myocardium, could be assumed for the myometrium, and that only a global propagation of the whole burst envelop could be measured [19], [20]. However, more recently, extensive measurements of the electrical activity of the guinea pig uterus using a grid of extracellular electrodes clearly demonstrated that also for the myometrium, similarly to the myocardium, a linear propagation of single electrical spikes occurs and can be measured [12], [21], [22].…”

“…The surface potential φ e (k x , h 3 , k z ) in (8) depends on the tissue thicknesses and conductivities, the source depth y 0 , and the parameters α, β, and A in (12). The tissue conductivities are, however, relatively invariant and the values reported in the literature are used [26]- [28].…”

Two-dimensional estimation of the electrohysterographic conduction velocity

“…Each burst correspond to a single mechanical contraction of the uterus. Most of the previous literature focused on the analysis of the entire burst and only few Chiara Rabotti and Massimo Mischi are with the Department of Electrical Engineering, Eindhoven University of technology, the Netherlands C.Rabotti@tue.nl studies were dedicated to the analysis of single surface APs [3], [4], [5], i.e., single spikes extracted from the EHG. However, in-vitro studies have demonstrated that individual surface APs propagate for longer distance and with higher conduction velocity (CV) at parturition than at preterm [3].…”