Tracking the changes in synchrony of the electrophysiological activity as the uterus approaches labor using magnetomyographic technique

An update on pacemaking in the myometrium

Timely and efficient contractions of the smooth muscle of the uterus - the myometrium - are crucial to a successful pregnancy outcome. These episodic contractions are regulated by spontaneous action potentials changing cell and tissue electrical excitability. In this short review we will document and discuss current knowledge of these processes. Those seeking a conclusive account of myometrial pacemaking mechanisms, or indeed a definitive description of the anatomical site of uterine pacemaking, may be disappointed. Rather, after almost a century of investigation, and in spite of promising studies in the last decade or so, there remain many gaps in our knowledge. We review the progress that has been made using recent technologies including in vivo and ex vivo imaging and electrophysiology and computational modelling, taking evidence from studies of animal and human myometrium, with particular emphasis on what may occur in the latter. We have prioritized physiological studies that bring us closer to understanding function. From our analyses we suggest that in human myometrium there is no fixed pacemaking site, but rather mobile, initiation sites produce the connectivity for synchronizing electrical and contractile activity. We call for more studies and funding, as physiological understanding of pacemaking gives hope to being better able to treat clinical conditions such as preterm and dysfunctional labours.

Assessing uterine electrophysiology prior to elective term induction of labor

OBJECTIVE

The purpose of this study was to determine if uterine electrophysiological signals gathered from 151 non-invasive biomagnetic sensors spread over the abdomen were associated with successful induction of labor (IOL).

STUDY DESIGN

Uterine magnetomyogram (MMG) signals were collected using the SARA (SQUID Array for Reproductive Assessment) device from 33 subjects between 37 and 42 weeks gestational age. The signals were post-processed, uterine contractile related MMG bursts were detected, and parameters in the time and frequency domain were extracted. The modified Bishop score calculated at admission was used to determine the method of IOL. Wilcoxon's rank-sum test was used to compare IOL successes and failures for differences in gestational age (GA), parity, modified Bishop's score, maximum oxytocin, and electrophysiological parameters extracted from MMG.

RESULTS

The average parity was three times (3x) higher (1.53 versus 0.50; p = 0.039), and the average modified Bishop score was 2x higher (3.32 versus 1.63; p = 0.032) amongst IOL successes than failures, while the average GA and maximum oxytocin showed a small difference. For the MMG parameters, successful IOLs had, on average, 3.5x greater mean power during bursts (0.246 versus 0.070; p = 0.034) and approximately 1.2x greater mean number of bursts (2.05 versus 1.68; p = 0.036) compared to the failed IOLs, but non-significant differences were observed in mean peak frequency, mean burst duration, and mean duration between bursts.

CONCLUSION

The study showed that inductions of labor that took less than 24 h to deliver have a higher mean power in the baseline electrophysiological activity of the uterus when recorded prior to planned induction. The results are indicative that baseline electrophysiological activity measured prior to induction is associated with successful induction.

Alignment of magnetic sensing and clinical magnetomyography

Neuromuscular diseases are a prevalent cause of prolonged and severe suffering for patients, and with the global population aging, it is increasingly becoming a pressing concern. To assess muscle activity in NMDs, clinicians and researchers typically use electromyography (EMG), which can be either non-invasive using surface EMG, or invasive through needle EMG. Surface EMG signals have a low spatial resolution, and while the needle EMG provides a higher resolution, it can be painful for the patients, with an additional risk of infection. The pain associated with the needle EMG can pose a risk for certain patient groups, such as children. For example, children with spinal muscular atrophy (type of NMD) require regular monitoring of treatment efficacy through needle EMG; however, due to the pain caused by the procedure, clinicians often rely on a clinical assessment rather than needle EMG. Magnetomyography (MMG), the magnetic counterpart of the EMG, measures muscle activity non-invasively using magnetic signals. With super-resolution capabilities, MMG has the potential to improve spatial resolution and, in the meantime, address the limitations of EMG. This article discusses the challenges in developing magnetic sensors for MMG, including sensor design and technology advancements that allow for more specific recordings, targeting of individual motor units, and reduction of magnetic noise. In addition, we cover the motor unit behavior and activation pattern, an overview of magnetic sensing technologies, and evaluations of wearable, non-invasive magnetic sensors for MMG.

Noninvasive electromyometrial imaging of human uterine maturation during term labor

Electromyometrial imaging (EMMI) was recently developed to image the three-dimensional (3D) uterine electrical activation during contractions noninvasively and accurately in sheep. Herein we describe the development and application of a human EMMI system to image and evaluate 3D uterine electrical activation patterns at high spatial and temporal resolution during human term labor. We demonstrate the successful integration of the human EMMI system during subjects' clinical visits to generate noninvasively the uterine surface electrical potential maps, electrograms, and activation sequence through an inverse solution using up to 192 electrodes distributed around the abdomen surface. Quantitative indices, including the uterine activation curve, are developed and defined to characterize uterine surface contraction patterns. We thus show that the human EMMI system can provide detailed 3D images and quantification of uterine contractions as well as novel insights into the role of human uterine maturation during labor progression.

Regional identification of information flow termination of electrohysterographic signals: Towards understanding human uterine electrical propagation

BACKGROUND AND OBJECTIVE

The uterine electrohysterogram (EHG) contains important information about electrical signal propagation which may be useful to monitor and predict the progress of pregnancy towards parturition. Directed information processing has the potential to be of use in studying EHG recordings. However, so far, there is no directed information-based estimation scheme that has been applied to investigating the propagation of human EHG recordings. To realize this, the approach of directed information and its reliability and adaptability should be scientifically studied.

METHODS

We demonstrated an estimation scheme of directed information to identify the spatiotemporal relationship between the recording channels of EHG signal and assess the algorithm reliability initially using simulated data. Further, a regional identification of information flow termination (RIIFT) approach was developed and applied for the first time to extant multichannel EHG signals to reveal the terminal zone of propagation of the electrical activity associated with uterine contraction. RIIFT operates by estimating the pairwise directed information between neighboring EHG channels and identifying the location where there is the strongest inward flow of information. The method was then applied to publicly-available experimental data obtained from pregnant women with the use of electrodes arranged in a 4-by-4 grid.

RESULTS

Our results are consistent with the suggestions from the previous studies with the added identification of preferential sites of excitation termination - within the estimated area, the direction of surface action potential propagation towards the medial axis of uterus during contraction was discovered for 72.15% of the total cases, demonstrating that our RIIFT method is a potential tool to investigate EHG propagation for advancing our understanding human uterine excitability.

CONCLUSIONS

We developed a new approach and applied it to multichannel human EHG recordings to investigate the electrical signal propagation involved in uterine contraction. This provides an important platform for future studies to fill knowledge gaps in the spatiotemporal patterns of electrical excitation of the human uterus.

Uterus Modeling from Cell to Organ Level: towards Better Understanding of Physiological Basis of Uterine Activity

The relatively limited understanding of the physiology of uterine activation prevents us from achieving optimal clinical outcomes for managing serious pregnancy disorders such as preterm birth or uterine dystocia. There is increasing awareness that multi-scale computational modeling of the uterus is a promising approach for providing a qualitative and quantitative description of uterine physiology. The overarching objective of such approach is to coalesce previously fragmentary information into a predictive and testable model of uterine activity that, in turn, informs the development of new diagnostic and therapeutic approaches to these pressing clinical problems. This article assesses current progress towards this goal. We summarize the electrophysiological basis of uterine activation as presently understood and review recent research approaches to uterine modeling at different scales from single cell to tissue, whole organ and organism with particular focus on transformative data in the last decade. We describe the positives and limitations of these approaches, thereby identifying key gaps in our knowledge on which to focus, in parallel, future computational and biological research efforts.

Contractions: Traditional concepts and their role in modern obstetrics

Contractions are produced through a complex interplay of hormonal, mechanical, and electrical factors. In labor, contractions are measured using the Montevideo unit. Clinical considerations in labor wherein contraction assessment becomes paramount include the care of women whose labor is complicated by abnormal progress or tachysystole. In an era of obstetrics in which the high cesarean rate is a major issue of concern, there remain many questions as to how to best incorporate contraction monitoring into practice in order to optimize care. Technological advancement has led to the development on new modalities that can be used to study contraction physiology, and there may be an opportunity in the future to apply these methods for use in the clinical setting. This article also makes a case for the need to reevaluate the current measures of uterine contractile activity and the definition of contraction adequacy using updated definitions of normal labor progress.

Connectivity Measures of Uterine Activity using Magnetomyography

This work explores the use of graph-theoretical metrics of network topography to investigate interactions in the uterine activity using a multi-channel SQUID array. Magnetomyography (MMG) is a noninvasive technique that records magnetic fields associated with the uterine activity. Graph analysis was applied to 30s no-overlap epochs of MMG data for evaluating the evolution of local and global connectivity, and centrality indicators within the network. Binary graphs were obtained by applying a range of thresholds from 10% to 35% of the strongest edges preserved. Network analysis was applied to 24 simulated MMG data when independent noise realizations were added. Simulated data was generated from a multiscale forward model that uses a realistic uterus representation. Additionally, we applied network analysis to repeated real MMG measurements obtained from a subject at different gestational ages (GA) to observe the evolution of the network until subject reaches active labor. Results show in the simulation setting that network metrics were higher during the burst activity reflecting the propagation activity of the signal across the uterus of the multiscale mathematical model. The local efficiency values were higher than the global efficiency for any threshold used. For real MMG recordings, global and local efficiency, and clustering coefficient values increased as the patient approached active labor at any binarized threshold whereas betweenness centrality quantity decreased with days to active labor.

An application of higher order multivariate cumulants in modelling of myoelectrical activity of porcine uterus during early pregnancy

The analysis of the uterine contraction have become a general practice in an effort to improve the clinical management of uterine contractions during pregnancy and labour in human beings. The fluctuations in uterine activity may occur without affecting progress of gestation, however the painful and fashion contractions may be the first threat of miscarriage. While pigs were considered as an referential preclinical model, the computational modelling of spontaneous myoelectrical activity of complex systems of porcine myometrium in peri-fertilization period has been proposed. The higher order statistic, multivariate cumulants and Joint Skewness Band Selection method, have been applied to study the dependence structure of electromyographic (EMG) signal with an effective EMG feature. Than the model of recognition of multivariate, myoelectricaly changes according to crucial stages for successful fertilization and early pregnancy maintenance has been estimated. We found that considering together time and frequency features of EMG signal was extremely non-Gaussian distributed and the higher order multivariate statistics such as cumulants, have to be used to determine the pattern of myoelectrical activity in reproductive tract. We confirmed the expectance that the probabilistic model changes on a daily base. We demonstrated the changes in proposed model at the crucial time points of in peri-fertilization period. We speculate the activity of the middle of uterine horn and the power (minimum and maximum) and pauses between myoelectrical burst features are essential for the functional role of uterine contractility in peri-fertilization period.

Multifractal Analysis of Uterine Electromyography Signals for the Assessment of Progression of Pregnancy in Term Conditions

OBJECTIVES

The objectives of this paper are to examine the source of multifractality in uterine electromyography (EMG) signals and to study the progression of pregnancy in the term (gestation period > 37 weeks) conditions using multifractal detrending moving average (MFDMA) algorithm.

METHODS

The signals for the study, considered from an online database, are obtained from the surface of abdomen during the second (T1) and third trimester (T2). The existence of multifractality is tested using Hurst and scaling exponents. With the intention of identifying the origin of multifractality, the preprocessed signals are converted to shuffle and surrogate data. The original and the transformed signals are subjected to MFDMA to extract multifractal spectrum features, namely strength of multifractality, maximum, minimum, and peak singularity exponents.

RESULTS

The Hurst and scaling exponents extracted from the signals indicate that uterine EMG signals are multifractal in nature. Further analysis shows that the source of multifractality is mainly owing to the presence of long-range correlation, which is computed as 79.98% in T1 and 82.43% in T2 groups. Among the extracted features, the peak singularity exponent and strength of multifractality show statistical significance in identifying the progression of pregnancy. The corresponding coefficients of variation are found to be low, which show that these features have low intersubject variability.

CONCLUSION

It appears that the multifractal analysis can help in investigating the progressive changes in uterine muscle contractions during pregnancy.

Embroidered archimedean spiral electrodes for contactless prosthetic control

With continuous advancements on active prosthetics the detection of the user's intention becomes the new technological bottleneck. While electromyography (EMG) is widely used to detect individual muscular contributions, sweat and relative sensor movements degrade the quality of the signal over time. In this paper, we bypass the problems created with the skin contact analyzing the muscular activation with Archimedean Spiral (AS) electrodes. We compare traditional EMG electrodes with AS electrodes, stacked up in textile embroidered layers to improve their functionality, and eventually adding a layer of cloth/silicon between the electrodes and the human skin to ascertain the feasibility of the method. We use n=9 volunteers to perform a loaded wrist extension and record signals from the extensor digitorum muscle group. We evaluate the amplitude and noise from all results and conclude that the AS electrode is capable of detecting muscular activation without touching the skin. As part of a low-cost prosthetic initiative, this EMG alternative can be potentially embedded to the prosthetic socket to improve usage and reduce adaptation problems.

Characteristics of bioelectrical activity of oviducts and uterus during early pregnancy in sows recorded by telemetry method

NEW FINDINGS

What is the central question of this study? The aim of present study was to record and analyse the myoelectrical activity in the female pig reproductive tract (uterus and oviduct) during early pregnancy. What is the main finding and its importance? Understanding the contractile activity of the uterus and oviducts is indispensable for understanding the physiological mechanisms as well as all irregularities associated with the period of conception and early pregnancy. The aim of the present study was to record the myoelectrical activity of the reproductive tract in sows during the oestrous phase and early pregnancy via a telemetry recording system. In a total of eight non-pregnant pigs, the bioelectrical activity was recorded through three silicone electrodes sutured on the oviduct (isthmus and ampulla) and the uterine horn. Blood samples were collected to monitor the concentrations of progesterone (P4) and luteinizing hormone (LH). The oestrous cycle was synchronized with equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG), and the animals were subjected to artificial insemination. Analysis of the EMG activity of the oviduct and uterus in the oestrous phase and in early stages of pregnancy suggests explicitly that telemetry could enable in vivo assessment of myoelectrical activity of parts of the reproductive system in sows. Off-line analysis of the duration of EMG activity bursts in the uterus, isthmus and ampulla were significantly higher during early pregnancy (phases II and III) than in the oestrous phase. The EMG signals demonstrated low mean amplitudes of activity in the oviduct and uterus during early pregnancy (phases I-III). Significant differences between the root mean square signals were observed in the isthmus and ampulla both during oestrus and in early pregnancy (phase I; P < 0.01). During the oestrous phase, the P4 concentration was estimated at <1 ng ml^-1 , whereas the LH concentration was >4 ng ml^-1 . In contrast, during early pregnancy, the P4 and LH concentrations were estimated at >4 and <1 ng ml^-1 , respectively.

Toward noninvasive monitoring of ongoing electrical activity of human uterus and fetal heart and brain

•

Evaluated a fetal-maternal scanner for monitoring electrical maternal and fetal organ activity.

•

The simulated scanner can monitor the uterine and fetal heart and brain activity online.

•

Biomagnetic monitors similar to this instrument should be useful in clinical neurophysiology.

Objective

To evaluate whether a full-coverage fetal-maternal scanner can noninvasively monitor ongoing electrophysiological activity of maternal and fetal organs.

Methods

A simulation study was carried out for a scanner with an array of magnetic field sensors placed all around the torso from the chest to the hip within a horizontal magnetic shielding enclosure. The magnetic fields from internal organs and an external noise source were computed for a pregnant woman with a 35-week old fetus. Signal processing methods were used to reject the external and internal interferences, to visualize uterine activity, and to detect activity of fetal heart and brain.

Results

External interference was reduced by a factor of 1000, sufficient for detecting signals from internal organs when combined with passive and active shielding. The scanner rejects internal interferences better than partial-coverage arrays. It can be used to estimate currents around the uterus. It clearly detects spontaneous activity from the fetal heart and brain without averaging and weaker evoked brain activity at all fetal head positions after averaging.

Conclusion

The simulated device will be able to monitor the ongoing activity of the fetal and maternal organs.

Significance

This type of scanner may become a novel tool in fetal medicine.

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

Uterine contractions are generated by myometrial smooth muscle cells (SMCs) that comprise most of the myometrial layer of the uterine wall. Aberrant uterine motility (i.e., hypo- or hyper-contractility or asynchronous contractions) has been implicated in the pathogenesis of infertility due to the failure of implantation, endometriosis and abnormal estrous cycles. The mechanism whereby the non-pregnant uterus initiates spontaneous contractions remains poorly understood. The aim of the present study was to employ linear synchronization measures for analyzing the pattern of EMG signal propagation (direction and speed) in smooth muscles of the non-pregnant porcine uterus in vivo using telemetry recording system. It has been revealed that the EMG signal conduction in the uterine wall of the non-pregnant sow does not occur at random but it rather exhibits specific directions and speed. All detectable EMG signals moved along the uterine horn in both cervico-tubal and tubo-cervical directions. The signal migration speed could be divided into the three main types or categories: i. slow basic migration rhythm (SBMR); ii. rapid basic migration rhythm (RBMR); and iii. rapid accessory migration rhythm (RAMR). In conclusion, the EMG signal propagation in smooth muscles of the porcine uterus in vivo can be assessed using a linear synchronization model. Physiological pattern of the uterine contractile activity determined in this study provides a basis for future investigations of normal and pathologicall myogenic function of the uterus.

Simultaneous Recording and Analysis of Uterine and Abdominal Muscle Electromyographic Activity in Nulliparous Women During Labor

OBJECTIVE

To record and characterize electromyography (EMG) from the uterus and abdominal muscles during the nonlabor to first and second stages of labor and to define relationships to contractions.

METHODS

Nulliparous patients without any treatments were used (n = 12 nonlabor stage, 48 during first stage and 33 during second stage). Electromyography of both uterine and abdominal muscles was simultaneously recorded from electrodes placed on patients' abdominal surface using filters to separate uterine and abdominal EMG. Contractions of muscles were also recorded using tocodynamometry. Electromyography was characterized by analysis of various parameters.

RESULTS

During the first stage of labor, when abdominal EMG is absent, uterine EMG bursts temporally correspond to contractions. In the second stage, uterine EMG bursts usually occur at same frequency as groups of abdominal bursts and precede abdominal bursts, whereas abdominal EMG bursts correspond to contractions and are accompanied by feelings of "urge to push." Uterine EMG increases progressively from nonlabor to second stage of labor.

CONCLUSIONS

(1) Uterine EMG activity can be separated from abdominal EMG events by filtering. (2) Uterine EMG gradually evolves from the antepartum stage to the first and second stages of labor. (3) Uterine and abdominal EMG reflect electrical activity of the muscles during labor and are valuable to assess uterine and abdominal muscle events that control labor. (4) During the first stage of labor uterine, EMG is responsible for contractions, and during the second stage, both uterine and abdominal muscle participate in labor.

Modeling Magnetomyograms of Uterine Contractions during Pregnancy Using a Multiscale Forward Electromagnetic Approach

Understanding the mechanisms of uterine contractions during pregnancy is especially important in predicting the onset of labor and thus in forecasting preterm deliveries. Preterm birth can cause serious health problems in newborns, as well as large financial burdens to society. Various techniques such as electromyography (EMG) and magnetomyography (MMG) have been developed to quantify uterine contractions. However, no widely accepted method to predict labor based on electromagnetic measurement is available. Therefore, developing a biophysical model of EMG and MMG could help better understand uterine contractions, interpret real measurements, and detect labor. In this work, we propose a multiscale realistic model of uterine contractions during pregnancy. At the cellular level, building on bifurcation theory, we apply generalized FitzHugh-Nagumo (FHN) equations that produces both plateau-type and bursting-type action potentials. At the tissue level, we introduce a random fiber orientation model applicable to an arbitrary uterine shape. We also develop an analytical expression for the propagation speed of transmembrane potential. At the organ level, a realistic volume conductor geometry model is provided based on magnetic resonance images of a pregnant woman. To simulate the measurements from the SQUID Array for Reproductive Assessment (SARA) device, we propose a sensor array model. Our model is able to reproduce the characteristics of action potentials. Additionally, we investigate the sensitivity of MMG to model configuration aspects such as volume geometry, fiber orientation, and pacemaker location. Our numerical results show that fiber orientation and pacemaker location are the key aspects that greatly affect the MMG as measured by the SARA device. We conclude that sphere is appropriate as an approximation of the volume geometry. The initial step towards validating the model against real MMG measurement is also presented. Our results show that the model is flexible to mimic the limited-propagation magnetic signature during the emergence and decay of a uterine contraction.

Characterizing the Propagation of Uterine Electrophysiological Signals Recorded with a Multi-Sensor Abdominal Array in Term Pregnancies

The objective of this study was to quantify the number of segments that have contractile activity and determine the propagation speed from uterine electrophysiological signals recorded over the abdomen. The uterine magnetomyographic (MMG) signals were recorded with a 151 channel SARA (SQUID Array for Reproductive Assessment) system from 36 pregnant women between 37 and 40 weeks of gestational age. The MMG signals were scored and segments were classified based on presence of uterine contractile burst activity. The sensor space was then split into four quadrants and in each quadrant signal strength at each sample was calculated using center-of-gravity (COG). To this end, the cross-correlation analysis of the COG was performed to calculate the delay between pairwise combinations of quadrants. The relationship in propagation across the quadrants was quantified and propagation speeds were calculated from the delays. MMG recordings were successfully processed from 25 subjects and the average values of propagation speeds ranged from 1.3-9.5 cm/s, which was within the physiological range. The propagation was observed between both vertical and horizontal quadrants confirming multidirectional propagation. After the multiple pairwise test (99% CI), significant differences in speeds can be observed between certain vertical or horizontal combinations and the crossed pair combinations. The number of segments containing contractile activity in any given quadrant pair with a detectable delay was significantly higher in the lower abdominal pairwise combination as compared to all others. The quadrant-based approach using MMG signals provided us with high spatial-temporal information of the uterine contractile activity and will help us in the future to optimize abdominal electromyographic (EMG) recordings that are practical in a clinical setting.

The location of pacemakers in the uteri of pregnant guinea pigs and rats

The pregnant uterus is a smooth muscle organ whose pattern of contraction is dictated by the propagation of electrical impulses. Such electrical activity may originate from one or more pacemakers, but the location of these sites has not yet been determined. To detect the location of the pacemaker in the gravid uterus, two approaches were used: 1) determine the site from where the contraction started using isolated uteri from the pregnant guinea pig, and videotape their contractions; and 2) record, in isolated uteri from pregnant term rats, with 240 extracellular electrodes simultaneously, and determine where the electrical bursts started. In both the contractile and electrophysiological experiments, there was not a single, specific pacemaker area. However, most contractions (guinea pig 87%) and bursts (rat 76%) started close to the mesometrial border (mean 2.7 ± 4.0 mm SD in guinea pigs and 1.3 ± 1.4 mm in rats). In addition, in the rat, most sites of initiations were located closer to the ovarial end of the horn (mean distance from the ovarial end 6.0 ± 6.2 mm SD), whereas such an orientation was not seen in the guinea pig. In both guinea pig and rat uteri at term, there is not one specific pacemaker area. Rather, contractile and electrical activity may arise from any site, with the majority starting close to the mesometrial border. Furthermore, in the rat, most activities started at the ovarial end of the horn. This may suggest a slightly different pattern of contraction in both species.

Why the heart is like an orchestra and the uterus is like a soccer crowd

The human uterus has no pacemaker or motor innervation, yet develops rhythmic, powerful contractions that increase intrauterine pressure to dilate the cervix and force the fetus through the pelvis. To achieve the synchronous contractions required for labor, the muscle cells of the uterus act as independent oscillators that become increasingly coupled by gap junctions toward the end of pregnancy. The oscillations are facilitated by changes in resting membrane potential that occur as pregnancy progresses. Reductions of potassium channels in the myocyte membranes in late pregnancy prolong myocyte action potentials, further facilitating transmission of signals and recruitment of neighboring myocytes. Late in pregnancy prostaglandin production increases leading to increased myocyte excitability. Also late in pregnancy myocyte actin polymerizes allowing actin-myosin interactions that generate force, following myocyte depolarization, calcium entry, and activation of myosin kinase. Labor occurs as a consequence of the combination of increased myocyte to myocyte connectivity, increased depolarizations that last longer, and activated intracellular contractile machinery. During labor the synchronous contractions of muscle cells raise intrauterine pressure to dilate the cervix in a process distinct from peristalsis. The synchronous contractions occur in a progressively larger region of the uterine wall. As the size of the region increases with increasing connectivity, the contraction of that larger area leads to an increase in intrauterine pressure. The resulting increased wall tension causes myocyte depolarization in other parts of the uterus, generating widespread synchronous activity and increased force as more linked regions are recruited into the contraction. The emergent behavior of the uterus has parallels in the behavior of crowds at soccer matches that sing together without a conductor. This contrasts with the behavior of the heart where sequential contractions are regulated by a pacemaker in a similar way to the actions of a conductor and an orchestra.