Contraction Waves Research Articles

Age as a dominant factor affecting gastric motility and emptying

Gastric motility is the process of continuous propagation of peristaltic waves from the anterior part of the stomach to the pylorus region. These waves aid in the digestion of foods, importantly play a major role in gastric emptying of foods. The present study aimed to investigate whether ageing influences gastric motility in response to apple consumption. Subjects were asked to consume apple and water in the ratio of 3:1 followed by MRI scanning in the right lying position. Antral contraction wave characteristics like speed, frequency, amplitude and width of the wave and occlusion percentage were calculated. Average contractions per minute were obtained as 2.67±0.06 for young age and 2.43±0.22 for middle-aged healthy humans. From the obtained results, no significant difference was found between the assessed motility parameters.

Acupoint sensitization enhances inhibitory effect of electroacupuncture on jejunum mobility in rats

To observe the effect difference of electroacupuncture (EA) at the sensitized and non-sensitized acupoint "Tianshu" (ST25) on the motility of jejunum in rats. Male SD rats were randomly divided into blank control, sensitized ST25 (sensitization), and non-sensitized ST25 (non-sensitization) groups (n=16 in each group). The sensitization and non-sensitization were induced by injection of 15% mustard oil (20 μL) and Paraffin oil (20 μL) into the left ST25 area respectively. The rats' behavior reactions were assessed by recording the numbers and duration of licking the local sensitized skin region. At the end of experiments and after regular trans-cardiac perfusion and fixing with 10% neutral formaldehyde, the skin and muscular tissues of the ST25 region (1 cm×1 cm) were taken for H.E. staining to observe the local histopathologic changes. The intestinal motility was detected by recording the contraction pressure waves of jejunum through a small balloon-connected pressure transducer and an amplifier, followed by calculating the ratios of amplitude and frequency of contraction waves between pre- and post-EA stimulation. EA (2 Hz, 0.2-6.0 mA) was applied to the sensitized and non-sensitized ST25 regions for 20 s for comparing their effects on jejunum motility. Compared with the blank control group, mustard oil injection but not Paraffin oil injection resulted in histological edema and neutrophils infiltration in tissues of ST25 region, and also striking increase of the number and duration of licking (P<0.01), suggesting a sensitization of ST25 area after mustard oil injection. The ratios of spontaneous contraction amplitude and frequency of jejunum were remarkably decreased in mustard oil-treated rats compared to baseline and Paraffin oil group (P<0.001，P<0.01). The maximum inhibitory effect of EA on the intestinal movement amplitude was significantly higher in the sensitization group than in the blank control and non-sensitization groups (P<0.05，P<0.01), and there was a dose-effect relationship between the current intensity of EA (0.5-3.0 mA) and the inhibitory rate 50% of the contraction amplitude (not the frequency) in the sensitization group (P<0.001), but not in the blank control and non-sensitization groups (P>0.05). Additionally, 1.5 mA EA stimulation at the sensitized ST25 (not at the non-sensitized ST25) had an inhibitory effect on the contraction amplitude (P<0.05) rather than on the contraction frequency (P>0.05) in comparison with the blank control group. Sensitization of acupoint ST25 can modulate the motility of jejunum and enhances the inhibitory effect of EA on the contraction amplitude of jejunum in rats. The inhibitory effect of sensitized ST25 EA is evidently stronger than that of the non-sensitized ST25 EA.

Nitric Oxide Is Essential for Generating the Minute Rhythm Contraction Pattern in the Small Intestine, Likely via ICC-DMP.

Nitrergic nerves have been proposed to play a critical role in the orchestration of peristaltic activities throughout the gastrointestinal tract. In the present study, we investigated the role of nitric oxide, using spatiotemporal mapping, in peristaltic activity of the whole ex vivo mouse intestine. We identified a propulsive motor pattern in the form of propagating myogenic contractions, that are clustered by the enteric nervous system into a minute rhythm that is dependent on nitric oxide. The cluster formation was abolished by TTX, lidocaine and nitric oxide synthesis inhibition, whereas the myogenic contractions, occurring at the ICC-MP initiated slow wave frequency, remained undisturbed. Cluster formation, inhibited by block of nitric oxide synthesis, was fully restored in a highly regular rhythmic fashion by a constant level of nitric oxide generated by sodium nitroprusside; but the action of sodium nitroprusside was inhibited by lidocaine indicating that it was relying on neural activity, but not rhythmic nitrergic nerve activity. Hence, distention-induced activity of cholinergic nerves and/or a co-factor within nitrergic nerves such as ATP is also a requirement for the minute rhythm. Cluster formation was dependent on distention but was not evoked by a distention reflex. Block of gap junction conductance by carbenoxolone, dose dependently inhibited, and eventually abolished clusters and contraction waves, likely associated, not with inhibition of nitrergic innervation, but by abolishing ICC network synchronization. An intriguing feature of the clusters was the presence of bands of rhythmic inhibitions at 4–8 cycles/min; these inhibitory patches occurred in the presence of tetrodotoxin or lidocaine and hence were not dependent on nitrergic nerves. We propose that the minute rhythm is generated by nitric oxide-induced rhythmic depolarization of the musculature via ICC-DMP.

Combining Ultrafast Ultrasound and High-Density EMG to Assess Local Electromechanical Muscle Dynamics: A Feasibility Study

Skeletal muscles generate force, enabling movement through a series of fast electro-mechanical activations coordinated by the central nervous system. Understanding the underlying mechanism of such fast muscle dynamics is essential in neuromuscular diagnostics, rehabilitation medicine and sports biomechanics. The unique combination of electromyography (EMG) and ultrafast ultrasound imaging (UUI) provides valuable insights into both electrical and mechanical activity of muscle fibers simultaneously, the excitation-contraction (E-C) coupling. In this feasibility study we propose a novel non-invasive method to simultaneously track the propagation of both electrical and mechanical waves in muscles using high-density electromyography and ultrafast ultrasound imaging (5000 fps). Mechanical waves were extracted from the data through an axial tissue velocity estimator based on one-lag autocorrelation. The E-C coupling in electrically evoked twitch contractions of the Biceps Brachii in healthy participants could successfully be tracked. The excitation wave (i.e. action potential) had a velocity of 3.9±0.5ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and the subsequent mechanical (i.e. contraction) wave had a velocity of 3.5±0.9ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The experiment showed evidence that contracting sarcomeres that were already activated by the action potential (AP) pull on sarcomeres that were not yet reached by the AP, which was corroborated by simulated contractions of a newly developed multisegmental muscle fiber model, consisting of 500 sarcomeres in series. In conclusion, our method can track the electromechanical muscle dynamics with high spatio-temporal resolution. Ultimately, characterizing E-C coupling in patients with neuromuscular diseases (e.g. Duchenne or Becker muscular dystrophy) may assess contraction efficiency, monitor the progression of the disease, and determine the efficacy of new treatment options.

Making waves: A proposed new role for myosin-binding protein C in regulating oscillatory contractions in vertebrate striated muscle.

Myosin-binding protein C (MyBP-C) is a critical regulator of muscle performance that was first identified through its strong binding interactions with myosin, the force-generating protein of muscle. Almost simultaneously with its discovery, MyBP-C was soon found to bind to actin, the physiological catalyst for myosin's activity. However, the two observations posed an apparent paradox, in part because interactions of MyBP-C with myosin were on the thick filament, whereas MyBP-C interactions with actin were on the thin filament. Despite the intervening decades since these initial discoveries, it is only recently that the dual binding modes of MyBP-C are becoming reconciled in models that place MyBP-C at a central position between actin and myosin, where MyBP-C alternately stabilizes a newly discovered super-relaxed state (SRX) of myosin on thick filaments in resting muscle and then prolongs the "on" state of actin on thin filaments in active muscle. Recognition of these dual, alternating functions of MyBP-C reveals how it is central to the regulation of both muscle contraction and relaxation. The purpose of this Viewpoint is to briefly summarize the roles of MyBP-C in binding to myosin and actin and then to highlight a possible new role for MyBP-C in inducing and damping oscillatory waves of contraction and relaxation. Because the contractile waves bear similarity to cycles of contraction and relaxation in insect flight muscles, which evolved for fast, energetically efficient contraction, the ability of MyBP-C to damp so-called spontaneous oscillatory contractions (SPOCs) has broad implications for previously unrecognized regulatory mechanisms in vertebrate striated muscle. While the molecular mechanisms by which MyBP-C can function as a wave maker or a wave breaker are just beginning to be explored, it is likely that MyBP-C dual interactions with both myosin and actin will continue to be important for understanding the new functions of this enigmatic protein.

Electrochemical detection of baicalein based on a three-dimensional micromixer

Baicalein, a kind of flavonoid, has many medical benefits, and therefore, its accurate and efficient determination is necessary in the field of medical ingredient detection. To achieve the rapid and precise detection of baicalein, a three-dimensional (3D) expansion–contraction wave micromixer was designed and used along with an electrochemical detection method to assemble a micromixing electrochemical detection system. First, the performances of the wave micromixers were investigated using the COMSOL Multiphysics 5.3 a software with three optimisation objectives, namely, the mixing uniformity, pressure drop, and mixing performance index, to comprehensively evaluate the properties of the micromixers. Second, a 3D expansion–contraction wave micromixer with optimal mixing properties was fabricated using the 3D printing technology. Third, a micromixing electrochemical detection system was built to study the redox behaviours of baicalein through the electrochemical cyclic voltammetry method. The effects of buffer varieties, buffer pH values, scanning speeds, and inlet flow rates on the redox curves of baicalein were studied to determine the appropriate experimental conditions. The results demonstrated that the currents of the oxidation peak increased linearly with the baicalein concentrations within the range of 3.55 × 10−6–5.92 × 10−5 mol l−1 and the detection limit of 1.861 × 10−8 mol l−1 (S/N = 3). The relative standard deviation among the results obtained through repeated experiments was 2.86%; this proves a high detection reproducibility of the new method. Compared with spectrophotometry, the error determined using the novel method in a real sample detection was 0.31%, thus achieving an efficient and precise detection of baicalein. The micromixing electrochemical detection method can remarkably improve the mixing efficiency, shorten the detection time, and decrease the detection limit, and therefore could be popularised for the exact content detection of other flavonoids.

Surface contraction waves or cell proliferation waves in the presumptive neurectoderm during amphibian gastrulation: Mexican axolotl versus African clawed frog

This essay represents a critical analysis of the literary data on various types of waves occurring in the amphibian embryos during gastrulation. A surface contraction wave travels through the presumptive neurectoderm during Mexican axolotl gastrulation. This wave coincides temporally and spatially with involution of the inducing chordomesoderm and with the prospective neural plate. By contrast, there is no similar surface contraction wave during African clawed frog gastrulation. However, the clawed frog displays the waves of DNA synthesis and mitosis in the presumptive neurectoderm during gastrulation, whereas no such waves were discovered in axolotl gastrulae. These sets of experimental data are in accordance with the contemporary concept of considerable ontogenetic diversity of the class Amphibia.

Modulation of contractions in the small intestine indicate desynchronization via supercritical Andronov\u2013Hopf bifurcation

The small intestine is covered by a network of coupled oscillators, the interstitial cells of Cajal (ICC). These oscillators synchronize to generate rhythmic phase waves of contraction. At points of low coupling, oscillations desynchronise, frequency steps occur and every few waves terminates as a dislocation. The amplitude of contractions is modulated at frequency steps. The phase difference between contractions at a frequency step and a proximal reference point increased slowly at first and then, just at the dislocation, increased rapidly. Simultaneous frequency and amplitude modulation (AM/FM) results in a Fourier frequency spectrum with a lower sideband, a so called Lashinsky spectrum, and this was also seen in the small intestine. A model of the small intestine consisting of a chain of coupled Van der Pol oscillators, also demonstrated simultaneous AM/FM at frequency steps along with a Lashinsky spectrum. Simultaneous AM/FM, together with a Lashinsky spectrum, are predicted to occur when periodically-forced or mutually-coupled oscillators desynchronise via a supercritical Andronov–Hopf bifurcation and have been observed before in other physical systems of forced or coupled oscillators in plasma physics and electrical engineering. Thus motility patterns in the intestine can be understood from the viewpoint of very general dynamical principles.

Optimizing the Direction and Order of the Motion Unveiled the Ability of Conventional Monolayers of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes to Show Frequency-Dependent Enhancement of Contraction and Relaxation Motion.

Contractility of the human heart increases as its beating rate is elevated, so-called positive force-frequency relationship; however, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been reported to exert a negative force-frequency relationship. We tested the hypothesis that the regulation of motion directions by electrical pacing and/or oxygen supply may improve the electro-mechanical properties of hiPSC-CMs monolayers. To better evaluate the spatial and temporal relationship between electrical excitation and contractile motion, we simultaneously observed the field potential and motion vector of hiPSC-CMs sheets. Under spontaneous contraction, although an electrical excitation originating from a region propagated unidirectionally over the cell sheet, contraction wave started from multiple sites, and relaxation wave was initiated from a geometric center of hiPSC-CMs sheet. During electrical pacing, contraction and relaxation waves were propagated from the stimulated site. Interestingly, the maximum contraction speed was more increased when the hiPSC-CMs sheet was stimulated at an area relaxation initiated under spontaneous condition. Furthermore, motion vector analysis demonstrated that “positive contraction velocity-frequency relationship” in contraction and “frequency-dependent enhancement of relaxation” were produced in the cell sheet by optimizing the direction and order of the contractile motion with pacing at the relaxation-initiating area. A close analysis of motion vectors along with field potential recording demonstrated that relaxation process consists of fast and slow phases, and suggest that intracellular Ca2+ dynamics may be closely related to functions of Ca2+-ATPase pump and Na+-Ca2+ exchangers. Namely, the slow relaxation phase occurred after the second peak of field potential, suggesting that the slow phase may be associated with extrusion of Ca2+ by Na+-Ca2+ exchangers during repolarization. Increase of oxygen concentration from 20 to 95% as well as β-adrenergic stimulation with isoproterenol accelerated the fast relaxation, suggesting that it could depend on Ca2+ uptake via Ca2+-ATPase during the depolarization phase. The ratio of maximum contraction speed to field potential duration was increased by the β-adrenergic stimulation, indicating the elevated contraction efficiency per Ca2+-influx. Thus, these findings revealed potential ability of conventional monolayers of hiPSC-CMs, which will help apply them to translational study filling the gap between physiological as well as pharmacological studies and clinical practice.

Coordinated crawling via reinforcement learning.

Rectilinear crawling locomotion is a primitive and common mode of locomotion in slender soft-bodied animals. It requires coordinated contractions that propagate along a body that interacts frictionally with its environment. We propose a simple approach to understand how this coordination arises in a neuromechanical model of a segmented, soft-bodied crawler via an iterative process that might have both biological antecedents and technological relevance. Using a simple reinforcement learning algorithm, we show that an initial all-to-all neural coupling converges to a simple nearest-neighbour neural wiring that allows the crawler to move forward using a localized wave of contraction that is qualitatively similar to what is observed in Drosophila melanogaster larvae and used in many biomimetic solutions. The resulting solution is a function of how we weight gait regularization in the reward, with a trade-off between speed and robustness to proprioceptive noise. Overall, our results, which embed the brain-body-environment triad in a learning scheme, have relevance for soft robotics while shedding light on the evolution and development of locomotion.

Modeling of hydraulic shock as one of the main risk factors of main arteries atherosclerosis in arrhythmias

Introduction. Atherosclerosis is the main reason of cardiocerebral events, its mechanisms and reasons are still being studied. Hydraulic shock in arrhythmias has not been studied before.&#x0D; Aim. To perform the modeling of hydraulic shock as a risk factor of the main arteries in arrhythmias with original experimental model created by the authors.&#x0D; Materials and methods. We created the original experimental model, it was used to imitate hydraulic shock in arrhythmias. It imitated the real arterial vessel and it allowed to make intra-vessel circulation of liquid in the regular rhythm and in arrhythmias (extrasystole).&#x0D; Results. In extrasystolic arrhythmia imitation in the first post-extrasystolic contraction the speed of liquid flow was revealed to rise in mean value 158% in comparison with the regular rhythm.&#x0D; Conclusion. In extrasystolic arrhythmia during the spread of the wave of the first post-extrasystolic contraction, blood flow accelerates and reflected waves and standing waves form. These hemodynamic changes are characterized by the term hydraulic shock. The use of our original experimental model helps to make the wide range of investigations and studies connected with intra-arterial hemodynamics in different conditions of functioning of cardiovascular system.

Effect of hydrogel particle mechanical properties on their disintegration behavior using a gastric digestion simulator

The interest in designing novel foods whose digestibility can be controlled based on life stage and health conditions continues to grow. Physical digestion is important for solid foods as their breakdown and resulting size reduction can promote enzymatic reactions. Our human gastric digestion simulator (GDS) enables the simulation and direct observation of food particle disintegration induced by simulated antrum contraction waves. The objectives of this study were to verify the disintegration performance of the GDS compared with previously reported in vivo data and evaluate the effects of the mechanical properties of hydrogel particles on their in vitro gastric disintegration behavior. Agar beads with four fracture forces were prepared and mixed with meal containing locust bean gum to adjust viscosity same as their in vivo data. The half residence time of intact beads was longer for hard agar beads than for soft agar beads, and a similar disintegration trend to in vivo data was obtained. Moreover, as solid food models, 5-mm hydrogel cubes with different fracture stresses and fracture strains were prepared by varying the agar and native type gellan gum concentrations. The hydrogel cubes disintegrated because of fracture and abrasion during in vitro gastric digestion in the presence of simulated antrum contraction waves. The degree of hydrogel cube disintegration was affected by their fracture strain rather than their fracture stress and was suppressed when their fracture strain was greater than 30%. Our findings may provide a better understanding of the gastric digestion behavior of solid foods with different mechanical properties.

Myosin heavy chain isoforms in the myocardium of the atrioventricular junction of Scyliorhinus canicula (Chondrichthyes, Carcharhiniformes).

The atrioventricular junction of the fish heart, namely the segment interposed between the single atrium and the single ventricle, has been studied anatomically and histologically in several chondrichthyan and teleost species. Nonetheless, knowledge about myosin heavy chain (MyHC) in the atrioventricular myocardium remains scarce. The present report is the first one to provide data on the MyHC isoform distribution in the myocardium of the atrioventricular junction in chondrichthyans, specifically in the lesser spotted dogfish, Scyliorhinus canicula, a shark species whose heart reflects the primitive cardiac anatomical design in gnathostomes. Hearts from five dogfish were examined using histochemical and immunohistochemical techniques. The anti-MyHC A4.1025 antibody was used to detect differences in the occurrence of MyHC isoforms in the dogfish, as the fast-twitch isoforms MYH2 and MYH6 have a higher affinity for this antibody than the slow-twitch isoforms MYH7 and MYH7B. The histochemical findings show that myocardium of the atrioventricular junction connects the trabeculated myocardium of the atrium with the trabeculated layer of the ventricular myocardium. The immunohistochemical results indicate that the distribution of MyHC isoforms in the atrioventricular junction is not homogeneous. The atrial portion of the atrioventricular myocardium shows a positive reactivity against the A4.1025 antibody similar to that of the atrial myocardium. In contrast, the ventricular portion of the atrioventricular junction is not labelled, as is the case with the ventricular myocardium. This dual condition suggests that the myocardium of the atrioventricular junction has two contraction patterns: the myocardium of the atrial portion contracts in line with the atrial myocardium, whereas that of the ventricular portion follows the contraction pattern of the ventricular myocardium. Thus, the transition of the contraction wave from the atrium to the ventricle may be established in the atrioventricular segment because of its heterogeneous MyHC isoform distribution. The findings support the hypothesis that a distinct MyHC isoform distribution in the atrioventricular myocardium enables a synchronous contraction of inflow and outflow cardiac segments in vertebrates lacking a specialized cardiac conduction system.

Understanding the Biology of Human Interstitial Cells of Cajal in Gastrointestinal Motility

Millions of patients worldwide suffer from gastrointestinal (GI) motility disorders such as gastroparesis. These disorders typically include debilitating symptoms, such as chronic nausea and vomiting. As no cures are currently available, clinical care is limited to symptom management, while the underlying causes of impaired GI motility remain unaddressed. The efficient movement of contents through the GI tract is facilitated by peristalsis. These rhythmic slow waves of GI muscle contraction are mediated by several cell types, including smooth muscle cells, enteric neurons, telocytes, and specialised gut pacemaker cells called interstitial cells of Cajal (ICC). As ICC dysfunction or loss has been implicated in several GI motility disorders, ICC represent a potentially valuable therapeutic target. Due to their availability, murine ICC have been extensively studied at the molecular level using both normal and diseased GI tissue. In contrast, relatively little is known about the biology of human ICC or their involvement in GI disease pathogenesis. Here, we demonstrate human gastric tissue as a source of primary human cells with ICC phenotype. Further characterisation of these cells will provide new insights into human GI biology, with the potential for developing novel therapies to address the fundamental causes of GI dysmotility.

Contraction waves in self-oscillating polymer gels

As one type of active soft matter, polymer gels coupled mechanical and chemical oscillations, such as Belousov–Zhabotinsky (BZ) gels are widely researched and developed into biomimetic actuators. In the previous literature, the self-oscillating BZ cylindrical gels can generate swelling waves along their longitudinal direction when they are operated without external stimuli. Here, we explore the contraction waves of BZ gels by the means of changing the external mechanical boundary. We firstly synthesize the self-oscillating gel, which is composed of N-isopropyl acrylamide (NIPAAm) gel and a covalently bound metal catalyst of the ruthenium complex. Then, the stress-curve of the gels is investigated to evaluate the elastic modulus of each state of the BZ gel and verified our method. Finally, we investigate the effects of several factors including initial diameters of the gel, various strain, and measuring process on the generation of contraction waves in gels undergoing the BZ reaction by experiments.

Effect of electroacupuncture of "Hegu" (LI4) and "Zusanli" (ST36) on intestinal sensitivity and motility in irritable bowel syndrome rats

To observe the effect of electroacupuncture (EA) of "Hegu"(LI4) and "Zusanli"(ST36)on changes of intestinal sensitivity and colonic motility and expression of colonic 5-hydroxytryptamine 3A receptor (5-HT3AR) in irritable bowel syndrome (IBS) rats, so as to reveal its mechanism underlying improvement of IBS. A total of 40 neonatal Wistar rats were randomly and equally divided into normal control, model, LI4 and ST36 groups (n＝10). The IBS model was induced by mother-infant separation, acetic acid enema and colorectal distension (CRD). EA (2 Hz/100 Hz, a tolerable strength) was applied to bilateral LI4 and ST36 for 20 min, once every other day for 5 times. The Bristol stool form scale was used to assess the gastrointestinal function, and the latency and number of abdominal muscular contraction waves of abdominal withdrawal reflex (AWR) were used to evaluate the intestinal sensitivity and motility respectively. The immunoactivity of 5-HT3AR of the colon tissue was detected by immunohistochemistry. After modeling, the score of Bristol fecal form scale, number of muscular contraction waves and expression levels of colonic 5-HT3AR in the myometrium and mucosal layers were significantly increased (P<0.01), and the latency of muscular initial contraction wave was obviously shortened in the model group relevant to the normal control group (P<0.01). After the intervention, the increased Bristol fecal form score, number of muscular contraction waves and expression levels of 5-HT3AR in the myometrium and mucosal layers as well as the decreased latency of muscular contraction were reversed in both LI4 and ST36 groups (P<0.01, P<0.05). The effect of EA of ST36 was significantly superior to those of EA-LI4 in lowering Bristol fecal scale score and 5-HT3AR expression in the muscular layer (P<0.01), but obviously inferior to those of EA-LI4 in increasing the latency of of muscular initial contraction wave and down-regulating muscular contraction waves and 5-HT3AR expression in the mucosal layer (P<0.05, P<0.01). Both EA-LI4 and EA-ST36 can significantly improve the symptoms of abdominal pain and diarrhea, but EA-LI4 is better in suppressing intestinal high sensitivity, and EA-ST36 is better in promoting intestinal motility, suggesting a specificity of effect of acupoints of different meridians.

On a coupled electro-chemomechanical model of gastric smooth muscle contraction

The stomach is a central organ in the gastrointestinal tract that performs a variety of functions, in which the spatio-temporal organisation of active smooth muscle contraction in the stomach wall (SW) is highly regulated. In the present study, a three-dimensional model of the gastric smooth muscle contraction is presented, including the mechanical contribution of the mucosal and muscular layer of the SW. Layer-specific and direction-dependent model parameters for the active and passive stress-stretch characteristics of the SW were determined experimentally using porcine smooth muscle strips. The electrical activation of the smooth muscle cells (SMC) due to the pacemaker activity of the interstitial cells of Cajal (ICC) is modelled by using FitzHugh-Nagumo-type equations, which simulate the typical ICC and SMC slow wave behaviour. The calcium dynamic in the SMC depends on the SMC membrane potential via a gaussian function, while the chemo-mechanical coupling in the SMC is modelled via an extended Hai-Murphy model. This cascade is coupled with an additional mechano-electrical feedback-mechanism, taking into account the mechanical response of the ICC and SMC due to stretch of the SW. In this way the relaxation responses of the fundus to accommodate incoming food, as well as the typical peristaltic contraction waves in the antrum for mixing and transport of the chyme, have been well replicated in simulations performed at the whole organ level. Statement of SignificanceIn this article, a novel three-dimensional electro-chemomechanical model of the gastric smooth muscle contraction is presented. The propagating waves of electrical membrane potential in the network ofinterstitial cells of Cajal (ICC) and smooth muscle cells (SMC) lead to a global pattern of change in the calciumdynamics inside the SMC. Taking additionally into account the mechanical response of the ICC and SMC due to stretch of the stomach wall, also referred to as mechanical feedback-mechanism, the result is a complex spatio-temporal regulation of the active contraction and relaxation of the gastric smooth muscle tissue. Being a firstapproach, in future view such a three-dimensional model can give an insight into the complexload transferring system of the stomach wall, as well as into the electro-chemomechanicalcoupling process underlying smooth muscle contraction in health and disease.

Coherent Capillary Wave Structure Revealed by ISS Experiments for Spontaneous Nozzle Jet Disintegration

A series of International Space Station (ISS) experiments were conducted to observe the disintegration feature of a water jet issued from an orifice/nozzle into atmospheric air. The purpose was to validate our proposal that any laminar liquid jet can spontaneously disintegrate by its own self-destabilizing loop formed along the jet. This paper reports the experiment results focusing on a water jet issued from a nozzle with a radius 0.4 mm and length 120 mm, in which the parabolic velocity profile relaxes toward that of a plug flow along the jet. As predicted in our proposal, the nozzle jet had a two-valued breakup distance in a certain jet issue speed range and exhibited hysteresis behaviors, indicating that the jet disintegration state is determined by past jet disintegration history. Analyses of video images suggest the establishment of a coherent capillary wave structure in the steady jet disintegration state. New fundamental theories were developed to examine the underlying physics involved. The short-length breakup mode was confirmed to essentially follow the same self-destabilizing mechanism as that of the plug flow jet, in which the upstream propagating capillary wave produced by the release of surface energy due to jet tip contraction or nonlinear unstable wave growth is reflected at the orifice, and becomes the unstable wave responsible for jet disintegration. In the long-length breakup mode, the velocity profile relaxation plays a role equivalent to an orifice and the average nozzle jet length is expressed as the sum of the velocity profile relaxation length and average orifice jet length at large jet issue speeds. This paper focuses on the coherent capillary wave structure of long-length breakup mode.

Peristaltic flow of Buongiorno model nanofluids within a sinusoidal wall surface used in drug delivery

AbstractThe current paper deals with the radiative heat transfer of the peristaltic flow of the Buongiorno model nanofluid through a two‐dimensional channel with a sinusoidal wall surface. A particular form of fluid transport occurring through progressive wave of expansion or contraction generating along a distensible tube containing fluid is known as peristaltic pumping, which takes place from the lower pressure region to the higher pressure region. Peristaltic transport finds several applications, such as blood pumping in heart, lung, and pharmacological delivery systems, and industrial applications—sanitary fluid transport, corrosive fluids transport, and so on. An approximate analytical solution is employed for the solution of the system of transformed differential equations with prescribed boundary conditions. The influences of physical parameters characterizing the flow phenomena are obtained and presented via graphs. The result warrants a good correlation with earlier studies in particular case. The following are the main findings: thermophoresis is favorable to enhance the fluid temperature near the channel center and also the axial velocity increases as an increase in the thermal buoyancy parameter. However, the main findings are elaborated in Section 3.

A myogenic motor pattern in mice lacking myenteric interstitial cells of Cajal explained by a second coupled oscillator network.

The interstitial cells of Cajal associated with the myenteric plexus (ICC-MP) are a network of coupled oscillators in the small intestine that generate rhythmic electrical phase waves leading to corresponding waves of contraction, yet rhythmic action potentials and intercellular calcium waves have been recorded from c-kit-mutant mice that lack the ICC-MP, suggesting that there may be a second pacemaker network. The gap junction blocker carbenoxolone induced a "pinstripe" motor pattern consisting of rhythmic "stripes" of contraction that appeared simultaneously across the intestine with a period of ~4 s. The infinite velocity of these stripes suggested they were generated by a coupled oscillator network, which we call X. In c-kit mutants rhythmic contraction waves with the period of X traveled the length of the intestine, before the induction of the pinstripe pattern by carbenoxolone. Thus X is not the ICC-MP and appears to operate under physiological conditions, a fact that could explain the viability of these mice. Individual stripes consisted of a complex pattern of bands of contraction and distension, and between stripes there could be slide waves and v waves of contraction. We hypothesized that these phenomena result from an interaction between X and the circular muscle that acts as a damped oscillator. A mathematical model of two chains of coupled Fitzhugh-Nagumo systems, representing X and circular muscle, supported this hypothesis. The presence of a second coupled oscillator network in the small intestine underlines the complexity of motor pattern generation in the gut.NEW & NOTEWORTHY Physiological experiments and a mathematical model indicate a coupled oscillator network in the small intestine in addition to the c-kit-expressing myenteric interstitial cells of Cajal. This network interacts with the circular muscle, which itself acts as a system of damped oscillators, to generate physiological contraction waves in c-kit (W) mutant mice.