Synchrony between circular and longitudinal muscle contractions during peristalsis in normal subjects.
ABSTRACT The current understanding is that longitudinal muscle contraction begins before and outlasts circular muscle contraction during esophageal peristalsis in normal subjects. The goal of our study was to reassess the relationship between the contractility of two muscle layers using novel ways to look at the muscle contraction. We studied normal subjects using synchronized high-frequency ultrasound imaging and manometry. Swallow-induced peristalsis was recorded at 5 and 10 cm above the lower esophageal sphincter (LES). Ultrasound (US) images were analyzed for muscle cross-sectional area (CSA) and circularity index of the esophagus during various phases of esophageal contraction. A plot of the M mode US image, muscle CSA, and esophageal circularity index was developed to assess the temporal correlation between various parameters. The muscle CSA wave began before and lasted longer than the contraction pressure wave at both 5 and 10 cm above the LES. M mode US images revealed that the onset of muscle CSA wave was temporally aligned with the onset of lumen collapse. The peak muscle CSA occurred in close proximity with the peak pressure wave. The esophagus started to become more circular (decrease in circularity index) with the onset of the muscle CSA wave. The circularity index and muscle CSA returned to the baseline at approximately the same time. In conclusion, the onset of lumen collapse and return of circularity index of the esophagus are likely to be the true markers of the onset and end of circular muscle contraction. Circular and longitudinal muscle layers of the esophagus contract in a precise synchronous fashion during peristalsis in normal subjects.
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ABSTRACT: The muscularis propria of the esophagus is organized into circular and longitudinal muscle layers. The function of the longitudinal muscle and its role in bolus propulsion are not clear. The goal of this review is to summarize what is known of the role of the longitudinal muscle in health, as well as in sensory and motor disorders of the esophagus. Simultaneous manometry and ultrasound imaging reveal that, during peristalsis, the two muscle layers of the esophagus contract in perfect synchrony. On the contrary, during transient lower esophageal sphincter (LES) relaxation, longitudinal muscle contracts independent of the circular muscle. Recent studies have provided novel insights into the role of the longitudinal muscle in LES relaxation and descending relaxation of the esophagus. In certain diseases (e.g. some motility disorders of the esophagus), there is discoordination between the two muscle layers, which likely plays an important role in the genesis of dysphagia and delayed esophageal emptying. There is close temporal correlation between prolonged contractions of the longitudinal muscles of the esophagus and esophageal 'angina-like' pain. Novel techniques to record longitudinal muscle contraction are reviewed. Longitudinal muscles of the esophagus play a key role in the physiology and pathophysiology of esophageal sensory and motor function. Neuro-pharmacologic controls of circular and longitudinal muscle are different, which provides an opportunity for the development of novel pharmacological therapies in the treatment of esophageal sensory and motor disorders.Current opinion in gastroenterology 07/2013; 29(4):421-30. · 4.33 Impact Factor
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ABSTRACT: Little is known about the architecture of the vagal motor units that control esophageal striated muscle, in spite of the fact that these units are necessary, and responsible, for peristalsis. The present experiment was designed to characterize the motor neuron projection fields and terminal arbors forming esophageal motor units. Nucleus ambiguus compact formation neurons of the rat were labeled by bilateral intracranial injections of the anterograde tracer dextran biotin. After tracer transport, thoracic and abdominal esophagi were removed and prepared as whole mounts of muscle wall without mucosa or submucosa. Labeled terminal arbors of individual vagal motor neurons (n=78) in the esophageal wall were inventoried, digitized and analyzed morphometrically. The size of individual vagal motor units innervating striated muscle, throughout thoracic and abdominal esophagus, averaged 52 endplates per motor neuron, a value indicative of fine motor control. A majority (77%) of the motor terminal arbors also issued one or more collateral branches that contacted neurons, including nitric oxide synthase-positive neurons, of local myenteric ganglia. Individual motor neuron terminal arbors co-innervated, or supplied endplates in tandem to, both longitudinal and circular muscle fibers in roughly similar proportions (i.e., two endplates to longitudinal for every three endplates to circular fibers). Both the observation that vagal motor unit collaterals project to myenteric ganglia and the fact that individual motor units co-innervate longitudinal and circular muscle layers are consistent with the hypothesis that elements contributing to peristaltic programming inhere, or are "hardwired," in the peripheral architecture of esophageal motor units.Autonomic neuroscience: basic & clinical 08/2013; · 1.82 Impact Factor
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ABSTRACT: Myogenic tone has long been recognised as an important component of gastrointestinal motility. Recent work has clarified the cellular mechanisms that engender tone and the neurogenic and mechanical stimuli that modulate it but has also highlighted cellular and regional specialisation in these mechanisms within the GI tract. Smooth muscle in all segments of the gut has the capability of latching, i.e. can generate ongoing specific rather than tetanic tone. This is likely modulated by both direct and indirect input from agonists such as acetylcholine and mechanoreceptors, the latter originating in ICC-IM, smooth muscle cells or elements of the ENS. Tonic contraction can occur in the absence of phasic contractions or concurrent with them, and it can modulate wall compliance and the capacity of particular segments, thereby affecting the level of on-flow and mixing, both luminal and adjacent to the mucosa. The review seeks to provide an overview of our understanding of the mechanism by which tone is generated and maintained, highlighting its modulation by neurogenic and mechanical stimuli, its mechanical consequences in the walls of the various segments of the gastrointestinal tract and its contribution to flow and mixing of contained digesta.Neurogastroenterology and Motility 09/2013; · 2.94 Impact Factor