Oesophageal motor functions and its disorders
Authors: R K Mittal
Journal: Gut (2004)

he function of the oesophagus is relatively straightforward-to transport the swallowed food into the stomach.In order to meet this functional need, the design of the oesophagus is simple; a relatively straight muscular tube that is guarded at it two ends by the upper and lower oesophageal sphincters.Following a voluntary act of a swallow, the two sphincters relax and open and a contraction wave or peristalsis sweeps behind the bolus autonomously.The contraction wave sweeps through the entire length of the oesophagus followed by closure of the two sphincters.Neuromuscular control mechanisms that bring about normal functioning of the two sphincters and oesophageal peristalsis are complex and require fine coordination of the muscles and nerves at the level of the central and peripheral nervous system.Disturbance of sphincters and peristalsis causes symptoms of dysphagia and oesophageal pain.The latter may manifest either as chest pain (pressure-like sensation) or heartburn (retrosternal burning).The nature of dysfunction in oesophageal motor disorders has been the subject of intense investigation for several decades.In this paper, we will review briefly the physiology of oesophageal peristalsis and lower oesophageal sphincter and then attempt to understand what may be wrong in motor disorders of the oesophagus.Novel pharmacological approaches to treat oesophageal motor disorders are also discussed. PHYSIOLOGY OF OESOPHAGEAL PERISTALSIS AND LOWER OESOPHAGEAL SPHINCTER cThe anatomy of the oesophagus is unique; it is made up of skeletal muscle in the upper one third, a mixture of skeletal and smooth muscle in the middle one third, and smooth muscle only in the distal one third in humans.The upper oesophageal sphincter is composed of all skeletal muscle and the lower oesophageal sphincter of all smooth muscle.The muscularis propria of the oesophagus, similar to the rest of the gastrointestinal tract, is made of two distinct muscle layers that are arranged in a circular and longitudinal fashion.Topographical studies by Clouse and colleagues demonstrate that during peristalsis a segment, rather than a focal point in the oesophagus, is contracted at any given time. 1 2 The length of this contracted segment may extend over 15¡0.7 cm and the segment traverses through the length of the oesophagus in a peristaltic fashion.Pressure in the contracted segment is distributed in the shape of a bell-shaped curve with peak pressure in the middle of the contracted segment.Peak pressure in the contracted segment is located several centimetres behind the tail end of the bolus.Transition between skeletal and smooth muscle oesophagus is not seamless, as revealed by a trough in the amplitude of contraction in the transition zone.Similarly, the transition zone between the proximal and distal smooth muscle oesophagus shows lower contraction amplitude.It is suggested that the distal transition zone may be related to the type of neural innervation of the two segments of the oesophagus.The proximal smooth muscle oesophagus is under greater cholinergic control and the distal smooth muscle oesophagus under greater inhibitory control 3 but hard evidence to support this hypothesis is lacking.Peristalsis by definition means sequential contraction of the muscles along the length of the oesophagus.It is clear that similar to circular muscles, peristalsis also occurs in longitudinal muscle layers. 46][7] The difference in the timing of contraction of the two muscle layers observed in the reported studies may be related to the techniques that have been used to measure circular and longitudinal muscle contraction in these experiments.For example, circular muscle contraction recorded by manometery is delayed because manometery can only record contraction when the lumen of the oesophagus is totally collapsed on the manometery catheter.Our own observations suggest that there is perfect synchrony between the two muscle layers. 8Furthermore, a stronger circular muscle contraction is associated with a stronger longitudinal muscle contraction in normal subjects. 7 9Fine coordination between the two muscle layers provides significant biomechanical advantage to circular muscle contraction; longitudinal 1536