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The mechanical model of gastroesophageal reflux:
what are the most important factors in causing gastro-esophageal reflux?
S.S. Kadirkamanathan, D.F. Evans, C.P. Swain (London)
Gastroesophageal reflux (GER) may be regarded as a mechanical process which occurs when the forces promoting reflux overcome those contributing to the reflux barrier. Negative intrathoracic pressure (ITP) and positive elevation of intra-gastric and intra-abdominal pressures (IGP and IAP) tend to promote reflux [1, 2]. Factors contributing to the reflux barrier include the lower esophageal sphincter (LES) [3], the diaphragm or the crural sling [4], gastric sling fibres [5], the angle of His [6] and the esophageal mucosal "choke" [7].
Investigations measuring some of these reflux parameters have demonstrated that there is an overlap between patients who reflux and those who do not. For example, patients with gastroesophageal reflux disease (GERD) could not be separated from controls on the basis of their LES pressure [8]. Such discrepancies have made it difficult to study the contribution of each individual factor in the pathogenesis of reflux. Static manometric investigations cannot detect the physiological effects of trans-sphincteric pressure changes (Figure 1) that occur during normal activities such as breathing [9] and exercise [10], two factors which can often give rise to GER.
Figure 1. Pressure effects around gastroesophageal junction.
Because of difficulties in studying the role of multitude of factors influencing reflux systematically in patients, physical models have been designed to study reflux under controlled, experimental conditions which would be more difficult to simulate in man. Models offer the ability to perform large numbers of repeatable experiments to illustrate and explain the mechanics of reflux by controlled changes of the parameters known to influence GER.
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