Gastroesophageal reflux disease can occur in the context of diminished LES pressure either by strain-induced or free reflux. Strain-induced reflux occurs when a hypotensive LES is overcome and "blown open" in association with an abrupt increase of intraabdominal pressure . Manometric data suggest that this rarely occurs when the LES pressure is greater than 10 mmHg , . It is also a rare occurrence in patients without hiatus hernia . Free reflux is characterized by a fall in intra-esopha-geal pH without an identifiable change in either intragastric pressure or LES pressure. Episodes of free reflux are observed only when the LES pressure is within 0-4 mmHg of intragastric pressure. A wide open or patulous hiatus will predispose to this free reflux as both the intrinsic and extrinsic sphincter are compromised.
A puzzling clinical observation, and one that supports the importance of transient LES relaxations, is that only a minority of patients with gastroesophageal reflux disease have a fasting LES pressure value of < 10 mmHg . This observation can be partially reconciled when one considers the dynamic nature of LES pressure. The isolated fasting measurement of
LES pressure is probably useful only for identifying patients with a grossly hypotensive sphincter; individuals constantly susceptible to stress and free reflux. However, there is probably a larger population of patients susceptible to strain induced or free reflux when their LES pressure periodically decreases as a result of specific foods, drugs, or habits (Table 1).
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