Esophageal pH is recorded from a point 5cm above the lower esophageal sphincter.
However, the mucosal changes of reflux esophagitis and intestinal metaplasia affect the segment of esophagus close to the squamocolumnar junction.
In this study, physicians from Glasgow, Scotland, assessed esophageal acid exposure of squamous mucosa close to the squamocolumnar junction.
The team performed dual channel 24-hour pH monitoring in 11 patients with endoscopy negative dyspepsia and no evidence of GERD.
Esophageal pH was recorded from electrodes positioned 5mm and 55mm proximal to the squamocolumnar junction. The team developed a technique which allowed them to secure the pH catheter to the esophageal mucosa and maintain the electrode positions.
Esophageal manometry indicated that the distal electrode was within the high pressure zone of the lower esophageal sphincter.
The physicians found that 24-hour esophageal acid exposure (% time pH < 4) was greater 5mm above the squamocolumnar junction, compared with the conventional position.
They also determined that this exposure was significantly greater in both the upright and supine positions, as well as during preprandial and postprandial periods.
The number of reflux events recorded close to the squamocolumnar junction was also higher than for the conventional position (168 versus 33).
The team did not identify any correlation between acid exposure at the 2 sites.
Dr Fletcher's team concluded, "The squamous mucosa of the most distal esophagus is exposed to substantial acidic reflux, even in patients without evidence of conventional reflux disease".
"This short segment reflux may explain the high incidence of metaplasia and neoplasia at the gastro-esophageal junction".