Figure 6 - Esophageal pH (a), manometric pressure (b), and esophageal wall thickness (c) as measured by high-frequency intraluminal ultrasound.

The vertical line (pain) represents the onset of chest pain. Sustained esophageal contraction (SEC) measured as an increase in wall thickness precedes the episode of chest pain and is accompanied by an increase in intraluminal pressure (arrows). (Source: Balaban et al.,⁵⁵ with permission from American Gastroenterological Association.)