. Author manuscript; available in PMC: 2014 Aug 25.

Published in final edited form as: Gastrointest Endosc. 2010 Jun 25;72(3):587–592. doi: 10.1016/j.gie.2010.04.029

Table 2.

Endosonographic characteristics of the upper esophageal sphincter high-pressure zone divided into 3 zones

Zone^*	I	II	III
No. of layers (% participants)	4–5 (77)	4–5 (8)	3 (100)
	3 (23)	3 (92)
MMMT (mm)	2.9	2.9	2.4

MMMT, Mean maximal muscle thickness.

The number of muscle layers on cross-sectional imaging (percentage of participants with the number of muscle layers) and MMMT were tabulated according to muscle zones. Note that the proximal UES (zones II and III) demonstrates predominantly 3 muscle layers, whereas the distal UES (zone I) demonstrates 4 to 5 muscle layers, similar to the number of layers found at the body of the esophagus.

Zone I (esophago-UES); zone II (UES); and zone III (UES-pharyngeal).