Lower Esophageal Sphincter Mechanics: Anatomic and Physiologic Relationships of the Esophagogastric Junction of Cat

Abstract

The in vivo lower esophageal sphincter was identified in cats, using a pressure measuring probe with a perfused side opening adjacent to a metal plug obstructing the distal tip. A suture was placed, under fluoroscopy, at the point of highest pressure. The esophagus and stomach were removed and mounted on a wax block. Consecutive rings were cut from the lower esophageal sphincter region, with blades held in a block 1.75 mm apart, and mounted in a muscle bath. Force-length curves were obtained in standard Tyrode solution, in Tyrode with high KCl, and in calcium-free Tyrode with ethylenediaminetetraacetic acid disodium salt to determine basal, total, and passive forces respectively. Active force was obtained as the difference between total and passive force. The ring identified by the suture is located immediately above the squamocolumnar junction. It exhibits the steepest basal force-length curve. The ring also exhibits the highest active and total force under maximal KCl stimulation. The passive force of this ring is the same as for esophageal rings. It is concluded that the highest pressure point in the in vivo lower esophageal sphincter occurs where circular muscle is capable of generating the highest basal, active, and total force. The higher active forces observed at the in vivo high pressure point, however, are due to a thickening of the circular muscles, while the higher basal forces are partly due to increased ability to generate stress (force per unit area of muscle) in the basal state.