The Contribution of the Diaphragm and an Intrinsic Sphincter to the Gastroesophageal Antireflux Barrier: An Experimental Study in the Dog

Abstract

The components of the mechanical gastroesophageal antireflux barrier were studied in anesthetized dogs (15–18.5 kg). Pressure in the gastroesophageal junction area was recorded by pull-through manometry (using an infused end-hole-provided catheter) during gastric filling (distension) with water. in addition, the gastric volume at which reflux occurred was used as a measure of function and competence. Each dog was studied while intact and spontaneously breathing, after muscle relaxation, after excision of the left half of the diaphragm, and after death. in the intact dogs a barrier with a mean resting pressure of 20 (range, 14–26) cm H₂O was recorded. During gastric filling the barrier pressure initially increased to 32 (16–42) cm H₂O before steadily decreasing until reflux occurred. the highest pressure was recorded with 625 ml (250–1500 ml) in the stomach. Reflux occurred at a gastric volume of 3200 ml (2300–4000 ml). Muscle relaxation changed neither resting pressure nor reflux volume significantly. After excision of the left half of the diaphragm a barrier with a resting pressure of 15 (6–22) cm H₂O was still recorded. Reflux then occurred at a gastric volume of 1400 ml (500–2500 ml). in dead dogs no pressure barrier could be recorded, and reflux was provoked already by 500 ml (250–750 ml) in the stomach. the presence of a mechanical barrier also after excision of the left half of the diaphragm, as evidenced by both pressure and reflux volume, can only be explained by an intrinsic sphincter, a lower esophageal sphincter (LES). However, the experiments also showed that the diaphragm contributed to the competence of the LES. This contribution was at first passive.

Key Words:

• Dog
• diaphragm
• lower esophageal sphincter
• manometry