MANOMETRIC AND ELECTROMYOGRAPHIC OBSERVATIONS OF THE OESOPHAGUS OF SHEEP IN ERUCTATION, REGURGITATION AND SWALLOWING

¹ Department of Physiology and Anatomy, Massey University, Palmerston North New Zealand
² Veterinary Research Institute, Parkville, Vic., 3052, Australia
³ Department of Veterinary Physiology, University of Sydney, Sydney, 2006, Australia

Manometric and electromyographic recordings during eructation, swallowing and the regurgitation of rumination in sheep revealed variable oesophageal activity during eructation in contrast to the uniform pattern of oesophageal activity in swallowing and regurgitation. In eructation the passive increase in pressure of about 7-15 mmHg - the filling phase - associated with entry of gas into the oesophagus was commonly (in 96·6% of thirty eructations) terminated by contractions in the caudal thoracic oesophagus (c.t.o.). Eructation contractions were present in 73·3% of thirty eructations in a site 130 mm cranial to the c.t.o. and in 36·6% of thirty eructations in a site 260 mm cranial to the c.t.o. These contractions moved cranially at about 420 mm.s^-1. In contrast during regurgitation the contractions of the oesophagus which moved cranially at about the same rate (410 mm.s^-1) were characteristically more intense (47-64 mmHg) than eructation contractions (10-36 mmHg). Also in contrast to those in eructation, regurgitation contractions were invariably of each site of the oesophagus from which recordings were made. Secondary contractions of the caudal cervical and thoracic oesophagus which sometimes followed eructation were interpreted as serving as clearing contractions returning residual gas in the oesophagus to the stomach. These swept over the oesophagus at about 200 mm.s^-1 and occurred without associated swallows. The variability of reactions of the oesophagus in eructation and differences in reactions of its different regions are discussed as arising from different degrees of sensitivity to, and stimulation by, gaseous distension of the oesophagus and stomach.

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