THORACIC OESOPHAGEAL MOTOR ACTIVITY DURING ERUCTATION IN SHEEP

¹ Departments of Veterinary Physiology University of Sydney, Sydney, Australia, 2006
² Veterinary Clinical Studies, University of Sydney, Sydney, Australia, 2006

Concurrent radiographic and electromyographic observations were made in sheep during naturally occurring eructations. The radiographic field extended from the base of the heart to the cranial region of the rumen. Electromyographic recording was from two sites on the caudal thoracic oesophagus within 20-70 mm of the diaphragm. Passage of gas from the rumen into the oesophagus was followed by passive gaseous distension of the caudal thoracic oesophagus for period of 540-2860 ms (n = 80), at the end of which there was both electromyographic and radiographic evidence of oesophageal contraction. The pattern of radiographic change was indicative of a cranially progressing contraction of the thoracic oesophagus. Movements of the diaphragm observed radiographically during ventilation ceased (at the end of expiration), or became shallower, during the period of oesophageal distension. This resulted in a varying degree of interruption of the rhythm of ventilation. The first inspiration marking a return of ventilation to its former character was deeper than normal. The events during eructation were essentially similar whether the animals were eating, ruminating, or doing neither. When swallowing occurred during eructation it appeared to continue normally, interrupting the train of oesophageal reactions in eructation. Gas sometimes entered the caudal thoracic oesophagus after a mixing contraction of the reticulo-rumen but it was returned to the stomach by a caudally moving oesophageal contraction.