Diaphragmatic and oesophageal activity in regurgitation in sheep: an electromyographic study

1. Electromyographic (e.m.g.) recordings of reactions of the oesophagus, vertebral and costal fibres of the diaphragm and from the reticulum-one of the cranial divisions of the stomach were made during the regurgitation of rumination in sheep. 2. E.m.g.s indicated that a contraction of the caudal thoracic oesophagus developed over a period of about 2 sec before, and ceased at the time of, the more forceful inspiratory effort associated with regurgitation. 3. This contraction was confined to the caudal region of the thoracic oesophagus in which it was characteristically more prolonged and intense in its most caudal part within 15-25 mm of the hiatus oesophageus. It is interpreted to contribute to development or intensification of a caudal thoracic oesophageal sphincter. 4. The more forceful inspiratory effort at the time of regurgitation was due to costal fibres of the diaphragm. Although active normally during inspiration the vertebral fibres of the hiatus oesophageus do not contribute to this more forceful inspiration. This may facilitate regurgitation of digesta. Similarly, inactivity of vertebral but not costal fibres detected during primary oesophageal contractions (of swallowing) may make for easier passage of digesta into the stomach.