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

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