Crural and costal diaphragm function during emesis.

Abstract

Background: Together the costal and crural diaphragm constitute the primary respiratory muscle in mammals, but functionally they are distinct. The crural segment has additional gastrointestinal function, wrapped around the esophagus at the esophagogastric junction, contributing to the esophageal sphincter. Emesis is an expulsive process that requires coordinated action of multiple muscles to rapidly force out gastric contents. Objective: The simultaneous mechanical action and neural activation of the diaphragm segments during the process of emesis, especially expulsion, is uncertain. Detailed divergence of the crural diaphragm to sphincter function during emesis has not been studied. Methods: In 6 awake, spontaneously breathing canines, electrical activity and corresponding muscle shortening of costal and crural diaphragm were measured at five phases of emesis (rest, early prodrome, mid prodrome, late prodrome, expulsion) induced by apomorphine. Results: Overall, baseline muscle length decreased and baseline EMG increased progressively from rest through prodrome for both costal and crural, but at expulsion, the crural segment diverged, lengthening abruptly. Shortening and EMG activity per breath for costal changed slightly throughout emesis; crural shortening and EMG activity increased abruptly at expulsion. The divergent action of crural during expulsion developed sequentially through each breath. Also, neuromechanical coupling of the segments reversed at expulsion, with contractility of the crural surpassing that of the costal. Conclusion: These measurements confirm a disparate action of crural diaphragm, compared to costal, to facilitate expulsion. During the process of emesis, while the costal persists as an obligatory respiratory muscle, the crural converts from respiratory muscle to opening sphincter.