Background:We investigated the hypothesis that the esophageal crus (EC, part of the crus surrounding the esophagus) is an “individual muscle” and does not share in the contractile activity of the costal diaphragm (CD).Material/Methods: The electric activities of the EC and the costal diaphragm (CD) were recorded in 21 subjects (12 men, 9 women, aged 41.6±10.4 years) scheduled for laparotomy. One needle electrode was introduced into the EC, one into each vertebral crus (VC), and one in the CD. Recording was performed before and after diaphragmatic paralysis by curarization. While the diaphragm was paralyzed, the responses of the EC and the 2 VCs to CD stimulation were registered.Results: The CD had significantly higher resting motor unit action potentials (MUAPs) than the EC and the 2 VCs (p<0.05), and the EC higher MUAPs than the 2 VCs (p<0.05). During diaphragmatic contraction on inspiration or by stimulation (5 square pulses, 1 ms apart, threshold 32.2±6.3 mA), the MUAPs of the CD increased significantly (p<0.01), while those of the EC or VCs exhibited no significant change (p<0.05).
Conclusions: The current findings suggest that the EC is an autonomous muscle which does not share in the contractile activity of the CD. The EC seems to be essentially involved in the competent mechanism of the lower esophagus and has no role in respiratory function.

Keywords: Abdominal Muscles - physiology, Diaphragm - physiology, Electrophysiology, Esophagus - physiology, Muscle Contraction - physiology, Respiratory Mechanics - physiology, Respiratory Paralysis - physiopathology, Abdominal Muscles - physiology, Diaphragm - physiology, Electrophysiology, Esophagus - physiology, Muscle Contraction - physiology, Respiratory Mechanics - physiology, Respiratory Paralysis - physiopathology