Distinct neural-mechanical efficiency of costal and crural diaphragm during hypercapnia.

Classic physiology suggests that the two distinct diaphragm segments, costal and crural, are functionally different. It is not known if the two diaphragm muscles share a common neural mechanical activation. We hypothesized that costal and crural diaphragm are recruited differently during hypercapnic stimulated ventilation, and the EMG recordings of the esophageal crural diaphragm segment does not translate to the same level of mechanical shortening for costal and crural segments In 30 spontaneously breathing canines, without confounding anesthetic, we measured directly electrical activity and corresponding mechanical shortening of both the costal and crural diaphragm, at room air and during increasing hypercapnia. During hypercapnic ventilation, the costal diaphragm showed a predominant recruitment over the crural diaphragm. The distinct mechanical contribution of the costal segment was not due to a different level of neural activation between the two muscles as measured by segmental EMG activity. Thus, the two diaphragm segments exhibited a significantly different neural-mechanical relationship.