Motor control of the diaphragm in anesthetized rabbits

Diaphragmatic regions are recruited in a specialized manner either as part of a central motor program during non-respiratory maneuvers, e.g. vomiting, or because of reflex responses, e.g. esophageal distension. Some studies in cats and dogs suggest that crural and costal diaphragm may be differentially activated also in response to respiratory stimuli from chemoreceptors or lung and chest wall mechanoreceptors. To verify whether this could occur also in other species, the EMG activity from the sternal, costoventral, costodorsal, and crural diaphragm was recorded in 42 anesthetized rabbits in response to various respiratory maneuvers, such as chemical stimulation, mechanical loading, lung volume and postural changes before and after vagotomy, or a non-respiratory maneuver such as esophageal distension. Regional activity was evaluated from timing of the raw EMG signal, and amplitude and shape of the moving average EMG. In all animals esophageal distension caused greater inhibition of the crural than sternal and costal diaphragm, whereas under all the other conditions differential diaphragmatic activation never occurred. These results indicate that in response to respiratory stimuli the rabbit diaphragm behaves as a single unit under the command of the central respiratory control system.