Diaphragmatic electrical activity during controlled and assisted mechanical ventilation in conscious human subjects.

Breathing during mechanical ventilation was analyzed in 8 conscious healthy volunteers by application of intermittent positive pressure ventilation through a mouthpiece. In controlled mechanical ventilation (CMV), the respiratory rate and tidal volume were fixed at 110 and 120% of the subject's corresponding spontaneous breathing parameters. The diaphragmatic electromyogram (EMGdi) decreased significantly but become synchronous with the rhythm of the CMV. In assisted mechanical ventilation (AMV), the EMGdi response developed prior to and during the inspiratory phase of AMV. Application of an unexpected mechanical breath elicited the EMGdi. As the triggering sensitivity was decreased, the EMGdi prior to and during a mechanical breath was augmented, however, its rate of rise was unaffected. Our results suggest that the EMGdi during mechanical ventilation in conscious subjects is initiated by the respiratory center, however, this activity is modulated strongly by input from the pulmonary afferents and from the cerebral cortex.