An early feasibility study to investigate the safety and feasibility of the Lungpacer Diaphragm Pacing Therapy System (DPTS) as a therapy to recondition and strengthen the diaphragm of patients who have been intubated and invasively mechanically ventilated for > or = 7 days, have failed two or more spontaneous breathing trials (SBT), and were not hypervolemic during the latest SBT.