Stage 1 of the study is acute in nature, such that subjects will undergo the placement of a stimulation lead, followed by assessment of stimulation of the phrenic nerve using the lead for up to 2 nights of sleep. A sensing lead may also be placed during the initial implant procedure. Observational data will be obtained and stimulation provided using an externalized system connected to the study leads. Following the study, all investigational components will be removed from the patient.