Apnea events may be detected based on a primary biomarker, e.g., respiration, in the one or more physiological signals. The apnea events may be characterized as one of an obstructive sleep apnea (OSA) event, a central sleep apnea (CSA) event, or a combination OSA/CSA event based on a secondary biomarker, e.g., a frequency spectrum or a morphology of the respirations in the one or more physiological signals. A first electrical stimulation may be provided to treat OSA in response to a first one or more of the apnea events being characterized as OSA events. A second electrical stimulation may be provided to treat CSA in response to a second one or more of apnea events being characterized as CSA events. A third electrical stimulation may be provided to treat combination OSA/CSA in response to a third one or more of the apnea events being characterized as combination OSA/CSA events.