A medical device system for comparing a cardiopulmonary signal to a brain signal. In one embodiment of the invention, a medical device system is provided that includes a brain monitoring element, respiratory monitoring element and a processor. The processor is configured to receive a brain signal from the brain monitoring element and a respiratory signal from the respiratory monitoring element. The processor is further configured to compare the brain signal to the respiratory signal. Methods of comparing a brain signal to a cardiopulmonary signal are also provided.