Carbon Dioxide (CO2) Chemosensitivity and SUDEP

Inclusion Criteria: 1. The subject is between 18 and 99 years of age. 2. Confirmed or suspected epilepsy. 3. Admission to the EMU for spell characterization (EMU group) or undergoing care in the University of Iowa Health Care Epilepsy Clinic. Exclusion Criteria: 1. History of uncontrolled cardiac, pulmonary, or hepatic disease. 2. Progressive or uncontrolled neurologic disease unrelated to epilepsy. 3. Current opioid use. 4. Women of child-bearing potential who are pregnant or capable of becoming pregnant (e.g. sexual activity within the past 21 days without a highly effective form of birth control or positive urine pregnancy test). 5. Other comorbid condition that may influence the safety or feasibility of HCVR testing. 6. Limited decision-making capacity and absence of a qualified representative.