Each year in the United States, out-of-hospital cardiac arrest (OHCA) causes an estimated 310,000 deaths before the patient reaches the hospital emergency department. Patients experiencing OHCA are given cardiopulmonary resuscitation (CPR), a combination of chest compressions, to keep oxygen-rich blood circulating to vital organs until an effective heartbeat is restored, and rescue breathing. CPR is performed manually or with a suction device placed on the chest to push it down and pull it up between compressions (active compression decompression). During decompression, some residual air fills the lungs and enters the chest cavity. This creates higher pressures within the chest, which prevents efficient return of blood flow to the heart and to the rest of the body. Since CPR has some limitations, and since the survival rate for OHCA is only about 5% to 10%, researchers have investigated methods to enhance CPR’s efficacy as a means to improve patient survival following OHCA.