 More than 300,000 Americans experience out-of-hospital cardiac arrest annually, with overall survival rates averaging less than 5. Low survival rates persist, in part, because manual chest compressions and ventilation, termed standard cardiopulmonary resuscitation S-CPR, is an inherently inefficient process, providing less than 25 of normal blood flow to the heart and the brain. Hemodynamics are often compromised further by poor S-CPR techniques, especially inadequate chest compression and incomplete chest recoil. Active Compression Decompression CPR ACD-CPR is performed with a hand-held device that is attached to the patients chest, and also includes a handle containing a metronome and force gauge to guide proper compression rate, depth and complete chest wall recoil. The impedance threshold device ITD is designed for rapid connection to an airway adjunct e.g. facemask or endotracheal tube and allows for positive pressure ventilation, while also impeding passive inspiratory gas exchange during chest wall decompression. Prior studies have shown that the combination of ACD-CPR ITD enhances refilling of the heart after each compression by augmenting negative intrathoracic pressure during the decompression phase of CPR, resulting in improved cardiac and cerebral perfusion. The intrathoracic pressure regulator ITPR is a next generation inspiratory impedance therapy. The ITPR uses a regulated external vacuum source to lower the negative intrathoracic pressure and is therefore less dependent on the quality of CPR e.g., completeness of chest wall recoil. The ITPR generates a pre-set continuous and controlled expiratory phase negative intrathoracic pressure that is interrupted only when positive pressure ventilation is needed to maintain oxygenation and provide gas exchange. 