Comparison of the Quality of Chest Compressions between CPR Performed by a Single Trained Rescuer and Two Rescuer CPR Performed by a Trained Rescuer and an Untrained Rescuer in a Prolonged Out-of-Hospital CPR Scenario Young Hoon Park, M.D., Kyung Woon Jeung, M.D., Ph.D., Young Hoe Hur, M.D.1, Byung Kook Lee, M.D., Hyun Ho Ryu, M.D., Jong Geun Yun, E.M.T.P.2, Geon Nam Kim, E.M.T.P., Tag Heo, M.D., Ph.D., Yong Il Min, M.D., Ph.D. Purpose: The aim of this study is to compare the quality of chest compressions between cardiopulmonary resuscitation (CPR) performed by a single trained rescuer and two rescuer CPR performed by a trained rescuer and an untrained rescuer in a prolonged out-of-hospital CPR scenario. Methods: For the phase I experiment, thirty-six emergency medical technician students (trained rescuers) were asked to perform 10 minutes of lone rescuer CPR on an instrumented manikin. For the phase II experiment, thirty-six volunteers with no previous CPR training