Systems and methods are provided for managing a time-shift buffer that is used for buffering video presentations. The heat exchange catheter is inserted into the esophagus and a cooled fluid is circulated within the catheter, cooling the esophagus, and by conduction, the heart. The resulting polyetherquinoxalines contain quinoxaline groups joined by ether linkages at the 2 and 3 positions of the quinoxaline groups.