Fig. 4. Core temperatures during and after cardiopulmonary bypass for patients participating in the nitroprusside protocol. The beginning of bypass cooling was designated time zero for cooling. Because the duration of cooling differed among patients, a second zero time was defined as the beginning of rewarming. Similarly, the end of rewarming identified time zero for the postbypass period. (Filled circles) Patients undergoing vasodilation with sodium nitroprusside. (Open circles) Control patients. Data are presented as the mean ± SD; see table 4for statistical analysis.