Fig. 2. Baroreflex control: Examples of baroreflex threshold diagrams for mean arterial pressure and cardiac interval ( A ) and diastolic arterial pressure and muscle sympathetic nerve activity (MSNA; B ). Independent variables were averaged in 2- to 3-mmHg intervals, and regression analyses were applied to the linear portion of each response curve. The X on each graph is located at the operating point for each variable, determined from the average of 10 cardiac cycles before injection of sodium nitroprusside.