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Figure 1 Computer output of beat-to-beat RR intervals and invasive systolic blood pressure (SAP) during phenylephrine tests in the baseline (left upper panel) and during balloon occlusion (right upper panel) of a 90% stenosis in left anterior descending coronary artery in a 58-year-old male patient. The lower panels show respective baroreflex slopes derived from the time windows shown by broken vertical lines in the upper panels. In this case, coronary occlusion (hatched bars, right upper panel) causes a mild, progressive bradycardia already before the phenylephrine bolus. Phenylephrine bolus (150 µg) causes a rise in systolic blood pressure, but at the end of the coronary occlusion RR intervals suddenly shorten despite continuing pressure rise. Baroreflex sensitivity could not be calculated because of the loss of linear relationship between the RR intervals and the preceding systolic blood pressure values despite adequate blood pressure reaction during coronary occlusion in 13 patients.