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Figure 1 The relation between the changes in systolic blood pressure increase and corresponding RR interval lengthening observed in a 33-year old man during downward tilting. (A) Top and middle panels: electrocardiographic tracing of V5 lead and computed RR intervals. Bottom panel: arterial blood pressure (BP) recorded with tonometry. Arrows indicate the beginning and the end of downward tilting. (B) Plotting of corresponding RR interval against systolic blood pressure in this subject revealed a strong correlation (r = 0.95; p < 0.0001), yielding a baroreflex sensitivity value of 14.0 ms/mm Hg. ECG = electrocardiogram.