Figure 3. Raw traces of RR interval (solid line) and systolic blood pressure (SBP; dotted line) in two representative hypertensive patients receiving placebo (top) or clonidine (bottom). Data were recorded for 20 min at baseline (BL; left) and 3 h postoperatively (R3; right). In the recovery period, the placebo patient (B) exhibited a lower mean RR interval (tachycardia) compared with baseline values with little beat-to-beat variability ("fixed heart rate," solid line), whereas SBP was markedly more labile (dotted line). By contrast, postoperatively, the patient given clonidine (D) exhibited an increase in mean RR interval (relative bradycardia) compared with baseline values with preserved heart rate rapid fluctuations and relatively low variability of SBP.