Fig. 2.

Changes in heart rate (HR) and systolic blood pressure (BP) in all postural tachycardia syndrome (POTS) and control subjects. Change in heart rate (ΔHR) with standing (A) and change in systolic BP (ΔBP) (B) in all POTS with or without initial orthostatic hypotension (IOH; all POTS, solid line) and all controls with or without IOH (all control, dashed line). All events after minimum BP (BP_min) occurred later in POTS than in controls. Only the minimum decrease in systolic BP was significantly lower in POTS. HR_{½ min}, midway point between peak HR (HR_max) and minimum HR (HR_min).