Figure 1.

Average ANS (left) and HRV (right) responses from 5-minutes seated to a quick stand followed by 5 minutes of standing from the predosing test (test N). (Left) Sympathetic (LFa) and parasympathetic (RFa) measures, sympathovagal balance (SB = LFa/RFa), systolic BP, and mean HR. (Right) Normalized low- and high-frequency parameters (LFnu and HFnu, respectively), total spectral power (TSP), and range HR. Data represent results from patients presenting with orthostatic symptoms as evidenced by the average decrease in systolic BP (P < 0.0010). Midodrine was introduced following this test in this subpopulation of patients. See text for details.