A shows individual values for systolic blood pressure (SBP) in patients with autonomic failure (AF, circles) and normal controls (NLS, triangles). At baseline, autonomic failure patients showed higher SBP values. They were subjected to graded head up tilt (Tilt) until a systolic blood pressure of about 110 mm Hg was reached, whereas autonomic blockade was induced in normal subjects with trimethaphan (TrMT). SBP were similar between groups after these interventions. The nitric oxide synthase inhibitor L-NMMA was then infused at increasing doses, individualized to reach a systolic blood pressure of 150 mm Hg. Panel B shows the cumulative total amount of L-NMMA required to increased systolic blood pressure to 150 mm Hg in autonomic failure patients (AF, gray bar) and normotensive controls (NLS, white bar).