The current definition of postural orthostatic tachycardia syndrome (POTS) dates back to a small case series of patients with a subacute illness who presented with excessive orthostatic tachycardia and orthostatic intolerance, in the absence of another recognized disease.

Abstract-Long-term nocturnal hemodialysis, which uses longer and more frequent sessions than conventional hemodialysis, lowers clinic blood pressure and left ventricular mass. We tested the hypotheses that short-term nocturnal hemodialysis would (1) reduce ambulatory blood pressure; (2) cause peripheral vasodilation; (3) lower plasma norepinephrine concentration; and (4) improve the arterial response to reactive hyperemia (a marker of endotheliumdependent vasodilation). We studied 18 consecutive patients (age, 41Ϯ2; [meanϮSEM]) before and 1 and 2 months after conversion from conventional (three 4-hour sessions per week) to nocturnal (six 8-hour sessions per week) hemodialysis. As the dialysis dose per session (Kt/V) increased from 1.24Ϯ0.06 to 2.04Ϯ0.08 after 2 months (Pϭ0.02), symptomatic hypotension developed and most antihypertensive medications were withdrawn. Nocturnal hemodialysis nonetheless lowered 24-hour mean arterial pressure (from 102Ϯ3 to 90Ϯ2 mm Hg after 2 months; Pϭ0.01), total peripheral resistance (from 1967Ϯ235 to 1499Ϯ191 dyne · s · cm Ϫ5; PϽ0.01) and plasma norepinephrine (from 2.66Ϯ0.4 to 1.96Ϯ0.2 nmol; Pϭ0.04). Endothelium-dependent vasodilation could not be elicited during conventional hemodialysis (Ϫ2.7Ϯ1.8%) but was restored (ϩ8.0Ϯ1.0%; Pϭ0.001) after 2 months of nocturnal hemodialysis. The brachial artery response to nitroglycerin also improved (from 6.9Ϯ2.8 to 15.7Ϯ1.6%; PϽ0.05). Nocturnal hemodialysis had no effect on weight or on stroke volume. Rapid reversal of these markers of adverse cardiovascular events with more intense hemodialysis may translate into improved outcome in this high-risk group of patients.