BackgroundThe effects of midodrine on chronic hypotension in hemodialysis (HD) patients have not been well investigated.MethodsWe evaluated midodrine’s effect on autonomic function and hemodynamics in 12 HD patients who had chronic systolic blood pressure less than 100 mm Hg. Midodrine (5.0 mg) twice a day was given for 4 weeks. Another 12 age- and sex-matched HD patients with normotension were selected as a control group. Autonomic function tests included the heart-rate responses to the Valsalva maneuver and 30:15 ratio as well as supine and standing blood pressure (BP) and sustained hand-grip test. Hemodynamic changes included 24-hour blood pressure, cardiac output, total peripheral resistance (TPR), and plasma renin and aldosterone concentrations.ResultsCompared with the control subjects, HD patients with chronic hypotension had more severe autonomic dysfunction and significantly lower TPR. After 4 weeks of midodrine therapy, sympathetic function (orthostatic and hand-grip tests) improved in conjunction with significant increases in mean arterial pressure (MAP) (79.5 ± 4.9 to 85.0 ± 5.1 mm Hg,P< 0.05) and TPR (768 ± 37 versus 1097 ± 72 dyne/sec/cm−5,P< 0.01) despite no significant change in Valsalva ratio, 30:15 ratio, and cardiac output. MAP changes were positively correlated with TPR changes (r = 0.82,P< 0.001). Supine plasma renin activity was significantly increased. In addition, MAP during HD was also significantly increased during midodrine therapy.ConclusionsMidodrine improves chronic hypotension in HD patients by modulating autonomic function and its direct effects on peripheral vessels.