Background: The effects of midodrine on chronic hypotension in hemodialysis (HD) patients have not been well investigated. Methods: We 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. Results: Compared 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. Conclusions: Midodrine improves chronic hypotension in HD patients by modulating autonomic function and its direct effects on peripheral vessels.
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