COMPARISON OF THE POSTURAL TACHYCARDIA SYNDROME (POTS) WITH ORTHOSTATIC HYPOTENSION DUE TO AUTONOMIC FAILURE

Postural tachycardia syndrome (POTS) is characterized by orthostatic d izziness, tremulousness, tachycardia and variable blood pressure chang es. Since some POTS patients have a marked reduction in pulse pressure on standing, a major mechanism of their symptoms might be venous pool ing. We therefore studied the cardiovascular response to head-up tilt, Valsalva maneuver and deep breathing in: control subjects (n = 11; F = 8; M = 3; 39.2 +/- 14.4 years); patients with orthostatic hypotensio n secondary to autonomic failure (n = 11; F = 9; M = 2; 61.7 +/- 13.0 years), and patients with POTS (n = 15); F = 13; M = 2; 32.3 +/- 10.6 years). Blood pressure was measured with a Finapres, and cardiac outpu t, stroke volume, end-diastolic volume and thoracic impedance (TFI) we re measured by thoracic electrical bioimpedance. During tilt (in contr ast to patients with orthostatic hypotensiom), patients with POTS had excessive tachycardia (P < 0.001), a normal to excessive total periphe ral resistance increase, and an exaggerated decrease in stroke volume (P < 0.001) and end-diastolic volume (P < 0.001). These findings sugge st that sympathetic arteriolar function remains relatively intact but that sympathetic venomotor function is selectively impaired. These fin dings may have significant implications for the treatment of patients with POTS.