Mechanisms of blood pressure alterations in response to the Valsalva maneuver in postural tachycardia syndrome

The postural tachycardia syndrome (POTS) is characterized clinically by ort hostatic lightheadedness and tachycardia. When these patients perform a Val salva maneuver, there is an excessive blood pressure increment after cessat ion of the maneuver (phase IV) that is sometimes associated with headaches. It is not known whether excessive phase IV is due to excessive peripheral vascular tone (an alpha-adrenergic mechanism) or is a manifestation of incr eased beta-adrenergic tone (hyperadrenergic state). The authors undertook a pharmacologic study evaluating the effect of intravenous phentolamine (alp ha-adrenergic antagonist) and propranolol (beta-adrenergic antagonist) on t he different phases of the Valsalva maneuver in a group of patients with PO TS and age-matched normal control subjects. Patients with POTS had mean pha ses, when compared with controls, that were characterized by more negative II_E (p = 0.07), smaller II_L (p = 0.04), and significantly larger phase IV (p = 0.001), The effect of phentolamine was qualitatively and quantitative ly different in POTS when compared with controls. Ten mg phentolamine in co ntrols resulted in a significant accentuation of phase II_E (p = 0.001), at tenuation of phase II_L (p = 0.002), and increase of phase IV (57.6 vs 30.7 mm Hg; p = 0.025). These changes resembled those of patients with POTS at baseline. In patients with POTS, the phase II abnormalities, already presen t, were further accentuated (p < 0.001), and phase IV became smaller (50.6 vs 73.8 mm Hg; p = 0.09). Propranolol had no significant effect on phases I I_E and II_L, but significantly reduced phase IV in both controls (p < 0.05 ) and in patients with POTS (p < 0.001) and improved the headache symptoms, when present, during and after phase IV. The authors conclude that phase I V is mainly under beta-adrenergic regulation and that the exaggerated phase IV in POTS is a result of a hyperadrenergic state.