Tilt training increases the vasoconstrictor reserve in patients with neurally mediated syncope evoked by head-up tilt testing

Abstract

Tilt training is a useful therapeutic option in neurally mediated syncope (NMS). We tested the hypothesis that tilt training will restore orthostatic tolerance by increasing the degree of vasomotor reserve during sustained orthostatic stress. METHODS AND RESULTS In this follow-up study we enrolled 17 patients (age 31 +/- 22 years, 11 females) with a clinical diagnosis of NMS and two consecutive positive tilt tests. The head-up tilt test was repeated day after day: one session per day. All patients were instructed to continue a programme of daily standing training at home. Follow-up tilt testing was performed after a period of 6 weeks in 14 patients. ECG and finger arterial blood pressure (Portapres) were recorded during subsequent tilt testing. Left ventricular stroke volume (SV), cardiac output, and systemic vascular resistance were computed from the pressure pulsations (Modelflow). Spontaneous cardiac baroreflex sensitivity was estimated by cross-spectral analysis of heart rate (HR) and systolic blood pressure. In all patients, orthostatic tolerance was restored after 4.1 +/- 0.9 tilt sessions, median 4. The follow-up tilt test was also negative in all patients. This was accompanied by a significant rise in systemic vascular resistance to compensate for a postural reduction in SV in the sustained head-up tilt position. No evidence could be provided of altered baroreflex control of HR after tilt training. Tilt training restores orthostatic tolerance at least in part by increasing the amount of vasoconstriction that can ultimately be made available during sustained orthostatic stress. The increased vasoconstrictor reserve is preserved after 6 weeks of continued standing training at home.