Microvascular blood flow fluctuations during tilt table induced syncope.

Aim of this study is to investigate the changes, in the frequency domain, of microvasculature blood flow (BF) occurring in neurally mediated syncope. We studied 20 patients with history of recurrent syncope and 10 control subjects. Peripheral BF was measured (laser Doppler technique) in the palmar region (PBF) and the manubrium sterni (SBF), together with ECG, respiration activity (RA) and blood pressure (BP), at rest (5 minute) and during 70 degrees head-up tilt test. SBF and PBF appear to be characterized by oscillations around 0.16 Hz (0.15-0.19 Hz), that do not have correspondence in the other cardiovascular variability signals. Mean BF was not significantly altered in tilt negative, control and tilt positive groups (11 patients) during tilt. In the tilt positive group a decrease of mean PBF and SBF and an increase of the oscillation frequency of PBF and SBF was observed in close proximity of the development of symptoms.