Reduction of carotid artery blood flow in pediatric patients with syncope: Evaluation with head-up tilt test

We investigated the effect of postural changes on cerebral circulation by measuring carotid artery blood flow (CABF) in the supine position and during head-up tilt (HUT) test using a Doppler flow meter. Subjects included 10 patients with neurally mediated syncope, 10 patients with orthostatic intolerance, 8 with epilepsy, aged between 8 to 24 years (mean +/- SD, 13.9 +/- 4.1 years). The test caused pallor and dizziness in 16 patients (symptomatic), while no symptoms were recognized in the other 12 patients (asymptomatic). Significant reductions in the mean CABF (Fm), maximum CABF (Fs) and minimum CABF (Fd), components of the CABF waveform, were noticed during HUT compared to before HUT (supine), and these reductions in symptomatic patients were more severe than those in asymptomatic patients (Fm: -2.8 +/- 2.0 SD vs -0.7 +/- 1.4SD; Fs: -2.7 +/- 1.5SD vs -0.9 +/- 1.3SD; Fd: -4.5 +/- 2.8SD vs -2.2 +/- 2.1 SD). Reductions in Fm, Fs and I'd in the symptomatic patients during HUT lasted longer than those of the asymptomatic patients, being statistically significant for I'm and Fs (Fm: p < 0.01; Fs: p < 0.05). The criteria during HUT for distinguishing neurally mediated syncope (NMS) from others was Fs: < - 4 SD and Fd: < - 5 SD. Our data suggest that reduction of CABF should be carefully evaluated for the diagnosis of neurally mediated syncope in pediatric patients. Such a reduction might be an essential mechanism of syncopal attacks.