Change of Cerebral Blood Flow during Tilt Tests in Children with Vasovagal Syncope

PURPOSE: Syncope appears to be common. However, the mechanism of syncope is not clear. Increased vagal activity and withdrawal of sympathetic stimulation cause hypotension, bradycardia and finally loss of consciousness. The purpose of this study was to evaluate changes of cerebral blood flow velocity, blood pressure, and heart rate during tilt test in children with vasovagal syncope. METHODS: Sixty four children with a past history of syncope were evaluated. The stand up test was performed for 15 minutes after a rest at supine position for 10 minutes, followed by an 80 degrees tilt test lasting 45 minutes. If presyncope(lightheadedness, nausea, blurred vision, or sweating) or syncope occurred, the study was discontinued. 12-lead electrocardiography, echocardiography, and electroencephalography were performed. Transcranial Doppler study was performed at the middle cerebral artery with 2 MHz continuous Doppler probe in 10 children with positive tilt test. Systolic, diastolic, mean cerebral blood flow velocity, integral, and pulsatility index were measured with blood pressure, heart rate, and O2 saturation. RESULTS: The positive rate of tilt test was 31.3%(20/64). Systolic, diastolic, and mean cerebral blood flow velocity decreased significantly in absence of hypotension or bradycardia during presyncope. Time velocity integral of cerebral artery also decreased significantly. CONCLUSION: Decreased cerebral blood flow velocity can predict the presyncope manifestation. Impairment of autoregulation of cerebral blood flow might play an important role in the pathophysiology of vasovagal syncope.

(Longitudinal Follow-up of Middle Cerebral Artery Stenosis with Transcranial Doppler Ultrasonography: Preliminary Study)

BACKGROUND: The natural history of intracranial arterial stenoses, particularly the middle cerebral artery (MCA), remains unknown. To monitor the progression of MCA stenoses over time, we conducted a prospective study using transcranial Doppler (TCD) study. METHODS: We performed TCD study on 14 stroke patients with angiographically documented MCA stenosis. The findings were compared to repeat TCD studies conducted more than 2 months apart with respect to changes in mean flow velocities (mFV) of the stenotic segment. RESULTS: Fourteen patients (13 men and 1 woman; mean age, 51 years) with 18 MCA stenoses were identified. During a mean follow-up period of 7.7 months, mFV corresponding to the areas of stenosis was increased in 7 (39%) arteries, demonstrating TCD evidence of stenosis progression. Three of those with MCA stenosis progression detected on TCD were confirmed with magnetic resonance angiogram. Flow velocities were not significantly changed in the remainder of the stenotic MCAs. Two patients whose MCA stenosis progressed also showed the suspicious development of new stenosis (mFV increase 119% and 41%, respectively) in the initially normal contralateral MCA. CONCLUSION: These findings suggest that MCA stenoses are dynamic lesions, and that they can evolve and cause further reductions of the arterial diameters after relatively short periods of time. TCD can noninvasively detect these changes.