347 THE VIS-A-TERGO FOR CEREBRAL PERFUSION

Abstract

Background: While requiring high steady flow, the brain is perfused in a pulsatile manner. Changes in flow pulsation have been linked to stroke. Flow pulsations in normal subjects have not been characterised, nor their relationship to pulsatile perfusion pressure. Methods: Data were obtained in 200 persons (age 52 years, 94 males), undergoing 24-hour BP monitoring for outpatient evaluation. Flow waveforms were recorded by transcranial Doppler in the right and left Anterior Cerebral, Middle Cerebral, and Basilar Arteries (ACA, MCA and BA, respectively). Radial artery tonometry was used with SphygmoCorTM to generate Ascending Aortic Pressure waveform (AP). Results: Similar flow waveforms were seen on the right and left sides for ACA and MCA. Mean flow velocity was high in all (ACA 54, MCA 61 and BA 38 cm/s, respectively), and continued throughout diastole. Flow waves showed prominent late systolic augmentation, more marked in the smaller BA than ACA or MCA. Flow augmentation index (FAI), calculated in similar fashion to aortic pressure, increased with age at all sites, but was higher in smaller (BA; 112%) than larger arteries (ACA; MCA; 93%) and in all, systematically greater than Pressure Augmentation Index. Conclusions: Wave reflection from the lower body increases Ascending Aortic pressure in late systole. This is caused by wave reflection from the lower body (vis-a-tergo). Wave reflection also boosts late systolic flow in the major cerebral arteries. Value of reduction in wave reflection by arterial dilating drugs needs be explored.