1661 ESTIMATION OF CEREBRAL BLOOD FLOW BY DOPPLER

Abstract

In an effort to determine the accuracy of range-gated Doppler ultrasound (DUS), we compared measures of flow through the exposed carotid artery of 6 anesthetized adult female cynomolgus monkeys using DUS (20 MHz) with those obtained using an electromagnetic flow (EMF) probe and direct measures of cerebral blood flow (CBF) using Xe 133 clearance. Vessel calibre was determined by calibrated angiography. A fast fourier transform was performed every 6.25 milliseconds on the DUS shifted spectra and averaged over 15 cardiac cycles. Mean flow velocity was derived and multiplied by vessel cross-sectional area to give volumic flow. Variations in CBF were produced by altering PaCO2. Pulsatility index (PI) was calculated from the output derived from a zero-crosser incorporated into the DUS device. Twenty-one comparisons were performed over a wide range of CBF (17 to 96 ml/ 100 gm/min). Correlation between Xe 133 and DUS volumic flow measurements was highly significant, r = 0.8, p <.0001). The correlation between Xe 133 and flow velocity, without correcting for vessel diameter, was poorer (r = 0.7, p <.0002) as was the correlation between DUS & EMF (r = .51, p <.05). The correlation between EMF & Xe 133 (r = .7, p <.0004) was lower than that between DUS & Xe. Even under these ideal conditions, PI did not correlate with CBF. This method for estimating CBF does not involve ionizing radiation and could be adapted to produce a totally non-invasive methodology for measuring CBF in real time.