Blood velocity and regional blood flow in defined cerebral artery systems

Cerebral artery blood velocity and regional blood flow (rCBF) were investigated in 17 normal subjects. Blood velocity was measured with 2 MHz pulsed Doppler ultrasound in the proximal segments of the middle, anterior and posterior cerebral artery (MCA, ACA, and PCA) and in the distal extracranial internal carotid artery (ICA). The rCBF in the regions of interest tentatively corresponding to the perfusion territories of these vessels was estimated using 133Xe inhalation and a rapidly rotating single photon emission computer tomograph. Concomitant capnograph recordings showed that the end-expiratory pCO2 was higher during the rCBF than during the blood velocity examinations. This differences was highly significant. While there was no significant correlation between blood velocity and rCBF when these clear differences in pCO2 were disregarded, we did find significant positive correlations when the data were normalized to a standard pCO2 (5.3 kPa) using accepted formulas. The best correlation was found for the MCA (r = 0.630, p less than 0.001) and the PCA (r = 0.73, p less than 0.001), with a lower correlation in the ACA (r = 0.49, p less than 0.01) and the ICA (r = 0.41, p less than 0.05). The estimated blood velocity (V) given rCBF = 0 was not significantly different from 0. The results support the validity of expressing the relationship between blood velocity (V) and rCBF in defined cerebral artery systems as: V = 1/60 (rCBF) T (A)-1, where A represents the area of the lumen of the vessel segment where the velocity is being measured, and T denotes the size of the brain region being perfused from this artery.