To the Editor:
We read with interest the report by Scheel and colleagues1 of the duplex ultrasound derived volumetric flows of the anterior and posterior components of the cerebral circulation published in Stroke. In discussing their main finding that the anterior circulation contributes 76% and the posterior circulation 24% to the total global cerebral blood flow, the authors noted that there were no other reports available for comparison.
We published a report in 19952 of our findings from a similar investigation in a series of 21 healthy adults describing the relative flow contributions of the anterior and posterior circulation to the total global cerebral blood flow. We found that the anterior and posterior circulations contributed 82% and 18%, respectively, to total global cerebral blood flow, which is in quite close agreement with the findings of Scheel and colleagues. We also noted that these relative flow contributions were independent of gender and in precise concordance with the expected blood flow distribution based on the differences in the measured internal lumen diameters of the internal carotid arteries and vertebral arteries. The absolute values, however, for the volumetric flow rates differed between the 2 studies, with our reported values uniformly lower by about 40%, despite the use in both studies of a similar time-averaged velocity calculation throughout the cardiac cycle of all particles within the sample volume overlaying the entire lumen. Our report discussed the numerous potential causes and sources of systematic error, and such considerations in combination with the lack of a gold standard by which to determine absolute or actual flow suggests to us that duplex-derived direct flow measurements be used as indices of flow magnitude rather than true determinations of actual flow. We agree with the authors that a reliable, noninvasive index of regioselective blood flow could provide clinically relevant information to benefit patients in the intensive care unit. Improvements in the understanding and measurement of all components of the cerebral circulation should particularly improve validation and monitoring of pharmacological and endovascular therapeutics for stroke.
- Copyright © 2000 by American Heart Association
We regret that the publication of Boyajian et alR1 escaped our notice—just as the paper we published a yearR2 before that apparently eluded theirs. In 1994 we first reported on global cerebral blood flow volume examinations in 48 healthy adults (mean age 35±12 years), where we found a mean contribution of 76% by the anterior and of 24% by the posterior circulation. Global cerebral blood flow volume was 701±104 mL/min, corresponding to a cerebral blood flow of 50–54 mL/100 g/min (assuming a mean adult brain weight of 1300–1400 g). In a study on children and adolescents,R3 the mean contribution of the posterior circulation to global cerebral blood flow volume declined significantly from 31% at the age of 4 years to 24% at the age of 18 years. During the same period, cerebral blood flow volume decreased significantly (3–9.9 years, 821±116 mL/min; 10–18 years, 727±106 mL/min).
In a recent interobserver study,R4 the reproducibility of global cerebral blood flow volume measurement was shown to be comparable to that of global cerebral blood flow measured with 15O-labeled water positron emission tomography. In this study, the ratio of anterior to posterior circulation flow volumes was already estimated to be 76% to 24% by both examiners.R5 In the article discussed here,R6 the mean contribution of the posterior circulation to cerebral blood flow volume remained constant (24%) from 20 to 85 years of age, whereas global cerebral blood flow volume decreased from 730±87 mL/min (age group 20–39 years) to 603±106 mL/min (age group 60–85 years).
The flow volumes measured by Boyajian et al in the internal carotid arteries on both sides (147 and 143 mL/min, respectively) and in the vertebral arteries (34 and 32 mL/min, respectively) of healthy young adults are much lower than those found by our group.R2 R5 R6 They add up to a mean global cerebral blood flow volume of 356 mL/min, which would correspond to a very low global cerebral blood flow of 25–27 mL/100 g/min. Most publications on normal cerebral blood flow in healthy adults, however, report reference data of ≈50 mL/100 g/min.R7 We can explain this difference only with a systematic error of flow volume measurement. In contrast to Boyajian and Otis, we are convinced that cerebral blood flow volume can be measured quantitatively, as long as a meticulous examination technique is observed. In a first attempt to pave the way for using this method in clinical routine, we studied cerebral blood flow volume in patients with vascular dementia, where a marked decrease of cerebral blood flow volume was found.R8 At present we are in the process of establishing bedside cerebral blood flow volume monitoring in neurointensive care patients. We would like to encourage neurologists, child neurologists, and neurosurgeons to learn and apply this technique, because we firmly believe in the great potential benefits of the clinical and scientific application of this method.
Boyajian RA, Schwend RB, Wolfe MM, Bickerton RE, Otis SM. Measurement of anterior and posterior circulation flow contributions to cerebral blood flow: an ultrasound-derived volumetric flow analysis. J Neuroimaging.. 1995;5:1–3.
Schöning M, Walter J, Scheel P. Estimation of cerebral blood flow through color duplex sonography of the carotid and vertebral arteries in healthy adults. Stroke.. 1994;25:17–22.
Scheel P, Ruge C, Petruch UR, Schöning M. Color duplex measurement of cerebral blood flow volume in healthy adults. Stroke.. 2000;31:147–150.
Scheel P, Puls I, Becker G, Schöning M. Volume reduction in cerebral blood flow in patients with vascular dementia. Lancet.. 1999;354:2137.