Effect Of Nitric Oxide Syntase Inhibition On Cerebral Blood Flow And Injury Volume.

interpretation of TCD velocities in patients harboring an intracranial AVM. We agree that some portion of the variance that accounted for the less-than-perfect correlations may have been attributable to errors related to the angle of insonation. We would point out the following considerations regarding AVMs. Distortion of the proximal conductance vessels is most likely to occur with mass lesion effects, as Finn et al have described for hydrocephalus; bowing of vessels may cause an underestimation of the true velocity of the blood column. True AVMs present with mass effect only in the rarest of cases. However, because AVMs sometimes result in bizarre changes even in proximal vessels, the authors' point is well taken and should be borne in mind in future studies or the interpretation of values from an individual patient. On an individual basis, this may be especially pertinent because feeding artery pressure, when considered in context with other factors, may influence the incidence of spontaneous intracranial hemorrhage from AVMs-" and therefore may affect the decision of whether or not to treat a particular lesion. It is worth noting that Manchola et al performed a study of AVM feeding arteries that was in some respects similar to ours (without pressure measurements). As a part of that study, they described a very careful inspection of the angiograms to optimize the best angle of insonation to minimize this source of error. Of their 40 patients, however, they did not describe any with the remarkable deviations suggested by Martin and Gaunt (ie, angle of insonation of >30°). A possible pitfall in trying to determine the actual angle of insonation should also be considered. Unless one performs the TCD during fluoroscopy (which is almost never the case), the exact relationship of probe angulation to the insonated vessel can only be approximated.