Age and sex variability and normal reference values for the V(MCA)/V(ICA) index.

BACKGROUND AND PURPOSE The index of mean blood flow velocity (V) in the middle cerebral artery (MCA) divided by respective velocity in the ipsilateral internal carotid artery (ICA), or V(MCA)/V(ICA) index, is commonly used as a marker of vasospasm, although reference values are not established. We sought to provide reference data for these velocities and index. METHODS Transcranial color-coded duplex and carotid duplex sonography was performed in 335 healthy volunteers (211 women, 124 men; mean age +/- SD, 42 +/- 18 years; range, 18-86 years). Age analyses were based on three groups: I, <40; II, 40-60; and III, >60 years. The V(MCA)/V(ICA) index was calculated based on angle-corrected blood flow velocities determined in the MCA and extracranial ICA. RESULTS Mean flow velocities in the MCA and ICA diminished with increasing age, most pronounced in those subjects >40 years. The V(MCA)/V(ICA) index increased significantly (1.67 + 0.005 [age]; P < .05) with age in women, but not in men. In women, reference values and ranges for the V(MCA)/V(ICA) index were as follows, by group: I, 1.82 (range, 0.88-2.68); II, 1.91 (range, 0.94-2.88); and III, 2.06 (range, 0.59-3.53). Respective values for men were as follows, by group: I, 2.10 (range, 0.96-3.24); II, 2.04 (range, 0.71-3.37); and III, 1.78 (range, 0.81-2.75). In subjects <40 years, the V(MCA)/V(ICA) index was significantly higher in men than in women. CONCLUSION The V(MCA)/V(ICA) index significantly varies with age and sex. Sonographic diagnosis of cerebral vasospasm should be based on age- and sex-adjusted reference values of the V(MCA)/V(ICA) index.