We hypothesized that visual stimulation results in blood flow increase in all main arteries of the posterior circulation territory (PCT). In an attempt to establish relation between visual stimulation and blood flow, we assessed visually evoked cerebral blood flow response (VEFR) in vertebral (VA), basilar (BA) and posterior cerebral arteries (PCA).

Methods: The study population consisted of 65 healthy volunteers (aged 21–57, median-35) subjected to elementary photostimulation (opening and closing of the eyes). We measured velocity and resistivity index (RI) using transcranial Doppler in VA (V4 segments), BA (in three different depths: 70mm, 80mm and 90mm), and PCA (P1 and P2 segments).

Results: Following photostimulation, we observed a significant increase in velocity and a decrease in RI in all arteries, in comparison with baseline values. The maximum VEFR was observed in PCA(P2) (Fig.1). The significant differences were detected between VEFR in VA and PCA (all segments), between VEFR in PCA(P2) and BA (all depths), PCA(P2) and PCA(P1). VEFR in BA was the same on different depths. VEFR was higher in right PCA and VA, although the difference was not statistically significant. Correlation analysis revealed significant relations between VEFR in left and right VA (r=0.59), PCA(P1) (r=0.35), PCA(P2) (r= 0.41) and between VEFR in BA in different depths (r=0.64–0.75). No significant correlations were observed for VEFR in different arteries.

Conclusions: VEFR is detected in all main arteries of the PCT. VEFR gradually increases as one goes from proximal segments to distal ones. The maximum VEFR is observed in PCA(P2).