The influence of visual contrast on visually evoked cerebral blood flow responses.

Transcranial Doppler (TCD) could be used to evaluate the visually evoked cerebral blood flow responses (VEFRs) during graded visual cortex activity. The purpose of the study was to evaluate the effects of visual contrasts on VEFR. The records were made from 30 healthy volunteers aged 38.0 +/- 9.6 years. The stimulus was a black-and-white checkerboard with visual contrasts of 1%, 10% and 100%. The VEFRs were measured in the posterior cerebral artery using TCD. We found that the VEFRs at 100% visual contrast were 36% higher than those at 10% visual contrast (p < 0.01). The VEFRs at 10% visual contrast were 81% higher than those at 1% visual contrast (p < 0.01). The linear regression showed significant relationships between the visual contrast and the VEFR (r = 0.61, p < 0.01). We have concluded that TCD monitoring of VEFR detects the changes of the blood flow in the visual cortex and that TCD could allow an assessment of neurovascular coupling.