Influence of biological factors on changes in mean cerebral blood flow velocity in normal ageing: a transcranial Doppler study.

Analysis of the blood flow velocities in the middle cerebral artery by transcranial Doppler ultrasonography was performed in 158 healthy volunteers (aged 14-70 years; 82 men and 76 women). In a subgroup of 38 men and 21 women the end-tidal [CO2] was also measured. The influence of biological factors such as age, sex, end-tidal [CO2], and pulsatility and resistance indices on the mean blood flow velocity in normal ageing was investigated by multiple regression analysis. In both sex groups the measured mean blood flow velocity decreased significantly with age (P values less than 0.0003 for women and less than 0.0001 for men). Women had significantly higher blood flow velocities than men (P = 0.008) and the age-corrected sex difference of 5.2 cm s-1 did not significantly depend on age (P = 0.93). The age-related linear decline of the mean blood flow velocity could not be explained by a concomitant decrease of the end-tidal [CO2]. In a group of subjects older than 50 years, the decrease of the mean blood flow velocity was significantly related to the increase of the pulsatility or resistance index.