Higher systolic blood pressure is associated with increased water diffusivity in normal-appearing white matter.

BACKGROUND AND PURPOSE Hypertension is associated with the development of white matter lesions in older people. Diffusion tensor MRI can detect subtle, previsible white matter damage, but relationships between diffusion tensor MRI parameters and blood pressure (BP) remain unclear. We examined correlations among mean diffusivity (MD), fractional anisotropy and BP in 45 men aged 71 to 76 years. METHODS MD and fractional anisotropy were measured in 6 regions of interest in normal-appearing white matter. Visible white matter lesions were quantified using the Fazekas scale. Both were correlated with systolic and diastolic BP. RESULTS Systolic BP was positively and significantly correlated with MD in all 6 regions (r=0.31 to 0.45; P=0.037 to 0.002). MD was also correlated with diastolic BP in the genu of the corpus callosum (r=0.34, P=0.018). A summary factor derived from principal component analysis of the MD measurements accounted for 53.8% of the variance and correlated at r=0.51 (P<0.001) with systolic BP and r=0.33 (P=0.028) with diastolic BP. Fractional anisotropy did not correlate significantly with BP. Deep white matter Fazekas scores correlated with diastolic BP (rho=0.35, P=0.019). CONCLUSIONS The increase in MD without change in fractional anisotropy indicates that, in normal-appearing white matter, higher BP may be associated with increased extracellular fluid before any cytoarchitectural damage occurs.