Abstract Body: Introduction
The Glymphatic System ensures the movement of cerebrospinal fluid, primarily produced by the choroid plexuses, through the perivascular and interstitial spaces of the brain, allowing the clearance of toxic byproducts of cerebral metabolism toward the meningeal and cervical lymphatic system. In humans, although arterial hypertension has been associated with white matter damage, its relationship with glymphatic function remains unknown, especially with respect to the night-time phase, during which the function of the glymphatic system is predominant.
Hypothesis
We hypothesized that arterial hypertension is detrimental for the glymphatic system. Therefore, with this study, we aimed to investigate the relationship between blood pressure, its variability and the glymphatic function measured by MRI (Magnetic Resonance Imaging) indices.
Methods
We used two independent indices of cerebral glymphatic function measured by MRI – the index of diffusivity along the perivascular space (ALPS index), positively associated with glymphatic function, and the choroid plexus volume (ChP volume from T2-FLAIR), negatively associated with it. 134 patients with pharmacologically well-controlled arterial hypertension underwent 24-hour blood pressure monitoring and MRI scans to assess white matter microstructural integrity through tractography.
Results
ALPS index and ChP volume parameters show a significant inverse association (r=-0.31, p=0.0004) in the population under study. Moreover, the ALPS index is positively correlated with day–night variability of systolic blood pressure (r=0.211, p=0.015) and negatively correlated with non-circadian variability of systolic blood pressure (r=-0.198, p=0.022) (Figure A). Finally, white matter tractography analysis shows an association between reduced glymphatic function (higher ChP volume) and structural deterioration of white matter (lower fractional anisotropy of the Forceps Minor) (Figure B).
Conclusions
The significant correlation between ALPS index and ChP volume shows that the two indices are complementary metrics of glymphatic function in hypertensive patients. Moreover, our results demonstrate that: i) the day–night component of systolic pressure variability is a protective factor for glymphatic function; ii) the non-circadian component of systolic pressure variability is instead associated with impairment of glymphatic function; iii) microstructural deterioration of white matter leads to reduced glymphatic functionality.