Hemorheology in Alzheimer's disease: correlation between real‐time microvascular abnormalities and whole blood viscosity

Abstract

We hypothesized that changes in hemorheologic parameters, including vessel diameter, flow velocity, and whole blood viscosity (WBV), would be present in Alzheimer's disease (AD) and would correlate with microvascular abnormalities (vasculopathy). Using the Rheolog™, we obtained WBV profiles, measured at shear rates of 1‐1,000 s−1, for 10 AD patients and age matched non‐AD controls. Vessel diameter, flow velocity, and vasculopathic changes were quantified using computer‐assisted intravital microscopy (CAIM) of the conjunctival microcirculation. A Severity Index (SI), scale 0–15, was computed to reflect degree of vasculopathy. AD patients had significantly higher WBV (3.96±0.29cp vs. 3.34±0.05cp, sheared at 300s−1; P<0.05) and SI (7.00±2.36 vs. 0.61±0.70; P<0.05) than controls. WBV positively correlated (r=0.68; P<0.05) with SI in AD patients. AD patients with severe dementia had significantly higher WBV (4.23±0.19cp vs. 3.68±0.13cp; P<0.05) and SI (8.60±2.30 vs. 5.4±0.89; P<0.05) than less demented patients. Severity of dementia in AD patients did not necessarily correlate with disease duration, but correlated significantly with WBV and severity of vasculopathy. These results strongly suggest the involvement of hemorheologic changes and peripheral vasculopathy in AD.