BACKGROUND:
Cerebral hypoperfusion is associated with vascular brain injury and neurodegeneration, but their longitudinal relationship is largely unknown, especially in healthy older adults.

METHODS:
We investigated the longitudinal relationship between cerebral hemodynamics and subclinical vascular brain disease in community-dwelling older adults without stroke or dementia at baseline. Participants underwent brain magnetic resonance imaging scans every 3 to 4 years between 2005 and 2016. Cerebral blood flow (CBF) was measured through 2-dimensional phase-contrast magnetic resonance imaging; the cerebrovascular resistance index (CVRi) was defined as the ratio of mean arterial blood pressure to total CBF. Simultaneous progression in subclinical brain disease was evaluated through repeated magnetic resonance imaging assessment of white matter hyperintensities (WMH), cerebral microbleeds, lacune, and brain atrophy. The longitudinal relationship was estimated using generalized estimating equations, with adjustment for age, sex, smoking habits, body mass index, systolic blood pressure (for CBF measures), lipid level, history of diabetes and cardiovascular disease, and the baseline burden of magnetic resonance imaging markers.

RESULTS:
Among 3623 older adults (mean age, 61.4±9.3 years; 54.6% women), large decreases and increases in CBF and increases in CVRi over time were associated with white matter hyperintensity progression. The risk ratios for white matter hyperintensity progression were 1.36 (95% CI, 1.19–1.55) for large decreases in total CBF (lowest quartile), 1.02 (95% CI, 0.91–1.14) for moderate decreases (second quartile), and 1.28 (95% CI, 1.14–1.45) for large increases (highest quartile), compared with stable CBF (third quartile). The corresponding risk ratios for changes in CVRi were 1.13 (95% CI, 1.00–1.30), 1.25 (95% CI, 1.09–1.43), and 1.33 (95% CI, 1.16–1.52) for the second to fourth (versus lowest) quartiles, respectively, showing a dose-response relationship. The changes in CBF also demonstrate a similar U-shaped association with the progression of brain atrophy and incident microbleeds, whereas increases in CVRi were associated with lower microbleed risk.

CONCLUSIONS:
Longitudinal changes in CBF and CVRi may capture distinct pathophysiologies linking cerebral hemodynamics to subclinical brain disease, extending beyond single–time point measurements.

The effect of the scarcely reported F phase on hydrogen-assisted cracking in nickel-based Alloy 725 was thoroughly studied by combining tensile tests, advanced characterization, and density functional theory (DFT) calculations. The results show grain boundary precipitate F phase promotes intergranular fracture in a hydrogen environment. DFT calculations further indicates hydrogen atoms lower the binding strength of the F phase and Ni matrix interfaces. More importantly, our study showed for the first time that the addition of approximately 0.01 wt.% boron can effectively suppress F phase precipitation, thereby elevating the hydrogen resistance of Alloy 725.