Fig. 19.

Vascular pulsing that is primarily responsible for CSF flow –the effects of aging and artery hardening. The aorta and carotid harden and lose their flexibility that is responsible for steady capillary flow (upper figure). But artery hardening causes intense heart pulses to pass through these two major arteries and increases the pulse intensity motion in the circle of Willis, the minor arteries, and capillaries, causing microbleeds [55]. Thus, the increased pulse intensity in the circle of Willis with age should be responsible for increased chaotic CSF flow in the neighborhood of the circle of Willis, namely in the basal cistern and its direct CSF connections. This increased motion could lead to higher energy Aβ and tau molecular states that are precursors to neurotoxic seeds, thus possibly initiating Aβ seeds leading to AD.