As noted here, the circulation of blood through the brain slows in specific ways with increasing age. Taken as a biomarker, this correlates with one of the noteworthy structural changes that take place in the aging brain, the enlargement of the ventricles that results from slowed fluid drainage. This is perhaps worth comparing with the work of recent years on the impaired drainage of cerebrospinal fluid in the aging of the brain, though this is more a matter of failing to remove molecular waste rather than fluid dynamics issues leading to damage to tissue structure. Another line of research to consider is the loss of capillary density in tissues with age, as perhaps this is an important mechanism involved in an age-related slowing of the passage of blood through brain tissue.
Ventriculomegaly is an abnormal condition in which fluid accumulates in the ventricles of the brain without properly draining, making them enlarged. Although ventricular enlargement within normal range is not itself considered a disease, when left unchecked it can lead to ventriculomegaly and dementia resulting from normal pressure hydrocephalus. In their study, the team found that ventriculomegaly was associated with changes in blood circulation of the brain.
After blood circulates through the brain providing necessary oxygen, the deoxygenated blood must return to the heart though our veins. This happens through two pathways, one draining blood from regions close to the surface of the brain, and the other from areas deep in the brain. By using MRI to measure changes in blood flow, the team recently found that as we age, the time it takes for blood to drain through these two pathways becomes out of sync. The result is a time lag between the deep drainage pathway and the surface pathway, which increases with age.
In the new study, the researchers found that in healthy aging, the time lag in circulation grows at almost the same rate as enlarging ventricles, but begins slightly earlier. A diagnostic MRI that measures an individual's lag between the two drainage pathways might be a good biomarker for the aging brain, and a possible predictor of ventriculomegaly. Because dementia resulting from hydrocephalus can be reversed by removing the fluid that builds up in the ventricles, early diagnosis is critical.