More than seven million Americans are currently living with Alzheimer’s disease, a devastating condition that gradually erodes memory and thinking ability.
Scientists know that the biological changes that lead to Alzheimer’s begin decades before symptoms appear, yet diagnosing the disease early has always been difficult.
Current methods often involve painful spinal taps, expensive brain scans, or simple cognitive tests that may not capture the full picture.
Now, new research from the University of Southern California suggests a groundbreaking alternative: looking at how blood flows through the brain.
For years, the dominant explanation of Alzheimer’s has been the “amyloid cascade hypothesis.” According to this theory, Alzheimer’s begins when a protein fragment called amyloid beta accumulates in the brain.
This buildup triggers another protein, tau, to form twisted tangles inside nerve cells. Together, these changes are believed to disrupt brain function and eventually kill neurons, leading to memory loss and confusion.
Diagnostic tests, such as PET scans, focus on measuring amyloid and tau, but they are costly and often only available in research settings.
Vasilis Marmarelis, a biomedical engineer at USC, and his team believe that a different factor may play an equally critical role: the brain’s ability to regulate its own blood flow.
Like a home’s plumbing system, blood vessels in the brain must respond quickly and efficiently to shifts in pressure and carbon dioxide (CO₂) levels, delivering oxygen and glucose exactly when needed.
If this delicate system breaks down, brain cells may not get the nutrients they require to function properly.
Fifteen years ago, Marmarelis noticed something striking—patients with Alzheimer’s had impaired “vasomotor reactivity,” meaning their blood vessels could not expand properly to increase blood flow during times of need.
In their new study, his team set out to measure this more carefully and develop a diagnostic tool around it.
The researchers followed 200 people for five years, tracking the interaction between blood pressure, CO₂ levels, cerebral blood flow, and oxygenation in brain tissue.
Using advanced modeling techniques, they created a new noninvasive test called the Cerebrovascular Dynamics Index (CDI). The test combines Doppler ultrasound, which measures blood flow velocity in the brain’s arteries, with near-infrared spectroscopy, which tracks oxygen levels in the cortex.
Together, these measurements provide a detailed picture of how well the brain regulates its blood supply.
The results were impressive. The CDI could distinguish people with mild cognitive impairment or Alzheimer’s from healthy participants with an accuracy far greater than existing methods.
The test achieved an Area Under the Curve (AUC) of 0.96, compared with 0.78 for amyloid PET scans and around 0.91 for standard cognitive tests. In other words, this new blood-flow-based approach outperformed the current gold standard for detecting Alzheimer’s.
Marmarelis believes this opens the door not just for earlier and easier diagnosis but also for new treatment strategies. Improving blood flow regulation in the brain could become a target for therapies, alongside efforts to reduce amyloid and tau.
Lifestyle changes such as daily aerobic exercise, healthier diets like the MIND diet, and stress reduction may help restore healthy vascular function.
Other promising experimental approaches include controlled breathing exercises to influence oxygen and CO₂ levels, as well as gentle nerve stimulation through the ear to improve blood flow regulation.
“This study shows that dysregulation of blood flow in the brain may be a critical factor in the development of Alzheimer’s,” Marmarelis said. “And because we now have a reliable, noninvasive way to measure it, we can start thinking differently about how to diagnose and treat this disease.”
The findings not only challenge decades of conventional wisdom but also provide new hope for patients and families.
By focusing on the brain’s “plumbing system,” researchers may be able to catch Alzheimer’s earlier, monitor its progression more accurately, and even slow it down with targeted therapies—offering a brighter path forward in the fight against dementia.
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