The veins are poorly studied in comparison to the brain's arteries because it is arterial blood flow that is critical for providing oxygen to the brain and occlusion of these vessels leads to stroke. Therefore, it is not well understood how blood travels through the brain's veins on its way back to the heart.
Dr Scott Kolbe, lead author on the study, is a senior research fellow in Central Clinical School's Department of Neuroscience. Dr Kolbe said, "This project started when we were looking at blood flow in the brain using MRI and noticed a unique signal that was very consistent across people in the white matter of the brain. The white matter contains the connections between brain regions and is affected in the brain disorder multiple sclerosis, or MS.
"Because our team has a strong interest in MS, we knew by looking at this signal that it was in exactly the same parts of the brain that are affected in people with MS. MS 'lesions' form when inflammatory cells in the bloodstream cross the veins into the brain's white matter and start to attack the myelin cells that support the neurons which are the main communication cells of the brain."
The researchers could see a new and unique blood flow signal in the regions of the brain most affected by MS. They then checked whether the vein's blood flow signal was affected in people with very early-stage MS and found that it was different.
Dr Kolbe said, "Understanding the difference requires a brief explanation of some interesting aspects of this venous blood flow signal.
"Most signals in the brain are very complex, due to the complex interactions between brain cells and their supporting cells. However, we discovered something that no-one has observed before - namely that the blood flow signal in the veins was completely rhythmic, going up and down over a period of around 20 seconds. The long duration of this rhythm meant it could not be a heartbeat or respiration signal, but something new.
"Perhaps most interestingly, the signal was almost the same rate across the entire network of veins, even when the vessels were at opposite ends of the brain, making it likely that the control of this signal was under some kind of central coordinating mechanism such as heart rate or respiration."
It's known that people with MS have damage to the veins in the brain, probably due to the breakdown of the vessel walls that happens when the brain is inflamed.
Dr Kolbe said they thought that perhaps this might lead to changes in the coordination of the venous blood flow signal across the brain, and that is exactly what they found. He said, "People who had more MS lesions, indicating that they had experienced more inflammation, had less coordination of blood flow across the venous network of the brain. Given that blood flow in the veins of healthy people is so tightly regulated, this loss of coordination in patients might have negative consequences. But we can't know this for certain without tracking people over time."
The next steps for this research, Dr Kolbe said, are to look at larger groups of people to see if there are also changes in the coordination of blood flow within the veins as we age or in people with other diseases that affect blood vessels including in people with dementia.
"This research has opened a new window into a part of our brain that previously we didn't know existed, and could shine a light on the importance of the 'poor cousin' of the brain's blood vessel system, the veins."
Scott SC, Gajamange SI, Cleary JO, Kilpatrick TJ. An Experimental Investigation of White Matter Venous Hemodynamics: Basic Physiology and Disruption in Neuroinflammatory Disease. Front Neurol. 2020 Jun 2;11:476. doi: 10.3389/fneur.2020.00476. eCollection 2020.