The puzzle of how the brain regulates blood flow to prevent it from being flooded and then starved every time the heart beats has been solved with the help of engineering.
Anyone who has felt the pulse in their own neck will have a sense of the sudden rush of blood that is pumped to their brain with each heartbeat.
As the heart contracts, a surge of blood flows through the arteries into the head and then as the heart expands, the blood levels drop again.
The human brain, however, requires a steady stream of blood to ensure it gets the constant supply of oxygen it needs to work properly.
Too much blood can cause the pressure in your head to increase and so damage delicate brain tissue, while too little blood will cause it to starve.
Exactly how the body manages to keep the blood flow in the brain so tightly controlled during the ups and downs of the cardiac cycle has remained largely a mystery.
But now researchers at Leeds Beckett University, the University of Bradford and the Don Carlo Gnocchi Foundation in Milan have helped to unravel what may be going on inside our heads.
Their findings provide new insights into the workings of the brain, which may be helpful in the diagnosis and treatment of neurological conditions such as vascular dementia and normal pressure hydrocephalus.
In a new study, published in the journal Biomedical Signal Processing and Control, they found blood appears to be stored in blood vessels in the space between the brain and skull.
These blood vessels expand to store excess blood as it is pumped into the cranium, pushing the fluid that surrounds the brain - known as cerebrospinal fluid - out into the spinal column.
When the heart relaxes, the elastic blood vessels contract to squeeze the stored into the brain, ensuring a steady flow.
This allows cerebrospinal fluid back in from the spine while blood vessels leading out of the brain also expand to store some blood until increasing pressure pushes it back towards the heart.
The researchers found that blood stored in the veins leading out of the brain appears to play an important role in regulating the behaviour of the whole system.
Clive Beggs, Professor of Applied Physiology at Leeds Beckett University, said: "How the intracranial arterial, venous and cerebrospinal fluid volumes interact with each other has been something of a mystery. In this study, we have been able to describe, for the first time, the interactions that take place in the whole fluid system within the cranium over the cardiac cycle.
“This is crucially important for understanding many diseases of the brain, especially those that occur with aging.”
The researchers used Magnetic Resonance Imaging (MRI) to scan of the necks of 12 healthy young adults, allowing them to monitor the flow of blood through their arteries and veins, and of cerebrospinal fluid into their spines. A series of algorithms developed by Professor Beggs and his colleague Simon Shepherd, Professor of Computational Mathematics at the University of Bradford, were then used to model the changes in different fluid volumes inside each volunteers’ skulls.
The study showed that when the blood volume stored in the cranial arteries reached its peak, the volumes of blood in the veins and cerebrospinal fluid in the cranium were at their lowest.
Then as the arterial volume decreased, so the volumes of venous blood and cerebrospinal fluid in the cranium increased.
Crucially, the study suggests that if for any reason the flow of the venous blood out of the cranium becomes restricted, then it could inhibit the ability of the brain to absorb the changes caused by the cardiac cycle.
This would result in the blood flow through the brain capillaries becoming more uneven.
While the implications of this are not fully understood, it is thought that changes in blood flow in the capillaries of the brain are associated with vascular dementia in the elderly.
The researchers hope the method they used to measure the changes in brain fluid volume could be useful to neurologists looking to study patients with brain disease.
Dr. Marcella Laganà, researcher at Don Gnocchi Foundation in Milan, where the MRI scans were performed, said "The innovative model can be translated into the clinical practice in further studies on subjects with different kinds of neurological disease."
Indeed in the future, the team hopes to compare the results from the healthy adults with those from patients suffering from a variety of neurological diseases to see if brain fluid changes play a role in these respective conditions.
Professor Beggs said: “Abnormal fluid behaviour in the cranium may be associated with a whole range of neurological conditions and may also be related to aging."
“As you get older, the flexibility of blood vessels decreases, so more of the pulse from the arteries will flow through the brain capillaries and over time this could lead to problems."
"The work we have done may help lay the groundwork for new ways to diagnose these problems."
Professor Shepherd added: "Aside from the significant advance in understanding the specific mechanics of cerebral fluid flow, the other important aspect of this work is the novel transfer of powerful analytic methodologies from the hard sciences such as maths, physics and engineering, into the world of medicine.
“The opportunities for putting medical theories on a much firmer theoretical footing, underpinned by hard science, is very important for establishing the credibility and acceptance of these ideas."