The pressure inside patient's skull can rise due to brain tumors and head trauma, including concussion. The elevated pressure inside the brain can destroy brain tissue or cut off the brain's blood supply. Being able to monitor the pressure inside the brains of affected people could help physicians in establishing the best possible treatment. However, the procedure is extremely invasive, as it requires drilling a hole into the patient's skull and is therefore only performed in patients who are severely injured.
A novel, less risky technique, described in the April 11 issue of Science Translational Medicine, could enable doctors to measure brain pressure in patients with less severe or milder head injuries, who would benefit from close monitoring.
Researchers at MIT's Research Laboratory of Electronics (RLE) developed the novel technique based on a computer model of the way blood flows through the brain. Based on the model, researchers are able to calculate brain pressure from two less invasive measurements, i.e. arterial blood pressure and an ultrasound measurement of the velocity of blood flow through the brain. This approach allows physicians to constantly monitor any changes in brain pressure, as well as being alerted of problems that may build up slowly.
Intracranial pressure (ICP), or the pressure in the brain, can become elevated because of excessive blood or cerebrospinal fluid building up, a brain tumor or swelling of the brain.
Until now, neurosurgeons had to drill a hole in the skull and insert a catheter into the brain tissue, or a fluid-filled cavity within the brain, in order to measure the pressure within the brain. According to study conducted by co-author George Verghese, a Henry Ellis Warren Professor of Electrical Engineering at MIT, the risk of infection or brain damage outweighs the benefits of this procedure, which is therefore only undertaken in only the most critically ill patients.
Verghese, whose lab concentrates on using computer models of human physiology to interpret patient data, explains:
"There's a much larger patient population for whom physicians would like this measurement, but the invasiveness stops them from obtaining it."
Lead author Faisal Kashif, a postdoc in Verghese's lab, designed a computer model in his PhD thesis, which links arterial blood pressure and blood flow through the brain to pressure within the brain.
Kashif's model calculates ICP by calculating the blood flow through the brain, which is caused by the difference in pressure between the blood entering the brain and the pressure inside the brain (ICP). Given that t he pressure of blood entering the brain cannot be measured directly, the MIT team used radial arterial pressure as a proxy measurement, which was obtained by inserting a catheter at the wrist before using their blood flow model to compensate for the difference in location.
Because it is possible to measure peripheral arterial pressure continuously and non-invasively by using a finger cuff, comparable to an arm cuff used for measuring blood pressure, the team is now examining whether data obtained in this way is sufficiently accurate enough to be used in their model.
They confirmed the accuracy of their technique by using data their collaborator Marek Czosnyka obtained a few years ago from patients with traumatic brain injury, which turned out to be one of the few data sets that included all necessary measurements, together with the proper time stamps. The MIT team received Czosnyka's data on radial arterial blood pressure and ultrasound blood flow velocity and used these numbers in their model to calculate an estimated ICP before sending the figures back to Czosnyka to compare.
The test revealed that the MIT results were marginally less precise, compared with those obtained from the best invasive procedures. However, they proved to be similar to other invasive procedures still in clinical use, as well as to some less invasive tried techniques.
James Holsapple, chief of neurosurgery at Boston Medical Center remarks:
"It's a holy grail of clinical neurosurgery to find a noninvasive way to measure pressure. It would be a big step if we could get our hands on something reliable."
He continues saying that the new MIT approach is promising and adds that the next significant step would be to incorporate the technology into a system that would be easy to use for hospital staff and which could record data over many hours or days.
The MIT team and Vera Novak of Beth Israel Deaconess Medical Center (BIDMC) in Boston are currently collaborating with doctors at BIDMC to test their approach on patients in the neurosurgical intensive care unit.
"It's still at the validation stage. To convince people that this works, you need to build up more [data] than we currently have. Our hope is that once it's been validated on additional sorts of patients, where you're able to show that you can match what the invasive measurement is, people will have confidence in starting to apply it to patients who are currently not getting monitored. That's where we see the big potential."
Senior author, Thomas Heldt, a research scientist in RLE states that once the data collection and model have manifested themselves sufficiently, the team hopes to test different patient populations, for instance athletes with concussions, or soldiers who experienced explosions to identify ways in which the extent of injury can be determined and whether or not it would be safe for individuals to return to work. Given that NASA has observed signs of elevated ICP in some astronauts and is now looking for new ways of measuring their ICP would open another avenue to apply the system.
Written By Petra Rattue