Medical Technology: 'SmartShunt' To Regulate Pressure In The Brain

Cerebrospinal fluid is a colorless liquid surrounding the brain and the spinal cord and filling the cavities in the brain. It protects the brain from impact and vibrations, carries nutrients to it and harmful substances away from it, and acts as one of the brain’s communication routes. If too much of this fluid is produced or too little flows away, excessive pressure builds up in the head and hydrocephalus occurs.

The liquid flows into the abdomen

As a rule nowadays, hydrocephalus is treated by using a “shunt”: this involves implanting into the patient a thin tube that carries excess cerebrospinal fluid from the head into the abdomen via a pressure relief valve. However, this process often drains away too much or too little fluid. Most valves can no longer be adjusted after implantation. Although some valves have this option, the patient must visit the doctor for adjustments to be made.

ETH Zurich researchers led by Dimos Poulikakos, Professor of Thermodynamics, and Vartan Kurtcuoglu, Director of the Biofluidics group in the Laboratory for Thermodynamics in Emerging Technologies, want to go one step further. They are working on a “SmartShunt”, a self-regulating pressure relief device. To achieve their aim they must understand exactly how the cerebrospinal fluid flows within the skull. For this, they simulated the motion of the fluid in three dimensions on a computer. Initial results were published in the February issue of the Journal of Biomechanical Engineering. Its title page shows a graphic image of the results, the research group having already made the title page in the January issue with a publication on aortic aneurysms (see the Literature references).

A brain scan is the first step

The cerebrospinal fluid fills the space between the skull and the brain, called the sub-arachnoid space, in which it pulses in a cycle controlled indirectly by the heart. With each heartbeat, the heart pumps blood through the brain, causing the blood vessels to expand and the space available for the cerebrospinal fluid to decrease correspondingly. The blood flows away again before the next heartbeat, and the space for the cerebrospinal fluid increases.

The publication came into being in collaboration with Peter Bösiger, Professor at the Institute of Biomedical Technology of ETH Zurich. His group scanned the sub-arachnoid space of a healthy 25-year-old man by magnetic resonance imaging (MRI). They also used a special MRI technique to measure the velocity of the fluid in three planes to provide the boundary conditions for the calculations.

The scientists built a computer model based on the results of the measurements. They used a series of partial differential equations to describe the motion of the cerebrospinal fluid. At the same time, they had to take into account the fact that the sub-arachnoid space is criss-crossed by a sort of fine, networklike bar of tissues that retard the movement of the fluid. Instead of computing with the single bar, they represented the sub-arachnoid space in their model as a uniform porous medium similar to a sponge.

Valve for self-regulation

Based on the results, the researchers in the multi-disciplinary “SmartShunt” Project are now developing the basis for a shunt to control the outflow of cerebrospinal fluid automatically in accordance with the patient’s specific needs. The goal is a valve that controls the pressure in the patient’s head in real time, saving him or her regular visits to the doctor.

Dimos Poulikakos says, “We attach importance to the fact that definitereal medical problems are addressed in the continuation of basic research.” The researchers work in close collaboration with the medical staff of the University Hospital Zurich and with other ETH Zurich institutes. The Swiss National Science Foundation is funding the interdisciplinary project to the tune of approximately CHF 850,000. Poulikakos plans to start developing the actual product together with the industry in about three year’s time.

Knowledge of the cerebrospinal fluid motion will also be useful for other medical applications. The liquid plays a part in Alzheimer’s disease, in multiple sclerosis and in meningitis. In addition, drugs that cannot cross the blood-brain barrier can be injected into the cerebrospinal fluid, from where they reach the brain. In other cases, for example regarding painkillers, injection into the cerebrospinal fluid can allow the dose to be decreased to reduce side-effects.