Research on the "FLOW-ER' Shunt Device

Introduction

November 1999 - The standard method of treatment for adults and children with hydrocephalus is the placement of a cerebrospinal fluid (CSF) shunt. This system of tubes and valves provides an outflow for accumulated CSF and prevents the dangerous situation of elevated intracranial pressure.

Shunts are not, however, without problems, the most common of which is malfunction of the system anywhere along its course. Catheters may become plugged, valves may malfunction or break, the child may "outgrow" the tubes and infections can develop. The symptoms of a malfunctioning shunt, no matter where or what the cause, may be subtle or obvious and can mimic a number of other conditions. The physician seeing such a child should consider that the shunt may not be functioning properly.

The initial evaluation of a shunt usually begins with a CAT scan of the brain to determine if the ventricles of the brain have dilated. This test is expensive and requires that the child not move. Additionally, it must often be compared to previous studies which may not be immediately available. In some situations, the ventricles do not dilate much, yet the shunt is not functioning properly.

The next step in evaluation is often a "tap" of the shunt. This painful procedure requires knowledge of the system in place and a familiarity of what flow rate is appropriate. The ability to tell if a shunt is working (CSF is flowing through the tubes) without the need for a CAT scan or tap of the shunt would be advantageous to the child and family especially if the measurement of flow could be accomplished simply and effectively.

Hypothesis:

CSF flow through a shunt system could be determined using the principle of ultrasound, which is non-invasive and does not require sedation of the child and is absolutely safe.

Principle of Ultrasound:

Ultrasound sends a sound wave through tissues to a target which is struck and then bounces the sound back to a receiver. It is the same principle as sonar in a submarine. Sound waves "excite" tissues and therefore raise the temperature of the tissue or a special device in the tissue proportionally to the characteristics of the wave.

Ultrasound and Shunts:

If one ultrasounds a fluid and then allows the fluid to move down a shunt tube, the temperature of the fluid which was raised at the site where the shunt tube was struck will gradually return to body temperature. A receiver placed farther down the tube system could then measure the temperature drop (return to normal) and with the use of a computer could calculate the rate of flow, if any.

The Research Project

In conjunction with Dr. Thomas Sachs, Ph. D., we are creating a handheld device which will hopefully measure the flow of CSF in a shunt system. The project is divided into several steps, one leading to the other.

In the first step, the device and receiver are being built with no attention to miniaturization. A specifically designed computer chip is required. At the same time a special device is being created which will conduct the "heat" and would be placed into every shunt. Fluid is then pumped through this shunt at specific rates and the computer is calibrated to measure the rate of flow.

If this is successful, shunt tubes will be implanted into a number of animals. The animals are already being used for other research projects and the device will be removed at the end of the testing. Measuring the flow with skin between the device and receiver is mandatory. After this phase, we anticipate a miniaturization phase which might actually be handled by private industry sources.

Madi's Fund provides the money to reach these phases of the project. The device and receiver have been built although one of the microprocessors has recently broken and must be replaced. Most of the work is being done by volunteers in the Physics Laboratory of Dr. Sachs although there are some plans for moving this project to the Neurosurgery Labs at the University of Vermont. No monies have been used for salaries or benefits to any members of the research team.

As with any research, there are ALWAYS unanticipated events which either slow the pace of development or actually stop it. All of us who are involved in this project believe that the flow device, currently named "FLOW-ER", can become reality and would significantly improve the care that children with Hydrocephalus deserve. There are a number of other projects and research efforts that this work will likely produce.

Steven L. Wald, M. D. Professor
Division of Neurosurgery, University of Vermont
and Fletcher Allen Health Care