The disease of hydrocephalus or some forms of brain injury can cause an increased stiffness of the brain. A measure of the stiffness of the brain is called its compliance. The condition of poor compliance is commonly treated by a surgical diversion of cerebrospinal fluid (CSF) by the placement of a ventriculoperitioneal (VP) shunt. These inserted devices frequently fail and require replacement. The current approach to assessing whether the shunt has failed is to surgically implant an intracranial pressure (ICP) sensor
It was the goal of the research work presented to develop a method and tools to allow measuring brain compliance non-invasively. It was learned that brain compliance can be determined by comparing the ICP waveform to the waveform of the artery feeding the brain. Obtaining waveforms from both of these signals is still an invasive process. Finding a way to obtain these signals non-invasively was an important goal. First, it was found that a reference signal from another artery, such as from the finger, or ear, or face provides the same information as the one directly feeding the brain. Second, it was found that the ICP waveform could be obtained from the ear drum. Moving from this anatomical information to sensors was a challenge. The digital artery waveform is derived from a common pulse oximeter. The ICP waveform is derived from a piezo sensor fitted into the external ear canal and worn as a headset. Having the necessary signals, the next challenge was to develop an algorithm that would provide the desired information. A signal processing algorithm was developed to allow the sampling of signals from these two sensors and then computes the compliance information. It is shown as a time-lag or phase relationship between the two waves, which widens with worsening brain stiffness or compliance. An instrument that implements the signal capture and the algorithm to compute compliance was developed.
The state of the work will be presented along with a summary of current directions in the research.