Microfabricated Implantable Flowmeter for CSF Shunts

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DESCRIPTION (provided by applicant): An implantable wireless flow meter is proposed that would enable measurement of the flow of cerebrospinal fluid (CSF) through the ventriculoperitoneal (VP) shunt, currently used to treat hydrocephalus patients. CSF flow is a key indicator of shunt function, and there is currently no way to measure it in situ, resulting in the absence of clinical methods to directly assess shunt function or to predict its failure. Using MEMS microfabrication methods, the proposed flow meter will be manufactured at a size small enough to be integratable with implanted VP shunts. The key elements in the flow meter are capacitive structures that change properties with change in CSF flow. Radioactive coupling between the internal passive circuitry and an external detection circuit allows implantation of the flow meter without the need for implanted batteries or transcutaneous wires. The proposed Phase I project will design and fabricate a set of MEMS flow sensor prototypes, which will then be inspected and bench tested to confirm key parameters. In parallel, the electronic circuitry required to wirelessly interrogate the sensor will be designed, assembled and tested. In order to perform a protocol that calls for testing of the sensor under realistic conditions, a test stand will be constructed that allows precise control of flow. Tests will be undertaken with the flow meter to confirm that it can meet a number of evaluation criteria: measurement range, accuracy, and measurement insensitivity to orientation and ambient conditions. In addition, testing which simulates a working shunt will evaluate the effectiveness of biocompatible coatings in preventing formation of occlusions in the sensor. Upon completion of Phase I, we will have proved feasibility of the proposed device. Upon completion of Phase II we intend to have developed a wireless flow sensor that could be included as part of an instrumented VP shunt for the treatment of hydrocephalus. PUBLIC HEALTH RELEVANCE: Every year there are approximately 23,000 shunt revisions performed in the U.S., in order to correct the relatively common failure of ventriculoperitoneal (VP) shunts used to treat hydrocephalus patients. However, children are still dying from shunt failure, and studies indicate that earlier detection would save a large fraction of these children. An implantable, wireless CSF flow meter would enable the clinician to monitor shunt function during routine office visits (rather than waiting for the re-appearance of hydrocephalus symptoms), allowing detection of impending shunt failure, avoidance of lifesaving treatment on an emergency basis, and reduction of mortality associated with VP shunt failure.