Publication
This thesis work aims to optimize the treatment of hydrocephalus. It consists of two distinct objectives: the optimization of the diagnosis of patients implanted with a shunt system for the derivation of cerebro-spinal fluid (CSF) and the optimization of the treatment by a better understanding of the fluidic characteristics of shunts. The diagnosis optimization was addressed by a pressure sensor allowing for the measurement of the intra-cranial pressure (ICP). It has been characterized experimentally in vitro and in vivo in animals. The pressure sensor is integrated along a shunt system for the derivation of CSF and it can be interrogated by telemetry. The non-invasive access to the ICP will allow the physician to verify that the implantation of a shunt system has successfully restored a physiological ICP level. It will also provide a method to verify that the shunt is not blocked and fully functional. Simple mathematical models of the hydrodynamics of shunt systems used clinically are presented to address the second objective. These simple models are verified experimentally by characterizing the shunts on a setup developed for that purpose. This setup allows the characterization of non-bijective flow-pressure characteristics. The integration of mathematical models of shunt systems in a broader model describing the circulation of CSF in a patient implanted with a shunt will permit to predict the dynamics of the CSF circulation. It will also be a useful tool for shunt manufacturers to identify shunt characteristics critical to successfully restore a physiological condition after implantation. The results of this thesis work are presented in the form of an introduction, three scientific publications and a short conclusion. The motivations for the thesis work are presented in the introduction chapter along with background information about hydrocephalus and its treatment. A mathematical model describing the circulation of CSF is described in the same chapter. This model illustrates the interactions between the fluidic constituents of the cranial vault that lead to a physiological CSF circulation and ICP level. This model has been adapted to account for the implantation of a shunt system. The key technical characteristics of the pressure sensor are exposed in the subsequent section along with the experimental techniques and a short summary of the publications and patents. The pressure sensor is described in the first publication with a focus on the pressure transducer, the original sensor encapsulation technique, the electronics embedded in the sensor and the telemetry technique. A capacitive pressure transducer, which provides an accurate measurement of the absolute pressure, has been developed. The transducer technology guarantees a minimal drift of its characteristics with time. The design and the key manufacturing steps of the transducer are exposed. A hermetically closed capsule protects the sensor electronics. The effect of the packaging compon