Implantable Devices for Hydrocephalus Management
For the past 60 years, hydrocephalus has been managed using passive drainage cerebral shunts. However, 40% of passive shunts fail within two years after implantation due to complications such as obstruction and incorrect drainage. A smart shunt is a powered device intended to solve these problems using cellular obstruction preventive techniques and patient specific drainage algorithms. This study has focused on obstruction resistive designs and obstruction clearing means for prolonging shunt patency. The integrated fluidic topology presented is capable of providing passive, energy efficient means for intracranial pressure regulation and comprises of a built-in flushing mechanism. The concept was realized using a rotary pump-valve peristaltic system, consisting of a novel peristaltic three-way variable-resistance valve. The shunt topology is capable of continuous drainage, zero opening pressure and is able to reverse flow direction for the purpose of unclogging the shunt. Feasibility calculations suggest it is capable of 150 valve adjustments or 5 flushing cycles before requiring a recharge when using a 2 gram coin-cell battery. A 40 gram smart phone battery could provide 2 weeks of closed loop operation when regulating intracranial pressure at 10 minute intervals. The mechanical wear the device is subjected to is negligible and intended to support operation for a lifetime. The DC motor, gearhead and encoder required to drive the hypothetical peristaltic system is the size of two AA batteries and weighs 50 gram. The dimensions of the peristaltic system were obtained via MATLAB simulations and a bench-top shunt system was evaluated using pressure-flow and back-pressure test rigs with LabVIEW. The shunt demonstrated an overall conductance of 0 - 4.90 ??L/min/mmH2O and a back-pressure of 3 mH2O. The peristaltic system demonstrated its efficacy as part of an obstruction-free smart shunt. Future development will include miniaturization of the shunting device. A bioreactor connected to the shunt system will start the evaluation of the effectiveness of flushing on cellular obstruction. Simulink computer simulations will allow energy efficient drainage hydraulic designs and algorithms to be tested using a hydrocephalus hydrodynamic model of the brain.