Testing the hydrocephalus shunt valve.

Unwanted results of shunting for hydrocephalus include slit and asymmetrical ventricles and the conversion of communicating hydrocephalus to noncommunicating hydrocephalus. Evidence suggests this may be due to a mismatch between the pressure/flow performance characteristics of the shunt valve and the pathologic hydrodynamics of the ventricular cerebrospinal fluid. Commercially available shunts are currently tested using a steady-state pressure/flow method. We have utilized a bench testing method which incorporates pulsed flow and varying compliance. Results indicate that with minimal compliance in the system, opening and closing pressures differ markedly in value with pulsed flow as compared to steady-state testing. The greater the compliance the less deviation was noted. It is recommended more effort be made to understand the value of matching pressure/flow characteristics of valve to the individual hydrocephalic state.