Analysis of design parameters for shunt valve and anti-siphon device used to treat patients with hydrocephalus

The present study investigated design parameters of shunt valves and anti-s iphon device used to treat patients with hydrocephalus. The shunt valve con trols drainage of cerebrospinal fluid (CSF) through passive deflection of a thin and small diaphragm. The anti-siphon device (ASD) is optionally conne cted to the valve to prevent overdrainage when the patients are in the stan ding position. The major design parameters influencing pressure-flow charac teristics of the shunt valve were analyzed using ANSYS structural program. Experiments were performed on the commercially available valves and showed good agreements with the computer simulation. The results of the study indi cated that predeflection of the shunt valve diaphragm is an important desig n parameter to determine the opening pressure of the valve. The predeflecti on was found to depend on the diaphragm tip height and could be adjusted by the diaphragm thicknesss and its elastic modulus. The major design paramet ers of the ASD were found to be the clearance(gap height) between the thin diaphragm and the flow orifice. Besides the gap height, the opening pressur e of the ASD could be adjusted by the diaphragm thickness, its elastic modu lus, area ratio of the diaphragm to the flow orifice. Based on the numerica l simulation which considered the increased subcutaneous pressure introduce d by the tissue capsule pressure on the implanted shunt valve system, optim um design parameters were proposed for the ASD.