Posture-independent piston valve: a novel valve mechanism that actuates based on intracranial pressure alone.
OBJECTIVE
Shunt valves are intended to maintain physiological intracranial pressure (ICP). A variety of mechanisms have been designed to accomplish this goal but have had limited success. Siphoning, in particular, has been a problem not effectively solved by proposed or manufactured valves. Poor control of ICP results in headache, neurological disturbances, decreased cognition, shunt malfunction, slit ventricles, subdural hematomas, decreased cranial volume, and maldevelopment. The authors of this study describe a prototype valve that was machined and tested ex vivo and that actuates based on ICP alone regardless of the presence of a siphon. Their object was to determine if a novel shunt mechanism that actuates perpendicular to the flow of fluid would eliminate the effect of siphoning in a valve for the treatment of hydrocephalus.


METHODS
A posture-independent piston valve (PIPV) was anchored to a graduated reservoir. Opening pressure was measured by noting the fluid level in the reservoir when the piston moved. Measurements were made using a 90-cm and a 120-cm water-filled siphon tube (1.3-mm standard distal catheter) to simulate an upright posture. A recumbent posture was simulated by the absence of a siphon.


RESULTS
Opening pressure of the valve did not change regardless of the presence or absence of a water-filled siphon.


CONCLUSIONS
The PIPV was triggered only by the pressure head at the inlet and did not actuate in the presence of a siphon, demonstrating proof of principle of the perpendicular actuating mechanism. The PIPV is a purely mechanical device that has practical application in the treatment of hydrocephalus.
Department of Neurosurgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA. medow@neurosurg.wisc.edu
Joshua E
JE
Medow
Christopher C
CC
Luzzio
D002557:Cerebrospinal Fluid Shunts / Q000295:instrumentation*; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D006849:Hydrocephalus / Q000503:physiopathology* / Q000601:surgery*; D006874:Hydrostatic Pressure; D066298:In Vitro Techniques; D007223:Infant; D007427:Intracranial Pressure / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D013525:Surgical Instruments; D017287:Ventriculoperitoneal Shunt / Q000295:instrumentation