1335. Simulation of CSF Production, ICP, Compliance, Siphoning and Pulse Pressures Demonstrates Effects on Shunt Drainage
Authors: Christopher Carmen Luzzio; Bermans Iskandar, MD; David Hsu, MD, PhD; Joyce Koueik, MD, MS; Mark Kraemer, MD (Madison, WI)
Crucial to VP shunt management is how posture, Valsalva, CSF pulsations, and brain stiffness affect valve performance. A concern is that “suctioning” dependent on compliance/pulsatility and siphoning/gravity promotes shunt failure. We developed a shunt valve evaluation system pseudo-ventricle (PV) that considers these physiological parameters.
Commercial pressure differential valves were examined: System drainage and PV pressures were recorded for three pulse pressures transmitted into the PV, in three compliance states, and in flat and upright drainage positions. The PV enclosure surrounds the proximal catheter. Water flows into the PV at constant pressure from a reservoir at physiologic rate. Controlled pressure pulses that simulate ICP due to cardiac action or Valsalva are introduced into the PV. Compliance is set by changing air volume above. The catheter exits and connects to the shunt valve which drains into a weighed vessel. Drain height determines siphon pressure. Data acquisition records PV, valve, and drain pressures. Microcontrollers control reservoir and pressure pulses. Drain rate is quantity of fluid exiting the reservoir. Flow into the PV is a function of the reservoir and PV pressure difference. The PV pressure is affected by the valve’s reaction to pressure pulses, compliance, and distal catheter drain height.
We observed: (1) Pulse waves increase drainage; (2) Low compliance leads to transmission of higher pulse waves to valve increasing drainage; (3) Siphoning from gravity leads to greater drainage independently of compliance and pulsatility. PV pressures that average low draw more fluid from the reservoir, thus simulating over-drainage, and those that average high draw less fluid from the reservoir, simulating under-drainage.
Although the PV system cannot exactly reproduce the environment of the shunted hydrocephalic, it provides opportunity to understand physiological parameters that affect shunt function and CSF drainage in response to differing valve mechanisms and future prototype shunt systems.