Welcome to our presentation entitled Design and Testing of High Resistance Ventricular Catheters, an Initial Feasibility Study. The current cerebrospinal fluid shunt system typically consists of a ventricular catheter with side circular holes as inlets and a valve that regulates flow. Ventricular catheters are frequently replaced within the first year, usually due to shunt malfunction as a result of proximal catheter occlusion. It is hypothesized that the continuous flow of CSF within the current inlet design may be a possible cause of occlusion. Our team performed a feasibility study to determine whether redesigning the inlet holes of the ventricular catheter may control flow of CSF, which may subsequently prevent occlusion. Five new catheter prototypes were developed using computational fluid dynamics and finite element analysis. The CFD analysis specifically was utilized to determine which designs will be easily modeled and prototyped. The five prototypes are listed here and include modified distal atrial catheter, a single U, a double U, a modified U, and finally a V. First is our control, a modified distal atrial catheter. Next is the U-shaped catheter. The design is such that the inlet will be closed when the pressure is low. Once intracranial pressure is high enough, the material should deflect inwards, which will allow the fluid to drain into the catheter. This ability to open and close at various ICPs was hypothesized to be a major advantage of the design. Next, the double U was predicted to have a lower flow rate than the single U due to the distribution of pressure over the two valves. Additionally, the flaps may obstruct flow from one another. The modified U was created in a similar fashion to the single U with the tip of the U additionally removed. With more material removed, the modified U was predicted to allow for easier flap deflection and thus higher flow rates. Next is the V-shaped catheter. Much like the U inlet, the flap of the V would remain closed when there is low intracranial pressure, and when the intracranial pressure is high, the flap would deflect inwards and fluid would be able to drain. Once ICP lowers to a normal value, the inlet will close again. The flow rate is predicted to be the highest due to its large deflection area. A testing apparatus was developed to simulate CSF flow through a catheter, and the prototypes were tested against a standard control catheter, pictured as a setup for testing. The pump pushed deionized water from a reservoir into the system that was calibrated by a centurion compass. The volume of liquid dispensed was measured in order to calculate the flow rate represented by the equation pictured. Once the flow rate was calculated for up to 20 data points, it was plotted against pressure in centimeters of water. Regression analysis was performed to determine linearity. The ultimate goal was to determine if each design exhibited an on-off phenomenon, whereby no flow occurs at low pressures and flow begins beyond a pressure threshold. Here are the results plotted as pressure versus flow rate. It was predicted that the V prototype would show the biggest improvement in flow rate compared to the other designs. In reality, however, the designs showed varying amounts of improved flow control, with the modified U-shaped inlet prototype showing the most flow rate control across various pressures when compared to the control with a p-value of 0.00388. In general, when compared to the standard control catheter, all designs showed a high resistance to flow. The modified U prototype showed the lowest resistance to flow among these. Prototypes single U, double U, modified atrial distal catheter, and V were not operating in a high enough pressure range to produce a large flow rate. Factors that affected flow rate include geometry, stiffness, and pressure range. In conclusion, this was an initial feasibility study designed to determine how plausible further manufacturing of high resistance catheters would be. We found that high resistance ventricular catheters can be designed and made to mimic the current catheter valve system. We hope in the future to improve on the designs with more consistencies in prototyping. The authors report no conflict of interest concerning the materials or methods utilized in the study or the findings reported. We would like to thank the Illinois Neurological Institute, OSF St. Francis Department of Neurosurgery, the University of Illinois College of Medicine Peoria, and Bradley University Department of Mechanical Engineering.

Design and Testing of High Resistance Ventricular Catheters

Inlet holes redesign

Shunt malfunction prevention

Computational fluid dynamics

Finite element analysis