Endoscopic Third Ventriculostomy

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Chapter 2: Topologies to Move CSF from A to B

This chapter describes the mechanisms and pathways required to achieve CSF diversion from the ventricles on the brain to the abdominal cavity. An active shunt consists of a connection of valves and or pumps placed at specific locations along a tubing network. Pumping layouts with the ability to deliver a pressure differential to unblock occlusions at any end of the shunt are of particular interest. In particular the chapter will investigate fluidic designs based on compact topologies and minimalistic hydraulic component layouts capable of:
 A low power consumption mode for ICP regulation with the capability of continuous CSF drainage AND
 An active pumping high power consumption mode with the capacity of unblocking obstructions anywhere along the shunt system All of the shunt topologies to be described took inspiration from the topology displayed as Figure 2.1 from the pending patent “Catheter and Shunt System Including the Catheter”, US20130303971 [96].

Shunt-line topology

The literature review presented in chapter 1 discussed that the majority of obstructions occur at the proximal end of the catheter.
Figure 2.1 above illustrates a general and adaptable, shunt topology describing the placement of hermetically enclosed hydraulic and sensing elements along a network of tubing. The topology depicts a shunt with the Left Proximal Catheter (LPC) on the left, Right Proximal Catheter (RPC) on the right and the distal tubing at the bottom. The hydraulic elements are represented by the four ovals, the pressure sensors are symbolized by the black dots and the hermetic casing is the rectangular enclosure.A simplified shunt-line topology, a shunt skeleton is shown in Figure 2.2 (a). The resultant topology shows the simplest tubing network which allow for continuous flushing of the shunt without drawing fluid from the abdominal cavity. From here onwards the working of the shunt-line when filled with fluid will be analyzed. For all the cases to be studied, the shunt-line skeleton is orientated with its distal end closest to the ground and its proximal ends furthest from the ground. Under the influence of gravity, fluid passively flows downwards to achieve a lower state of gravitational potential energy. For all scenarios it is assumed that there is an infinite supply of fluid into the proximal catheters. The principle scenario takes place when no part of the shunt is occluded. In this case, equal amounts of fluid flow from each proximal catheter, converge at the proximal-distal node, flow through the distal tubing and out of the shunt. The skeleton in Figure 2.2 (b) depicts the scenario in which an occlusion has occurred somewhere along the length of one proximal tubing. This is probably the most common form of obstruction for the shuntline being discussed. The ideal method of unblocking this obstruction is to close off the distal cathete and draw fluid from the non-obstructed proximal catheter; which in turn pushes material out of the shunt. The less common case of obstruction in the distal tubing is depicted in the Figure 2.2 (c). Fluid can be pumped from one or both proximal catheters and be used to clear obstruction in the distal section. The shunt-line skeleton in Figure 2.2 (d) depicts the exceptional case where both of the proximal catheters are blocked. To clear this obstruction the distal tubing is first closed off, the pump then draws fluid from one proximal catheter which creates a pressure within the fluid to push material out the other proximal catheter’s end.An alternative and less ideal workaround does exist in the case when the above process is unable to clear the shunt by allowing the fluid already within the shunt tubes to be pump upwards. However, this is likely to need a reservoir as drawing abdominal fluid is unlikely to be an acceptable (or viable) mechanism.

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Chapter 1: Hydrocephalus and Cerebral Shunts
1.1 Hydrocephalus
1.2 Current treatments 
1.2.1 Closed CSF drainage
1.2.2 Endoscopic Third Ventriculostomy
1.3 Shunt malfunction
1.3.1 Obstruction via physical processes
1.3.2 Hydrocephalic insult & histological responses
1.3.3 Mechanical related issues
1.4 Active shunting
1.5 Recent work and challenges
1.6 Research objectives
1.7 Thesis outline 
Chapter 2: Topologies to Move CSF from A to B
2.1 Shunt-line topology
2.2 Hydraulic schematics
2.2.1 Hydraulic components
2.2.2 Variable resistance valve topologies
2.2.3 Stagnant fluid free topology
2.2.4 3-channel diaphragm valve topology
2.3 Peristaltic schematics
2.3.1 Schematic convention
2.3.2 Flushing sequence
Chapter 3: Feasibility Analysis of an Active Shunt 
3.1 Solving the mechanical criteria 
3.1.1 Torque investigation
3.1.2 Sizing the actuators and sensors
3.2 Device reliability
3.2.1 Open loop operation
3.2.2 Closed loop pressure regulation
3.2.3 Mechanical lifetime
3.2.4 Abnormal operation
3.2.5 Feasible operation
Chapter 4: Valve Resistance Simulations
4.1 Variable radius housing
4.1.1 Operational principle
4.1.2 Mathematical modeling
4.1.3 Simulation results
4.1.4 Limitations
4.2 Constant radius housing
4.2.1 Operational principle
4.2.2 Mathematical modeling
4.2.3 Simulation results
4.2.4 Limitations
Chapter 5: Bench-top Implementation and Testing of an Active Shunt
5.1 Shunt’s mechanical interface 
5.1.1 Standard peristaltic pumps
5.1.2 Custom housing design
5.1.3 Cam system
5.1.4 Custom tubing
5.1.5 Realizing a bench-top setup
5.2 Shunt’s electronic interface 
5.2.1 Electronic components
5.2.2 Interfacing Software
5.3 Pressure-flow evaluation setup
5.3.1 Experimental principles
5.3.2 Physical system
5.3.3 Software
5.3.4 Experimental procedure
5.4 Shunt flushing evaluation setup
5.4.1 Experimental principles
5.4.2 Physical system
5.4.3 Software
5.4.4 Experimental procedure
5.5 Results and discussion
5.5.1 Pressure-flow response
5.5.2 Shunt flushing
Chapter 6: Progressing to an Implantable Smart Shunt
6.1 Bioreactor experiments
6.2 Computational models
6.3 Fabrication
6.4 Shunt evaluation 
6.5 Envisioned implantable smart device 
6.6 Conclusion
References
Appendix A: Flushing Sequence 
Appendix B: Feasibility Calculation 
Appendix C: Simulation Code 
Appendix D: Flow & Pressure Results 

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Implantable Devices for Hydrocephalus Management

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