Overview of bioengineering and hydrocephalus: 50 years in 30 ...

Barry Lutz, Ph.D. 

Research Assistant Professor 

Department of Bioengineering 

University of Washington 

Samuel R. Browd, M.D., Ph.D. 

Assistant Professor of Neurological Surgery 

Department of Neurological Surgery 

University of Washington 

Attending Pediatric Neurosurgeon 

Seattle Children’s Hospital 

Disclaimer: co‐founder of Aqueduct Neurosciences, Inc with 

q , 

Sam Browd and Tom Clement (developing a smart shunt)

Shunt history: 50 years in 5 minutes 

1950s 

Silicone 

1-way differential 

pressure valves 

(Hakim, Pudenz, 

Heyer-Schulte) 

today 

Dates derived from “The scientific history of hydrocephalus and its treatment.” 

Aschoff, Kremer, Hashemi, Kunze. Neurosurg. Reviews (1999).



Silicone 





1970s 

Siphon control 

(ASD, SCD, gravity) 

Some adjustable 

designs (Portnoy, 

Hakim) 

today 





Silicone 





1970s 





Hakim) 

1980s 

Programmable 

(Medos-Hakim) 

Flow control 

valve (OSV) 

today 





Silicone 





1970s 





Hakim) 

1980s 

Programmable 

(Medos-Hakim) 

Flow control 

valve (OSV) 

1990s onward 

Modest changes 

Many clone devices 



• Limited options for type of control 

• Nearly every device is dff differential pressure valve 

• Siphon‐control (add‐on or integrated) 

• Adjustable pressure set point (from all majors) 

• A few flow control valves (OSV, Diamond) 

• Et Extraordinary failure rates 

• 40% by year 1, 50% by year 2, 98% by year 10 

• Obstruction is key cause: proximal (60%), valve (30%) 

• No sensors, no reliable failure diagnostics, no 

monitoring i capability

What can we do to really advance the 

status quo? 

• Methods/designs that reduce obstruction & 

in vitro biological models to test them 

• Diagnostics for shunt failure & monitoring 

• Smart Shunts for advanced control and 

diagnostics & bench models to test them 

(dynamic models) 

• Improved understanding di of the desirable 

control approaches (and devices to carry 

them out)

Shunt obstruction 

• Proximal catheter obstruction 

• Catheter geometry 

• Anti‐fouling coatings 

• Active methods to fight in‐growth 

• How do we test new methods?

Proximal obstruction: geometry 

• Early efforts (from The Shunt Book!)

Proximal obstruction: geometry 

• Tissue in‐growth may favor distal holes 

• What effect does hole size have on flow?

Proximal obstruction: coatings 

Promising priority area, no clear winners yet

Filter added to proximal catheter 

• NJ Institute of Technology 

• Filter added to catheter 

• Group has large NIH grant 

for related work

Proximal obstruction: active method 

• Jack Judy, UCLA 

• Microelectromechanical 

(MEMS) “flappers” in 

catheter holes break 

tissue growth 

• Activated by external 

magnetic field 

US Patent Disclosure‚ Self-Clearing 

Catheter for Clinical Implantation (2004)

Proximal obstruction: testing 

• Pat McAllister, Carolyn Harris 

• Flow‐based cell culture system for testing 

proximal catheter obstruction (& valves too) 

“Mechanical contribution to astrocyte adhesion using a novel in vitro model of catheter 

obstruction.” Harris, Resau, Hudson, West, Moon, McAllister. Exptl Neurology (2010).

Obstruction: status and needs 

• Proximal catheter obstruction (60%) 

• Coatings: no proven solutions yet, but promising 

• Active methods: intriguing but research stage 

• Better CSF control may reduce failure (OSV) 

• Valve obstruction (30%) 

• Possible issues with ih valve designs: complex flow 

path, small gaps, CSF contacts intricate parts 

• Little‐to‐no activity to reduce valve obstruction 

• Need in vitro biological models to evaluate 

new obstruction‐prevention bt ti ti methods

Shunt failure diagnostics 

• Common components: 

• Sensors (pressure or flow) 

• Some source of power (wireless or battery) 

• Option #1. External reader & transmitted 

power: on‐demand measurement (clinic, home) 

• Option #2. Implant with battery: potential for 

continuous monitoring to identify problems 

before they occur (and generate useful data)

Reader‐based flow diagnostics 

• NeuroDx ShuntCheck with Micropumper 

• Flow sensor based on classic “ice cube” test 

• Over‐skin sensor (no implanted parts) 

• multiple NIH SBIRs, some clinical testing


• Transonic Systems 

• Ultrasonic flow 

detection (CSF 

flow is near 

detection limit for 

this technology) 

• External reader & 

transmitted power 

• Several clinical 

trials, outcome?


• New Jersey 

Institute of 

Technology 

(w/ Infoscitex) 

• Large NIH 

grant for flow 

sensor and 

proximal 

catheter filter 

• SmartShunt TM

Sensorized Shunt Concept 

• Alfred Mann Foundation pressure sensors 

Current 

Technology 

Intermediate 

Goal 

Final Goal 

20

Pressure Sensor Requirements 

AMF minimum sensor requirements demonstrated 

• Range: 680 to 1220 cm H2O absolute (‐350 to +200 

cm H2O gauge) 

• Accuracy: ±2.7 cm H2O 

• Resolution: 0.27 cm H2O 

• Low current RF coupled power system 

• Package‐capable for long‐term implantation 

• Rlibl Reliable pressure measurement 

• Functional lifetime: at least 1 year 

21

Reader‐based pressure diagnostics 

• Many active developers, including majors 

Meithke 

• External‐power (no battery) 

• On‐demand measurements 

• Meithke SensorReservior (left) 

• Radionics Telesensor 

• Medtronic InSite 

• Codman (2009 patent) 

• H‐cubed (development stage?) 

• Issys (development stage?) 

• Alfred Mann Foundation

Diagnostics: status of systems 

• High value, lots of activity (including majors) 

• Potential payoff: cost savings for averted 

diagnostic procedures ($1.3B/year???) 

• Sensor challenges: required accuracy (mL/hr, 

cm H2O) pushes technology limits 

• Other challenges: cost, regulatory 

• Most require external power (MRI issues?) 

• Little activity on stand‐alone implants 

• Early detection, potential use in a smart shunt 

• But, must be stand‐alone with power source

“Smart” Shunts –the common vision 

• Sensors (flow or pressure) 

• Pump or valve 

• Electronics 

• Implanted power (battery) 

• Control algorithm 

• Measure things 

• Change pump/valve setting 

• Two‐way way communications 

(diagnostics, intervention) 

Anticipated for decades. Why don’t we have one yet?

Smart Shunts: Codman & Shurtleff 

• Based on adjustable Codman‐Hakim valve 

• Smart actuator on adjustment cam 

actuator

Smart Shunts: Medtronic 

• Positive displacement pump (e.g. drug pump) 

• Timed pump program or P‐sensor controlled

Smart Shunts: Integra Lifesciences 

• Regulation based on 

transient component of 

ICP as a measure of 

brain compliance

Smart Shunts: Meithke valve 

• Meithke valve mechanism (on‐off switch) 

• Drainage via on‐off valve schedule 

• Al‐Nuaimy group developing algorithms 

Meithke patent (2005) 

Al-Nuaimy group (Univ. of Liverpool)

Smart Shunts: tube squeezer 

• Tube squeezer with feedback control 

• Aachen University (Leonhardt) simulated 

control dynamics 

“Simulation of….future electromechanical valves….” Leonhardt group (2012)

Early models of the CSF system 

• Early models: static single‐compartment 

• Bench testing of shunts follows similar 

“plumbing” approach 

Hakim physical model 

Maramou electrical model

Advanced models of CSF dynamics 

• Dynamic models needed to test smart shunts 

• e.g., R. Penn (left), A. Linninger, Dr. Bradley 

• ETH Zurich SmartShunt project (right) 

Penn group

Smart shunts: challenges & payoff 

• Remaining challenges/needs 

• Sensors with sufficient accuracy (pressure, flow) 

• Power consumption (lifetime 5+ years?) 

• Size, MRI compatibility 

• Cost (viable under existing reimbursement?) 

• Regulatory (what is acceptable e testing?) 

• Potential payoff 

• Diagnostics, failure detection, improved safety 

• Data logging, new insight into condition 

• Opportunity to implement sophisticated control

Summary: potential wins in next 5 years 

• Reducing obstruction remains a key need 

• Proximal: coatings, active methods 

• Valve: almost no activity on this problem 

• Need biological models to evaluate methods 

• Shunt diagnostics & monitoring 

• Many folks developing on‐demand diagnostics 

• Continuous monitoring could alert before problems 

occur and provide patient data – does not exist 

• Smart shunts (anticipated for decades) 

• Needs: designs to defeat the power draw problem, 

g p p , 

implantable sensors, good regulatory strategies

This just in – CSF glucose power for brain 

machine interface (June 2012)

Needs with promise in next 3‐5 years 

1) Obstruction‐resistant shunts (proximal, valve) and in 

vitro biological models to test them 

2) Fully‐implanted battery‐powered sensors for shunt 

failure diagnostics (& monitoring to generate better 

data) 

3) Improved understanding of desirable algorithms for 

CSF drainage 

4) Smart shunts with diagnostics, advanced control, and 

maintenance and bench models to test them 

5) Funding for collaborations between clinicians, 

scientists, and engineers (program, center)

Questions 

1) What CSF control methods are needed that we don’t 

have today (pressure, flow, combination, time 

variable, shunt weaning)? 

2) What are the arguments for and against antisiphoning 

in a differential pressure shunt? 

3) What are the key needs of different patient 

populations (pediatric, i adult, NPH)? 

4) For implanted electrical systems (diagnostics, smart 

shunts), is there an acceptable battery replacement 

model by elective surgery (e.g., pacemaker) ? 

5) What testing threshold is needed (bench, animal, 

human) to reach a comfort level for clinician adoption 

(for implantable diagnostics, smart shunts)?

Overview of bioengineering and hydrocephalus: 50 years in 30 ...

Create successful ePaper yourself

Delete template?

Save as template?