Experimental determination of the Ahmed Valve FP-7 flow facility and a mathematical

model predicting conventional flow-rate post sub-conjunctival surgery.

Supervised byDr. Matthew Rickard

Associate Professor in Mechanical EngineeringCalifornia Baptist University

Research Title

Joseph Nelly Sugu Sugira

• Engineering analysis• Literature surveys• Design of research prototypes• Laboratory testing• Data analysis• Results documentation

Summer of 2012 gave me a taste of what grad school work or a careers in

bioengineering or research can be

My Assigned duties

The aqueous humor flows into the anterior chamber and drains the Schlemm’s canal

via the trabecular meshwork

Aqueous humor

Schlemm’scanal

Background Information

Increased TM resistance, which slow down the AH drainage, increases the IOP. This results in

Glaucoma

Background Information cont.

Therefore, GDDs are implanted in the eye to bypass the TM increased resistance

Background Information cont.

Thus, lowering the IOP

westcostglaucoma.com

We used many technologies were used to determine the AGV flow facility

Part1 of the Research Project

New Era Pump Systems, Model NE-300

Pasco Science Workshop 750 Interface DataStudio Software

P-601 PiezoMove ™ Z-Actuator

Honeywell 26PCBFBGG pressure sensor

C++ programming language

New World Medical FP7 AGV

Data taking & analysis, observation, and applying the acquired knowledge were key

to the project

Part1 of the Research Project cont.

UNSTEADY PRESSURES UNSTEADY PRESSURES

For example we had a ran into unsteady pressures no matter our setup(SP: Syringe Pump)

CASE 1: SP draining the AGV hooked to a 27-gauge cannula through rubber tubing

CASE 2: SP draining a 25-gauge cannula (No AGV) through rubber tubing

Data taking & analysis, observation, and applying the acquired knowledge were key to

project

OBSERVATION 1:All data taken with SP resulted in unsteady pressures

Part1 of the Research Project cont.

CASE 3: SP, No AGV, with rigid fitting

UNSTEADY PRESSURES

THUS:Replace the SP with a column of water (CASE 4)

OBSERVATION 2:Also data taken with column of water w/ ‘upward resistance’ resulted in unsteady Pressures

CASE 4: water column, AGV, upward resistance

After examining all possible cases and their results we better understood our system

Part1 of the Research Project cont.

SIMILARITIESSyringe Pump: is one-way, thus prevents

flow backwardsBlocked Tube: is one way, thus prevents

flow backwards

CASE 5: Water Column, AGV, no upward resistance

OBSERVATION 3:Data taken with column of water w/o ‘upward resistance’ resulted in steadier Pressures

CONCLUSION:Any apparatus with a 2-way resistance willcause unsteady pressures no matter what.

TRADEOFF!SP causes unsteady pressures but we had a constant flow. On the other hand, with the water column, pressures were steadier but the flow rate wasn’t.

SinceAqueous humor

(uL/min) Electric current (mA)

Can be simulated With

Trabecular Meshwork (drainage resistance)

Electric resistance (kΩ)

GDD (drainage resistance)

Electric resistance (kΩ)

IOP (mmHg) Electric voltage (V)

I modeled the drainage structures of the eye using electrical current components

Part2 of the Research Project

The post-op model with valved GDD (R_V varies with pressure/voltage)

The post-op model with valveless GDD (R is constant)

The pre-op model of the eye

Part2 of the Research Project cont.

Therefore, the pre & post-op ocular dynamics can be modeled electrically

The model with a valveless GDD is simplified because the resistance is then

considered zero

R_TM = (V1-V2)/I_AH (V1 in post op model is V1’)

i_1 = (V1’-V2)/R_TMi_2 = I_AH – i_1 (i_AH = 2.5 mA)R_downstream = V1’/i_2% of I_AH through GDD = (i_AH/i_2)*100

The pre-op model The post-op model

A significant proportion of the AH still follows its natural path (through the TM)

• preOpIOP = 30 mmHg• postOPIOP = 12 mmHg• EPV = 5 mmHg

General Case study

MODELi_1 = 0.7 uL/mini_2 = 1.8 uL/min% of AH through GDD = 72%

Worst Cases study• preOpIOP = 20 mmHg• postOPIOP = 12 mmHg• EPV = 5 mmHg

MODELi_1 = 1.17 uL/mini_2 = 1.33 uL/min% of AH through GDD = 53.4%

• preOpIOP = 40 mmHg• postOPIOP = 12 mmHg• EPV = 11 mmHg

MODELi_1 = 0.08 uL/mini_2 = 2.42 uL/min% of AH through GDD = 96.6%

The model with a valved GDD is complex because its resistance varies with pressure

R_TM = (V1-V2)/I_AH

The pre-op model

The post-op model

If (i1+i2) > 2.5 v1’ = v1’ – 0.1 else if (i1+i2) < 2.5 v1’ = v1’ + 0.1

References

• © 2000 - 2012 American Health Assistance Foundation (http://www.ahaf.org/glaucoma/about/understanding/flow-of-aqeous-humor.html )

• Glaucoma Consultants of Texas (http://www.gcot.net/what-is-glaucoma.html )

• Pedersen & Associates Optometry (http://www.pedersenoptometry.com/eyeconditions/glaucoma.html )

References (cont.)

• Health and Fitness (http://healthinessbox.wordpress.com/2012/04/04/eye-disease-glaucoma-leads-to-blindness/)