Servo-Controlled Blood Vessel Occluder

Ahmed El-Gawish, Alan Chen,Hugo Loo, & Imad Mohammad

Advisor: Ki Chon

Background

• Renal autoregulation keeps blood pressure stable in the renal system

• The device will increase or decrease blood pressure by ~20 mmHg with fast response times

• The response time should be in order of 100 ms.

The Output

KI Chon project proposal

Design Alternatives

• Mechanical hydraulic occluder

• Water based syringe pump occluder

• Regulated compressed air occluder

Regulated Compressed Air Occluder

Electrical Regulator

Valve

Stage Regulation

• Stage 1: regulator/valve– 125 psi → 18 psi– ON/OFF control– Safety feature

• Stage 2: regulator/controller– Specific control over range– 18 psi → 120 mmHg < p < 200 mmHg

Regulator Properties

• < 70 milliseconds response time

• Analog/digital inputs/outputs available

• Allow users to develop own software for interface

Valve

Compressed Air Occluder

Limitation of Air System

• Compliance of air

• Biocompatibility of gas

• Budget limit

Mechanical Occluder Components

i. Occluder

ii. Solenoid

iii. Spring

iv. Jagged teeth

v. Hydraulic system

Mechanical Occluder

Hydraulic System vs Motor

Hydraulic system

• Pros– Compact– Control over distance

• Cons– Low precision

Motor

• Pros– Precision

• Cons– Over heating issues– Noise– Bulkiness

Forces Involved• A – Force of Spring

• B – Force by Blood Vessel

• C – Force by flexible Hydraulic Tubing

• D – Friction force on jagged teeth (from 1 or 2 below)

• E – Friction force on jagged teeth (from solenoid)

• F – Friction force on slope (from solenoid)

• G – Friction force on slope (from 1 and 2 below)

• 1 > A + B + C + D + E (one click)

• 2 << A + B + C + D + E (holding)

Forces Involved

• A =

• B =

• C =

• D =

• E =

• F =

• G =

xk1

xk22

L L ha

adzdrdzadP

0 002sin

coscos2,1sin2,1 Fs

F

sincos2,1sin2,1 Fs

F

`cos90coscos ss FFs

sin90coscos ss FFs

Solenoid

Solenoid Forces

sinqvBFsolenoid

nIB 0

gfFF BBneqn

solenoid 22

2

Limitations of Mechanical System

• Limited resolution

• Overheating

• Control limited to occluding

• Jerky occlusion

Syringe Pump Occluder

Syringe Pump Reaction Time

• Syringe pump bottleneck is in withdrawal

• Change in volume is cylindrical: πr2h, where d = 5mm and h = 5mm

2

3

325 14 4 1000

1sec1minmin 60sec 1000

5 100 0.1

60 : 70 0.001

0.1 0.001 100 !

d mlmm

ml mlmsms

mlms

Vol h mm ml

ccSyringe

ml ms

Syringe Size Calculation

• Accuracy ▲ as size ▼

• Speed ▼ as size ▼

• Therefore, accuracy ▼ as speed ▲

• Response time is more important than the accuracy, since the accuracy is always within 1%

Communication with Syringe Pump

• Standard RS232 port at 9600 baud 8N1

• Text input/output using terminal program

• Commands change as well as query the rate/volume of injection and withdrawal

• DASYLab has RS232 input and output

Syringe Pump Reaction Time

• Rate can be changed without stopping pump

• Communications with computer conducted with 8 data bits and 1 stop bit for 9 bits per byte.

sec sec9600 1000 1

10

10

bytes bytebitsms

response

commands bytes

t ms

Occluder In Action

Advantages/Disadvantages

• Cost effective: pump supplied by customer

• Water is non-compressible

• Modular– Use syringes of different sizes– Use occluders of different sizes

The Chosen Design

• Water Based Syringe Pump Occluder!

– Simplistic

– Low cost

– Easily modified

Control Software

DASYLab

• Data acquisition hardware

• Amplifier and filter

• Virtual Instrumentation

• PID control ( loop time response <.05 ms)

Regulation of PID

• Controllable effects of PID

– Rate to reach set point

– Overshoot magnitude

– Oscillation

System Calibration

• Required to get optimal results from system

• Trial runs to get effects relationship (trend)

• Literature shows relationship is usually linear

• PID control set to follow trend after each calibration

Questions