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 =

Solenoid

Solenoid Forces

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: πr 2 h, where d = 5mm and h = 5mm

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.

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