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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.
Design Alternatives
• Mechanical hydraulic occluder
• Water based syringe pump occluder
• Regulated compressed air occluder
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
Mechanical Occluder Components
i. Occluder
ii. Solenoid
iii. Spring
iv. Jagged teeth
v. Hydraulic system
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
Limitations of Mechanical System
• Limited resolution
• Overheating
• Control limited to occluding
• Jerky occlusion
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
Advantages/Disadvantages
• Cost effective: pump supplied by customer
• Water is non-compressible
• Modular– Use syringes of different sizes– Use occluders of different sizes
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