Docstoc

Stony Brook University Stony Brook New York

Document Sample
Stony Brook University Stony Brook New York Powered By Docstoc
					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            Motor

• Pros                      • Pros
  – Compact                   – Precision
  – Control over distance   • Cons
• Cons                        – Over heating issues
  – Low precision             – 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=      k1 x
                                                 ah
                   Psin  ad dz  2
          L                               L
• B=     
          0   0                           0      a
                                                          drdz


• C=      2k 2 x

•         
    D = s  sin   F1, 2 cos  cos
              1, 2 F
                                              
• E=     s    Fs
              cos
                                     
                         cosFs    cos `
                               90



• F=     s    Fs
              cos                    
                          cosFs    sin 
                                90


         s                                  
                             F1, 2 cos  sin 
                    F1, 2
• G=               sin 
Solenoid
     Solenoid Forces

       Fsolenoid  qvB sin 



                B   0 nI


                eqn2 n
Fsolenoid       2        2 B FB  f  g
 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


  Vol     d2
            4    h    25
                        4     5  100mm3  1000ml 3  0.1ml
                                              1
                                                 mm

   60ccSyringe : 70 ml min  60sec  1000 ms  0.001 ml ms
                             1min     1sec


                 0.1ml  0.001 ml ms  100ms !
     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.


       9600 bits sec  1000 bytes sec  1 byte ms
           commands  10bytes
                  tresponse  10ms
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