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Servo-Controlled Blood Vessel Occluder

Servo-Controlled Blood Vessel Occluder. Ahmed El-Gawish, Alan Chen, Hugo Loo, & Imad Mohammad Advisor: Ki Chon. Background. Goal: measure effect of drugs and hypertension on MYO and TGF in mediation of renal autoregulation

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Servo-Controlled Blood Vessel Occluder

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  1. Servo-Controlled Blood Vessel Occluder Ahmed El-Gawish, Alan Chen, Hugo Loo, & Imad Mohammad Advisor: Ki Chon

  2. Background • Goal: measure effect of drugs and hypertension on MYO and TGF in mediation of renal autoregulation • Needed: a device that will automatically occlude and release blood vessels based on the user’s settings

  3. Requirements • Pressure control intervals: 20 mmHg - simulating rapid step change in renal arterial pressure (RAP) • Control over period of 200 secs – stabilizes pressure effects • Mean controlled pressure range 80 – 120 mmHg – range over which the MYO and TGF mechanisms hypothetically take effect in autoregulation

  4. Components • Occluder • Sensor • Pump • Motor • Software

  5. Occluder • Made from 100% silicon material • Proven to be physiology compatibility • Size used is depends on lumen diameter • Range is between 2mm to 24 mm • Inject air or liquid into occluder to adjust the diaphragm/lumen diameter

  6. Air • Advantages • Simplicity • Availability • Ease of pressure control • Doesn’t damage occluder • Disadvantage • Dangerous! • Used for either short or long-term occlusion

  7. Water and saline solution • Advantages • Simplicity • Availability • Ease of pressure control • Biocompatibile • Disadvantage • Transpires/Evaporates through silicone rubber • Causes damage of silicone rubber Used for short-term occlusion (up to one hour)

  8. Glycerin • Advantages • No transpiration • No evaporation • Doesn’t cause damage occluder • Biocompatible Use for long-term occlusion (excess of one hour)

  9. Sensor • Blood pressure sensor is an invasive or non-invasive sensor • Invasive - used or implanted directly at the measurement site (e.g., intra cardiac, blood vessel) • Non-Invasive - measure systolic and diastolic blood pressure utilizing the oscillometric technique • Designed to measure human blood pressure

  10. Invasive Sensors • Internally placed catheter-tip sensor • Catheter fluid is coupled directly to an external transducer • Blood pressure is measured by observing the cavity’s changes in length with an optical signal conditioner • Measuring scheme is based on white light interferometry • Can be used on rats as well as humans

  11. Fiber Optic Pressure Sensors (Invasive)

  12. Non-Invasive Sensors • For humans: the sensor is attached to the cuff on the wrist. • Oscillometric technique is used to measure the blood pressure • For rats: high cost

  13. Photoplethysmography • Relatively inaccurate • Imprecisely measures systolic blood pressure • Over-saturation of the blood pressure signal by ambient light • Difficulty in obtaining adequate blood pressure signals in dark skinned rodents • Correlate poorly with direct blood pressure measurements

  14. Piezoplethysmography • Similar clinical limitations to Photoplethysmography • Utilizes piezoelectric ceramic crystals to record blood pressure readings • More accurate than light-based/LED sensors • Correlate poorly with direct blood pressure measurements.

  15. Volume Pressure Recording-VPR • Independent clinical validation study in 2003 conducted at Yale University • VPR correlated almost 100% with direct blood pressure measurement • Utilizes a specially designed differential pressure transducer • Measure six (6) blood pressure parameters simultaneously: systolic blood pressure, diastolic blood pressure, mean blood pressure, heart pulse rate, tail blood volume, and tail blood flow

  16. Non-Invasive Sensors

  17. Motor • Drives the medium based on control signals • Two Types • Stepper Motor • Servo Controlled Motor

  18. Stepper Motors • Resolution is set at steps per revolution • Inexpensive • No need for feedback • Remembers current position and knows number of steps to reach another position • Uses current even when stationary • Generates heat (50C - 90C)

  19. Stepper Motors (cont’d) • Digitally controlled • Signals cause it to settle in positions based on coil states • Speed determined by controller • Maintains position without signal changes • Higher holding torque

  20. Stepper Motors in Action Animation source: http://www.interq.or.jp/japan/se-inoue/e_step1.htm

  21. Servo-Controlled Motors • Higher resolution • Smoother motion • Less heat generated • More expensive than stepper motors • Lower Holding Torque

  22. Servo-Controlled Motors (cont’d) • Faster than stepper motor • Feedback determines correct positioning • More complex than stepper motor • Oscillates when close to the desired position due to feedback

  23. Servo-Controlled Motors (cont’d) Diagram Source: http://www.machinedesign.com/ASP/viewSelectedArticle.asp?strArticleId=58153&strSite=MDSite&Screen=CURRENTISSUE&CatID=3

  24. On-Off Controller • Logic control with only two states • e.g. temperature control with a boiler that can only be turned on or off • Determines whether the measurement is below a threshold • If below threshold, take action • Otherwise, no action is required

  25. PID Controller • Proportional Integral Differential Controller • Alternative to on-off control • (error) = (set point) – (measurement) • Set point is what you would like the value to • Error would be the difference between the set point and actual value

  26. PID Controller (cont’d) Image Source: http://www.netrino.com/Publications/Glossary/PID.html

  27. P (proportional) • If the proportional gain is well chosen, the time it takes to reach a new set point will be as short as possible, with overshoot (or undershoot) and oscillation minimized. • Large proportional gain needed for quick response • Small proportional gain needed to minimize overshoot and oscillation • Achieving both at the same time may not be possible in all systems.

  28. D (differential) • If the output is changing rapidly, there is a high chance of overshoot or undershoot • The derivative is the change in value from the previous sample to the current sample • Adding this to the proportional controller slows down the response time, but also decreases overshoot and ripple effects

  29. I (integral) • If the is no change in value over time, the output may settle at the wrong value. • Integral value is small in general • Persistent error will cause sum to become large enough to cause a change

  30. PID Controller Summary • Derivative and/or integral terms are added to proportional controllers to improve qualitative properties of a particular response. • When all three terms are used together, the acronym used to describe the controller is PID.

  31. Schematic Presentation of PID

  32. Software • Used to configure the PID controller • Manages data acquisition from sensor • DataLab 2000

  33. References • Wang, H. Siu, K., Ju, K., Moore L. C., and Chon, K. H., Identification of Transient Renal Autoregulatory Mechanism Using Time-Frequency Spectral Techniques. IEEE Transactions on Biomedical Engineering, June 2005 (52) 6:1033-1039 • - • -

  34. Brainstorming . . .

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