LVAD System Review

1. LVAD System Review

2. System Overview SmihaSayal

3. System Overview • Left Ventricular Assist Device (LVAD) • Mechanical device that helps pump blood from the heart to the rest of the body. • Implanted in patients with heart diseases or poor heart function.

4. System Goal • Miniaturize the existing LVAD system to achieve portability while retaining its safety and reliability.

5. Original System • “Black box” architecture used during development • Large, not portable • Runs on AC power

6. P10021’s System • Has both internal / external components • Equivalent to our “Option 2” • Unfinished implementation

7. Customer Needs • Safe • Robust • Affordable • Easy to wear and use • Interactive with user • Controllable by skilled technician • Comparable performance • Compatible with existing pump

8. Other LVAD Technologies CorAide (NASA)

9. Other LVAD Technologies

10. Concepts: Option 1 All electronics external

11. Concepts: Option 2 ADC internal only

12. Concepts: Option 3 Pump and motor control internal

13. Concepts: Option 4 All electronics and battery internal

14. Concept Generation

15. Concept Generation Highlights Best Option 350 273 200 153

16. Enclosure Design Nicole Varble and Jason Walzer

17. Material and Processing Selection • Needs • The external package should be lightweight/ robust/ water resistant • The devices should be competitive with current devices • The device should fit into a small pouch and be comfortable for user • Specification • Based on the HeartMate II • Optimum weight of 4 lbs • Optimum volume of 56 in3 • Risks • Housing for the electronics is too heavy/large/uncomfortable • Preventative measures • Eliminate heavy weight materials • Eliminate weak, flexible materials • Material is ideally machinable

18. Concept Generation- Materials/Manufacturing Process

19. Water Resistant Testing • Need: The external package should resist minor splashing • Specification: Water Ingress Tests • Once model is constructed, (user interface, connectors sealed, lid in place) exclude internal electronics and perform test • Monitor flow rate (length of time and volume) of water • Asses the quality to which water is prevented from entering case • Risk: Water can enter the external package and harm the electronics • Preventative measures: • Spray on Rubber Coating or adhesive • O-rings around each screw well and around the lid • Loctite at connectors Spray on Rubberizd Coating Spray on Silicon Guard http://scoutparts.com/products/?view=product&product_id=14074 http://safetycentral.com/watspraysilw.html http://www.smooth-on.com/Spray-Materials-St/c1281_1287/index.html?catdepth=1 Urethane Plastic Spray-On Coat

20. Robustness Testing • Need: The device should survive a fall from the hip • Specification: Drop Test • Drop external housing 3-5 times from hip height, device should remain fully intact • Specify and build internal electrical components • Identify the “most venerable” electrical component(s) which may be susceptible to breaking upon a drop • Mimic those components using comparable (but inexpensive and replaceable) electrical components • Goal • Show the housing will not fail • Show electronics package will not fail, when subjected to multiple drop tests • Risks • The housing fails before the electronic components in drop tests • The electronic components can not survive multiple drop tests • Preventative Measures • Eliminate snap hinges from housing (screw wells to secure lid) • Test the housing first • Take careful consideration when developing a thickness of the geometry • Design a compact electronics package

21. Heat Dissipation to the Body • Need • Internal Enclosure must dissipate a safe amount of heat to the body • Risk • Internal electronics emit unsafe amounts of heat to body causing tissue necrosis • Benchmarking • Series of tests studied constant power density heat sources related to artificial hearts • 60-mW sources altered surface temperatures 4.5, 3.4, 1.8 °C above normal at 2, 4, 7 weeks • Internal devices must not increase surrounding tissue by more than 2°C • Specifications • 40mW/cm2 (source increased to upper limit of 1.8 °C) Wolf, Patrick D. "Thermal Considerations for the Design of an Implanted Cortical Brain–Machine Interface (BMI)." Ncib.gov. National Center for Biotechnology Information, 2008. Web. 30 Sept. 2010. <http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=frimp∂=ch3>.

22. Ergonomics • Need: Device should be comfortable for user • ANSUR Database • Exhaustive military database outlining body dimensions • Waist Circumference (114) • Males: 137.3 mm • Females: 126.0 mm • Waist Depth (115) • Males: 113.1 mm • Females: 102 mm • Calculated average radius of hip • Males: 125.2 mm • Females: 114.0 mm • Acceptable Avg. Radius of hip • ~120 mm

23. Rapid Prototyping • Machinable • Material can be drilled (carefully) and tapped • Accepts CAD drawings • Obscure geometries can be created easily • Ideal for proposed ergonomic shape • Builds with support layer • Models can be built with working/moving hinges without having to worry about pins • Capable of building thin geometries • Stereolithography • UV curable polymer resin • Creates a non-porous solid • Enclosure will be waterproof and not require additional coating • Lightweight – Specific gravity of 1.17 • Dimension System • ABSplus • Industrial thermoplastic • Lightweight - Specific gravity of 1.04 • Porous • Does not address water resistant need http://www.dimensionprinting.com/

24. ABS Plastic • Important Notes • Relatively high tensile strength • Glass Transition well above body temperature • Specific Gravity indicates lightweight material

25. Enclosure Concept • CAD model is can be easily resized • Removable top panel for electronics access

26. Embedded Control System Andrew Hoag and Zack Shivers

27. Control System • Requirements • Selecting suitable embedded control system • Designing port of control logic to embedded system architecture • Customer Needs • Device is compatible with current LVAD • Device is portable/small • Allows debug access

28. Impeller Levitation • Impeller must be levitating or “floating” • Electromagnets control force exerted on impeller • Keeps impeller stabilized in the center • Position error measured by Hall Effect sensors

29. Levitation Algorithm • Algorithm complexity influences microcontroller choice • Electronics choices affect volume / weight • Proportional – Integral – Derivative (PID) • Very common, low complexity control scheme http://en.wikipedia.org/wiki/PID_controller

30. Embedded System Selection • Requirements: • Can handle PID calculations • Has at least 8x 12-bit ADC for sensors at 2000 samples/sec • Multiple PWM outputs to motor controller(s) • Same control logic as current LVAD system • Reprogrammable

31. Embedded System Selection • Custom Embedded • dsPIC Microcontroller • Blocks for Simulink • Small • Inexpensive (<$10 a piece) • TI MSP430 • Inexpensive (<$8 a piece) • Small, low power • COTS Embedded • National Instruments Embedded • Uses LabVIEW • Manufacturer of current test and data acquisition system in “Big Black Box” • Large to very large • Very expensive (>$2000)

32. Control Logic/Software • Closed-loop feedback control using PID – currently modeled in Simulink for use with the in “Big Black Box” • Additional microcontroller-specific software will be required to configure and use A/D, interrupts, timers.

33. Life Critical System • Not at subsystem level detail yet. • Life-critical operations would run on main microcontroller. • User-interface operations run on separate microcontroller. • Possible LRU (Least Replaceable Unit) scheme

34. Separation of Main/UI Microcontroller Concept Selection

35. Technician/Field Software Debug Interface • USB • USB is everywhere. • Requires custom PC-side software. • Requires processor support. • Serial (RS-232) • Many computers don’t have serial ports anymore. • Can use $15 COTS USB to Serial adapter. • Can use COTS terminal tools.

36. Technician/Field Software Debug Interface • Example of using COTS tool – Windows HyperTerminal (free/part of Windows)

37. Technician/Field Software Debug Interface Concept Selection

38. Microcontroller Search Parameters • A/D • 0-5V • 8x12-bit @5ksps (kilo-samples/sec) • This equates to 40ksps minimum for A/D • PWM • General I/O for UI controls • At least 10x digital • At least 5x analog • UART (for Serial connection)

39. Microcontroller Packaging • L/TQFP – Low-profile/Thin Quad Flat Pack • Small surface-mount (PCB mount) chip package. • Is solderable (by skilled solderer) • Body thickness up to 1.0mm, sizes range from 5x5mm to 20x20mm

40. Microcontroller • 2 families of Microcontrollers • dsPIC from Microchip • MSP430 from Texas Instruments

41. Microchip dsPIC • dsPIC30F5011 (16-bit architecture) • Max CPU speed 30 MIPS (Million Instructions/sec) • 2.5-5.5V operating voltage • 66KB Flash, 4KB RAM, 1KB EEPROM • 16x12-bit ADC @ 200ksps • -40 to 85C operating temp • 64-lead TQFP – body 10x10mm, overall 12x12mm • Cost [1-25 units] = $7.21

42. TI MSP430 • MSP430F5435A (16-bit architecture) • Max CPU speed 25 MIPS (Million Instructions/sec) • 2.2-3.6V operating voltage • 192KB Flash, 16KB RAM • 16x12-bit ADC @ 200ksps • 3 Timer modules (with total of 15 timer channels) • -40 to 85C operating temp • 80-lead LQFP – body 10x10mm, overall 12x12mm

43. Microcontroller Concept Selection

44. Next Steps Juan Jackson

45. Tasks • Battery analysis • Motor controller research and selection • Enclosure final design • Further microcontroller analysis • Embedded code • Cost analysis

46. Timeline

47. Questions / Comments Help us improve our design!