lvad system review
DESCRIPTION
LVAD System Review. System Overview. Smiha Sayal. 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. System Goal. - PowerPoint PPT PresentationTRANSCRIPT
LVAD System Review
System OverviewSmiha Sayal
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.
System Goal
Miniaturize the existing LVAD system to achieve portability while retaining its safety and reliability.
Original System
“Black box” architecture used during development
Large, not portable Runs on AC power
P10021’s System
Has both internal / external components Equivalent to our “Option 2” Unfinished implementation
Customer Needs
Safe Robust Affordable Easy to wear and use Interactive with user Controllable by skilled technician Comparable performance Compatible with existing pump
Other LVAD Technologies
CorAide (NASA)
Other LVAD Technologies
Concepts: Option 1
All electronics external
Concepts: Option 2
ADC internal only
Concepts: Option 3
Pump and motor control internal
Concepts: Option 4
All electronics and battery internal
Concept Generation
Selection Criteria Weight Rating Notes Score Rating Notes Score Rating Notes Score Rating NotesSmall Internal Volume 9 5 45 4 36 2 18 1Small External Volume 4 2 8 3 12 4 16 4Low internal weight 8 5 40 4 32 2 16 1Feasible within timeline 9 5 45 3 27 2 18 1Low Probibility of Failure 10 3 30 3 30 3 30 3Easy to maintain 8 5 40 4 32 2 16 1Low number of wires thru body 4 1 20 wires 4 2 10 wires 8 4 3 wires 16 4 3 wiresLow signal noise 2 4 8 1 high bandwidth 2 4 8 4Low heat dissipation to body 8 5 40 4 32 2 16 1Debug signals avalible externally 8 5 40 4 32 2 16 2Additional Processes (biocompatibility/waterproofing)5 5 25 3 15 3 15 3Affordability 5 5 1 enclosure 25 3 2 enclosures 15 3 2 enclosures 15 2 2 enclosuresNet Score 350 273 200Rank 1 2 3
Concepts"Option 1" "Option 2" "Option 3" "Option 4"
Concept Generation Highlights
Option 1•Smallest internal volume•Feasible within timeline•Easiest to maintain•Minimum 20 wires
Option 2•Relatively small internal volume•Slightly higher risk of internal failure•Minimum 10 wires
Option 3•Large internal volume•Difficult to design•Electronics failure is fatal•Minimum 3 wires
Option 4•Large internal volume•Difficult to design•Electronics failure is fatal•Minimum 3 wires
Best Option
350
273
200
153
Enclosure DesignNicole Varble and Jason Walzer
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
Concept Generation- Materials/Manufacturing Process
Manufacturing Processes
Rapid Prototyping (ABS
Plastic) Stereolithography Injection Molded Machine Metal or Polymer
Selection Criteria Weight Rating Notes Score Rating Notes Score Rating Notes Score Rating Notes ScoreCost 9 4 36 3 27 1 $30k for mold 9 2 18Feasibility within timeline 10 5 50 4 long lead time 40 1 10 3 30Strength 6 4 37 MPa 24 5 58 MPa 30 5 35-70 MPa 30 5 ~580 MPa 30Material Interaction with water 4 2 8 4 resin based 16 5 20 4 16Ease of Manufacturing 3 5 15 5 15 3 9 3 9 0 0 0 0 20 wires 0 10 wires 0 3 wires 0 3 wires 0Net Score 133 128 78 103Rank 1 2 3 4
Continue? no no
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
http://scoutparts.com/products/?view=product&product_id=14074http://safetycentral.com/watspraysilw.htmlhttp://www.smooth-on.com/Spray-Materials-St/c1281_1287/index.html?catdepth=1
Spray on Rubberizd Coating Spray on Silicon Guard
Urethane Plastic Spray-On Coat
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
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>.
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
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/
ABS Plastic
Mechanical Property
Test Method
Imperial Metric
Tensile Strength ASTM D638
5,300 psi 37 MPa
Tensile Modulus ASTM D638
330,000 psi 2,320 MPa
Tensile Elongation
ASTM D638
3% 3%
Heat Deflection ASTM D648
204°F 96°C
Glass Transition DMA (SSYS)
226°F 108°C
Specific Gravity ASTM D792
1.04 1.04
Coefficient of Thermal Expansion
ASTM E831
4.90E-5 in/in/F
• Important Notes• Relatively high tensile strength• Glass Transition well above body temperature• Specific Gravity indicates lightweight material
Enclosure Concept
CAD model is can be easily resized Removable top panel for electronics access
Embedded Control SystemAndrew Hoag and Zack Shivers
Control System
Requirements Selecting suitable embedded control
system Designing port of control logic to
embedded system architectureCustomer Needs
Device is compatible with current LVAD Device is portable/small Allows debug access
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
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
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
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)
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.
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
Separation of Main/UI Microcontroller Concept Selection
Selection Criteria Weight Rating Notes Score Rating Notes ScoreCost 7 3 2x chips, PCBs 21 5 more pins/memory 35Feasibility within timeline 10 3 30 4 40Separation of concerns (separate subsystems) 8 5 40 1 8Ease of design 6 3 need comm bus 18 4 24Ease of manufacturing 6 3 2x chips, PCBs 18 4 1 chip, 1 PCB 24Net Score 127 131Rank 2 1
Continue? No Yesweight 1- low importance
10- high importancerating 1- does not meet cirteria
5- meets cirteria
Concept Generation- Microcontroller Separation
Microcontroller SetupsSeparate Main and UI uCs Single uC
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.
Technician/Field Software Debug Interface
Example of using COTS tool – Windows HyperTerminal (free/part of Windows)
Technician/Field Software Debug Interface Concept Selection
Selection Criteria Weight Rating Notes Score Rating Notes Score Rating Notes ScoreCost 7 5 35 4 28 4 28Feasibility within timeline 10 5 50 4 40 4 40Easy to connect to PC 8 3 Some PC's not built-in 24 5 40 5 40No custom software for PC host 7 4 28 1 7 5 35Ease of design 6 5 30 3 18 3 18Ease of manufacturing 6 4 24 3 18 3 18Net Score 191 151 179Rank 1 2 2
Continue? Yes No Noweight 1- low importance
10- high importancerating 1- does not meet cirteria
5- meets cirteria
Serial (RS-232) USB FT232Microcontroller Setups
Concept Generation- Technican and SW Debug Port
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)
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
Microcontroller
2 families of Microcontrollers dsPIC from Microchip MSP430 from Texas Instruments
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
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
Microcontroller Concept Selection
Selection Criteria Weight Rating Notes Score Rating Notes ScoreCost 6 4 24 4 24Feasibility within timeline 10 5 50 5 50A/D 9 5 Is 0-5V 45 3 Not 0-5V 27Ease of design 6 4 24 4 24Ease of manufacturing 6 4 24 4 24Net Score 167 149Rank 1 2
Continue? Yes Noweight 1- low importance
10- high importancerating 1- does not meet cirteria
5- meets cirteria
Concept Generation- Technican and SW Debug Port
Microcontroller SetupsdsPIC MSP430
Next StepsJuan Jackson
Tasks
Battery analysis Motor controller research and
selection Enclosure final design Further microcontroller analysis Embedded code Cost analysis
Timeline
Tasks Time to Finish 11th - 17th 18th - 24th 25th - 31st 1st - 7th M T W R F S S M T W R F S S M T W R F S S M T W R F S SAnalyze Battery Needs Hot Swapping Choose Connectors Decide Voltage Find Back up Battery Choose Battery Controller Choose Power Regulator Design PCB Research Motor Controller Choose Amplier Redesign RC Filter Define Ideal Curvature
Define Material and Processes
Create Open CAD Drawing Define External Coating Priliminary CAD drawing Helical thread insert Spec out O rings Layout User Interface Control Law Pseudocode Select Microcontroller Generate SDD Addition components Bill of Materials Cost Analysis System Design Review
Questions / CommentsHelp us improve our design!