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!