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.

Engineering ProcessAll team members

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

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

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

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

Optimum weight of 5 lbs Optimum dimensions of ~6” x 2” x 2”

Risks Housing for the electronics is too heavy/large/uncomfortable

Preventative measures Eliminate heavy weight materials Eliminate weak, flexible materials Material is ideally machinable

Material and Processing Comparison

Rapid Prototyping

Dimension System ABSplus

Industrial thermoplastic Typically used for product development Machinable

Material can be dilled (carefully) and tapped Accepts CAD drawings

Obscure geometries can be created easily Ideal for proposed ergonomic shape

Lightweight Specific gravity of 1.04

Porous Does not address water resistant need

0.007” material/layer Capable of building thin geometries

Builds with support layer Models can be built with working/moving

hinges without having to worry about pins

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

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 connectorshttp://scoutparts.com/products/?

view=product&product_id=14074

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 “tight” electronics package

Heat Dissipation to the Body Need: Internal Enclosure

dissipates a safe amount of heat to the body

Risk: Internal electronics emit unsafe amounts of heat to body

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

40mW/cm2 source increased to upper limit of 1.8 °C

Specifications: Internal devices must not increase surrounding tissue by more than 2°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

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

Questions / CommentsHelp us improve our design!