B1102010712

IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE)
e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 11, Issue 2 Ver. I (Mar. – Apr. 2016), PP 07-12
www.iosrjournals.org
DOI: 10.9790/1676-1102010712 www.iosrjournals.org 7 | Page
Designing and Modelling a Ventricular Assist Device
Praveen Kumar C 1
, Neeth Antony2
1
Assistant Professor, Eee Department, Nss College Of Engineering, Palakkad
2
Pg Scholar, Eee Department Nss College Of Engineering, Palakkad
Abstract: An Increase In The Number Of Cardiac Patients And A Decrease In Number Of Heart Donors
Hastriggered The Development Of Artificial Heart Pump To Support The Proper Functioning Of The Heart.
This Study Presents Design Of Magnetically Levitated (Maglev) Axial Magnetic Flux Brushless Direct Current
Motor (Af-Bldc) For Axial Blood Flow Ventricular Assist Device (Vad). It Has Three Phase, Twelve Salient
Stator Poles And Eight Rotor Magnet Poles. Twin Af-Bldc Motors Are Placed To Vad Symmetrically And Rotors
Are Coupled To The Pump From Two Sides. Stator And Rotor Of Proposed Motor Have Designed With A Hole
Since Magnetic Flux Doesn’t Pass Through The Central Part. Pump Impellers May Be Placed In This Hole For
Larger Pump Chamber’s Volume And Lower Speed. Motor Has Passive Magnetic Bearing And Doesn’t Involve
Contact And Friction To Minimize Blood Damage. Axial Magnetic Fluxes Are Parallel To Blood Flow
Direction Thus Minimizing Penetration Of Magnetic Field To Blood.
Keywords: Axial Flux Bldc Motor Design, Vad Motors
I. Introduction
Left Ventricular Assist Devices (Lvads) Are Blood Pumps Used To Augment The Cardiac Output Of
Patients With Left Heart Failure. These Devices Are Used Either As A Therapy To Allow The Patient‟s Heart
To Recover, As A Temporary Support To The Patient Until A Heart Transplant Can Be Performed, Or Even As
A Long Term Alternative To Heart Transplantation. Rotary Blood Pumps Offer Several Advantages Over The
Pusher-Plate Type Pulsatile Pumps Because Of Their Simplicity, Low Cost, Small Size, And High Efficiency
[1]. Control Of The Rotary Blood Pump Is Usually Maintained By Setting The Pump At A Fixed Speed Such
That The Pump Can Provide Enough Blood Flow For The Patient‟s Organ Perfusion. However, Determination
Of An Appropriate Pump Speed Setting To Achieve A Desired Blood Flow Rate Based On Patient‟s Body
Demand Is Difficult. A High Pump Speed With Low Right Heart Return Can Cause Collapse Of The Left
Atrium Or Left Ventricle, Thereby Damaging The Blood And The Heart Tissue. On The Other Hand, A Low
Pump Speed At A High Arterial Pressure May Cause Retrograde Flow Into The Heart Through The Lvad Due
To Its Valve-Less Design. . Moreover Regardless Of Pump Speed, An Improperly Fixed Conduit Can Lead To
Blockage Of The Conduit Causing A Dangerous Flow Restriction Through The Device. For These Reasons, It
Is Crucial To Monitor The Pump Flow To Determine A Proper Pump Speed Setting As Well As To Detect
Potential Risk From Inappropriate Device Operation. Direct Flow Measurementwithin The Pump Would
Require An Implantable Flow Transducer. This Is Undesirable For Long Term Implant Because Of The Risk Of
Sensor Failure And The Need For Additional Wires Passing Into The Patient‟s Chest Cavity.
Recent Studies Focus On Bearing Less Maglev Vad Which Is Also Called The 3rd Generation [3].
Vads Should Have A Very Durable, Light And Compact Structure [4] As They Are Implanted To The Human
Body Through Surgical Methods.Permanent Magnets Are Embedded In Pump Impellers. In Radial Flux Bldc
Motors, Magnetic Flux Is Perpendicular To Blood Flow. As Blood Hemoglobin Includes Iron, There Are Some
Studies In Literature Discussing That Magnetic Field Has A Negative Impact On Blood [6].In Vad, The
Anticipated Major Problem Is Blood Damage. Because Volume Of The Pump Chamber Is Smaller In The Axial
Flow Vads, It Needs High Speed Rotor. For This Reason It Causes Blood Damage Due To High Shear Stress.
Proposed Design Has Larger Volume Of The Pump House Than Conventional Vads So Pump Rotor Rotates In
Lower Speeds For Same Pumped Blood Amount Per Minute. Therefore Shear Stress Is Reduced In Blood. In
Proposed Motor, Magnetic Flux Is Not Perpendicular To Blood Flow So Magnetic Field Is Not Affected Blood
Negatively.
In The Proposed Design Our Aim Is To Find Out The Rating Of The Motor Which Are Placed
Symmetrically And Rotors Are Coupled To The Pump From Two Sides. Stator And Rotor Of The Af-Bldc
Motor Have Been Left With A Hole As Magnetic Flux Doesn‟t Pass Through The Central Section. Pump
Impellers Are Recommended To Be Placed In This Hole. Pump Can Be Operated At Low Speed Since Pump‟s
Chamber Is Bigger Than Those Of Normal Axial Vads Which Have Impellers Placed On Inner Surface Of The
Rotor. Motor Is Designed With Magnetic Bearing And Doesn‟t Involve Contact And Friction. Passive Bearing
Magnets Are Placed To Motor To Ensure Maglev. Axial Magnetic Flux Direction Is Parallel To Blood Flow
Direction Thus Minimizing Penetration Of Magnetic Field To Blood.

Designing And Modelling A Ventricular Assist Device
Pump Design
The Blood System Is The Main Transport System For Fuel Supply And Disposal Of Body By-Product.
It Serves For Distribution Of Food Contents From The Digestive System And Of Oxygen From The Respiratory
System To The Body Cells. It Also Serves As Transport System For The Disposing Of By-Products Like Co2 In
The Combustion Process. Heart Is The Main Component Of Cardiac Vascular System. It Includes The
Pulmonary Circulation, A "Loop" Through The Lungs Where Blood Is Oxygenated; And The Systemic
Circulation, A "Loop" Through The Rest Of The Body To Provide Oxygenated Blood. The Systemic
Circulation Can Also Be Seen To Function In Two Parts–A Macro Circulation And A Microcirculation. An
Average Adult Contains Five To Six Quarts (Roughly 4.7 To 5.7 Liters) Of Blood, Accounting For
Approximately 7% Of Their Total Body Weight. The Heart Pumps Oxygenated Blood To The Body And
Deoxygenated Blood To The Lungs. In The Human Heart There Is One Atrium And One Ventricle For Each
Circulation, And With Both A Systemic And A Pulmonary Circulation There Are Four Chambers In Total: Left
Atrium, Left Ventricle, Right Atrium And Right Ventricle. The Right Atrium Is The Upper Chamber Of The
Right Side Of The Heart. The Blood That Is Returned To The Right Atrium Is Deoxygenated (Poor In Oxygen)
And Passed Into The Right Ventricle To Be Pumped Through The Pulmonary Artery To The Lungs For Re-
Oxygenation And Removal Of Carbon Dioxide. The Left Atrium Receives Newly Oxygenated Blood From The
Lungs As Well As The Pulmonary Vein Which Is Passed Into The Strong Left Ventricle To Be Pumped
Through The Aorta To The Different Organs Of The Body.
Cardiac Output (Known As „Q‟) Is A Measure Of The Amount Of Blood That Is Pumped Out Of The
Heart In One Minute. „Q‟ Specifically Refers To The Amount Of Blood Pumped Out Of The Left Ventricle As
This Is The Ventricle That Supplies Blood To The Muscles And Organs Of The Body. Cardiac Output Is Made
Up Of Two Components, Heart Rate (Hr) And Stroke Volume (Sv). Heart Rate (Hr) Refers To The Number Of
Times The Heart Beats Every Minute (Bpm). Stroke Volume (Sv) Refers To The Quantity Of Blood Pumped
Out Of The Left Ventricle With Every Heart Beat. The Exact Volumes Are Not Easily Measured, So They Are
Often Estimated Based On What We Know About Stroke Volume And The Factors That It Affects Such As
Blood Pressure Which We Can Measure. The Equation For Cardiac Output Is: Q = Hr X Sv Blood Pressure
(Bp) Is A Measure Of The Force Being Exerted On The Walls Of Arteries As Blood Is Pumped Out Of The
Heart.The Maximum Pressure During Ventricular Contraction Is Called The Systolic Pressure. The Lowest
Pressure That Remains In The Artery Before The Ventricular Contraction Is Called Diastolic Pressure. Ideally,
We Should All Have A Blood Pressure Below 120 Over 80 (120/80). This Is The Ideal Blood Pressure For People
Wishing To Have Good Health.Since Variation In The Pressure Is Difficult During Design We Take Average Of
Pressure (100mmhg).
The Heart Can Be Described By Simple Model Of A Pump. The Heart Muscles Contracts Which
Cause Decrease In The Volume Of Respective Heart Chambers.Amount Of Work Done By Heart Muscle Can
Be Calculated By Force F Of The Muscle,
∆W = ∫F.Dr (1)
The Work Can Be Expressed In Terms Of Pressure P Exerted On The Surface Area A Of The Heart Chamber.
∆W =
F
A
A. Dr(2)
∆W = ∫
𝐹
𝐴
𝑑𝑉(3)
∆W = ∫ P𝑑𝑉(4)
∆W = 𝑃𝑑𝑉
𝑉2
𝑉1
(5)
∆W = P(𝑉2 − 𝑉1)(6)
V2 − V1 Is The Volume Of Pumped Blood During Each Compression P Is The Average Pressure. Change In
Work Done ∆Wis Given By,
∆W =Average Pressure * Stroke Volume.
The Power Or Work Rate Depends On The Frequency Of Theheartbeat.
Output Power Required To Pump =
∆𝑊
𝑡
(7)
During The Calculation Of The Input Power Of The Motor Of The Motor We Have To Consider The
Blood Flow Conditions, Flow Resistance, Viscosity And Turbulence. Blood Flows Only If There Is Pressure
Difference Between Points Along A Tube Originates A Flow F.
F Α ∆P(8)
Flow Is Determined By Average Velocity (V) Of Particle And Area Of Cross Section (A) Is Given By,
F = A*V(9)
According To Law Of Continuity Flow Is A Constant.Therefore Average Velocity Is Inversely
Proportional To Square Of The Radius Of The Tube. The Resistance R Of The Flow F Is Determined By The
Pressure Difference Between The Tubes. The Resistance Can Be Calculated By The Following Relations.

Figure 1 Tubes In Series
Rtotal=R1+R2+R3(10)
Figure 2 Tubes In Parallel
1
RTotal
=
1
R1
+
1
R2
(11)
Figure 3 Tubes In Parallel
1
RTotal
=
1
R11
+
1
R12
+
1
R21
+
1
R22
(12)
By Using The Expression For The Flow In The Case Of Branching We Obtain Relation Between The
Main Flow F And The Branch Flows F1 And F2.
F = F1 + F2(13)
Flow Resistance Can Be Calculated By,
R =
∆𝑃
𝐹
(14)
Viscosity Is Temperature Dependent Which Reflects Friction Between The Fluid Components. The Velocity
Profile For Viscous Or Laminar Flow Is As Shown In The Figure.
Figure 4 Velocity Profile For Viscous Or Laminar Flow Velocity Is Maximum Along Center Axis Of The Tube
And The Velocity At The Adjacent Tube Walls Is Zero. Flow Is Determined By Viscosity Of Fluid Θ
𝐹 =
𝜋 𝑟4∆𝑃
8𝜗 𝐿
(15)
If Velocity Of Fluid Increases Above A Critical Velocity Laminar Flow Is Turbulent.During Turbulence Linear
Relation Between Pressure And Flow Becomes Invalid.
Turbulence Is Less Efficient So More Work Is Required For The Heart. Critical Velocity Of Turbulence
Depends On Viscosity Of The Fluid, Densityρ, Average Velocity V, Radius Of The Tube R,
𝑁𝑅 =
2𝜌𝑟𝑉
𝜗
(16)
Flow Will Be Laminar If The Reynolds's Number Is Less Than 2000.Flow Will Be Turbulent If The Reynolds's
Number Is Greater Than 3000.
Iii. Axial Flow Bldc Pump
This Study Presents Design Of Magnetically Levitated (Maglev) Axial Magnetic Flux Brushless Direct
Current Motor (Af-Bldc) For Axial Blood Flow Ventricular Assist Device (Vad). It Has Three Phase, Twelve
Salient Stator Poles And Eight Rotor Magnet Poles. It Is Designed In Miniature Size. Twin Af-Bldc Motors Are
Placed To Vad Symmetrically And Rotors Are Coupled To The Pump From Two Sides. Stator And Rotor Of
Proposed Motor Have Designed With A Hole Since Magnetic Flux Doesn‟t Pass Through The Central Part.
Pump Impellers May Be Placed In This Hole For Larger Pump Chamber‟s Volume And Lower Speed. Motor
Has Passive Magnetic Bearing And Doesn‟t Involve Contact And Friction To Minimize Blood Damage. Bearing
Magnets Are Ensured Magnetic Suspension. Axial Magnetic Fluxes Are Parallel To Blood Flow Direction Thus
Minimizing Penetration Of Magnetic Field To Blood. Recent Studies Focus On Bearingless Maglev Vad Which
Is Also Called The 3rd Generation [3]. Vads Should Have A Very Durable, Light And Compact Structure [4] As

They Are Implanted To The Human Body Through Surgical Methods. Tissue Compatible Material Should Be
Used In Places Of Contact With Blood. No Damage Should Be Given To Blood For Hemolysis And Clotting. It
Should Have Low Power And Low Energy Consumption Due To Heating. A Major Part Of These Problems
Regarded As An Important Risk For Vads Has Been Reduced With The Changes Provided In Pump Design
Only [5]. Radial Pumps Have Larger Pump Chambers In Comparison With Axial Ones. There Is Liquid
Pressure Difference Between Pump Input And Output. In Contrast, Axial Pumps Give Larger Flow Rate,
Contributing To Reduced Pump Size. Therefore, When Radial And Axial Pumps Are Used As Vads, Assuming
Same Flow Rate And Liquid Head For Both Models, The First Operates With Lower Rotation In The Rotor, But
They Have Larger Dimensions. It Is Equivalent To Say That Axial Vads Make Possible A More Compact Vad
But They Demand A High Speed In The Rotor. Thus, Both Types Of Vads Present Potential Advantages And
Disadvantages. The Reduced Size Is Very Interesting For The Development Of Implantable Vads.
This Design Provides An Advantage For The Magnetic Bearing Design In Addition To Driving The
Pump From Both Sides. Rotors Are Symmetrically Mounted In Two Parts Of The Pump Unit. In This Design,
The Pump Forms A Whole With The Rotors.Af-Bldc Motors Generate High Magnitude Rotor Pull Force (Fz)
And Torque Generating Forces (Fx, Fy). However, Pull Force Causes Friction And Blockage In Bearing Less
Motors.The Proposed Design Uses Twin Symmetric Motor And Allows Magnetic Bearing Design By Rotor
Forces Balancing Each Other And It Has Passive Bearing Magnets. In Addition, Pump Will Push The Rotor In
Reverse Direction Of Blood Flow Due To Fluid Dynamics During Pump Operation. In This Sense, Passive
Bearing Magnets Provide Opposite Push Force Against The Pump Rotor To Balance By This Way Motor Is
Levitated Magnetically.
Figure 5 Simulation Model Of Af-Bldc
Figure 6 Geometrical Parameters Of Af-Bldc Motor
The Proposed Motor Has Three Phases And Star Connections. During Operation, Two Phases Are
Simultaneously Excited According To Rotor Position And Direction. There Is No Excitation In Another
Remaining Phase. Excited Phase Current Directions Are Opposite To Each Other. Magnetic Flux Path Of The
Motor In The State Of Excitation Of Phase A And B Is Given In Figure 7.
Figure 7 Flux Path Of Af-Bldc Motor

Sequence Of Phase To Be Switched Depends On The Direction And Rotor Position. Rotation Is Single
Direction As The Motor Is Proposed For Driving A Blood Pump. Due To 12-Pole Stator, Rotor Position
Information Is Taken From Hall Effect Sensors That Are Embedded To The Stator With An Angle Of 300
.
Rotor Rotates By 30o
For Each Phase Excitation. As The Magnetic Permeability Of Core Is Accepted To Be
Infinite, Core Reluctance Is Zero. Air Gap Reluctance Rg And Permanent Magnet Reluctance Rm Is Calculated
With Equation17. 𝑅 𝑔 =
𝐼 𝑔
𝜇0 𝑆
𝑅 𝑚 =
𝐼 𝑚
𝜇 𝑚 𝑆
(17)
Where Lg Is Air Gap Distance And Lm Is Magnet Length. S Is The Effective Surface Area Of Stator
Pole. When The Permeability Of Magnet Is Taken Equal To The Permeability Of Magnet Total Reluctance Ro Is
Calculated With Equation 18
𝑅 𝑜 = 𝑅 𝑔 + 𝑅 𝑚 =
𝐼 𝑔+𝐼 𝑚
𝜇0 𝑆
(18)
In This Case We Obtainpermeance Expression From Equation 19
Ρ0 =
1
R0
=
Μ0S
IG +IM
(19)
Magneto Motive Force (Mmf) Of Magnetic Circuit According To The Air Gap And Field Magnitudes Of
Magnets Is Calculated Using Equation 20 In Accordance With Ampere Law.
Ni = HM IM + HGIG(20)
Magnetic Flux Density Is Obtained With Equation21∅ = 𝐵 𝑚 𝐴 𝑚 = 𝐵𝑔 𝐴 𝑔(21)
Magnetic Flux Density Is Derived From Eq.21 And Is Calculated By Eq.22.
BM = −Μ0
AG
AM
IM
IG
HM +
Μ0N
IG
AG
AM
I(22)
Current To Be Applied According To Bm And Hm Values By Taking Operation Range Of Magnet Into
Consideration Is Calculated With Equation 22.
I = BM + Μ0
AG IM
AG IG
HM
AM IG
Μ0NAG
(23)
Basically Torque Can Be Calculated Using Equation 24 Through The Multiplication Of Rotor Diameter Rro
With Radial Force Frad.
T=RRo × FRad (24)
Radial Force Fradwhich Generates Torque Is Obtained Through Equation 25 And Axial Force Which Is
Applying Pull Force To Rotor Fax Is Obtained By Equation 26.
𝐹𝑟𝑎𝑑 = 𝐼. (𝐼 × 𝐵𝑔)𝑒𝑟𝑎𝑑 (25)
FAx
BG
2
.A
2Μ0
EAx (26)
Figure 8 Maglev Design Of Af-Bldc
In Motor Geometry, Active Coil Length Is L And I Is The Current Applied To Coil. Bg Is The Air Gap
Magnetic Flux Density [2]. Axial Force Is The Pull Force Of Rotor. In Magnetic Bearing Motors, This Force
Causes Friction And Blockage If It Is Not Compensated. Proposed System Design Uses Symmetrically Placed
Twin Motor And Passive Bearing Magnets Therefore Basic Axial Forces Generated By Motors Compensate
Each Other In Unloaded Operation. Due To Dynamics Of The Pumped Liquid In Loaded Operation, Pump
Rotor Will Be Pushed In Reverse Direction Depending On The Motor Speed And Liquid Viscosity. In This
Case Axial Balance Is Ensured By Bearing Magnets In Maglev Design Which Is Presented In Figure.
II. Conclusion
The Efficiency Of The Heart Pump Is Very Low (12-20%) So Due To This Variation In The Efficiency
We Take Average Value Of Efficiency As 15%. The Mechanical Power Required For Pumping Blood Is ~1.3
Watts. So The Required Motor Has To Supply An Input Power (~13 Watts) To Provide This Mechanical Power,
Since The Mechanical Efficiency Of Heart Is Very Low, Af-Bldc Motor Design Was Proposed For Axial Blood
Flow Vads With Magnetic Bearing. This Motor Has Miniature Size And Includes A Hole In The Central Part.
Inlet, Outlet Channels And Impellers Were Placed To This Hole For Blood Flow. As The Compact Design Is
One The Most Significant Aspects Of Vad, It May Be Proposed Pediatric Patients. A Three Phased Af-Bldc

Motor Has 12 Salient Stator Poles And Rotor Has 8 Ndfeb Magnet Poles. Rotors Were Symmetrically Placed In
The Pump Chamber. Twin Motors Were Balanced Axial Pull Forces Mutually.
Authors Profile
Mr. Praveen Kumar.C Is Working Presently As Assistant Professor In The Electrical And
Electronics Engineering Dept. Of Nss College Of Engineering Palakkad. His Research Areas
Include: Plasma Physics, Electric Propulsion, Mechatronics, Biomedical Devices
Andelectromagnetism.
Neeth Antony A B-Tech In Electrical And Electronics Engineering From M G University
Kottayam. Now He Is A P G Student In Nss College Of Engineering, Palakkad. .His Research
Interest Concern The Area Of Power Electronics And Control .
References
[1] Schima, H., W. Trubel, A. Moritz, G. Wieselthaler, H. G. Stöhr, H. Thoma, And E. Wolner, “Noninvasive Monitoring Of Rotary
Blood Pumps: Necessity, Possibilities, And Limitations”, Artificial Organs, Vol.16, 1992, Pp. 195-202.
[2] Pohlmann A, Hameyer K. A Study On Permanent Magnet Topologies For Hybrid Bearings For Medical Drives Applied In
Ventricular Assist Devices. Archives Of Electrical Engineering 2011; 60: 371-380.
[3] Timms D, A. Review Of Clinical Ventricular Asisst Devices. Medical Engineering & Physics 2011; 33: 1041-1047.
[4] Okada Y, Yamashiro N, Ohmori K, Masuzawa T, Yamane T, Konishi Y, Ueno S. Mixed Flow Artificial Heart Pump With Axial
Self-Bearing Motor. Ieee/Asme Transactions On Mechatronics 2005; 10: 658,665.
[5] Wu H, Wang Z, Lv X. Design And Simulation Of Axial Flow Maglev Blood Pump. Int. Journal Of Information Engineering And
Electronic Business 2011; 2: 42-48.
[6] Mckay J C, Prato F S, Thomas A W. A Literature Review: The Effects Of Magnetic Field Exposure On Blood Flow And Blood
Vessels In The Microvasculature. Bioelectromagnetics 2007; 28: 81-98.

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