Biomedical Engineering FacultyBiomedical Engineering Faculty

Biological System Modeling seminarBiological System Modeling seminar

Modeling of Ventricular Assist Modeling of Ventricular Assist Devices(VADs)Devices(VADs)

InstructorInstructor::

Dr. towhidkhahDr. towhidkhahPresented byPresented by::

Ehsan RouhaniEhsan Rouhani

SpiringSpiring

20082008

IntroductionIntroduction

Heart disease is the leading cause of death in the united Heart disease is the leading cause of death in the united states.The traditional soluation to end stage states.The traditional soluation to end stage congestive congestive heart failureheart failure(is one diseas that the heart muscle is too (is one diseas that the heart muscle is too weak to provide enough perfusion for the body) is heart weak to provide enough perfusion for the body) is heart transplantion.some patients are eligible for a transplant transplantion.some patients are eligible for a transplant beacause of age or health reasons.Therefore mechanical beacause of age or health reasons.Therefore mechanical circulatory assist devices,called circulatory assist devices,called artificial heart artificial heart pumps(AHPspumps(AHPs) have been introduced to save some lives of ) have been introduced to save some lives of

end-stage CHF patients since the 1960send-stage CHF patients since the 1960s..

Artificial HeartsArtificial Hearts

It pumps blood continously yhrough the circulatory systemIt pumps blood continously yhrough the circulatory system..

- -Total Artificial Hearts(TAHs)Total Artificial Hearts(TAHs)The Institute of Medicine(in the US) estimates that 10,000 to The Institute of Medicine(in the US) estimates that 10,000 to 20,000 people per year will be condidates for the TAHs20,000 people per year will be condidates for the TAHs..

Left Ventricular Assist Devices(LVADs)Left Ventricular Assist Devices(LVADs) - -A left ventricular assist device(LVAD) is a battery operated, A left ventricular assist device(LVAD) is a battery operated, mechanical pump type device that is surgically implantedmechanical pump type device that is surgically implanted..

This device is sometimes called a This device is sometimes called a ““bridge to transplantbridge to transplant””. .

AdvantagesAdvantages

Less costlyLess costly

Uneligible for heart transplantsUneligible for heart transplants

Recovery of the failed ventricleRecovery of the failed ventricle

LVADsLVADs

- -Arroe LionHeart LVAD(Pulsatile pumps)Arroe LionHeart LVAD(Pulsatile pumps)::Since the 1960s. It pumps blood in a cycle of pump/relax, Since the 1960s. It pumps blood in a cycle of pump/relax, just like the heart doesjust like the heart does..The pulsatile pump up to 10 litrs of blood per minuteThe pulsatile pump up to 10 litrs of blood per minute..

- - Rotary pumpsRotary pumps::These pumps are currently under developmentThese pumps are currently under development..Some studies have showed this type of pumps Some studies have showed this type of pumps demonstrating as excellent hemolytic performance over demonstrating as excellent hemolytic performance over some rotary pump with contact bearingsome rotary pump with contact bearing..

Total artificial Heart

Left Ventricular Assist Device

Percutaneous Ventricular Assist Device

Nimbus pump(LVAD)Nimbus pump(LVAD)

The pump ModelThe pump Model

• The rotary pump is a mechanical device driven by a motor

• The electrical power is converted to mechanical power

Mechanical PartMechanical Part

Damping coefficient

Load torque exerted on the pump

Motor torque

J Inertia load of the rotor

( )( )i e p

d tJ T T B t T

dt

B

eT

PT

3 20 1PT a aQ 2

0 1

3( )

2 b

dJ K B Q a a

dt

Electrical PartElectrical Part

( )( ) ( ) ( )b

di tv t L Ri t K t

dt

( )t

bK

Rotating speed

EMF constant

Pump effieiencyPump effieiency

hT HQ

( )sN

H is pressure difference between the outlet and the inlet of the pump

Q is flow rate

1/ 2

3/ 4s

NQN

H

• specific speed , a none-dimensional is used to describe the characteristic of the pump in the design range

• the design objective is to achive the maximal efficiency at a specific speed

Patient status in LVAD applicationPatient status in LVAD application

I . I . if the left ventricle has no contractility ,Thif the left ventricle has no contractility ,Th becomes a becomes a constant,the speed and current of LVAD will become constant,the speed and current of LVAD will become constant evetually constant evetually

II . II . if the left ventricle has contractility , Thif the left ventricle has contractility , Th fluctuates , fluctuates , speed , current will be under the influence of this termspeed , current will be under the influence of this term

Because of difficulties of solving these equations for H Because of difficulties of solving these equations for H and Q directly,some researches turn to estimating H and Q directly,some researches turn to estimating H and Q with functions of current and speedand Q with functions of current and speed

experiment

0.916 16

0.66 6

J e

B e

0

1

0.738 12

0.198 10

a e

a e

20 1 2

0 1 20.296, 0.027, 0.0000933

pp

dQH Q

dt

20 1

3( )

2 b

dJ K B Q a a

dt

Pump characteristic equationPump characteristic equation

i o

2

R =R =0.0677mmHg/(ml/s)

0.0127 /( / )i oL L mmHg ml s

0 1 2

0 1 2

0.1707 0.02177 0.000090, ,

,

3

0.296 0.027 0.0000933,

20 1 2

pp

dQH Q

dt

Modeling of suctionModeling of suction

1

1

0 if x

3.5 3.5 otherwise

1

thk

th

th

PR

x P

P mmHg

Another pump modelAnother pump model

The motor inductance and the pump moment of inertia J are small,the motor equation is simplified as :

2

2 1 02 2

1 2linearization

et

Q P P

PQRV K Q P V

K

Mock human circulatory loop

�َA mock human circulatory loop was set up an in vitro test rig for a different versions of prototype LVADs, as shown in figure . This test rig can simulate different normal or pathologic states and activities of a cardiovascular system. A small pump MY2 was used in the place od an LVAD in the testing

Percutaneous Ventricular Assist DevicesPercutaneous Ventricular Assist Devices(PVADs)(PVADs)

IntroductionIntroduction is a device that bypasses bloodis a device that bypasses blood from left atrium to femoral artery through a blood pump from left atrium to femoral artery through a blood pump

A percutaneous left heart assist systemA percutaneous left heart assist system ,, including a transseptal cannula, a blood pump, and aincluding a transseptal cannula, a blood pump, and a femoral arterial cannulafemoral arterial cannula

Selecting an appropriate size of arterial cannula to maximize the blood flow rate Selecting an appropriate size of arterial cannula to maximize the blood flow rate

Determining the system performance based on the selection of arterial cannula Determining the system performance based on the selection of arterial cannula

The computer model could also be a tool for cardiologist to choose appropriate size of arterial The computer model could also be a tool for cardiologist to choose appropriate size of arterial cannula for patients cannula for patients

Electrical analog of the modelElectrical analog of the model

since the purpose of this model is to predict the average flow,the transient response in the system negligible

Nonlinear function of fluid flowNonlinear function of fluid flow

* *

2 * 2* *

2

* *

20 1

0

0

( )

( )( ) ( )

2

( ),

.

. . .

Q Q Q Q

I

I I II

P f Q

f f Q QP f Q Q Q

Q Q

P P f Q Q Q Q

P R Q R Q

R R R Q

P R Q R Q Q

Determined by Least square fit to exprimental data

I. Single arterial cannulaI. Single arterial cannula

The switch is openThe switch is open

1Q Q

2 4. . . 0

2

p I OP P P MAP LAP

B B ACA Q Q B Q C Q

A

II. Dual arterial cannula with the same sizesII. Dual arterial cannula with the same sizes

The switch is closedThe switch is closed

1 2 2

QQ Q

1 2O O OP P P

1 2

10 1110 1 11 1 1. . . . . .

2 2

O O O

O OO O O

P P P

R RP R Q R Q Q Q Q Q

III. Dual arterial cannula with the different sizesIII. Dual arterial cannula with the different sizes

10 1 11 1 1 20 2 21 2 2

2

10 10

11 11 11

10 11

2

10 11

. . . . . .

1(1 )

2 2

.1 1

.1 1

O O O O O

O O O

O O O

O O O

EQ O O

P R Q R Q Q R Q R Q Q

R R PQ

R R R

P Q R R Q

R R R Q

20

10

O

O

R

R

Experiment(test loop)Experiment(test loop)

• Generating data to identify the model parameters

• Providing data to validate the accuracy of the model in predicting total bypass flow by changing pump speed

Model parameter identificationModel parameter identification

2

1

2

1

[ ( ) ( )]*100%

( )

n

measured estimatek

I n

measuredk

Q k Q kE

Q k

ConclusionConclusion

• sensorless method for evaluate hemodynamic variable of pump

• PVAD : A simple nonlinear circuit model

• Model can predict the bypass flow rate through the system

• Adavantage : cardiac catheterization laboratory within a short period of time with a major open-heart surgery

RefrencesRefrences]]11[[ S Chen,J R Boston and J F Antaki ”S Chen,J R Boston and J F Antaki ”An Investigation of the Pump Operating An Investigation of the Pump Operating

Characteristics as a Novel Control Index for LVAD ControCharacteristics as a Novel Control Index for LVAD Control”International l”International Journal of Control,Automation,and Systems,vol. 3,no. 1,March 2005Journal of Control,Automation,and Systems,vol. 3,no. 1,March 2005

]]22 [ [Yi Wu,Paul E.Allaire and Gang Tao ”Yi Wu,Paul E.Allaire and Gang Tao ”Modeling , Estimation and control of Modeling , Estimation and control of Human circulatory system with a Left Ventricular Assist DevicesHuman circulatory system with a Left Ventricular Assist Devices”IEEE ”IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,vol.15.No 4 TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,vol.15.No 4

July 2007July 2007 . .

]]33 [ [S.H.Chen,S.H.Chen,BAROREFLEX-BASED PHYSIOLOGICAL CONTROL OF A BAROREFLEX-BASED PHYSIOLOGICAL CONTROL OF A LEFT VENTRICULAR ASSIST DEVICE,LEFT VENTRICULAR ASSIST DEVICE,PHD thesis,Pittsburgh,2006PHD thesis,Pittsburgh,2006

]]44 [ [Y.C.Yu,M.A.Simaan,N.V.Zorn and S.MushiY.C.Yu,M.A.Simaan,N.V.Zorn and S.Mushi ”Model-based Prediction of a ”Model-based Prediction of a Percutaneous Ventricular Assist Device Performance”Percutaneous Ventricular Assist Device Performance”IEEE IEEE Conference,portland 2005Conference,portland 2005

]]55[[ S Choi,J R Boston,D Thomas and J F Antaki ”S Choi,J R Boston,D Thomas and J F Antaki ”Modeling and Identification of Modeling and Identification of an Axial Flow Blood Pumpan Axial Flow Blood Pump”Proceeding of the American Control Conference ”Proceeding of the American Control Conference

19971997. .

Thanks for your attentionThanks for your attention!!

Any Questions?