SMIT 2005 Conference: An Elastancebased Artificial Ventricle to Test Cardiovascular Prostheses

8/14/2019 SMIT 2005 Conference: An Elastancebased Artificial Ventricle to Test Cardiovascular Prostheses

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An elastance-based artificial ventricle to test cardiovascular prosthesesFabio Piedimonte

Smit 2005 17th International Conference 29th September 2005, 1st October 2005, Naples, Italy

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AN ELASTANCE-BASED

ARTIFICIAL VENTRICLE TO TEST

CARDIOVASCULAR PROSTHESES

Fabio Piedimonte

University of Rome Tor Vergata, [email protected]

Maurizio Arabia

Francesco Maria Colacino & Franesco Moscato

University of Calabria, Mechanical Engineering Department

Smit 2005

17th International Conference

29th September 2005 - 1st October 2005, Naples, Italy
mailto:[email protected]:[email protected]:[email protected]


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Introduction

In-vitro experiments performed in many laboratories worldwideare conducted by using pneumatically driven ventricles whose

Starlings law and elastance mechanism result inadequate when

compared to those of a natural ventricle.

The final target of this research has been the development of aninnovative test bench to design and test cardiovascular

prostheses. The test bench is conceived to conjugate a software

environment, which mimics the elastance mechanism of a

natural ventricle, with a hardware environment comprising avascular part of the circulation made up of hydraulic

components which have been properly designed and to which

the ventricle is connected to.


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Pneumatic Ventricle System

The primary energy isprovided by compressedair, produced by anexternal driving unit

A system of electric valvesconnects, in turn, thedriving chamber with asource of pressurized gas(pressure tank) and a

source of decompressedgas (vacuum tank), tocreate the systole and thediastole.

Schematic of pneumatic ventricleby David Wurzel, Ph.D., Cardiac

Systems,


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Pneumatic Ventricle System

The electric valves are of the on-off type andit is, therefore, possible to control systoleand diastole times, but not the air pressurewaveform; consequently, it is difficult toobtain a ventricular pressure pattern similarto that in physiological conditions.

Pressure waves in the ventricle are madesimilar to those in physiological conditionsby exploiting the filtering action of the tube

connecting the valve to the driving chamberand with the aid of an adjustable pneumaticresistance inserted below the high-pressuretank.

Pneumatic mockventricle


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The Elastance-Based Artifcial Ventricle

A reciprocating pump (the hardware ventricle) of a variable

volume chamber completed by two valves allowing

respectively, inflow and outflow of the blood;

An hydraulic circuit that represents the cardiovascularsystem;

A software environment, which mimics the elastance

mechanism of a natural ventricle;

There is a strong interation between the hardware and the

software environments.


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The Differantial Time Varing Model for

Ventricles

Fiso(t)=0

Fiso(t)=1

jA

jP

Maximal Stimulation

At Rest

Elastance Curves

h


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The Differantial Time Varing Model for

Ventricles

*2

0

*

*

0

0min

0

1

*)()()(),(

),()(

PVV

tVV

V

K

VtVV

KVtVE

FtVtVtVttV

dt

tdVRttVPtP

a

satsat

p

isopap

j

j

jjjj

j

TtTT

TTtT

T

TTt

Tt

T

t

tFiso

21

211

2

21

1

1

;0

;2

cos1

0

;2

cos1

S i h I i l C f th S b t O b N l I l


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Control Strategy

The software module of the bench reproduces the time-varying elastance mechanism of the ventricle. It receives thevalue of the ventricular chamber volume Vlv(t) as input, andinstantaneously outputs a reference value of pressure,Plv_des(t), to drive the mock ventricle.

A measured pressure signal Plv(t) is fed back into the softwaremodule for pressure tracking. The difference between Plv_des(t)and Plv(t) is the input to the LQG pressure controller which

has been designed to accurately and rapidly track thereference pressure signal.

S i 2005 17 h I i l C f 29th S b 2005 1 t O b 2005 N l I l


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Control Strategy

P*

Software

Heart Rate (HR) & P* : software input

Mean Systemic Pressure (Pms) & Aortic Resistance (Ras): hardware input

S it 2005 17th I t ti l C f 29th S t b 2005 1st O t b 2005 N l It l


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The artificial ventricle & the Mock Loops

Artificial Ventricle

Cardiovascular

System



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Smit 2005 17th International Conference

29th September 2005, 1st October 2005, Naples, Italy

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Results

Ras decreasePms increasePms decrease Ras increase



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ResultsBlue Reference Ventricular pressure

Red Measured Ventricular Pressure

Green Aortic Pressure

Smit 2005 17th International Conference 29th September 2005 1st October 2005 Naples Italy


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Results: PV loops

HR variation

P* variationPms variation

Ras variationP P

P P

V

V

V

V



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Conclusions

The solution proposed is a necessary step to radically improvein-vitro tests

An elastance-based mock loop has been designed, built, andtested;

Its evaluated not only the prosthesis but also how theventricle reacts to its implant.



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Future Work

The next step

Acquire and test cardiovascular prostheses (VAD and

artificial valves).

The final step: Hybrid Test Bench The prosthesis to be tested will be inserted between two

electro-hydraulic interfaces

A library of mathematical models will allow to mimic all the

testing scenarios

Electro-hydraulic interfaces will link the mathematical

environment and the prostheses

SMIT 2005 Conference: An Elastancebased Artificial Ventricle to Test Cardiovascular Prostheses

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