Smit 2005 Conference: An Elastancebased Artificial Ventricle To Test Cardiovascular Prostheses

Smit 2005

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

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

AN ELASTANCE-BASED ARTIFICIAL VENTRICLE TO TEST CARDIOVASCULAR PROSTHESES Fabio Piedimonte University of Rome “Tor Vergata”, D.I.S.P. [email protected]

Maurizio Arabia Francesco Maria Colacino & Franesco Moscato An elastance-based artificial ventricle to test cardiovascular prostheses University of Calabria, Mechanical Engineering Fabio Piedimonte

Department

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

Introduction • In-vitro experiments performed in many laboratories worldwide are conducted by using pneumatically driven ventricles whose Starling’s 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 an innovative 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 a vascular part of the circulation made up of hydraulic components which have been properly designed and to which the ventricle is connected to. An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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Smit 2005

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

Pneumatic Ventricle System • The primary energy is provided by compressed air, produced by an external driving unit • A system of electric valves connects, in turn, the driving chamber with a source of pressurized gas (pressure tank) and a source of decompressed gas (vacuum tank), to create the systole and the diastole.

Schematic of pneumatic ventricle by David Wurzel, Ph.D., Cardiac Systems,

An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

Pneumatic Ventricle System • The electric valves are of the on-off type and it is, therefore, possible to control systole and diastole times, but not the air pressure waveform; consequently, it is difficult to obtain a ventricular pressure pattern similar to that in physiological conditions. • Pressure waves in the ventricle are made similar to those in physiological conditions by exploiting the filtering action of the tube connecting the valve to the driving chamber and with the aid of an adjustable pneumatic Pneumatic mock ventricle resistance inserted below the high-pressure tank. An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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Smit 2005

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

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 cardiovascular system; • A software environment, which mimics the elastance mechanism of a natural ventricle; • There is a strong interation between the hardware and the software environments. An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

The Differantial Time Varing Model for Ventricles Fiso(t)=1

Elastance Curves Maximal Stimulation

jA

At Rest

Fiso(t)=0 An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

jP

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Smit 2005

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

The Differantial Time Varing Model for Ventricles dV t  dt j V (t ), t   j p V (t )  j a V (t )  j p V (t )* Fiso   P(t )  P0  j V (t ), t   R

j p  Emin V t   V0  

K K  Vsat  V t   V0  Vsat

  V *  V t   2     P * j a  1   *   V  V0  

  t  1  cos   T1  ;   2  0  t  T1     t  T1  T2   Fiso t   1  cos   T 2  ;   2  T1  t  T1  T2    0; T1  T2  t  T

An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

Control Strategy • The software module of the bench reproduces the timevarying elastance mechanism of the ventricle. It receives the value of the ventricular chamber volume Vlv(t) as input, and instantaneously 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 software module 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 the reference pressure signal.

An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

Control Strategy

P*

Software

Heart Rate (HR) & P* : software input Mean Systemic Pressure (Pms) & Aortic Resistance (Ras): hardware input An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

The artificial ventricle & the Mock Loops

Artificial Ventricle

Cardiovascular System

An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

Results Pms increase

Pms decrease

Ras increase

An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

Ras decrease

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

Results Blue – Reference Ventricular pressure Red – Measured Ventricular Pressure Green – Aortic Pressure

An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

Results: PV loops P

HR variation

P

V

P

Pms variation

Ras variation

V

P

V An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

P* variation

V

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

Conclusions • The solution proposed is a necessary step to radically improve in-vitro tests • An elastance-based mock loop has been designed, built, and tested; • It’s evaluated not only the prosthesis but also how the ventricle reacts to its implant.

An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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

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 An elastance-based artificial ventricle to test cardiovascular prostheses Fabio Piedimonte

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