Biomedical Engineering Faculty Biological System Modeling seminar Modeling of Ventricular Assist Devices(VADs) Instructor: Dr. towhidkhah Dr. towhidkhah Presented by: Ehsan Rouhani Ehsan RouhaniSpiring2008

Introduction Heart disease is the leading cause of death in the united states.The traditional soluation to end stage congestive heart failure(is one diseas that the heart muscle is too weak to provide enough perfusion for the body) is heart transplantion.some patients are eligible for a transplant beacause of age or health reasons.Therefore mechanical circulatory assist devices,called artificial heart pumps(AHPs) have been introduced to save some lives of end-stage CHF patients since the 1960s.

Artificial Hearts It pumps blood continously yhrough the circulatory system. - Total Artificial Hearts(TAHs) The Institute of Medicine(in the US) estimates that 10,000 to 20,000 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, mechanical pump type device that is surgically implanted. This device is sometimes called a “ bridge to transplant ”.

Advantages Less costly Uneligible for heart transplants Recovery of the failed ventricle

LVADs - Arroe LionHeart LVAD(Pulsatile pumps): Since the 1960s. It pumps blood in a cycle of pump/relax, just like the heart does. The pulsatile pump up to 10 litrs of blood per minute. - Rotary pumps: - Rotary pumps: These pumps are currently under development. Some studies have showed this type of pumps demonstrating as excellent hemolytic performance over some rotary pump with contact bearing.

Total artificial Heart Left Ventricular Assist Device Percutaneous Ventricular Assist Device

Nimbus pump(LVAD)

The pump Model The rotary pump is a mechanical device driven by a motor The electrical power is converted to mechanical power

Mechanical Part Damping coefficient Load torque exerted on the pump Motor torque Inertia load of the rotor

Electrical Part Rotating speed EMF constant

Pump effieiency H is pressure difference between the outlet and the inlet of the pump Q is flow rate 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 application I. if the left ventricle has no contractility,Th becomes a constant,the speed and current of LVAD will become constant evetually II. if the left ventricle has contractility, Th fluctuates, speed, current will be under the influence of this term Because of difficulties of solving these equations for H and Q directly,some researches turn to estimating H and Q with functions of current and speed Because of difficulties of solving these equations for H and Q directly,some researches turn to estimating H and Q with functions of current and speed

experiment

Pump characteristic equation

Modeling of suction

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

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 Devices (PVADs)

Introduction is a device that bypasses blood from left atrium to femoral artery through a blood pump is a device that bypasses blood from left atrium to femoral artery through a blood pump A percutaneous left heart assist system, including a transseptal cannula, a blood pump, and a femoral arterial cannula A percutaneous left heart assist system, including a transseptal cannula, a blood pump, and a femoral 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 cannula for patients The computer model could also be a tool for cardiologist to choose appropriate size of arterial cannula for patients

Electrical 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 flow Determined by Least square fit to exprimental data

I. Single arterial cannula The switch is open The switch is open

II. Dual arterial cannula with the same sizes The switch is closed The switch is closed

III. Dual arterial cannula with the different sizes

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 identification

Conclusion 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

Refrences [1] S Chen,J R Boston and J F Antaki ”An Investigation of the Pump Operating Characteristics as a Novel Control Index for LVAD Control”International Journal of Control,Automation,and Systems,vol. 3,no. 1,March 2005 [2] Yi Wu,Paul E.Allaire and Gang Tao ”Modeling, Estimation and control of Human circulatory system with a Left Ventricular Assist Devices”IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY,vol.15.No 4 July [3] S.H.Chen,BAROREFLEX-BASED PHYSIOLOGICAL CONTROL OF A LEFT VENTRICULAR ASSIST DEVICE,PHD thesis,Pittsburgh,2006 [4] Y.C.Yu,M.A.Simaan,N.V.Zorn and S.Mushi ”Model-based Prediction of a Percutaneous Ventricular Assist Device Performance”IEEE Conference,portland 2005 [5] S Choi,J R Boston,D Thomas and J F Antaki ”Modeling and Identification of an Axial Flow Blood Pump”Proceeding of the American Control Conference 1997.

Thanks for your attention! Any Questions?