Poster Ifac 2005 Conf A Preload And Afterload Sensitive Artificial Ventricle For Testing Cardiovascular Prostheses

Paper ID: 4458

A PRELOAD AND AFTERLOAD SENSITIVE ARTIFICIAL VENTRICLE TO TEST CARDIOVASCULAR PROSTHESES M. Arabia1, F.M. Colacino1, G.A. Danieli1, F. Moscato1, S. Nicosia2, F. Piedimonte2. 1Dip.

di Meccanica; Università della Calabria, Arcavacata di Rende, CS, Italia; 2Dip. Informatica, Sistemi, Produzione; Università TorVergata, Roma, Italia; E-mail to contact author: [email protected]

Methods

Hydraulic layout and control scheme

Hydraulic mock circulatory systems have low flexibility to allow tests of different cardiovascular devices and low precision in reproducing the reference model. A new bench is described. It combines the computer modeling of the environment in which the device will operate, and electro-hydraulic interfaces (E-H-I). The latter are used to link the software module with the inputs and outputs of the device under test.

The hydraulic afterload and venous return have been reproduced by Windkessel and Guyton’s models, respectively. This closed loop setup represents an hydraulic simulator of the systemic circulation with left atrium.

LV

The control strategy proposed in this paper is based on the regulation of the mean ventricular and atrial pressures. This result is obtained by choosing a real-time simulated flow rate waveform in one cardiac cycle as input to the system. Some parameters of this simulation are tuned to properly estimate some physical variables of the hydraulic circuit. If the model of the system is enough accurate, it will be possible to use the flow rate waveforms as input signal of the open loop system, and get the correct pressure waveforms as output. In order to achieve this result, all the components of the loop have been characterized, including those spurious (always present in physical systems). Nevertheless, since the mean systemic pressure Pms and the arterial systemic resistance Ras are not known a-priori, it becomes necessary to continuously estimate them while the experiment is running. The real time variations of Pms and Ras in the simulated model lead to the correct sensitivity of the test bench to preload and afterload changes. The unknown parameters are continuously estimated by means of the difference between simulated ( P _ S ) and measured (P ) mean pressures, by using the following relation:

Cas

Ras

Cla

Cvs

Electric analog of the test layout

Layout to test the E-H-I

F(k  1)  F(k )  KF P (k )  P _ S (k )

where F is the parameter to be estimated and KF is the control parameter.

Control scheme

Results of the elastance-based mock loop: Afterload and Preload Sensitivity High frequency signal represents data continuosly recorded during the experiment whose waweforms have been zoomed once steady state is reached to show agreement with physiological data. PV loops show the Starling behavior of the hydraulic simulator. Valves have high leakage. HR = 90 [bpm]; Cas= 1.2, Cvs= 80, Cla= 10 [ml/mmHg]; Rid= 0.035, Rii= 10, Rod= 0.065, Roi= 6 [mmHg*s/ml], and by varying Pms from 11.5 to 13.5 [mmHg] and Ras from 1.35 to 1.15 [mmHg*s/ml].

Pms decrease

Pms increase

Ras increase

Ras decrease

Pressure data (bleu: simulated values for EHI; red: measured values into E-H-I; green: measured values into Cas)

Results in short Pms ↑

Estimates (upper row); mean pressures (lower row); bleu: measured, green: simulated

Q↑ Ves↑ Ved↑↑ SV↑ Vmean↑ Pas-mean↑ Pas-min↑ Pas-max↑↑

Ras↑ Q↓ Ves↑↑ Ved↑ SV↓ Vmean↑ Pas-mean↑ Pas-min↑↑ Pas-max↑

P-V Loops (bleu: reference, red: Pms increase)

P-V Loops (bleu: reference, red: Ras increase)