Hydrodynamic function of second generation mechanical and bioprosthetic heart valves

466

Abstracts

HEMODYNAMICS AND CARDIOVASCULAR MECHANICS PULSATILE

FLOW INVESTIGATIONS

OF MECHANICAL AND BIOLOGICAL PROSTHESIS

OF

CARDIAC VALVES F. Klimeg Institute

of Hydrodynamics,

Seven mechanical a comparative

in vitro

flow conditions

study.

are realized

by the artificial A 40 % mixture

Czechoslovak

heart

flowmeter,

of opening of the threeleaflet luable indicator

valves

are investigated

measurements

under

stationary

system

provinience) differential

anemometer

of flow resistancies,

The comparative

completed

Prague

of cardiac

where the left heart

with the electromagnetic

and water is used to simulate the viscosity

lization and the laser-Doppler measurements

Hitherto

on a mock-circulatory

(Czechoslovak

of glycerol

An electromagnetic

Academy of Sciences,

and five biological prosthesis

evaluation

and pulsatory is simulated

control

unit.

of blood. camera for flow visua-

traversing

system facilitated

field before and behind the valve and the process

valves.

of the hydrodynamic

for the assessment

transducer,

with a computer-driven

velocity

biological

pressure

in

of expected

properties

of these heart

valves

is a va-

clinical performance.

HYDRODYNAMIC FUNCTIONOF SECOND GENRRATIONMRCHANICAL AND BIOPROSTHETIC VALVES M. Butterfield, J. Fisher, G-A. Davies, J.N. Kearney Cardiac Research Unit, Killingbeck Hospital, Leeds, U.K.

HEART

The hydrodynamic function of second generation prosthetic and bioprosthetic heart valves Improvement in have been studied and compared to the function of earlier valve designs. function has been related to changes in design and manufacturing processes. Six size 29 mm the Carbomedics and St. Jude valves, mitral and five size 23 mm aortic valves were studied: the Bjork Shiley Monostrut valve, a tilting disc valve; both bileaflet mechanical valves; (mitral position only) and Intact valves, the Hancock II, Carpentier Edwards Su ra-Annular P-axed porcine bioprosehetic heart valves. Valves were all of which are low or zero pressure the mean pressure difference tested using five flow condrtions at different heart rates; during forward flow, closing and closed valve regurgitant volumes were obtained. Pressure difference was also obtained during steady flows of between 20 and 160 ml/s in order to

assess the leaflet opening pressures. Low pressure fixed porcine valves showed significantly larger pressure differences during forward flow than mechanical valves of similar size, but significantly lower pressure differences when compared fo the first Closing regurgitant volumes were significantly larger in the generation porcine valves. Closed valve leakage remained high in the second mechanical valves than the porcine valves. generation mechanical valves and was higher in the aortic position due to the length of time zn which the valves remain closed. Low pressure fixation of porcine valves did not affect valvular regurgitation when compared to first generation valves. Valve function remains dependant on valve type - porcine or mechanical - low or high pressure fixed - rather then on specific design features introduced by individual manufacturers of a particular type.

HYDRODYNAMIC ASPECTS OF THE CLOTTING OF BLOOD AND MILK AT FLOW OBSTRUCTIONS J.R.E.Christy and N.Macleod Department of Chemical Engineering, University of Edinburgh, Scotland, UK. Fluid flow in the vicinity of artificial cardiovascular implants is known strongly to influence the deposition of thrombus around such devices. But, while the deposition of flow-related thrombus has been studied in-viva or in-vitro and valve flow characteristics in artificial circulatory systems have been reported, in no Case have flow parameters and deposition been correlated within the same system. To facilitate such studies, the use of rennetised milk, a fluid analogous in clotting behaviour to blood but more readily handled in-vitro, has been proposed. The validity and efficacy of this analogue fluid technique is here explored for simple and determinate flow situations. The clotting of blood flows paat certain solids of revolution placed in the canine aorta, observed in410 by Vorhauer, is compared with that of flows of milk about similar test bodies and correlated with observed flow patterns. The extent of deposition of coagulum from steady, rather than pulsatile, milk flows around the test bodies is found to bear closer similarity to thrombus deposition in the canine aorta. The studies also reveal that although stasis occurs in all regions where milk is found to deposit, it is not apparently a sufficient condition for deposition, agitation in the region of a solid surface appearing to be a necessary concomitant. The effect of agitation is by no means clear; high shear stresses may limit deposit growth and high mass transfer rates may promote it. In order to appraise the influence of these flow properties the authors now intend to observe ultrasonically the growth of deposit as it occurs.