In Vitro Hydrodynamic Performance Test And Evaluation Methods Of Heart Valve

The cardiovascular system is one of the most important systems in the human.The heart is the source of power for blood circulate and divided into left/right ventricles and atria,with atrioventricular valves(mitral valve and tricuspid valve)and arterial valves(aortic valve and pulmonary valve).The valves ensure unidirectional flow of blood.Valvular disease is a common disease in heart and can cause blood to not flow in the desired direction or increase resistance and make the heart less efficient.The treatment of moderate or severe patients often adopts valve prosthesis replacement or valve repair.Whether valve prosthesis replacement or valve repair,it has to be good hemodynamic performance.Due to technical and ethical factors,the advantages of valve testing in vitro are unmatched by experiments in vivo(animal or clinical experiments).The ISO 5840 standard is an international standard for the assessment of valve performance and specifies the methods and conditions for valves testing in vitro.The pulsatile flow testing simulates the work environment of the valve after implantation or after the repair of the pathological valve,and is the "gold standard" for valve testing in vitro.Although the valve in vitro test has been developed for more than half a century,there are still many problems to be solved,such as: inconsistent pulsatile flow test results in various laboratories,inaccurate flow detection in pulsatile flow test,existing valve performance evaluation indicators are not comprehensive,traditional valve testing methods and equipments are not competent for the new valve prosthesis and valve repair technologies that have appeared in recent years.The objective of this study was to develop a novel single opening&closing pulsatile flow invitro valve tester for direct measurement of closing volume of the heart valve.The single opening&closing valve tester was composed of a piston pump,valve mounting chamber,reservoir,measurement and control system.The piston pump was used to drive a valve to open and close with control flow which comprised three phases of accelerated,constant and decelerated flow with 6 slopes.A high-speed camera was used to record valve opening and closing images.Two pressure transducers were used to capture the ending time of valve closing which was verified by the highspeed photography.The closing time was measured and closing volume was calculated with a piston displacement volume during valve closing.A tilting disc valve and porcine mitral valve were tested.The transvalvular pressure was minor during valve opening and then increased sharply during valve closing.A novel single opening&closing pulsatile flow in-vitro valve tester for the heart valve has successfully been developed and can be used to simulate and evaluate the opening and closing hemodynamics of the heart valve.The tester can be used to measure valve closing volume and time accurately with a standardized testing protocol free from effect of other components such as the resistance,compliance units and auxiliary valve in the continuous pulsatile flow valve tester.In the valve test in vitro,the flow detection is important and necessary.The result of the flow directly affects the evaluation of the hemodynamic performance of heart valve.Doubted about the accuracy of the current flowmeter,so made a flow generator to test and evaluate the Transonic flowmeter,which was widely used in the pulsatile blood flow.The test contents included a series of small steady flow,pulsatile flow and valve regurgitation,which were commonly seen in valve testing.The results show that the Transonic flowmeter has good linearity for steady flow,but there are errors(1-137 %)and delays(11-43 ms)for unsteady flow,and the closing volume also exists errors(2.9-44 %).The relationship between the flow wave and the valve hydromechanical performance was studied,as the application research of the single opening&closing valve tester.Eight physiological and pathological transmitral flow waves were accurately simulated by the single opening&closing valve tester,and the tilting disc valve,bileaflet valve and mitral valve were tested.Test the opening,forward flow and closing performance of the valve under different flow waves.From the results,The flow wave will affect the performance of the valve upto >30%.The EAT has little effect on the valve opening performance,E:A ratio and heart rate can affect the valve forward flow performance and the ADT is closely related to the valve closing performance.This study has important support for standardizing pulsatile flow testing in the ISO 5840 standard and evaluation of valve replacement and repair.In view of the valve performance parameters,the forward flow and regurgitation performance are assessment separately.It is impossible to compare the valves.A new concept of valve loss rate was proposed.By analyzing the ventricular pressure-volume loop,the heart work and valve energy loss were derived.Through assumptions and approximations,the formula of valve loss rate was simplified and more suitable for clinical and engineering.Using the single opening&closing valve tester to simulate different myocardial functions,and the M25 Bileaflet valve was tested.The valve performance parameters such as the transvalvular pressure,regurgitation fraction and loss rate were calculated.It can be seen from the results that the valve loss rate not only integrates the performance of forward and reverse flow,but also is not sensitive with myocardial function.The valve loss rate can reflect the hydrodynamic characteristics of the valve,and is suitable as a valve evaluation index.In this study,the single opening&closing valve tester and valve loss rate was proposed for the first time.These new method and evaluation indicator will provide new methods for the development of valve testing and valve research.