Biomedical subjects

Yubing Shi

Publications and source records attributed to Yubing Shi.

6 recordsLinked to original sources

PubMed2006

Numerical simulation of cardiovascular dynamics with left heart failure and in-series pulsatile ventricular assist device.

This article presents a numerical model for investigations of the human cardiovascular circulation system response, where the function of the impaired left ventricle is augmented by the pumping action of a pulsatile ventricular assist device (VAD) connected in series to the native heart. The numerical model includes a module for detailed heart valve dynamics, which helps to improve the accuracy of simulation in studying the pulsatile type VAD designs. Simulation results show that, for the case with left ventricular (LV) failure, the VAD support successfully compensates the impaired cardiovascular response, and greatly reduces the after-load of the diseased ventricle, thus assisting possible recovery of the ventricle from the diseased condition. The effects of these conditions on pulmonary circulation are also shown. To investigate the effect of different pumping-activation functions (VAD motion profiles) on the cardiovascular response, three different VAD motion profiles are investigated. The numerical results suggest that Hermitian type motion profiles (smooth curves skewed toward early systole) have the advantage of requiring minimum power to the VAD, and producing the minimum after-load to the left ventricle, minimum ventricular wall stress, and minimum ventricular work to the diseased ventricle; while sawtooth type motions need slightly more power input, and induce slightly increased aortic pressure in diastole, thus improving coronary perfusion.

Computer Simulation↗

PubMed2005

Effects of atrial contraction, atrioventricular interaction and heart valve dynamics on human cardiovascular system response.

Various simulation models of different complexity have been proposed to model the dynamic response of the human cardiovascular system. In a related paper we proposed an improved numerical model to study the dynamic response of the cardiovascular system, and the pressures, volumes and flow-rates in the four chambers of the heart, which included the effects of atrial contraction, atrioventricular interaction, and heart valve dynamics. This paper investigates the effects of each one of these aspects of the model on the overall dynamic system response. The dynamic response is studied under different situations, with and without including the effect of various features of the model, and these situations are studied and compared among themselves and to detailed aspects of expected healthy-system response. As an important contribution with potential clinical applications, this paper examines the corresponding effects of atrioventricular interaction, and heart valve opening and closing dynamics to the general system dynamic response. This isolation of physical cause-effect relationships is difficult to study with purely experimental methods. The simulation results agree well with results in the open literature. Comparison shows that introduction of these new features greatly improves the simulation accuracy of the effects of a, v and c waves, and in predicting regurgitant valve flow, the dichrotic notch, and E/A velocity ratio.

Animals↗

PubMed2005

A concentrated parameter model for the human cardiovascular system including heart valve dynamics and atrioventricular interaction.

Numerical modeling of the human cardiovascular system has always been an active research direction since the 19th century. In the past, various simulation models of different complexities were proposed for different research purposes. In this paper, an improved numerical model to study the dynamic function of the human circulation system is proposed. In the development of the mathematical model, the heart chambers are described with a variable elastance model. The systemic and pulmonary loops are described based on the resistance-compliance-inertia concept by considering local effects of flow friction, elasticity of blood vessels and inertia of blood in different segments of the blood vessels. As an advancement from previous models, heart valve dynamics and atrioventricular interaction, including atrial contraction and motion of the annulus fibrosus, are specifically modeled. With these improvements the developed model can predict several important features that were missing in previous numerical models, including regurgitant flow on heart valve closure, the value of E/A velocity ratio in mitral flow, the motion of the annulus fibrosus (called the KG diaphragm pumping action), etc. These features have important clinical meaning and their changes are often related to cardiovascular diseases. Successful simulation of these features enhances the accuracy of simulations of cardiovascular dynamics, and helps in clinical studies of cardiac function.

Atrial Function↗

PubMed2005

Numerical simulation of cardiovascular dynamics with healthy and diseased heart valves.

This paper presents a new concentrated parameter model for cardiovascular dynamics that includes an innovative model of heart valve dynamics, which is embedded in the overall model of the four chambers of the heart and the systemic and pulmonary circulation loops. The heart chambers are described with a variable elastance model, and the systemic and pulmonary loops are described with modified Windkessel models. In modelling the heart valve dynamics, the various factors that influence the valve motion are examined, and the governing differential equation for valve motion is derived. The heart valve model includes the influence of the blood pressure effect, the friction effect from the tissue, and from blood motion. As improvement from previous works, the contribution of the blood vortex effect in the vicinity of the valve leaflets to valve motion is specially considered. The proposed model is then used in simulation of healthy and certain pathological conditions such as mitral valve stenosis and aortic regurgitation. The predicted results agree well with results illustrated in cardiology textbooks.

Adult↗

PubMed2003

Numerical simulation of opening process in a bileaflet mechanical heart valve under pulsatile flow condition.

BACKGROUND AND AIM OF THE STUDY: Most previous computational fluid dynamics (CFD) studies of blood flow in mechanical heart valves (MHVs) have not efficiently addressed the important features of moving leaflet and blood-leaflet interaction. Herein, computationally efficient approaches were developed to study these features and to obtain better insight into the pulsatile flow field in bileaflet MHVs. METHODS: A simple and effective method to track the moving boundary was proposed, and an efficient method for calculating the blood-leaflet interaction applied. In this way, a CFD code was developed to study the pulsatile flow field around bileaflet MHVs. The CFD code was parallelized on a supercomputer to reduce turn-around time in the simulation. The solver was then used to study the opening process in a St. Jude Medical (SJM) size 29 bileaflet MHV. RESULTS: CFD results showed that, in the opening process, the flow field was consistently partitioned into two side channels and a central channel due to the presence of the two leaflets. In the flow field near the surface of the two leaflets, the fluid velocity followed the local surface velocity of the leaflets, thus showing a strong blood-leaflet interaction effect. Throughout the valve-opening process, peak velocities were always observed near the tips of the valve leaflet. The CFD simulation showed that the opening process took approximately 0.044 s, which compared well with experimental findings. CONCLUSION: The new computational approaches were efficient and able to address the moving leaflet and blood-leaflet interaction. The flow field in the opening process of a SJM 29 bileaflet MHV was successfully simulated using the developed solver.

Blood Flow Velocity↗

PubMedDate not supplied

Numerical simulation of a systemic flow test rig.

In this study, numerical simulation was carried out to investigate the dynamic response of a systemic flow test rig that is widely used for in vitro study of prosthesis in the cardiovascular system. In the system the physiological impedance of systemic circulation was modeled as a resistance-capacitance-resistance type. The system analysis was directly based on differential equations describing the system dynamics, and numerically solved using the fourth-order Runge-Kutta method. Results showed that pressure in the systemic circulation test rig could be successfully simulated with the developed model. From the numerical experiment, it was found that the maximum stroke of the driving mechanism, the flow coefficients and opening of the control valves, and the initial volume of air in the compliance strongly affect the dynamic performance of the test rig. The numerical method developed is a useful tool in the design and optimization of the system configuration.

Biomechanical Phenomena↗