Federico Domenichini

Three-dimensional filling flow into a model left ventricle

A numerical study of the three-dimensional fluid dynamics inside a model left ventricle during diastole is presented. The ventricle is modelled as a portion of a prolate spheroid with a moving wall, whose dynamics is externally forced to agree with a simplified waveform of the entering flow. The flow equations are written in the meridian bodyfitted system of coordinates, and expanded in the azimuthal direction using the Fourier representation. The harmonics of the dependent variables are normalized in such a way that they automatically satisfy the high-order regularity conditions of the solution at the singular axis of the system of coordinates. The resulting equations are solved numerically using a mixed spectral–finite differences technique. The flow dynamics is analysed by varying the governing parameters, in order to understand the main fluid phenomena in an expanding ventricle, and to obtain some insight into the physiological pattern commonly detected. The flow is characterized by a well-defined structure of vorticity that is found to be the same for all values of the parameters, until, at low values of the Strouhal number, the flow develops weak turbulence.

Fluid dynamics of the left ventricular filling in dilated cardiomyopathy

Modifications in diastolic function occur in a broad range of cardiovascular diseases and there is an increasing evidence that abnormalities in left ventricular function may contribute significantly to the symptomatology. The flow inside the left ventricle during the diastole is here investigated by numerical solution of the Navier-Stokes equations under the axisymmetric assumption. The equation are written in a body-fitted, moving prolate spheroid, system of coordinates and solved using a fractional step method. The system is forced by a given volume time-law derived from clinical data, and varying the two-degrees-of-freedom ventricle geometry on the basis of a simple model. The solution under healthy conditions is analysed in terms of vorticity dynamics, showing that the flow field is characterised by the presence of a vortex wake; it is attached to the mitral valve during the accelerating phase of the E-wave, and it detaches and translate towards the ventricle apex afterwards. The flow evolution is discussed, results are also reported as an M-mode representation of colour-coded Doppler velocity maps. In the presence of ventricle dilatation the mitral jet extends farther inside the ventricle, propagation velocity decreases, and the fluid stagnates longer at the apex.

On the Left Ventricular Vortex Reversal after Mitral Valve Replacement

The blood flow in the human left ventricle is known to develop a vortical motion that should facilitate the ejection of blood into the primary circulation. This study shows that such a rotary motion can be totally reversed after the implant of a prosthetic valve. This phenomenon, in agreement with clinical observation, appears mostly imputable to the symmetry of the implant. The reversed rotation increases energy dissipation and modifies the pressure distribution with the potential development of new pathologies. The results provide preliminary, physically based, elements for the improvement of surgical procedures or prosthesis.

Model and influence of mitral valve opening during the left ventricular filling

The flow inside a model left ventricle during filling (diastole) is simulated by the numerical solution of the equations of motion under the axisymmetric approximation. The left ventricle is taken with a truncated ellipsoid geometry, and a simple conceptual model is introduced to simulate the presence of the moving mitral valve. A relevant role during the left ventricle diastolic flow, as already discussed by other authors, is played by the travelling vortex wake that is formed from the transmitral jet during the early filling acceleration phase. The presence of a moving valve is found to produce a non-simultaneous spatial development of the entering bulk flow and a slightly more complex vortex wake structure; the results are discussed in comparison with fixed valve ones. They are analysed also in terms of M-mode representation suggesting a physical interpretation of the pattern detected in the clinical measurements that extends the one given previously on the basis of fixed valve models.

Comparative numerical study on left ventricular fluid dynamics after dilated cardiomyopathy

INTRODUCTION The role of flow on the progression of left ventricular (LV) remodeling has been presumed, although measurements are still limited and the intraventricular flow pattern in remodeling hearts has not been evaluated in a clinical setting. Comparative evaluation of intraventricular fluid dynamics is performed here between healthy subjects and dilated cardiomyopathy (DCM) patients. METHODS LV fluid dynamics is evaluated in 20 healthy young men and 8 DCM patients by combination of 3D echocardiography with direct numerical simulations of the equation governing blood motion. Results are analyzed in terms of quantitative global indicators of flow energetics and blood transit properties that are representative of the qualitative fluid dynamics behaviors. RESULTS The flow in DCM exhibited qualitative differences due to the weakness of the formed vortices in the large LV chamber. DCM and healthy subjects show significant volumetric differences; these also reflect inflow properties like the vortex formation time, energy dissipation, and sub-volumes describing flow transit. Proper normalization permitted to define purely fluid dynamics indicators that are not influenced by volumetric measures. CONCLUSION Cardiac fluid mechanics can be evaluated by a combination of imaging and numerical simulation. This pilot study on pathological changes in LV blood motion identified intraventricular flow indicators based on pure fluid mechanics that could potentially be integrated with existing indicators of cardiac mechanics in the evaluation of disease progression.

Describing the Highly Three Dimensional Right Ventricle Flow

Visualization of the three-dimensional flow within the Right Ventricle (RV) is a challenging issue due to the fully three-dimensional geometry of the ventricular cavity. To date proper characterization and quantification of the RV flow still remains incomplete, and techniques that can be easily applied to current medical imaging are scarce. A method for simulating the highly complex, multi directional flow within the RV is presented by coupling 4D echocardiography imaging with numerical simulations based on the Immersed Boundaries Method (IBM). A novel formulation for accurately computing the space–time distribution of the blood residence time inside the cavity is introduced. Results showed an initial compact vortex forming past the tricuspid orifice at early diastole that quickly breaks into a weakly turbulent flow pattern and rearranges, during systole, into a peculiar stream-wise vortex spinning out towards the pulmonary orifice. This arrangement is maintained when the Ejection Fraction (EF) is reduced from 58 to 32%. The average blood transit time is found to scale almost inversely proportional to the EF. A careful analysis of the residence time permitted to assess the relative significance of the different flow components (from the direct flow, with a residence time less than one heartbeat, to the residual volume, that stagnates in the ventricle) and their distribution in space.

Vortex dynamics in a model left ventricle during filling

Analysis of the properties of the left ventricle flow during filling (diastole) is known to allow early detection of potential malfunctions during the fundamental heart pumping phase (systole). Diagnoses are now usually based on Doppler measurement of the flow velocity for which interpretative schemes and quantitative references are sought. The flow inside an ideal model of the left ventricle is here studied numerically by a finite difference method in prolate spheroid moving coordinates. The axisymmetric assumption is employed in this first study. The vortex dynamics is characterised by the formation of a wake vortex attached at the valvular edge which is shed at the end of the ventricle expansion. Major features are its translation by self-induced velocity and vortex-induced separations from the ventricle internal wall. Results are represented as, and compared with, clinical data showing a good general agreement and allowing an improved physical interpretation of the latter.  2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Left Ventricular Fluid Mechanics: The Long Way from Theoretical Models to Clinical Applications

The flow inside the left ventricle is characterized by the formation of vortices that smoothly accompany blood from the mitral inlet to the aortic outlet. Computational fluid dynamics permitted to shed some light on the fundamental processes involved with vortex motion. More recently, patient-specific numerical simulations are becoming an increasingly feasible tool that can be integrated with the developing imaging technologies. The existing computational methods are reviewed in the perspective of their potential role as a novel aid for advanced clinical analysis. The current results obtained by simulation methods either alone or in combination with medical imaging are summarized. Open problems are highlighted and perspective clinical applications are discussed.

Intraventricular vortex flow changes in the infarcted left ventricle: numerical results in an idealised 3D shape

The cardiac diagnostic process is primarily based on the evaluation of myocardial mechanics whereas little is known about blood dynamics that is rarely considered to this purpose. The intraventricular blood flow is analysed here for akinetic and dyskinetic myocardial motion corresponding to the presence of an ischaemic pathology. This study is performed through a 3D numerical model of the left ventricular flow. Results show that the presence of an anterior–inferior wall infarction leads to the shortening and weakening of the diastolic mitral jet. A region of stagnating flow is found near the apex and close to the ischaemic wall. These results are in agreement with previous clinical findings based on echographic imaging. The described phenomena are also noticed for moderate degrees of the ischaemic pathology and suggest a potential value of the study of the intraventricular flow to develop early diagnostic indicators.

Three-dimensional impulsive vortex formation from slender orifices

The vortex formation behind an orifice is a widely investigated phenomenon, whichhas been recently studied in several problems of biological relevance. In the case of acircular opening, several works in the literature have shown the existence of a limitingprocessforvortexringformationthatleadstotheconceptofcritical formation time.Inthedifferentgeometricarrangementofaplanarflow,whichcorrespondstoanopeningwith straight edges, it has been recently outlined that such a concept does not apply.This discrepancy opens the question about the presence of limiting conditions whenapertures with irregular shape are considered. In this paper, the three-dimensionalvortex formation due to the impulsively started flow through slender openings isstudied with the numerical solution of the Navier–Stokes equations, at values ofthe Reynolds number that allow the comparison with previous two-dimensionalfindings. The analysis of the three-dimensional results reveals the two-dimensionalnature of the early vortex formation phase. During an intermediate phase, the flowevolution appears to be driven by the local curvature of the orifice edge, and the timescale of the phenomena exhibits a surprisingly good agreement with those found inaxisymmetric problems with the same curvature. The long-time evolution shows thecomplete development of the three-dimensional vorticity dynamics, which does notallow the definition of further unifying concepts.Key words: vortex dynamics, wakes/jets