For the left ventricle (LV) to function as an effective pump it must be able to fill from a low left atrial pressure. However, this ability is lost in patients with heart failure. We investigated LV filling by measuring the cardiac blood flow using 2D phase contrast magnetic resonance imaging and quantified the intraventricular pressure gradients and the strength and location of vortices. In normal subjects, blood flows towards the apex prior to the mitral valve opening, and the mitral annulus moves rapidly away after the valve opens, with both effects enhancing the vortex ring at the mitral valve tips. Instead of being a passive by-product of the process as was previously believed, this ring facilitates filling by reducing convective losses and enhancing the function of the LV as a suction pump. The virtual channel thus created by the vortices may help insure efficient mass transfer for the left atrium to the LV apex. Impairment of this mechanism contributes to diastolic dysfunction, with LV filling becoming dependent on left atrial pressure, which can lead to eventual heart failure. Better understanding of the mechanics of this progression may lead to more accurate diagnosis and treatment of this disease.
"Nevertheless, FTLE ridge features can be used to determine the underlying transport structure in complex flow fields (Holmes et al. 1996; Lekien and Ross 2010; Senatore and Ross 2011), revealing mixing barriers that inhibit transport, or when there is a high density of rapidly moving LCS, regions of increased mixing (Shadden et al. 2005; Tallapragada and Ross 2008; Peng and Dabiri 2009). While the calculation of LCS from FTLE fields has been used to better understand fluid dynamics behavior both numerically (Haller and Yuan 2000; Lekien and Ross 2010; Tallapragada and Ross 2013) and experimentally (Shadden et al. 2006; Shinneeb et al. 2006; Mathur et al. 2007; Charonko et al. 2013), their application has been limited. Part of the limitation is due to the high computational cost in calculating the FTLE fields. "
[Show abstract][Hide abstract] ABSTRACT: This work presents two new methods for computing finite-time Lyapunov exponents (FTLEs) from noisy spatiotemporally resolved experimentally measured image data of the type used for particle image velocimetry (PIV) or particle tracking velocimetry (PTV). These new approaches are based on the simple insight that the particle images recorded during PIV experiments represent Lagrangian flow tracers whose trajectories lend themselves to the direct computation of flow maps, and related quantities such as flow map gradients and FTLEs. We show that using this idea we can improve the reliability and accuracy of FTLE calculation through the use of either direct pathline flow map (PFM) calculation, where individual particle pathlines over a fixed period of time are used to determine the flow map, or particle tracking flow map compilation (FMC), where instantaneous tracking results are used to estimate small snapshots of the flow map which are then compiled to describe the complete flow map. Comparisons of the traditional velocity field integration (VFI) method for computing FTLE fields with these new methods show that FMC produces significantly more accurate estimates of the FTLE field for both synthetic data and experimental data especially in cases where the particle number density is low. This is because the VFI estimates particle motion while PTV directly measures particle motion and therefore generates a more accurate flow map. Overall, our results suggest that VFI is not always a reliable approach when applied to noisy experimental PIV data. For cases where particle loss between frames is minimal, the PFM can also produce better results, but the final field is susceptible to error due to the unstructured nature of the raw flow maps. When comparing the ability to match the true separatrix of a flow, FMC is shown to be a far superior method. The separatrix from FMC has an 80 % overlap with the true solution as compared to approximately 25 % for the PFM and only 1 % for the VFI method. FMC shows a significant advantage when the particle seeding is low, which is particularly relevant for applications to environmental or biological flows where adding seed particles is not always practical, and investigation of Lagrangian flow structures must rely on naturally occurring flow tracers.
Experiments in Fluids 01/2014; 55(1):1638. DOI:10.1007/s00348-013-1638-8 · 1.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Novel processing of Doppler-echocardiography data was used to study blood transport in the left ventricle (LV) of six patients with dilated cardiomyopathy and six healthy volunteers. Bi-directional velocity field maps in the apical long axis of the LV were reconstructed from color-Doppler echocardiography. Resulting velocity field data were used to perform trajectory-based computation of Lagrangian coherent structures (LCS). LCS were shown to reveal the boundaries of blood injected and ejected from the heart over multiple beats. This enabled qualitative and quantitative assessments of blood transport patterns and residence times in the LV. Quantitative assessments of stasis in the LV are reported, as well as characterization of LV vortex formations from E-wave and A-wave filling.
[Show abstract][Hide abstract] ABSTRACT: We propose a new approach to quantification of intracardiac vorticity based on conventional color Doppler images -Doppler vortography. Doppler vortography relies on the centrosymmetric properties of the vortices. Such properties induce particular symmetries in the Doppler flow data that can be exploited to describe the vortices quantitatively. For this purpose, a kernel filter was developed to derive a parameter, the blood vortex signature (BVS), that allows detection of the main intracardiac vortices and estimation of their core vorticities. The reliability of Doppler vortography was assessed in mock Doppler fields issued from simulations and in vitro data. Doppler vortography was also tested in patients and compared with vector flow mapping by echocardiography. Strong correlations were obtained between Doppler vortography-derived and ground-truth vorticities (in silico: r(2) = 0.98, in vitro: r(2) = 0.86, in vivo: r(2) = 0.89). Our results indicate that Doppler vortography is a potentially promising echocardiographic tool for quantification of vortex flow in the left ventricle.
Ultrasound in medicine & biology 11/2013; 40(1). DOI:10.1016/j.ultrasmedbio.2013.09.013 · 2.21 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.