Total cavopulmonary connection is the result of a series of palliative surgical repairs performed on patients with single ventricle heart defects. The resulting anatomy has complex and unsteady hemodynamics characterized by flow mixing and flow separation. Although varying degrees of flow pulsatility have been observed in vivo, non-pulsatile (time-averaged) boundary conditions have traditionally been assumed in hemodynamic modeling, and only recently have pulsatile conditions been incorporated without completely characterizing their effect or importance. In this study, 3D numerical simulations with both pulsatile and non-pulsatile boundary conditions were performed for 24 patients with different anatomies and flow boundary conditions from Georgia Tech database. Flow structures, energy dissipation rates and pressure drops were compared under rest and simulated exercise conditions. It was found that flow pulsatility is the primary factor in determining the appropriate choice of boundary conditions, whereas the anatomic configuration and cardiac output had secondary effects. Results show that the hemodynamics can be strongly influenced by the presence of pulsatile flow. However, there was a minimum pulsatility threshold, identified by defining a weighted pulsatility index (wPI), above which the influence was significant. It was shown that when wPI < 30%, the relative error in hemodynamic predictions using time-averaged boundary conditions was less than 10% compared to pulsatile simulations. In addition, when wPI < 50, the relative error was less than 20%. A correlation was introduced to relate wPI to the relative error in predicting the flow metrics with non-pulsatile flow conditions.
Limited knowledge exists regarding the forces which act on devices implanted to the heart's mitral valve. Developing a transducer to measure the peak force magnitudes, time rates of change, and relationship with left ventricular pressure will aid in device development. A novel force transducer was developed and implanted in the mitral valve annulus of an ovine subject. In the post-cardioplegic heart, septal-lateral and transverse forces were continuously measured for cardiac cycles reaching a peak left ventricular pressure of 90. mmHg. Each force was seen to increase from ventricular diastole and found to peak at mid-systole. The mean change in septal-lateral and transverse forces throughout the cardiac cycle was 4.4±0.2. N and 1.9±0.1. N respectively. During isovolumetric contraction, the septal-lateral and transverse forces were found to increase at peak rate of 143±8. N/s and 34±9. N/s, respectively. Combined, this study provides the first quantitative assessment of septal-lateral and transverse forces within the contractile mitral annulus. The developed transducer was successful in measuring these forces whose methods may be extended to future studies. Upon additional investigation, these data may contribute to the safer development and evaluation of devices aimed to repair or replace mitral valve function.
This feature article introduces our recent work on understanding the roles played by citrate and poly(vinyl pyrrolidone) (PVP) as capping agents in seed-mediated syntheses of Ag nanocrystals with controlled shapes. We have demonstrated that citrate and PVP selectively bind to Ag(111) and Ag(100) surfaces, respectively, and thus favor the formation of Ag nanocrystals enclosed preferentially by {111} or {100} facets. In addition, we have quantified the coverage density of PVP adsorbed on the surface of Ag nanocubes. On the basis of the mechanistic understanding, a series of Ag nanocrystals with controlled shapes and sizes have been successfully synthesized by using different combinations of seeds and capping agents: single-crystal spherical/cubic seeds with citrate for cuboctahedrons and octahedrons or with PVP for cubes and bars and plate-like seeds with citrate for enlarged thin plates or with PVP for thickened plates.