Michele Milano

Impact of acute moderate elevation in left ventricular afterload on diastolic transmitral flow efficiency: analysis by vortex formation time.

BACKGROUND The formation of a vortex alongside a diastolic jet signifies an efficient blood transport mechanism. Vortex formation time (VFT) is an index of the optimal conditions for vortex formation. It was hypothesized that left ventricular (LV) afterload impairs diastolic transmitral flow efficiency and therefore shifts the VFT out of its optimal range. METHODS In 9 open-chest pigs, LV afterload was elevated by externally constricting the ascending aorta and increasing systolic blood pressure to 130% of baseline value for 3 minutes. RESULTS Systolic LV function decreased, diastolic filling velocity increased only during the late (atrial) phase from 0.46 +/- 0.06 to 0.63 +/- 0.19 m/s (P = .0231), and end-diastolic LV volume and heart rate remained unchanged. VFT decreased from 4.09 +/- 0.27 to 2.78 +/- 1.03 (P = .0046). CONCLUSION An acute, moderate elevation in LV afterload worsens conditions for diastolic vortex formation, suggesting impaired blood transport efficiency.

Flow Velocity Vector Fields by Ultrasound Particle Imaging Velocimetry In Vitro Comparison With Optical Flow Velocimetry

We performed an in vitro study to assess the precision and accuracy of particle imaging velocimetry (PIV) data acquired using a clinically available portable ultrasound system via comparison with stereo optical PIV.

Impact of pericardial adhesions on diastolic function as assessed by vortex formation time, a parameter of transmitral flow efficiency

BackgroundPericardial adhesions are a pathophysiological marker of constrictive pericarditis (CP), which impairs cardiac filling by limiting the total cardiac volume compliance and diastolic filling function. We studied diastolic transmitral flow efficiency as a new parameter of filling function in a pericardial adhesion animal model. We hypothesized that vortex formation time (VFT), an index of optimal efficient diastolic transmitral flow, is altered by patchy pericardial-epicardial adhesions.MethodsIn 8 open-chest pigs, the heart was exposed while preserving the pericardium. We experimentally simulated early pericardial constriction and patchy adhesions by instilling instant glue into the pericardial space and using pericardial-epicardial stitches. We studied left ventricular (LV) function and characterized intraventricular blood flow with conventional and Doppler echocardiography at baseline and following the experimental intervention.ResultsSignificant decreases in end-diastolic volume, ejection fraction, stroke volume, and late diastolic filling velocity reflected the effects of the pericardial adhesions. The mean VFT value decreased from 3.61 ± 0.47 to 2.26 ± 0.45 (P = 0.0002). Hemodynamic variables indicated the inhibiting effect of pericardial adhesion on both contraction (decrease in systolic blood pressure and +dP/dt decreased) and relaxation (decrease in the magnitude of -dP/dt and prolongation of Tau) function.ConclusionPatchy pericardial adhesions not only negatively impact LV mechanical functioning but the decrease of VFT from normal to suboptimal value suggests impairment of transmitral flow efficiency.

Increase in the late diastolic filling force is associated with impaired transmitral flow efficiency in acute moderate elevation of left ventricular afterload.

Objective. Analysis of intraventricular flow force and efficiency is a novel concept of quantitatively assessing left ventricular (LV) hemodynamic performance. We have parametrically characterized diastolic filling flow by early inflow force, late inflow force, and total inflow force and by vortex formation time (VFT), a fundamental parameter of fluid transport efficiency. The purpose of this study was to determine what changes in inflow forces characterize a decrease in diastolic blood transport efficiency in acute moderate elevation of LV afterload. Methods. In 8 open‐chested pigs, the flow force and VFT parameters were calculated from conventional and flow Doppler echocardiographic measurements at baseline and during a brief (3‐minute) moderate elevation of afterload induced by increasing the systolic blood pressure to 130% of the baseline value. Results. Systolic LV function decreased significantly during elevated afterload. Early inflow force did not significantly change, whereas late inflow force increased from 5,822.09 ± 1,656.5 (mean ± SD) to 13,948.25 ± 9,773.96 dyne (P = .049), and total inflow force increased from 13,783.35 ± 4,816.58 to 21,836.67 ± 8,635.33 dyne (P = .031). Vortex formation time decreased from 4.09 ± 0.29 to 2.79 ± 1.1 (P = .0068), confirming suboptimal flow transport efficiency. Conclusions. Even a brief moderate increase of LV afterload causes a significant increase in late diastolic filling force and impairs transmitral flow efficiency.

The Flying Brick: A Cautionary Note on Testing Flying Robots Using Guide Wires

A simple experiment demonstrates that an average vertical force can be produced by a small vibrator motor attached to a frame constrained to slide vertically on guide wires. The vertical force produced is sufficient to make the sliding element hover, similarly to a biologically inspired robotic insect. We show that this effect depends on the natural resonance frequency of the guide wires and the nature of the mechanical coupling between wires and sliding element. Based on the result of this experiment, we recommend that a control experiment should be performed in order to reach unambiguous conclusions concerning the actual flying capabilities of robotic insects tested using this kind of methodology.

A Controls-Based Methodology for Generating Turbulence in Direct and Large-Eddy Simulations of Wall-Bounded Flows

An integral control scheme is used to optimize a method for generating turbulent fluctuations for DNS and LES of wall-bounded flows. Similar to previous investigations, the method employs a series of control planes in which a body force is applied to the wall-normal momentum equation that amplifies and shapes velocity fluctuations seeded into the flow towards a target resolved shear-stress profile. The focus of the current work is on a methodology for specifying the controller gains and ensuring numerical stability without the introduction of criteria that override the control commands in order to prevent unphysical effects. The first method used to analyze the control process is based on identification of a linear model formed from the open-loop response of the shear stress to random inputs at the control planes. Optimal gains for the controller are specified based on the location of the poles of the linear model in the closed-loop configuration. The second method consists of measuring the response of the non-linear system to preset gain values and incrementally increasing the gains until the onset of numerical instabilities. The schemes have been tested using computations of turbulent channel flow at Reynolds numbers based on friction velocity and channel halfwidth of 400 and 5000. Simulation results obtained using both methods show that using the second approach the resolved shear stress reaches the target levels at the control planes, without ad hoc tuning of the control parameters. The predicted optimal gain values at the control planes are sensitive to the stirring force used to create fluctuations. In addition, the magnitude of the stirring force also affects rms values of the velocity fluctuations downstream of the control planes.© 2007 ASME