Diastolic Vortex Alterations With Reducing Left Ventricular Volume: An In Vitro Study.

Despite the large number of studies of intraventricular filling dynamics for potential clinical applications, little is known as to how the diastolic vortex ring properties are altered with reduction in internal volume of the cardiac left ventricle (LV). The latter is of particular importance in LV diastolic dysfunction (LVDD) and in congenital diseases such as hypertrophic cardiomyopathy (HCM), where LV hypertrophy (LVH) can reduce LV internal volume. We hypothesized that peak circulation and the rate of decay of circulation of the diastolic vortex would be altered with reducing end diastolic volume (EDV) due to increasing confinement. We tested this hypothesis on physical models of normal LV and HCM geometries, under identical prescribed inflow profiles and for multiple EDVs, using time-resolved particle image velocimetry (TR-PIV) measurements on a left heart simulator. Formation and pinch-off of the vortex ring were nearly unaffected with changes to geometry and EDV. Pinch-off occurred before the end of early filling (E-wave) in all test conditions. Peak circulation of the vortex core near the LV outflow tract (LVOT) increased with lowering EDV and was lowest for the HCM model. The rate of decay of normalized circulation in dimensionless formation time (T*) increased with decreasing EDV. When using a modified version of T* that included average LV cross-sectional area and EDV, normalized circulation of all tested EDVs collapsed closely in the normal LV model (10% maximum difference between EDVs). Collectively, our results show that LV shape and internal volume play a critical role in diastolic vortex ring dynamics.

Aerodynamic effects of varying solid surface area of bristled wings performing clap and fling.

The smallest flying insects with body lengths under 2 mm show a marked preference for wings consisting of a thin membrane with long bristles, and the use of clap and fling kinematics to augment lift at Reynolds numbers (Re) of approximately 10. Bristled wings have been shown to reduce drag forces in clap and fling, but the aerodynamic roles of several bristled wing geometric variables remain unclear. This study examines the effects of varying the ratio of membrane area (A M) to total wing area (A T) on aerodynamic forces and flow structures generated during clap and fling at Re on the order of 10. We also examine the aerodynamic consequences of scaling bristled wings to Re = 120, relevant to flight of fruit flies. We analyzed published forewing images of 25 species of thrips (Thysanoptera) and found that A M/A T ranged from 14% to 27%, as compared to 11% to 88% previously reported for smaller-sized fairyflies (Hymenoptera). These data were used to develop physical bristled wing models with A M/A T ranging from 15% to 100%, which were tested in a dynamically scaled robotic clap and fling model. At all Re, bristled wings produced slightly lower lift coefficients (C L) when compared to solid wings, but provided significant drag reduction. At Re = 10, largest values of peak lift over peak drag ratios were generated by wing models with A M/A T similar to thrips forewings (15% to 30%). Circulation of the leading edge vortex and trailing edge vortex decreased with decreasing A M/A T during clap and fling at Re = 10. Decreased chordwise circulation near the wing tip, vortex shedding, and interaction between flow structures from clap with those from fling resulted in lowering C L generated via clap and fling at Re = 120 as compared to Re = 10. Clap and fling becomes less beneficial at Re = 120, regardless of the drag reduction provided by bristled wings.