Clinically, the current transcatheter aortic valve (TAV) technology has shown a propensity for paravalvular leakage; studies have correlated this flaw to increased calcification at the implantation site and with nonideal geometry of the stented valve. The present study evaluated the hydrodynamics of different geometric configurations, in particular the intravalvular considerations. Three TAV devices were made to create a representative, size 26 mm TAV. Hydrodynamics were assessed using a pulse duplicator. The geometries tested were composed of the nominal, elliptical, triangular, and undersized shapes; along with half-constriction, a conformation in which only a portion of the stent was constrained. The TAVs were assessed for transvalvular pressure gradient (TVG), effective orifice area (EOA), and regurgitant fraction. The nominal-sized shape posed a larger TVG (6.2 ± 0.3 mm Hg) than other configurations (P < 0.001) except the undersized valves. EOA of the nominal sized TAV (1.7 ± 0.1 cm(2) ) was smaller than that of the triangular and half-elliptical versions (P < 0.001). The half- and full-undersized geometries had EOAs smaller than the nominal type (P < 0.001). Nominal shape had smaller regurgitation (6.7 ± 1.4%) than all configurations (P < 0.001) except for the half-undersized (4.0 ± 0.7, P < 0.001) with no statistically significant difference from the full-undersized (6.8 ± 1.3, P = 0.724). The testing of variable geometries showed significant differences from the nominal geometry with respect to TVG, EOA, and regurgitant fraction. In particular, many of these nonideal configurations demonstrated an increased intravalvular regurgitation.
A bicycle or inverted pendulum can be balanced, that is kept nearly upright, by accelerating the base. This balance is achieved by steering on a bicycle. Simultaneously one can also control the lateral position of the base: changing of the track line of a bike or the position of hand under a balanced stick. We show here with theory and experiment that if the balance problem is removed, by making the system neutrally stable for balance, one cannot simultaneously maintain balance and control the position of the base. We made a bricycle, essentially a bicycle with springy training wheels. The stiffness of the training wheel suspension can be varied from near infinite, making the bricycle into a tricycle, to zero, making it effectively a bicycle. The springy training wheels effectively reduce or even negate gravity, at least for balance purposes. One might expect a smooth transition from tricycle to bicycle as the stiffness is varied, in terms of handling, balance and feel. Not so. At an intermediate stiffness, when gravity is effectively zeroed, riders can balance easily but no longer turn. Small turns cause an intolerable leaning. Thus there is a qualitative difference between bicycles and tricycles, a difference that cannot be met halfway.
Mushrooms have unique properties in arsenic metabolism. In many commercial and wild-grown mushrooms, arsenobetaine (AsB), a non-toxic arsenical, was found as the dominant arsenic species. The AsB biosynthesis remains unknown, so we designed experiments to study conditions for AsB formation in the white button mushroom, Agaricus bisporus. The mushrooms were treated with various arsenic species including arsenite (As(III)), arsenate (As(V)), methylarsenate (MAs(V)), dimethylarsenate (DMAs(V)) and trimethylarsine oxide (TMAsO), and their accumulation and metabolism were determined using inductively coupled mass spectrometer (ICP-MS) and high-pressure liquid chromatography coupled with ICP-MS (HPLC-ICP-MS), respectively. Our results showed that mycelia have a higher accumulation for inorganic arsenicals while fruiting bodies showed higher accumulation for methylated arsenic species. Two major arsenic metabolites were produced in fruiting bodies: DMAs(V) and AsB. Among tested arsenicals, only MAs(V) was methylated to DMAs(V). Surprisingly, AsB was only detected as the major arsenic product when TMAsO was supplied. Additionally, AsB was only detected in the fruiting body, but not mycelium, suggesting that methylated products were transported to the fruiting body for arsenobetaine formation. Overall, our results support that methylation and AsB formation are two connected pathways where trimethylated arsenic is the optimal precursor for AsB formation.
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