105 research outputs found
Quantifying the Impact of Altered Hemodynamics and Vascular Biomechanics to Changes in Structure and Function in Native and Corrected Aortic Coarctation
Coarctation of the aorta (CoA) is associated with substantial cardiovascular morbidities despite successful treatment through surgical or catheter-based intervention. Although specific mechanisms leading to these morbidities remain elusive, abnormal hemodynamics and vascular biomechanics are implicated. We used a novel animal model that facilitates quantification of CoA-induced hemodynamic and vascular biomechanics alterations and their impact on vascular structure and function, independent of genetic or confounding factors. Rabbits underwent thoracic CoA at 10 weeks of age (~9 human years) to induce a 20 mmHg blood pressure (BP) gradient using permanent or dissolvable suture thereby replicating untreated and corrected CoA. Computational fluid dynamics (CFD) was performed using subject-specific imaging and BP data at 32 weeks to quantify velocity, strain, and wall shear stress (WSS). Vascular structure and function were evaluated at proximal and distal locations by histology, immunohistochemistry, and myograph analysis.
Results revealed proximal systolic and mean BP was elevated in CoA compared to corrected and control rabbits leading to vascular remodeling, endothelial dysfunction proximally and distally, and increased stiffness and reduced active force response proximally. Corrected rabbits had reduced but significant medial thickening, endothelial dysfunction, and stiffening limited to the proximal region despite 12 weeks of alleviated systolic and mean BP (~4 human years) after the suture dissolved. Proximal arteries of CoA and corrected groups demonstrated increased non-muscle myosin expression and decreased myosin heavy chain expression, and this dedifferentiation may influence vascular remodeling and aortic stiffening. CFD analysis of untreated CoA rabbits demonstrated significantly reduced WSS proximal to CoA and markedly elevated WSS distally due to the presence of a stenotic velocity jet. Results from corrected rabbits indicate the velocity jet may have persistent effects on hemodynamics, as WSS remained significantly reduced. These hemodynamic and morphological observations are consistent with alterations in human patients.
Using these coupled imaging and experimental results, we may determine changes in structure and function specific to CoA and correction and how they are influenced by hemodynamics and vascular biomechanics. We are now poised to augment clinical treatment of CoA through several methods, including investigation of specific cellular mechanisms causing morbidity in CoA and the development of therapies to improve endothelial function and restore vascular stiffness
Natural Supersymmetry and Implications for Higgs physics
We re-analyze the LHC bounds on light third generation squarks in Natural
Supersymmetry, where the sparticles have masses inversely proportional to their
leading-log contributions to the electroweak symmetry breaking scale. Higgsinos
are the lightest supersymmetric particles; top and bottom squarks are the
next-to-lightest sparticles that decay into both neutral and charged Higgsinos
with well-defined branching ratios determined by Yukawa couplings and
kinematics. The Higgsinos are nearly degenerate in mass, once the bino and wino
masses are taken to their natural (heavy) values. We consider three scenarios
for the stop and sbottom masses: (I) is light, (II)
and are light, and (III) , , and
are light. Dedicated stop searches are currently sensitive to
Scenarios II and III, but not Scenario I. Sbottom-motivated searches () impact both squark flavors due to \tilde{t} \ra b \charp_1 as well
as \tilde{b} \ra b \neut_{1,2}, constraining Scenarios I and III with
somewhat weaker constraints on Scenario II. The totality of these searches
yield relatively strong constraints on Natural Supersymmetry. Two regions that
remain are: (1) the "compressed wedge", where , and (2) the "kinematic limit" region, where
m_{\tilde{q}} \gsim 600-750 GeV, at the kinematic limit of the LHC searches.
We calculate the correlated predictions for Higgs physics, demonstrating that
these regions lead to distinct predictions for the lightest Higgs couplings
that are separable with \simeq 10% measurements. We show that these
conclusions remain largely unchanged once the MSSM is extended to the NMSSM in
order to naturally obtain a large enough mass for the lightest Higgs boson
consistent with LHC data.Comment: 18 pages, 8 figure
Standard model explanation of a CDF dijet excess in Wjj
We demonstrate the recent observation of a peak in the dijet invariant mass
of the Wjj signal observed by the CDF Collaboration can be explained as the
same upward fluctuation observed by CDF in single-top-quark production. In
general, both t-channel and s-channel single-top-quark production produce
kinematically induced peaks in the dijet spectrum. Since CDF used a Monte Carlo
simulation to subtract the single-top backgrounds instead of data, a peak in
the dijet spectrum is expected. The D0 Collaboration has a small upward
fluctuation in their published t-channel data; and hence we predict they would
see at most a small peak in the dijet invariant mass spectrum of Wjj if they
follow the same procedure as CDF.Comment: 3 pg., 2 figs, revtex, minor clarifications, to appear in Phys. Rev.
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