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Clinical Utility of Echocardiography in Former Preterm Infants with Bronchopulmonary Dysplasia.
BackgroundThe clinical utility of echocardiography for the diagnosis of pulmonary vascular disease (PVD) in former preterm infants with bronchopulmonary dysplasia (BPD) is not established. Elevated pulmonary vascular resistance (PVR) rather than pulmonary artery pressure (PAP) is the hallmark of PVD. We evaluated the utility of echocardiography in infants with BPD in diagnosing pulmonary hypertension and PVD (PVR >3 Wood units × m2) assessed by cardiac catheterization.MethodsA retrospective single center study of 29 infants born ≤29 weeks of gestational age with BPD who underwent cardiac catheterization and echocardiography was performed. PVD was considered present by echocardiography if the tricuspid valve regurgitation jet peak velocity was >2.9 m/sec, post-tricuspid valve shunt systolic flow velocity estimated a right ventricular systolic pressure >35 mm Hg, or systolic septal flattening was present. The utility (accuracy, sensitivity, and positive predictive value [PPV]) of echocardiography in the diagnosis of PVD was tested. Subgroup analysis in patients without post-tricuspid valve shunts was performed. Echocardiographic estimations of right ventricular pressure, dimensions, function, and pulmonary flow measurements were evaluated for correlation with PVR.ResultsThe duration between echocardiography and cardiac catheterization was a median of 1 day (interquartile range, 1-4 days). Accuracy, sensitivity, and PPV of echocardiography in diagnosing PVD were 72%, 90.5%, and 76%, respectively. Accuracy, sensitivity, and PPV increased to 93%, 91.7%, and 100%, respectively, when infants with post-tricuspid valve shunts were excluded. Echocardiography had poor accuracy in estimating the degree of PAP elevation by cardiac catheterization. In infants without post-tricuspid valve shunts, there was moderate to good correlation between indexed PVR and right ventricular myocardial performance index (rho = 0.89, P = .005), systolic to diastolic time index (0.84, P < .001), right to left ventricular diameter ratio at end systole (0.66, P = .003), and pulmonary artery acceleration time (0.48, P = .05).ConclusionsEchocardiography performs well in screening for PVD in infants with BPD and may be diagnostic in the absence of a post-tricuspid valve shunt. However, cardiac catheterization is needed to assess the degree of PAP elevation and PVR. The diagnostic utility of echocardiographic measurements that correlate with PVR should be evaluated prospectively in this patient population
Boundary effects on the scaling of the superfluid density
We study numerically the influence of the substrate (boundary conditions) on
the finite--size scaling properties of the superfluid density in
superfluid films of thickness within the XY model employing the Monte Carlo
method. Our results suggest that the jump at the
Kosterlitz--Thouless transition temperature depends on the boundary
conditions.Comment: 2 pages, 1 Latex file, 1 postscript figure, 2 style file
Possible Glassiness in a Periodic Long-Range Josephson Array
We present an analytic study of a periodic Josephson array with long-range
interactions in a transverse magnetic field. We find that this system exhibits
a first-order transition into a phase characterized by an extensive number of
states separated by barriers that scale with the system size; the associated
discontinuity is small in the limit of weak applied field, thus permitting an
explicit analysis in this regime.Comment: 4 pages, 2 Postscript figures in a separate file
Critical Currents of Josephson-Coupled Wire Arrays
We calculate the current-voltage characteristics and critical current
I_c^{array} of an array of Josephson-coupled superconducting wires. The array
has two layers, each consisting of a set of parallel wires, arranged at right
angles, such that an overdamped resistively-shunted junction forms wherever two
wires cross. A uniform magnetic field equal to f flux quanta per plaquette is
applied perpendicular to the layers. If f = p/q, where p and q are mutually
prime integers, I_c^{array}(f) is found to have sharp peaks when q is a small
integer. To an excellent approximation, it is found in a square array of n^2
plaquettes, that I_c^{array}(f) \propto (n/q)^{1/2} for sufficiently large n.
This result is interpreted in terms of the commensurability between the array
and the assumed q \times q unit cell of the ground state vortex lattice.Comment: 4 pages, 4 figure
Patterns of Striped order in the Classical Lattice Coulomb Gas
We obtain via Monte Carlo simulations the low temperature charge
configurations in the lattice Coulomb gas on square lattices for charge filling
ratio in the range . We find a simple regularity in the low
temperature charge configurations which consist of a suitable periodic
combination of a few basic striped patterns characterized by the existence of
partially filled diagonal channels. In general there exist two separate
transitions where the lower temperature transition () corresponds to the
freezing of charges within the partially filled channels. is found to be
sensitively dependent on through the charge number density within the channels.Comment: 4 pages, 8 figure
The Effect of Columnar Disorder on the Superconducting Transition of a Type-II Superconductor in Zero Applied Magnetic Field
We investigate the effect of random columnar disorder on the superconducting
phase transition of a type-II superconductor in zero applied magnetic field
using numerical simulations of three dimensional XY and vortex loop models. We
consider both an unscreened model, in which the bare magnetic penetration
length is approximated as infinite, and a strongly screened model, in which the
magnetic penetration length is of order the vortex core radius. We consider
both equilibrium and dynamic critical exponents. We show that, as in the
disorder free case, the equilibrium transitions of the unscreened and strongly
screened models lie in the same universality class, however scaling is now
anisotropic. We find for the correlation length exponent , and
for the anisotropy exponent . We find different dynamic
critical exponents for the unscreened and strongly screened models.Comment: 30 pages 12 ps figure
Vortex lattce melting in 2D superconductors and Josephson arrays
Monte Carlo simulations of 2D vortex lattice melting in a thin
superconducting film (or alternatively an array of Josephson junctions) are
performed in the London limit. Finite size scaling analyses are used to make a
detailed test of the dislocation mediated melting theory of KTNHY. We find that
the melting transition is weakly first order, with a jump in the shear modulus
very close to that predicted by the KTNHY theory. No hexatic liquid phase is
found.Comment: 12 pages, 4 figures (available on request from
[email protected]), REVTEX [we revise our conclusion on the order of the
melting transition from second to first order - new figure 4 added
Heterogeneous Dynamics, Marginal Stability and Soft Modes in Hard Sphere Glasses
In a recent publication we established an analogy between the free energy of
a hard sphere system and the energy of an elastic network [1]. This result
enables one to study the free energy landscape of hard spheres, in particular
to define normal modes. In this Letter we use these tools to analyze the
activated transitions between meta-bassins, both in the aging regime deep in
the glass phase and near the glass transition. We observe numerically that
structural relaxation occurs mostly along a very small number of
nearly-unstable extended modes. This number decays for denser packing and is
significantly lowered as the system undergoes the glass transition. This
observation supports that structural relaxation and marginal modes share common
properties. In particular theoretical results [2, 3] show that these modes
extend at least on some length scale where
corresponds to the maximum packing fraction, i.e. the jamming
transition. This prediction is consistent with very recent numerical
observations of sheared systems near the jamming threshold [4], where a similar
exponent is found, and with the commonly observed growth of the rearranging
regions with compression near the glass transition.Comment: 6 pages, improved versio
Positional Disorder (Random Gaussian Phase Shifts) in the Fully Frustrated Josephson Junction Array (2D XY Model)
We consider the effect of positional disorder on a Josephson junction array
with an applied magnetic field of f=1/2 flux quantum per unit cell. This is
equivalent to the problem of random Gaussian phase shifts in the fully
frustrated 2D XY model. Using simple analytical arguments and numerical
simulations, we present evidence that the ground state vortex lattice of the
pure model becomes disordered, in the thermodynamic limit, by any amount of
positional disorder.Comment: 4 pages, 4 eps figures embedde
Results of 102 cases of complete repair of congenital heart defects in patients weighing 700 to 2500 grams
AbstractBackground: Published data suggest that low birth weight is a risk factor for poor outcome in corrective surgery for many cardiac defects. Congenital heart defects in low birth weight infants are typically managed with supportive therapy or palliative operations, with definitive repair delayed. The morbidity associated with such approaches is high. Methods: Since 1990 complete repair of congenital heart defects (other than patent ductus arteriosus) has been performed in 102 infants no larger than 2500 g (median 2100 g, range 700-2500 g), including 16 no larger than 1500 g. Defects included ventricular septal defect (n = 22), tetralogy of Fallot complexes (n = 20), transposition complexes (n = 13), aortic coarctation (n = 12), interrupted arch (n = 10), truncus arteriosus (n = 8), atrioventricular septal defect (n = 6), total anomalous pulmonary venous return (n = 5), and other (n = 6). Results: Preoperative morbidity was more common among patients referred late for surgical correction. There were 10 early deaths (10%) attributable to cardiac failure (n = 4), arrhythmia (n = 1), multiorgan failure (n = 1), sepsis (n = 1), idiopathic coronary artery intimal necrosis (n = 1), foot gangrene (n = 1), and pulmonary hemorrhage (n = 1). No patient had postbypass intracerebral hemorrhage. At follow-up (median 36 months) there were 8 late deaths, and 8 patients underwent 10 reinterventions. There was no evidence of neurologic sequelae attributable to the operation. Conclusions: In general, delaying repair of congenital heart defects in low birth weight infants does not confer a benefit and is associated with higher preoperative morbidity. Complete repair of both simple and complex lesions can be achieved in such cases with good results. Growth after repair approximates the normal curve for low birth weight infants without heart disease. It is recommended that such infants, especially when they have symptoms, undergo early surgical repair rather than prolonged medical management or other forms of palliation. (J Thorac Cardiovasc Surg 1999;117:324-31
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