98 research outputs found
Inhibition of Ion Channels and Heart Beat in Drosophila by Selective COX-2 Inhibitor SC-791
Recent findings suggest that modulation of ion channels might be implicated in some of the clinical effects of coxibs, selective inhibitors of cyclooxygenase-2 (COX-2). Celecoxib and its inactive analog 2,5-dimethyl-celecoxib, but not rofecoxib, can suppress or augment ionic currents and alter functioning of neurons and myocytes. To better understand these unexpected effects, we have recently investigated the mechanism of inhibition of human Kv2.1 channels by a highly selective COX-2 inhibitor SC-791. In this study we have further explored the SC-791 action on ion channels and heartbeat in Drosophila, which lacks cyclooxygenases and thus can serve as a convenient model to study COX-2-independent mechanisms of coxibs. Using intracellular recordings in combination with a pharmacological approach and utilizing available Drosophila mutants, we found that SC-791 inhibited voltage-activated K+ and L-type Ca2+ channels in larval body-wall muscles and reduced heart rate in a concentration-dependent manner. Unlike celecoxib and several other K+ channel blockers, SC-791 did not induce arrhythmia. Instead, application of SC-791 resulted in a dramatic slowing of contractions and, at higher concentrations, in progressively weaker contractions with gradual cessation of heartbeat. Isradipine, a selective blocker of L-type Ca2+ channels, showed a similar pattern of heart arrest, though no prolongation of contractions was observed. Ryanodine was the only channel modulating compound of those tested additionally that was capable of slowing contractions. Like SC-791, ryanodine reduced heart rate without arrhythmia. However, it could not stop heartbeat completely even at 500 µM, the highest concentration used. The magnitude of heart rate reduction, when SC-791 and ryanodine were applied together, was smaller than expected for independent mechanisms, raising the possibility that SC-791 might be interfering with excitation-contraction coupling in Drosophila heart
Rotating traversable wormholes
The general form of a stationary, axially symmetric traversable wormhole is
discussed. This provides an explicit class of rotating wormholes that
generalize the static, spherically symmetric ones first considered by Morris
and Thorne. In agreement with general analyses, it is verified that such a
wormhole generically violates the null energy condition at the throat. However,
for suitable model wormholes, there can be classes of geodesics falling through
it which do not encounter any energy-condition-violating matter. The possible
presence of an ergoregion surrounding the throat is also noted.Comment: 15 pages, harvmac; 1 figure in PicTeX; minor changes; to appear in
Phys. Rev.
Inflating Lorentzian Wormholes
It has been speculated that Lorentzian wormholes of the Morris- Thorne type
might be allowed by the laws of physics at submicroscopic, e.g. Planck, scales
and that a sufficiently advanced civilization might be able to enlarge them to
classical size. The purpose of this paper is to explore the possibility that
inflation might provide a natural mechanism for the enlargement of such
wormholes to macroscopic size. A new classical metric is presented for a
Lorentzian wormhole which is imbedded in a flat deSitter space. It is shown
that the throat and proper length of the wormhole inflate. The resulting
properties and stress-energy tensor associated with this metric are discussed.Comment: 24 pg
Natural Wormholes as Gravitational Lenses
Visser has suggested traversable 3-dimensional wormholes that could plausibly
form naturally during Big Bang inflation. A wormhole mouth embedded in high
mass density might accrete mass, giving the other mouth a net *negative* mass
of unusual gravitational properties. The lensing of such a gravitationally
negative anomalous compact halo object (GNACHO) will enhance background stars
with a time profile that is observable and qualitatively different from that
recently observed for massive compact halo objects (MACHOs) of positive mass.
We recommend that MACHO search data be analyzed for GNACHOs.Comment: 4 pages; plus 4 figures; ReV_TeX 3.0; DOE/ER/40537-001/NPL94-07-01
Quantum Dynamics of Lorentzian Spacetime Foam
A simple spacetime wormhole, which evolves classically from zero throat
radius to a maximum value and recontracts, can be regarded as one possible mode
of fluctuation in the microscopic ``spacetime foam'' first suggested by
Wheeler. The dynamics of a particularly simple version of such a wormhole can
be reduced to that of a single quantity, its throat radius; this wormhole thus
provides a ``minisuperspace model'' for a structure in Lorentzian-signature
foam. The classical equation of motion for the wormhole throat is obtained from
the Einstein field equations and a suitable equation of state for the matter at
the throat. Analysis of the quantum behavior of the hole then proceeds from an
action corresponding to that equation of motion. The action obtained simply by
calculating the scalar curvature of the hole spacetime yields a model with
features like those of the relativistic free particle. In particular the
Hamiltonian is nonlocal, and for the wormhole cannot even be given as a
differential operator in closed form. Nonetheless the general solution of the
Schr\"odinger equation for wormhole wave functions, i.e., the wave-function
propagator, can be expressed as a path integral. Too complicated to perform
exactly, this can yet be evaluated via a WKB approximation. The result
indicates that the wormhole, classically stable, is quantum-mechanically
unstable: A Feynman-Kac decomposition of the WKB propagator yields no spectrum
of bound states. Though an initially localized wormhole wave function may
oscillate for many classical expansion/recontraction periods, it must
eventually leak to large radius values. The possibility of such a mode unstable
against growth, combined withComment: 37 pages, 93-
Is Quantum Spacetime Foam Unstable?
A very simple wormhole geometry is considered as a model of a mode of
topological fluctutation in Planck-scale spacetime foam. Quantum dynamics of
the hole reduces to quantum mechanics of one variable, throat radius, and
admits a WKB analysis. The hole is quantum-mechanically unstable: It has no
bound states. Wormhole wave functions must eventually leak to large radii. This
suggests that stability considerations along these lines may place strong
constraints on the nature and even the existence of spacetime foam.Comment: 15 page
Evolving wormhole geometries
We present here analytical solutions of General Relativity that describe
evolving wormholes with a non-constant redshift function. We show that the
matter that threads these wormholes is not necessarily exotic. Finally, we
investigate some issues concerning WEC violation and human traversability in
these time-dependent geometries.Comment: 12 pages latex, 3 figures, to appear in Phys. Rev. D., Title
correcte
Classical Scalar Fields and the Generalized Second Law
It has been shown that classical non-minimally coupled scalar fields can
violate all of the standard energy conditions in general relativity. Violations
of the null and averaged null energy conditions obtainable with such fields
have been suggested as possible exotic matter candidates required for the
maintenance of traversable wormholes. In this paper, we explore the possibility
that if such fields exist, they might be used to produce large negative energy
fluxes and macroscopic violations of the generalized second law (GSL) of
thermodynamics. We find that it appears to be very easy to produce large
magnitude negative energy fluxes in flat spacetime. However we also find,
somewhat surprisingly, that these same types of fluxes injected into a black
hole do {\it not} produce violations of the GSL. This is true even in cases
where the flux results in a decrease in the area of the horizon. We demonstrate
that two effects are responsible for the rescue of the GSL: the acausal
behavior of the horizon and the modification of the usual black hole entropy
formula by an additional term which depends on the scalar field.Comment: 25 pages, 2 figures; paper substantially rewritten, major changes in
the conclusion
ГОСПИТАЛЬНЫЕ РЕЗУЛЬТАТЫ БИМАММАРНОГО КОРОНАРНОГО ШУНТИРОВАНИЯ
HighlightsThe present study was conducted to evaluate in-hospital outcomes of one of the most effective and simultaneously controversial surgical techniques for myocardial revascularization using two internal thoracic arteries (ITA).To this date, this is the most complete analysis that has been carried out at the Research Institute on the topic of studying bilateral internal thoracic artery grafting (BITA). The results obtained are of great importance for the subsequent evaluation of long-term results. AbstractAim. To analyze in-hospital outcomes of BITA.Methods. The study included 232 patients who were admitted to the Cardiac Surgery Department for coronary artery bypass grafting (CABG). All patients were divided into 2 groups depending on the use of either single or bilateral ITA conduits. Both groups included equal number of patients – 116. In-hospital outcomes were analyzed.Results. BITA and CABG with single ITA were proven to be comparable regarding myocardial infarction, stroke, the need for percutaneous coronary intervention, death, and composite endpoint. At the same time BITA patients significantly more often had longer hospital stay and required inotropic drugs.Conclusion. BITA is a safe procedure comparable to classic CABG in terms of in-hospital complications, but at the same time, this intervention is associated with longer hospital stay, and extended inotropic drugs use.Основные положенияНастоящее исследование проведено для оценки госпитальных результатов одной из самых эффективных и одновременно противоречивых хирургических технологий реваскуляризации миокарда с применением двух внутренних грудных артерий.Представленный анализ является наиболее крупным из когда-либо выполненных специалистами НИИ КПССЗ по изучению бимаммарного коронарного шунтирования. Также полученные данные имеют важное значение для последующей оценки отдаленных результатов. РезюмеЦель. Оценить госпитальные результаты бимаммарного коронарного шунтирования.Материалы и методы. Изучены данные 232 историй болезни пациентов, поступивших в кардиохирургическое отделение для проведения коронарного шунтирования. Все больные были разделены на две группы в зависимости от использования одной или двух внутренних грудных артерий. В первую и вторую группы вошло равное количество пациентов – по 116 (50%) в каждой. Оценены результаты госпитального послеоперационного периода.Результаты. Бимаммарное и аортокоронарное шунтирование с использованием одной внутренней грудной артерии сопоставимы по таким госпитальным осложнениям, как инфаркт миокарда, инсульт, необходимость в чрескожном коронарном вмешательстве, а также по комбинированной конечной точке. Вместе с тем пациенты, перенесшие бимаммарное шунтирование, достоверно чаще нуждались в приеме инотропных препаратов, а также дольше находились в стационаре.Заключение. Бимаммарное шунтирование – безопасная процедура, сравнимая по госпитальным осложнениям с классическим аортокоронарным шунтированием, вместе с тем такое вмешательство требует более продолжительного пребывания пациентов в стационаре, а также дополнительного использования инотропных препаратов.
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