127 research outputs found
The Bezold-Jarisch reflex revisited: Clinical implications of inhibitory reflexes originating in the heart
AbstractThe concept of depressor reflexes originating in the heart was introduced by von Bezold in 1867 and was later revived by Jarisch. The Bezold-Jarisch reflex originates in cardiac sensory receptors with nonmyelinated vagal afferent pathways. The left ventricle, particularly the inferoposterior wall, is a principal location for these sensory receptors. Stimulation of these inhibitory cardiac receptors by stretch, chemical substances or drugs increases parasympathetic activity and inhibits sympathetic activity. These effects promote reflex bradycardia, vasodilation and hypotension (Bezold-Jarisch reflex) and also modulate renin release and vasopressin secretion. Conversely, decreases in the activity of these inhibitory sensory receptors reflexly increase sympathetic activity, vascular resistance, plasma renin activity and vasopressin.Long regarded as pharmacologic curiosities, it is now clear that reflexes originating in these inhibitory cardiac sensory receptors are important to the pathophysiology of many cardiovascular disorders. This paper reviews the role of inhibitory cardiac sensory receptors in several clinical states including 1) bradycardia, hypotension and gastrointestinal disorders with inferoposterior myocardial ischemia and infarction, 2) bradycardia and hypotension during coronary arteriography, 3) exertional syncope in aortic stenosis, 4) vasovagal syncope, 5) neurohumoral excitation in chronic heart failure, and 6) the therapeutic effects of digitalis
Mechanisms of insulin action on sympathetic nerve activity
Insulin resistance and hyperinsulinemia may contribute to the development of arterial hypertension. Although insulin may elevate arterial pressure, in part, through activation of the sympathetic nervous system, the sites and mechanisms of insulin-induced sympathetic excitation remain uncertain. While sympathoexcitation during insulin may be mediated by the baroreflex, or by modulation of norepinephrine release from sympathetic nerve endings, it has been shown repeatedly that insulin increases sympathetic outflow by actions on the central nervous system. Previous studies employing norepinephrine turnover have suggested that insulin causes sympathoexcitation by acting in the hypothalamus. Recent experiments from our laboratory involving direct measurements of regional sympathetic nerve activity have provided further evidence that insulin acts in the central nervous system. For example, administration of insulin into the third cerebralventricle increased lumbar but not renal or adrenal sympathetic nerve activity in normotensive rats. Interestingly, this pattern of regional sympathetic nerve responses to central neural administration of insulin is similar to that seen with systemic administration of insulin. Further, lesions of the anteroventral third ventricle hypothalamic (AV3V) region abolished increases in sympathetic activity to systemic administration of insulin with euglycemic clamp, suggesting that AV3V-related structures are critical for insulin-induced elevations in sympathetic outflow
Chandra Observations of the Anomalous X-ray Pulsar 4U 0142+61
We present X-ray imaging, timing, and phase resolved spectroscopy of the
anomalous X-ray pulsar 4U 0142+61 using the Chandra X-ray Observatory. The
spectrum is well described by a power law plus blackbody model with power law
index = 3.35(2), kT_BB=0.458(3) keV, and N_H=0.91(2) x 10^{22} cm^{-2}$; we
find no significant evidence for spectral features (0.5-7.0 keV). Time resolved
X-ray spectroscopy shows evidence for evolution in phase in either index, or
KT_BB, or some combination thereof as a function of pulse phase. We derive a
precise X-ray position for the source and determine its spin period,
P=8.68866(30) s. We have detected emission beyond 4 arcsec from the central
source and extending beyond 100 arcsec, likely due to dust scattering in the
interstellar medium.Comment: 15 pages, accepted for publication in Ap
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
Solar System Objects Observed in the SDSS Commissioning Data
We discuss measurements of the properties of about 10,000 asteroids detected
in 500 deg2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data.
The moving objects are detected in the magnitude range 14 < r < 21.5, with a
baseline of 5 minutes. Extensive tests show that the sample is at least 98%
complete, with the contamination rate of less than 3%.
We find that the size distribution of asteroids resembles a broken power-law,
independent of the heliocentric distance: D^{-2.3} for 0.4 km < D < 5 km, and
D^{-4} for 5 km < D < 40 km. As a consequence of this break, the number of
asteroids with r < 21.5 is ten times smaller than predicted by extrapolating
the power-law relation observed for brighter asteroids (r < 18). The observed
counts imply that there are about 530,000 objects with D>1 km in the asteroid
belt, or about four times less than previous estimates.
The distribution of main belt asteroids in the 4-dimensional SDSS color space
is bimodal, and the two groups can be associated with S (rocky) and C
(carbonaceous) asteroids. A strong bimodality is also seen in the heliocentric
distribution of asteroids and suggests the existence of two distinct belts: the
inner rocky belt, about 1 AU wide (FWHM) and centered at R~2.8 AU, and the
outer carbonaceous belt, about 0.5 AU wide and centered at R~3.2 AU. The colors
of Hungarias, Mars crossers, and near-Earth objects are more similar to the
C-type than to S-type asteroids, suggesting that they originate in the outer
belt. (abridged).Comment: 89 pages, 31 figures, submitted to A
The Imaging X-ray Polarimetry Explorer (IXPE): Technical Overview
The Imaging X-ray Polarimetry Explorer (IXPE) will expand the information space for study of cosmic sources, by adding linear polarization to the properties (time, energy, and position) observed in x-ray astronomy. Selected in 2017 January as a NASA Astrophysics Small Explorer (SMEX) mission, IXPE will be launched into an equatorial orbit in 2021. The IXPE mission will provide scientifically meaningful measurements of the x-ray polarization of a few dozen sources in the 2-8 keV band, including polarization maps of several x-ray-bright extended sources and phase-resolved polarimetry of many bright pulsating x-ray sources
The Sloan Digital Sky Survey: Technical Summary
The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed
investigations of the distribution of luminous and non- luminous matter in the
Universe: a photometrically and astrometrically calibrated digital imaging
survey of pi steradians above about Galactic latitude 30 degrees in five broad
optical bands to a depth of g' about 23 magnitudes, and a spectroscopic survey
of the approximately one million brightest galaxies and 10^5 brightest quasars
found in the photometric object catalog produced by the imaging survey. This
paper summarizes the observational parameters and data products of the SDSS,
and serves as an introduction to extensive technical on-line documentation.Comment: 9 pages, 7 figures, AAS Latex. To appear in AJ, Sept 200
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