189 research outputs found
Microvascular oxygen delivery-to-utilization mismatch at the onset of heavy-intensity exercise in optimally treated patients with CHF
Sperandio PA, Borghi-Silva A, Barroco A, Nery LE, Almeida DR, Neder JA. Microvascular oxygen delivery-to-utilization mismatch at the onset of heavy-intensity exercise in optimally treated patients with CHF. Am J Physiol Heart Circ Physiol 297: H1720-H1728, 2009. First published September 4, 2009; doi:10.1152/ajpheart.00596.2009.-Impaired muscle blood flow at the onset of heavy-intensity exercise may transiently reduce microvascular O(2) pressure and decrease the rate of O(2) transfer from capillary to mitochondria in chronic heart failure (CHF). However, advances in the pharmacological treatment of CHF (e. g., angiotensin-converting enzyme inhibitors and third-generation beta-blockers) may have improved microvascular O(2) delivery to an extent that intramyocyte metabolic inertia might become the main locus of limitation of O(2) uptake ((V)over dot(O2)) kinetics. We assessed the rate of change of pulmonary (V)over dot(O2) ((V)over dot(O2p)), (estimated) fractional O(2) extraction in the vastus lateralis (similar to Delta[deoxy-Hb + Mb] by near-infrared spectroscopy), and cardiac output ((Q)over dot(T)) during high-intensity exercise performed to the limit of tolerance (Tlim) in 10 optimally treated sedentary patients (ejection fraction = 29 +/- 8%) and 11 controls. Sluggish (V)over dot(O2p) and (Q)over dot(T) kinetics in patients were significantly related to lower Tlim values (P < 0.05). the dynamics of Delta[deoxy-Hb + Mb], however, were faster in patients than controls [mean response time (MRT) = 15.9 +/- 2.0 s vs. 19.0 +/- 2.9 s; P < 0.05] with a subsequent response overshoot being found only in patients (7/10). Moreover, tau(V)over dot(O2)/MRT-[deoxy-Hb + Mb] ratio was greater in patients (4.69 +/- 1.42 s vs. 2.25 +/- 0.77 s; P < 0.05) and related to (Q)over dot(T) kinetics and Tlim (R = 0.89 and -0.78, respectively; P < 0.01). We conclude that despite the advances in the pharmacological treatment of CHF, disturbances in central and peripheral circulatory adjustments still play a prominent role in limiting (V)over dot(O2p) kinetics and tolerance to heavy-intensity exercise in nontrained patients.Fed Univ São Paulo UNIFESP, Dept Med, Div Resp Med, Pulm Funct & Clin Exercise Physiol Unit SEFICE, São Paulo, BrazilFed Univ São Paulo UNIFESP, Dept Med, Div Cardiol, São Paulo, BrazilFed Univ Sao Carlos UFSCar, Nucleus Res Phys Exercise, Cardiopulm Lab, Sao Carlos, SP, BrazilFed Univ São Paulo UNIFESP, Dept Med, Div Resp Med, Pulm Funct & Clin Exercise Physiol Unit SEFICE, São Paulo, BrazilFed Univ São Paulo UNIFESP, Dept Med, Div Cardiol, São Paulo, BrazilWeb of Scienc
A Cautionary Tale: MARVELS Brown Dwarf Candidate Reveals Itself To Be A Very Long Period, Highly Eccentric Spectroscopic Stellar Binary
We report the discovery of a highly eccentric, double-lined spectroscopic
binary star system (TYC 3010-1494-1), comprising two solar-type stars that we
had initially identified as a single star with a brown dwarf companion. At the
moderate resolving power of the MARVELS spectrograph and the spectrographs used
for subsequent radial-velocity (RV) measurements (R ~ <30,000), this particular
stellar binary mimics a single-lined binary with an RV signal that would be
induced by a brown dwarf companion (Msin(i)~50 M_Jup) to a solar-type primary.
At least three properties of this system allow it to masquerade as a single
star with a very low-mass companion: its large eccentricity (e~0.8), its
relatively long period (P~238 days), and the approximately perpendicular
orientation of the semi-major axis with respect to the line of sight (omega~189
degrees). As a result of these properties, for ~95% of the orbit the two sets
of stellar spectral lines are completely blended, and the RV measurements based
on centroiding on the apparently single-lined spectrum is very well fit by an
orbit solution indicative of a brown dwarf companion on a more circular orbit
(e~0.3). Only during the ~5% of the orbit near periastron passage does the
true, double-lined nature and large RV amplitude of ~15 km/s reveal itself. The
discovery of this binary system is an important lesson for RV surveys searching
for substellar companions; at a given resolution and observing cadence, a
survey will be susceptible to these kinds of astrophysical false positives for
a range of orbital parameters. Finally, for surveys like MARVELS that lack the
resolution for a useful line bisector analysis, it is imperative to monitor the
peak of the cross-correlation function for suspicious changes in width or
shape, so that such false positives can be flagged during the candidate vetting
process.Comment: 16 pages, 11 figures, 6 table
Very Low Mass Stellar and Substellar Companions to Solar-Like Stars From MARVELS V: A Low Eccentricity Brown Dwarf from the Driest Part of the Desert, MARVELS-6b
We describe the discovery of a likely brown dwarf (BD) companion with a
minimum mass of 31.7 +/- 2.0 M_Jup to GSC 03546-01452 from the MARVELS radial
velocity survey, which we designate as MARVELS-6b. For reasonable priors, our
analysis gives a probability of 72% that MARVELS-6b has a mass below the
hydrogen-burning limit of 0.072 M_Sun, and thus it is a high-confidence BD
companion. It has a moderately long orbital period of 47.8929 +0.0063/-0.0062
days with a low eccentricty of 0.1442 +0.0078/-0.0073, and a semi-amplitude of
1644 +12/-13 m/s. Moderate resolution spectroscopy of the host star has
determined the following parameters: T_eff = 5598 +/- 63, log g = 4.44 +/-
0.17, and [Fe/H] = +0.40 +/- 0.09. Based upon these measurements, GSC
03546-01452 has a probable mass and radius of M_star = 1.11 +/- 0.11 M_Sun and
R_star = 1.06 +/- 0.23 R_Sun with an age consistent with less than ~6 Gyr at a
distance of 219 +/- 21 pc from the Sun. Although MARVELS-6b is not observed to
transit, we cannot definitively rule out a transiting configuration based on
our observations. There is a visual companion detected with Lucky Imaging at
7.7 arcsec from the host star, but our analysis shows that it is not bound to
this system. The minimum mass of MARVELS-6b exists at the minimum of the mass
functions for both stars and planets, making this a rare object even compared
to other BDs.Comment: 15 pages, 15 figures, 5 tables. Accepted for publication in The
Astronomical Journa
Acoustic scale from the angular power spectra of SDSS-III DR8 photometric luminous galaxies
We measure the acoustic scale from the angular power spectra of the Sloan
Digital Sky Survey III (SDSS-III) Data Release 8 imaging catalog that includes
872,921 galaxies over ~ 10,000 deg^2 between 0.45<z<0.65. The extensive
spectroscopic training set of the Baryon Oscillation Spectroscopic Survey
(BOSS) luminous galaxies allows precise estimates of the true redshift
distributions of galaxies in our imaging catalog. Utilizing the redshift
distribution information, we build templates and fit to the power spectra of
the data, which are measured in our companion paper, Ho et al. 2011, to derive
the location of Baryon acoustic oscillations (BAO) while marginalizing over
many free parameters to exclude nearly all of the non-BAO signal. We derive the
ratio of the angular diameter distance to the sound horizon scale D_A/r_s=
9.212 + 0.416 -0.404 at z=0.54, and therefore, D_A= 1411+- 65 Mpc at z=0.54;
the result is fairly independent of assumptions on the underlying cosmology.
Our measurement of angular diameter distance D_A is 1.4 \sigma higher than what
is expected for the concordance LCDM (Komatsu et al. 2011), in accordance to
the trend of other spectroscopic BAO measurements for z >~ 0.35. We report
constraints on cosmological parameters from our measurement in combination with
the WMAP7 data and the previous spectroscopic BAO measurements of SDSS
(Percival et al. 2010) and WiggleZ (Blake et al. 2011). We refer to our
companion papers (Ho et al. 2011; de Putter et al. 2011) for investigations on
information of the full power spectrum.Comment: 16 pages, 14 figures, 3 tables, submitted to Ap
Proportional Assist Ventilation Improves Leg Muscle Reoxygenation After Exercise in Heart Failure With Reduced Ejection Fraction
BackgroundRespiratory muscle unloading through proportional assist ventilation (PAV) may enhance leg oxygen delivery, thereby speeding off-exercise oxygen uptake (V.O2) kinetics in patients with heart failure with reduced left ventricular ejection fraction (HFrEF).MethodsTen male patients (HFrEF = 26 ± 9%, age 50 ± 13 years, and body mass index 25 ± 3 kg m2) underwent two constant work rate tests at 80% peak of maximal cardiopulmonary exercise test to tolerance under PAV and sham ventilation. Post-exercise kinetics of V.O2, vastus lateralis deoxyhemoglobin ([deoxy-Hb + Mb]) by near-infrared spectroscopy, and cardiac output (QT) by impedance cardiography were assessed.ResultsPAV prolonged exercise tolerance compared with sham (587 ± 390 s vs. 444 ± 296 s, respectively; p = 0.01). PAV significantly accelerated V.O2 recovery (τ = 56 ± 22 s vs. 77 ± 42 s; p < 0.05), being associated with a faster decline in Δ[deoxy-Hb + Mb] and QT compared with sham (τ = 31 ± 19 s vs. 42 ± 22 s and 39 ± 22 s vs. 78 ± 46 s, p < 0.05). Faster off-exercise decrease in QT with PAV was related to longer exercise duration (r = −0.76; p < 0.05).ConclusionPAV accelerates the recovery of central hemodynamics and muscle oxygenation in HFrEF. These beneficial effects might prove useful to improve the tolerance to repeated exercise during cardiac rehabilitation
The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
We measure the Milky Way's rotation curve over the Galactocentric range 4 kpc
<~ R <~ 14 kpc from the first year of data from the Apache Point Observatory
Galactic Evolution Experiment (APOGEE). We model the line-of-sight velocities
of 3,365 stars in fourteen fields with b = 0 deg between 30 deg < l < 210 deg
out to distances of 10 kpc using an axisymmetric kinematical model that
includes a correction for the asymmetric drift of the warm tracer population
(\sigma_R ~ 35 km/s). We determine the local value of the circular velocity to
be V_c(R_0) = 218 +/- 6 km/s and find that the rotation curve is approximately
flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also
measure the Sun's position and velocity in the Galactocentric rest frame,
finding the distance to the Galactic center to be 8 kpc < R_0 < 9 kpc, radial
velocity V_{R,sun} = -10 +/- 1 km/s, and rotational velocity V_{\phi,sun} =
242^{+10}_{-3} km/s, in good agreement with local measurements of the Sun's
radial velocity and with the observed proper motion of Sgr A*. We investigate
various systematic uncertainties and find that these are limited to offsets at
the percent level, ~2 km/s in V_c. Marginalizing over all the systematics that
we consider, we find that V_c(R_0) 99% confidence. We find an
offset between the Sun's rotational velocity and the local circular velocity of
26 +/- 3 km/s, which is larger than the locally-measured solar motion of 12
km/s. This larger offset reconciles our value for V_c with recent claims that
V_c >~ 240 km/s. Combining our results with other data, we find that the Milky
Way's dark-halo mass within the virial radius is ~8x10^{11} M_sun.Comment: submitted to Ap
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