Expiratory muscle fatigue impairs exercise performance

High-intensity, exhaustive exercise may lead to inspiratory as well as expiratory muscle fatigue (EMF). Induction of inspiratory muscle fatigue (IMF) before exercise has been shown to impair subsequent exercise performance. The purpose of the present study was to determine whether induction of EMF also affects subsequent exercise performance. Twelve healthy young men performed five 12-min running tests on a 400-m track on separate days: a preliminary trial, two trials after induction of EMF, and two trials without prior muscle fatigue. Tests with and without prior EMF were performed in an alternate order, randomly starting with either type. EMF was defined as a ≥20% drop in maximal expiratory mouth pressure achieved during expiratory resistive breathing against 50% maximal expiratory mouth pressure. The average distance covered in 12min was significantly smaller during exercise with prior EMF compared to control exercise (2872±256 vs. 2957±325m; P=0.002). Running speed was consistently lower (0.13ms−1) throughout the entire 12min of exercise with prior EMF. A significant correlation was observed between the level of EMF (decrement in maximal expiratory mouth pressure after resistive breathing) and the reduction in running distance (r 2=0.528, P=0.007). Perceived respiratory exertion was higher during the first 800m and heart rate was lower throughout the entire test of running with prior EMF compared to control exercise (5.3±1.6 vs. 4.5±1.7 points, P=0.002; 173±10 vs. 178±7beatsmin−1, P=0.005). We conclude that EMF impairs exercise performance as previously reported for IM

Methodology and reliability of respiratory muscle assessment

The optimal method for respiratory muscle endurance (RME) assessment remains unclear. This study assessed the test-retest reliability of two RME-test methodologies. Fifteen healthy adults attended the laboratory on four occasions, separated by 5 ± 2 days, and completed each test in a random, “one on two” order. They performed spirometry testing, maximal respiratory pressure assessment and two different RME tests: an inspiratory resistive breathing (IRB) and an isocapnic hyperpnea endurance (IHE) test. Typical error, expressed as coefficient of variation, for IRB maximal inspiratory pressure (MIP) and IHE maximal ventilation were 12.21 (8.85–19.67) % and 10.73 (7.78–17.29) %, respectively. Intraclass correlation coefficients for the same parameters were 0.83 (0.46-0.94) and 0.80 (0.41-0.93), respectively. No correlations were found between RME parameters derived from the IHE and IRB tests (all p > 0.05). Significant positive correlations were found between both IRB and IHE outcomes and spirometry parameters, MIP and maximal expiratory pressure (p < 0.05).Given these results, IRB and IHE appear to be suitable for RME testing in healthy people, although they may reflect different physiological mechanisms (respiratory mechanics and respiratory muscle capacity for IHE test vs. inspiratory muscle capacity for IRB test). Future studies are therefore warranted that compare IRB and IHE tests in clinical settings

Structural Disorder Induced Polaron Formation and Magnetic Scattering in the Disordered Holstein-Double Exchange Model

In this paper we present results on the disordered Holstein-Double Exchange model, explicitly in three dimension and `metallic' densities, obtained by using a recently developed Monte Carlo approach. Following up on our earlier paper, cond-mat/0406085, here we provide a detailed microscopic picture of the thermally driven metal-insulator transition (MIT) that arises close to the ferromagnet to paramagnet transition in this problem. This paper is focused mainly on the `diagnostics', clarifying the origin of the effective disorder that drives the MIT in this system. To that effect, we provide results on the thermal evolution of the distributions of (i) lattice distortions, (ii) the net `structural disorder' and (iii) the `hopping disorder' arising from spin randomness feeding back through the Hunds coupling. We suggest a phenomenology for the thermally driven MIT, viewing it as an `Anderson-Holstein' transition.Comment: 6 pages, latex, JPSJ style, 7 eps figs. Style files included. Proceedings of the SPQS Meeting at Sendai, Japan, 2004. To appear in JPS

Propagation of social representations

Based on a minimal formalism of social representations as a set of associated cognems, a simple model of propagation of representations is presented. Assuming that subjects share the constitutive cognems, the model proposes that mere focused attention on the set of cognems in the field of common conscience may replicate the pattern of representation from context into subjects, or, from subject to subject, through actualization by language, where cognems are represented by verbal signs. Limits of the model are discussed, and evolutionist perspectives are presented with the support of field data

Partially gapped fermions in 2D

We compute mean field phase diagrams of two closely related interacting fermion models in two spatial dimensions (2D). The first is the so-called 2D t-t'-V model describing spinless fermions on a square lattice with local hopping and density-density interactions. The second is the so-called 2D Luttinger model that provides an effective description of the 2D t-t'-V model and in which parts of the fermion degrees of freedom are treated exactly by bosonization. In mean field theory, both models have a charge-density-wave (CDW) instability making them gapped at half-filling. The 2D t-t'-V model has a significant parameter regime away from half-filling where neither the CDW nor the normal state are thermodynamically stable. We show that the 2D Luttinger model allows to obtain more detailed information about this mixed region. In particular, we find in the 2D Luttinger model a partially gapped phase that, as we argue, can be described by an exactly solvable model.Comment: v1: 36 pages, 10 figures, v2: minor corrections; equation references to arXiv:0903.0055 updated

Implications of Charge Ordering for Single-Particle Properties of High-Tc Superconductors

The consequences of disordered charge stripes and antiphase spin domains for the properties of the high-temperature superconductors are studied. We focus on angle-resolved photoemission spectroscopy and optical conductivity, and show that the many unusual features of the experimentally observed spectra can be understood naturally in this way. This interpretation of the data, when combined with evidence from neutron scattering and NMR, suggests that disordered and fluctuating stripe phases are a common feature of high-temperature superconductors.Comment: 4 pages, figures by fax or mai

Zinc oxide as an ozone sensor

Journal of Applied Physics, Vol. 96, nº3This work presents a study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet sUVd photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process performed at room temperature. The films analyzed were produced by spray pyrolysis, dc and rf magnetron sputtering. The dc resistivity of the films produced by rf magnetron sputtering and constituted by nanocrystallites changes more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. On the other hand, porous and textured zinc oxide films produced by spray pyrolysis at low substrate temperature exhibit an excellent ac impedance response where the reactance changes by more than seven orders of magnitude when exposed to the same UV dose, with a response frequency above 15 kHz, thus showing improved ozone ac sensing discrimination

Superconductivity of a Metallic Stripe Embedded in an Antiferromagnet

We study a simple model for the metallic stripes found in $La_{1.6-x}Nd_{0.4}Sr_xCuO_4$: two chain Hubbard ladder embedded in a static antiferromagnetic environments. We consider two cases: a ``topological stripe'', for which the phase of the Neel order parameter shifts by $\pi$ across the ladder, and a ``non-topological stripe'', for which there is no phase shift across the ladder. We perform one-loop renormalization group calculations to determine the low energy properties. We compare the results with those of the isolated ladder and show that for small doping superconductivity is enhanced in the topological stripe, and suppressed in the non-topological one. In the topological stripe, the superconducting order parameter is a mixture of a spin singlet component with zero momentum and a spin triplet component with momentum $\pi$. We argue that this mixture is generic, and is due to the presence of a new term in the quantum Ginzburg-Landau action. Some consequences of this mixing are discussed.Comment: 6 pages, 3 eps figure

Interrelationships Between the Kinetics of VLDL Subspecies and HDL Catabolism in Abdominal Obesity: A Multicenter Tracer Kinetic Study

Context: Low plasma high-density lipoprotein (HDL) cholesterol is a major abnormality in abdominal obesity. This relates due to accelerated HDL catabolism, but the underlying mechanism requires further elucidation. The relationships between HDL catabolism and other variables that may be modified in abdominal obesity, such as very low-density lipoprotein (VLDL) subspecies (VLDL1, VLDL2) kinetics, liver fat, or visceral adiposity, remain to be investigated. Objectives: Our aim was to study the associations between HDL apolipoprotein (apo)-A-I fractional catabolic rate (FCR) and the kinetics of VLDL subspecies and estimates of liver and visceral and sc fat. Design: We carried out a multicenter in vivo kinetic study using stable isotopes (deuterated leucine and glycerol) in 62 individuals with abdominal obesity. Results: In a multivariate analysis, among the morphological and biological parameters that may predict apoA-I FCR, liver fat (beta = .400, P = .003), and VLDL1-apoB (beta = .307, P = .020) were independently associated with apoA-I FCR. In a multivariate analysis, among the kinetic parameters, VLDL1-triglycerides (TGs) indirect FCR (beta = .357, P = .001), VLDL1-TG production rate (beta = 0.213, P = .048), and apoA-II FCR (beta = .667, P < .0001) were independently associated with apoA-I FCR. After adjustment for VLDL1-TG production rate, liver fat was no more correlated with apoA-I FCR. No association between apoA-I FCR and visceral fat was observed. Conclusions: We show that VLDL1 is an important independent determinant of apoA-I FCR and more precisely that apoA-I FCR is independently associated with both catabolism and the production of VLDL1-TG. In addition, we show an association between liver fat and apoA-I FCR that is mostly mediated by VLDL1-TG production. These data indicate that, in abdominal obesity, dysfunctional VLDL1 metabolism is an important modulator of HDL apoA-I catabolism