323,156 research outputs found
Atenolol depresses post-ischaemic recovery in the isolated rat heart
No full textMetabolic events during ischaemia are probably important in determining post-ischaemic myocardial recovery. The aim of this study was to assess the effects of the β-blocker atenolol and the high energy demand in an ischaemia-reperfusion model free of neurohormonal and vascular factors. We exposed Langendorff-perfused isolated rat hearts to low-flow ischaemia (30 min) and reflow (20 min). Three groups of hearts were used: control hearts (n = 11), hearts that were perfused with 2.5 μg l-1 atenolol (n = 9), and hearts electrically paced during ischaemia to distinguish the effect of heart rate from that of the drug (n = 9). The hearts were freeze-clamped at the end of reflow to determine high-energy phosphates and their metabolites. During ischaemia, the pressure-rate product was 2.3 ± 0.2, 5.2 ± 1.1, and 3.3 ± 0.3 mmHg 103 min in the control, atenolol and paced hearts, respectively. In addition, the ATP turnover rate, calculated from venous (lactate), oxygen uptake and flow, was higher in atenolol (11.2 ± 1.7 μmol min-1) and paced (8.1 ± 0.8 μmol min-1) hearts than in control (6.2 ± 0.8 μmol min-1). At the end of reflow, the pressure x rate product recovered 75.1 ± 6.4% of baseline in control vs 54.1 ± 9.1 and 48.8 ± 4.4% in atenolol and paced hearts (P < 0.05). In addition, the tissue content of ATP was higher in the control hearts (15.8 ± 1.0 μmol g(dw)-1) than in atenolol (10.5 ± 2.6 μmol g(dw)-1) and paced (10.9 ± 1.3 μmol g(dw)-1) hearts. Thus, by suppressing the protective effects of down-regulation both atenolol and pacing apparently depress myocardial recovery in this model
Fractal analysis of heart rate variability reveals alterations of the integrative autonomic control of circulation in paraplegic individuals
No full textThe autonomic nervous system plays a major role in the integrative control of circulation, possibly contributing to the 'complex' dynamics responsible for fractal components in heart rate variability. Aim of this study is to evaluate whether an altered autonomic integrative control is identified by fractal analysis of heart rate variability. We enrolled 14 spinal cord injured individuals with complete lesion between the 5th and 11th thoracic vertebra (SCIH), 14 with complete lesion between 12th thoracic and 5th lumbar vertebra (SCIL), and 34 able-bodied controls (AB). These paraplegic subjects have an altered autonomic integrative regulation, but intact autonomic cardiac control and, as to SCILindividuals, intact autonomic splanchnic control. Power spectral and fractal analysis (temporal spectrum of scale coefficients) were performed on 10 min tachograms. AB and SCILpower spectra were similar, while the SCILfractal spectrum had higher coefficients between 12 and 48 s. SCIHindividuals had lower power than controls at 0.1 Hz; their fractal spectrum was morphologically different, diverging from that of controls at the largest scales (120 s). Therefore, when the lesion compromises the autonomic control of lower districts, fractal analysis reveals alterations undetected by power spectral analysis of heart rate variability
Novæ Observationes Et Additiones Ad A. R. P. D. Bartholomæi Gavanti Congreg. Cleric. Regul. S. Pauli ac Sac. Rit. Congregat. Consultoris Commentaria In Rubricas Missalis Et Breviarii Romani : Adjectis Summorum Pontificum & Sac. Rit. Congreg. Decretis usque ad præsens emanatis
No full textAuthore R. P. D. Cajetano Maria Merati Cler. Reg. & ejusdem Sac. Rit. Congregat. ConsultoreVorlageform des Erscheinungsvermerks: Augustæ Vindelicorum. Sumptibus Jodoci Henrici Müller Bibliopolæ. Anno MDCCXL.Titelbl. von Bd. 1,1 und 2,1 in Rot- und Schwarzdr.Erschienen: Bd. 1,1 (1740) - 2,2 (1740
Effects of passive stretching on post-activation potentiation and fibre conduction velocity of biceps brachii muscle
No full textStretching is usually part of warm-up routines in many sports, but it affects the subsequent muscle force; therefore, it could negatively influence post-activation potentiation (PAP), one of the warm-up's main effects. The aim of this study was to evaluate the acute effects of passive stretching on PAP and fibre conduction velocity (CV). Seven subjects underwent 2 experimental sessions, control (C) and stretching (S), each consisting of 2 series (7 min resting) of 3 maximal voluntary contractions (MVC) of biceps brachii (5 s isometric contraction, 10 s recovery). During the resting phase of the S session, the biceps brachii was passively stretched (5×45 s stretches, 15 s recovery). Root mean square (RMS), mean frequency (MF) and CV were calculated from electromyography. Peak torque (pT) and half-contraction time (1/2CT) were measured and normalised by the arm muscular area (pTn). After C, pTn increased and 1/2CT decreased (p < 0.05); moreover, MF and CV increased (p < 0.05). After S, 1/2CT increased (p < 0.05) and RMS decreased (p < 0.05). Passive stretching could blunt the effects of PAP, presumably due to mechanical and neuromuscular changes. The observed changes in CV suggest a possible decrease in Ca2+ sensitivity in contractile proteins. Therefore, the use of passive stretching in warm-up routines remains questionable
The Acute Administration of Carnosine and Beta-Alanine Does Not Improve Running Anaerobic Performance and has No Effect on the Metabolic Response to Exercise
No full textAn increase in muscle carnosine content, following its chronic supplementation, has been shown to im- prove anaerobic performance. In addition, carnosine can affect plasma glucose concentration and insulin response. However, it is not clear whether the acute ingestion of carnosine can have the same effects. Aim of this study was to investigate the acute effects of carnosine ingestion on anaerobic intermittent per- formance and the responses of blood insulin, glucose, bicarbonate and lactate concentrations to exercise. Twelve healthy, young, active participants (BMI 23.5 ± .6, age: 22 ± 2 years) underwent in two separate occasions (double-blind, randomized, crossover design) the running-based anaerobic test (RAST), con- sisting of 6 × 35-m sprints interspersed with 10 s rest after acute (4 hours before the test) ingestion of ei- ther 1 g of L-carnosine and 1 g of β-alanine or placebo. None significant difference was found between the acute ingestion of carnosine and the placebo conditions in terms of running performance (30.0 ± .8 and 29.8 ± .8, p = .302), perceptual response to exercise (RPE), blood lactate, insulin (23.8 ± 13.0 and 19.5 ± 9.0 μU·ml−1, p = .329), blood glucose (109 ± 23 and 104 ± 12 mg·dl−1, p = .969), and blood bicar-bonates (16 ± 2 and 16 ± 2 mEq·l−1, p = .277). In conclusion, the acute ingestion of carnosine had no ef-fect on performance, perceptual response to exercise, blood lactate concentration, insulin, glucose, and bicarbonates responses to exercise compared to a placebo treatment. It is not clear whether these results may be attributed to an insufficient dose of carnosine or to a lack of acute effect per sé
Computer simulation of experimental surface charge for isomorphous oxides
No full textThe interfacial electrification behaviokr of cobalt ferrite samples kith different dekrees of skbstitktion, is analyzed; the experimental charke vs. pH ckrves are compared kith charke ckrves calcklated on the basis of the model of Davis et al. [8,9]. The extent of akreement betkeen calcklated and experimental resklts varies kith varyink the concentration of the base electrolyte; fkrther, in the case of the fklly skbstitkted CoFe2O4, charke vs. pH ckrves are reprodkced ksink very hikh and markedly different inner capacitance valkes in the positive and nekative rekions of charke. © 1988
Effect of school backpack on energy cost of walking, cardio-respiratory changes, and low back pain in children.
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[Thrombolysis & arrhythmias]
No full textIn this study, we assessed one particular aspect of the arrhythmogenic phenomena that occur during reperfusion secondary to thrombolysis, that is the therein involved metabolic mechanisms. The employed experimental model (isolated Langendorff-perfused rat heart) allowed us to distinguish which factor involved during ischemia, low coronary flow or low oxygen tension, is primarily involved during arrhythmogenesis. This was made possible by comparing two settings characterized by the same oxygen supply, but with different coronary flows and PO2 values, i.e., ischemia and hypoxemia. As expected, the contractile dysfunction was higher during reoxygenation at the end of hypoxemia than during reperfusion at the end of ischemia (p < 0.05). However, the incidence of arrhythmias was similar in both cases. Therefore, whereas the contractile dysfunction appears to be more sensitive to coronary flow, the incidence of arrhythmias appears to be more sensitive to the total oxygen supply to the heart. This implies that the mechanisms underlying the development of contractile dysfunction and arrhythmogenesis follow different paths
Complexity analysis of surface electromyography for assessing the myoelectric manifestation of muscle fatigue: A review
No full textThe surface electromyography (sEMG) records the electrical activity of muscle fibers during contraction: one of its uses is to assess changes taking place within muscles in the course of a fatiguing contraction to provide insights into our understanding of muscle fatigue in training protocols and rehabilitation medicine. Until recently, these myoelectric manifestations of muscle fatigue (MMF) have been assessed essentially by linear sEMG analyses. However, sEMG shows a complex behavior, due to many concurrent factors. Therefore, in the last years, complexity-based methods have been tentatively applied to the sEMG signal to better individuate the MMF onset during sustained contractions. In this review, after describing concisely the traditional linear methods employed to assess MMF we present the complexity methods used for sEMG analysis based on an extensive literature search. We show that some of these indices, like those derived from recurrence plots, from entropy or fractal analysis, can detect MMF efficiently. However, we also show that more work remains to be done to compare the complexity indices in terms of reliability and sensibility; to optimize the choice of embedding dimension, time delay and threshold distance in reconstructing the phase space; and to elucidate the relationship between complexity estimators and the physiologic phenomena underlying the onset of MMF in exercising muscles
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