564 research outputs found
Dehydration affects cerebral blood flow but not its metabolic rate for oxygen during maximal exercise in trained humans
No full textThis article has been made available through the Brunel Open Access Publishing Fund.Key points: Dehydration accrued during exercise in the heat challenges systemic and locomotor muscle blood flow, but its impact on cerebral blood flow (CBF) and metabolism remains unknown. This study assessed whether dehydration compromises CBF and the cerebral metabolic rate for oxygen (CMRO2) during incremental exercise to exhaustion in trained males. Dehydration induced an early reduction in CBF during progressive exercise, but increased O2 extraction secured CMRO2. In all hydration conditions declining CBF at high exercise intensities was correlated to decreasing arterial carbon dioxide tension and increasing jugular venous plasma noradrenaline. These results suggest that dehydration impairs CBF at high exercise intensities, but this circulatory strain on the human brain does not compromise CMRO2. Intense exercise is associated with a reduction in cerebral blood flow (CBF), but regulation of CBF during strenuous exercise in the heat with dehydration is unclear. We assessed internal (ICA) and common carotid artery (CCA) haemodynamics (indicative of CBF and extra-cranial blood flow), middle cerebral artery velocity (MCA Vmean), arterial-venous differences and blood temperature in 10 trained males during incremental cycling to exhaustion in the heat (35°C) in control, dehydrated and rehydrated states. Dehydration reduced body mass (75.8 ± 3 vs. 78.2 ± 3 kg), increased internal temperature (38.3 ± 0.1 vs. 36.8 ± 0.1°C), impaired exercise capacity (269 ± 11 vs. 336 ± 14 W), and lowered ICA and MCA Vmean by 12-23% without compromising CCA blood flow. During euhydrated incremental exercise on a separate day, however, exercise capacity and ICA, MCA Vmean and CCA dynamics were preserved. The fast decline in cerebral perfusion with dehydration was accompanied by increased O2 extraction (P < 0.05), resulting in a maintained cerebral metabolic rate for oxygen (CMRO2). In all conditions, reductions in ICA and MCA Vmean were associated with declining cerebral vascular conductance, increasing jugular venous noradrenaline, and falling arterial carbon dioxide tension (P aCO 2) (R2 ≥ 0.41, P ≤ 0.01) whereas CCA flow and conductance were related to elevated blood temperature. In conclusion, dehydration accelerated the decline in CBF by decreasing P aCO 2 and enhancing vasoconstrictor activity. However, the circulatory strain on the human brain during maximal exercise does not compromise CMRO2 because of compensatory increases in O2 extraction. © 2014 The Authors
Book Review: Aboriginal Customary Law: A Source of Common Law Title to Land
No full textBook Title: Aboriginal Customary Law: A Source of Common Law Title to LandBook Author: U Secher(2014 Hart Publishing Oxford and Portland Oregon) ISBN 978-1-84946-553-
The norite belt in the Mesoarchaean Maniitsoq structure, southern West Greenland: conduit-type Ni-Cu mineralisation in impact-triggered, mantle-derived intrusions?
No full textWith the recent discovery of the giant, deeply eroded, 3 Ga Maniitsoq impact structure in southern West Greenland (Garde 2010), an enigmatic, c. 75 by 15 km large, curvilinear belt of undeformed norite intrusions with Ni-Cu mineralisation was re-interpreted as representing crustally contaminated melts derived from the mantle in the wake of the impact (Fig. 1; Garde et al. 2012). The norite belt (Nielsen 1976; Secher 1983) was discovered in the early 1960s by the mining and exploration company Kryolitselskabet Øresund A/S, and more than one hundred shallow exploration holes were drilled by the company in the period 1965–1971. The mineralisation has subsequently been investigated by Cominco Ltd., Falconbridge Ltd. and NunaMinerals A/S. In 2011, the re-interpretation of the norite belt, and recent availability of improved airborne geophysical exploration tools, prompted the Canadian company North American Nickel Inc. (NAN) to resume exploration
Brain serotonin and dopamine modulators, perceptual responses and endurance performance during exercise in the heat following creatine supplementation
No full textBackground:The present experiment examined the responses of peripheral modulators and indices of brain serotonin (5-HT) and dopamine (DA) function and their association with perception of effort during prolonged exercise in the heat after creatine (Cr) supplementation. Methods:Twenty one endurance-trained males performed, in a double-blind fashion, two constant-load exercise tests to exhaustion at 63 ± 5% V O2 max in the heat (ambient temperature: 30.3 ± 0.5°C, relative humidity: 70 ± 2%) before and after 7 days of Cr (20 g·d-1 Cr + 140 g·d-1 glucose polymer) or placebo (Plc) (160 g·d-1 glucose polymer) supplementation.Results:3-way interaction has shown that Cr supplementation reduced rectal temperature, heart rate, ratings of perceived leg fatigue (P < 0.05), plasma free-tryptophan (Trp) (P < 0.01) and free-Trp:tyrosine ratio (P < 0.01) but did not influence the ratio of free-Trp:large neutral amino acids or contribute in improving endurance performance (Plc group, n = 10: 50.4 ± 8.4 min vs. 51.2 ± 8.0 min, P > 0.05; Cr group, n = 11: 47.0 ± 4.7 min vs. 49.7 ± 7.5 min, P > 0.05). However, after dividing the participants into "responders" and "non-responders" to Cr, based on their intramuscular Cr uptake, performance was higher in the "responders" relative to "non-responders" group (51.7 ± 7.4 min vs.47.3 ± 4.9 min, p < 0.05).Conclusion:although Cr influenced key modulators of brain 5-HT and DA function and reduced various thermophysiological parameters which all may have contributed to the reduced effort perception during exercise in the heat, performance was improved only in the "responders" to Cr supplementation. The present results may also suggest the demanding of the pre-experimental identification of the participants into "responders" and "non-responders" to Cr supplementation before performing the main experimentation. Otherwise, the possibility of the type II error may be enhance
Bovine colostrum and immune function after exercise
No full textStrenuous and/or prolonged exercise causes transient perturbations in immune function. It is well accepted that this is one mechanism contributing to the higher occurrence of infection (e.g. upper respiratory tract infection (URTI)) in athletes, especially endurance athletes. URTI or upper respiratory tract (URT) symptoms can negatively affect training and competition performance but athletes must train intensively to be successful. Therefore, interventions that can legitimately enhance immune function and reduce URTI risk can be of benefit to athletes. Bovine colostrum supplementation has been investigated as a possible nutritional countermeasure to enhance (or maintain) immune function, and reduce URTI risk, following strenuous or prolonged exercise and during intensive training periods. There is convincing evidence that daily supplementation with bovine colostrum, for a number of weeks (and preliminary evidence for acute effects after a single dose), can maintain intestinal barrier integrity, immune function and reduce the chances of suffering URTI or URT symptoms in athletes or those undertaking heavy training. The mechanisms are not fully understood at present but there is preliminary evidence suggesting that the effects on immune function are attributable, at least in part, to small bioactive components that survive digestion and are biologically available after consumption, but further work is required. In summary, the balance of existing evidence does support the notion that bovine colostrum is beneficial for certain groups of athletes, such as those involved in strenuous training (e.g. endurance athletes), in terms of immunity and resistance to infection
Transient influence of end-tidal carbon dioxide tension on the postural restraint in cerebral perfusion
No full textImmink RV, Truijen J, Secher NH, Van Lieshout JJ. Transient influence of end-tidal carbon dioxide tension on the postural restraint in cerebral perfusion. J Appl Physiol 107: 816-823, 2009. First published July 2, 2009; doi: 10.1152/japplphysiol.91198.2008.-In the upright position, cerebral blood flow is reduced, maybe because arterial carbon dioxide partial pressure (Pa-CO2) decreases. We evaluated the time-dependent influence of a reduction in Pa-CO2, as indicated by the end-tidal P-CO2 tension (PETCO2), on cerebral perfusion during head-up tilt. Mean arterial pressure, cardiac output, middle cerebral artery mean flow velocity (MCA V-mean), and dynamic cerebral autoregulation at supine rest and 70 head-up tilt were determined during free breathing and with PETCO2 clamped to the supine level. The postural changes in central hemodynamic variables were equivalent, and the cerebrovascular autoregulatory capacity was not significantly affected by tilt or by clamping PETCO2. In the first minute of tilt, the decline in MCA V-mean (10 +/- 4 vs. 3 +/- 4 cm/s; mean +/- SE; P <0.05) and PETCO2 (6.8 +/- 4.3 vs. 1.7 +/- 1.6 Torr; P <0.05) was larger during spontaneous breathing than during isocapnic tilt. However, after 2 min in the head-up position, the reduction in MCA V-mean was similar (7 +/- 5 vs. 6 +/- 3 cm/s), although the spontaneous decline in PETCO2 was maintained (P <0.05 vs. isocapnic tilt). These results suggest that the potential contribution of Pa-CO2 to the postural reduction in MCA V-mean is transient, leaving the mechanisms for the sustained restrain in MCA V-mean to be identifie
Was Dali's Wife Malign-Or Misunderstood
No full textAn article promoting ""Gala Salvador Dali: A Room of One's Own"" at the Museo Nacional d'Arte de Catalunya. The argument that Gala was not the nasty, mone-hungry woman she was painted to be, but instead, something more benign is presented by Curator, Estrella de Diego. The author provides a brief background of Gala, and multiple examples of strong, negative opinions people had about her
Schizzo storico-topografico di Fizenze e dintorni... / Compilata da Giuseppe Crivellari
No full textÉchelle(s) : 1:20 00
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