Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans

Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans. Am J Physiol Regul Integr Comp Physiol 292: R598–R606, 2007. First published September 7, 2006; doi:10.1152/ajpregu.00269.2006.—We hypothesized that severe hypoxia limits exercise performance via decreased contractility of limb locomotor muscles. Nine male subjects [mean SE maximum O2 uptake (V˙ O2 max) 56.5 2.7 ml kg 1 min 1] cycled at 90% V˙ O2 max to exhaustion in normoxia [NORM-EXH; inspired O2 fraction (FIO2) 0.21, arterial O2 saturation (SpO2) 93 1%] and hypoxia (HYPOX-EXH; FIO2 0.13, SpO2 76 1%). The subjects also exercised in normoxia for a time equal to that achieved in hypoxia (NORM-CTRL; SpO2 96 1%). Quadriceps twitch force, in response to supramaximal single (nonpotentiated and potentiated 1 Hz) and paired magnetic stimuli of the femoral nerve (10–100 Hz), was assessed pre- and at 2.5, 35, and 70 min postexercise. Hypoxia exacerbated exercise-induced peripheral fatigue, as evidenced by a greater decrease in potentiated twitch force in HYPOX-EXH vs. NORM-CTRL ( 39 4 vs. 24 3%, P 0.01). Time to exhaustion was reduced by more than two-thirds in HYPOX-EXH vs. NORM-EXH (4.2 0.5 vs. 13.4 0.8 min, P 0.01); however, peripheral fatigue was not different in HYPOX-EXH vs. NORM-EXH ( 34 4 vs. 39 4%, P 0.05). Blood lactate concentration and perceptions of limb discomfort were higher throughout HYPOX-EXH vs. NORM-CTRL but were not different at end-exercise in HYPOX-EXH vs. NORM-EXH. We conclude that severe hypoxia exacerbates peripheral fatigue of limb locomotor muscles and that this effect may contribute, in part, to the early termination of exercise

Studies of Decay and Snapback Effects on LHC Dipole Magnets

LHC model magnets have dynamic field imperfections of various nature. Two effects of particular importance are field component decay during injection and ''snapback'' during the first few seconds of acceleration, which happens over typically 15 to 20 mT. The dynamic behaviour of the model magnets was measured as a function of several parameters in the operation cycle and powering history. We demonstrate how the systematic variation of only one single operation cycle parameter can affect the behaviour of the sextupole component

Developmental errors in the common marmoset retina

Although retinal organization is remarkably conserved, morphological anomalies can be found to different extents and varieties across animal species with each presenting unique characteristics and patterns of displaced and misplaced neurons. One of the most widely used non-human primates in research, the common marmoset (Callithrix jaccus) could potentially also be of interest for visual research, but is unfortunately not well characterized in this regard. Therefore, the aim of our study was to provide a first time description of structural retinal layering including morphological differences and distinctive features in this species. Retinas from animals (n = 26) of both sexes and different ages were immunostained with cell specific antibodies to label a variety of bipolar, amacrine and ganglion cells. Misplaced ganglion cells with somata in the outermost part of the inner nuclear layer and rod bipolar cells with axon terminals projecting into the outer plexiform layer instead of the inner plexiform layer independent of age or sex of the animals were the most obvious findings, whereas misplaced amacrine cells and misplaced cone bipolar axon terminals occurred to a lesser extent. With this first time description of developmental retinal errors over a wide age range, we provide a basic characterization of the retinal system of the common marmosets, which can be taken into account for future studies in this and other animal species. The finding of misplaced ganglion cells and misplaced bipolar cell axon terminals was not reported before and displays an anatomic variation worthwhile for future analyzes of their physiological and functional impact

Excessive gas exchange impairment during exercise in a subject with a history of bronchopulmonary dysplasia and high altitude pulmonary edema

A 27-year-old male subject (V(O2 max)), 92% predicted) with a history of bronchopulmonary dysplasia (BPD) and a clinically documented case of high altitude pulmonary edema (HAPE) was examined at rest and during exercise. Pulmonary function testing revealed a normal forced vital capacity (FVC, 98.1% predicted) and diffusion capacity for carbon monoxide (D(L(CO)), 91.2% predicted), but significant airway obstruction at rest [forced expiratory volume in 1 sec (FEV(1)), 66.5% predicted; forced expiratory flow at 50% of vital capacity (FEF(50)), 34.3% predicted; and FEV(1) /FVC 56.5%] that was not reversible with an inhaled bronchodilator. Gas exchange worsened from rest to exercise, with the alveolar to arterial P(O2) difference (AaD(O2)) increasing from 0 at rest to 41 mmHg at maximal normoxic exercise (VO(2) = 41.4 mL/kg/min) and from 11 to 31 mmHg at maximal hypoxic exercise (VO(2) = 21.9 mL/kg/min). Arterial P(O2) decreased to 67.8 and 29.9 mmHg at maximal normoxic and hypoxic exercise, respectively. These data indicate that our subject with a history of BPD is prone to a greater degree of exercise-induced arterial hypoxemia for a given VO(2) and F(I(O2)) than healthy age-matched controls, which may increase the subject's susceptibility to high altitude illness

Interaction between current imbalance and magnetization in LHC cables

The quality of the magnetic field in superconducting accelerator magnets is associated with the properties of the superconducting cable. Current imbalances due to coupling currents ¿I, as large as 100 A, are induced by spatial variations of the field sweep rate and contact resistances. During injection at a constant field all magnetic field components show a decay behavior. The decay is caused by a diffusion of coupling currents into the whole magnet. This results in a redistribution of the transport current among the strands and causes a demagnetization of the superconducting cable. As soon as the field is ramped up again after the end of injection, the magnetization rapidly recovers from the decay and follows the course of the original hysteresis curve. In order to clarify the interactions between the changes in current and magnetization during injection the authors performed a number of experiments. A magnetic field with a spatially periodic pattern was applied to a superconducting wire in order to simulate the coupling behavior in a magnet. This model system was placed into a stand for magnetization measurements and the influence of different powering conditions was analyze

No evidence for age-related alterations in the marmoset retina

The physiological aging process of the retina is accompanied by various and sometimes extensive changes: Macular degeneration, retinopathies and glaucoma are the most common findings in the elderly and can potentially lead to irreversible visual disablements up to blindness. To study the aging process and to identify possible therapeutic targets to counteract these diseases, the use of appropriate animal models is mandatory. Besides the most commonly used rodent species, a non-human primate, the common marmoset (Callithrix jacchus) emerged as a promising animal model of human aging over the last years. However, the visual aging process in this species is only partially characterized, especially with regard to retinal aberrations. Therefore, we assessed here for the first time potential changes in retinal morphology of the common marmoset of different age groups. By cell type specific immunolabeling, we analyzed different cell types and distributions, potential photoreceptor and ganglion cell loss, and structural reorganization. We detected no signs of age-related differences in staining patterns or densities of various cell populations. For example, there were no signs of photoreceptor degeneration, and there was only minimal sprouting of rod bipolar cells in aged retinas. Altogether, we describe here the maintenance of a stable neuronal architecture, distribution and number of different cell populations with only mild aberrations during the aging process in the common marmoset retina. These findings are in stark contrast to previously reported findings in rodent species and humans and deserve further investigations to identify the underlying mechanisms and possible therapeutic targets

Limited Wildlife Diversity at Highway Right-of-Way Crossings

This project included estimation of animal occurrence near and using structures (e.g., culverts, street, and RR crossing structures) to cross the Interstate-80 right-of-way in the Sierra Nevada, California. A combination of track plates near over-crossings and remote cameras at under-crossings was used to index wildlife occurrence and crossings. Diversity was relatively low in the highway right-of-way and at highway under-crossings. Across six highway under-crossings, only eight of 38 possible species were observed moving through these crossings from one side of the highway right-of-way to the other. Alpha diversity at highway crossings ranged widely for wildlife near street under and over-crossings, but was not related to nearby land development. Wildlife use of existing under-crossing structures was inversely proportional to the presence of humans and frequency of human use of the same structures. This has important implications for effectiveness of existing structures and purpose-built “wildlife crossings” to provide for wildlife movement

Degaussing and Decay Reduction in the Short Superconducting Dipole Models for the LHC

The time decay of field harmonics during current plateaus is a known drawback of superconducting accelerator magnets. The present understanding of this phenomenon refers to a combination of flux creep and of the interaction between the redistribution of currents in Rutherford cables and the filament magnetization. Current cycles of decreasing amplitude, called here degaussing, were found to reduce significantly the decay observed in accelerator magnets. This paper reports on the measured reduction of decay obtained in short dipole models for the LHC and on one experiment with a single LHC strand

Геотемпературный режим баженовской свиты и нефтеперспективные зоны меловых отложений (Нюрольская мегавпадина)

По замерам пластовых температур верхнеюрских отложений построена карта распределения геотемператур баженовской свиты Нюрольской мегавпадины и структур ее обрамления. По геотемпературному критерию выделены очаги интенсивной генерации баженовских нефтей. Местоположения эпицентров очагов рекомендованы в качестве первоочередных зон для выявления объектов в меловом нефтегазоносном комплексе

A Fast Sextupole Probe for Snapback Measurement in the LHC Dipoles

In superconducting particle accelerators a fast change of the magnetic field occurs during the first few seconds after the start of an energy ramp. Standard magnetic measurements using a coil rotating at 1 Hz do not have the time resolution required to completely resolve this phase, usually called snapback. For this reason we have developed a new and fast system dedicated to sextupole measurements. The basic component consists of three Hall plates mounted on a ring. In an ideal case this arrangement compensates the main dipole field and produces a signal proportional to the sextupole only. Mechanical tolerances and differences in the sensitivity of the Hall plates are compensated by instrumentation amplifiers and an in situ fine adjustment of the probe orientation. Using this hybrid compensation technique we have measured sextupole variations in an LHC dipole prototype during snapback at a rate of 5 Hz. In this paper we present details on the device and the results of our measurements