Exploring the Change in Metabolic Cost of Walking before and after Familiarization with a Passive Load-Bearing Exoskeleton: A Case Series.

OCCUPATIONAL APPLICATIONSMilitary personnel are at greater risk of injuries due to frequent load carriage. Novel exoskeleton technology may have benefits for soldiers, such as reduced physical burden through load carriage support that may result in decreased metabolic cost, reduced fatigue, and lower risk of injuries during walking. However, as for most assistive devices, a familiarization period is likely necessary to obtain the full potential of the device. Our results show that the metabolic cost of walking (MWC) was initially increased significantly upon provision of the passive exoskeleton, though it returned to baseline values after a 9-day familiarization period. The exoskeleton remained effective after a three-month pause, with a MCW below baseline. These results suggest that to properly assess the assistance of an exoskeleton, a sufficient familiarization period should be mandatory.

Background: Military load carriage has been shown to alter gait patterns, resulting in an increased metabolic cost during walking (MCW). Soldiers' burden could be mitigated by wearing a passive exoskeleton, but the additional payload of the device can alter movement patterns during gait, rendering it detrimental. Integrating principles of motor learning during a familiarization period could allow users to develop adaptive motor strategies, thereby decreasing MCW.Purpose: The aim of this study was to explore the influence of a familiarization period on MCW when soldiers wear a passive, load-bearing, prototype exoskeleton (Exo).Methods: Three male soldiers walked on a treadmill with a 38 kg payload at eight speeds (1.8-6.0 km/h) under five conditions: 1) no exoskeleton (NoExo); 2) exoskeleton pre-familiarization (Exo_Pre); 3) exoskeleton post-familiarization (Exo_Post); 4) no exoskeleton follow-up (NoExo_FU); and 5) exoskeleton follow-up (Exo_FU). Each experimental trial consisted of 10 minutes of standing followed by 10 minutes of walking at a constant speed. Metabolic data were normalized to walking speed (J/kg·m) to obtain the MCW. The familiarization period consisted of 9 days of activities with the exoskeleton using a standardized protocol. Differences in MCW with and without the Exo were compared at the eight walking speeds using a nonparametric analysis of Longitudinal Data.Results: There was a statistically significant decrease in MCW after familiarization with the Exo, particularly during Exo_FU with a relative treatment effect of 0.11 − 0.19. There were also significant reductions in MCW during Exo_FU when compared to NoExo_FU [participant 01 = 0.37; participant 02 = 0.27; participant 03 = 0.35].Conclusions: A first exposure to the exoskeleton increased MCW. After familiarization, however, the MCW with the Exo returned to the NoExo level or below with a payload of 38 kg among three soldiers. A familiarization period of 3 hours per day over 2 weeks of familiarization may optimize the use of an exoskeleton.

Linear and non-linear dielectric properties of a short-pitch ferroelectric liquid crystal stabilized by a polymer network.

Linear and non-linear dielectric measurements were carried out on a ferroelectric liquid crystal stabilized by an anisotropic polymer network. The polymerization process was achieved at room temperature. It was performed from an achiral monomer in the ferroelectric chiral smectic C phase, exhibiting a very short helical pitch and a large polarization. The linear and non-linear dielectric spectroscopy were also completed by textural morphology as well as structural and ferroelectric characterizations. All these measurements were carried out on a pure ferroelectric liquid crystal material and on composite films containing two polymer concentrations. The increase of the polymer network density leads to a decrease of the dielectric strength determined in the linear and non-linear dielectric spectroscopy. The complementarity between the linear and non-linear dielectric measurements and their confrontation with a theoretical model allowed the simultaneous determination of some physical parameters such as macroscopic polarization, rotational viscosity and twist elastic energy. We also discuss the effect of the polymer network density on the obtained physical parameters.

Cationic switchable lipids: pH-triggered molecular switch for siRNA delivery.

A pH-sensitive molecular switch able to change its conformation upon protonation at endosomal pH values is embedded into the structure of cationic lipidoid materials, thus conferring endosomal escape properties. Involvement of the conformational switch in the endosomal escape process was confirmed and leading material identified was able to induce efficient gene knockdown both in vitro and in vivo. The lipid nanoparticles reported here are promising for therapeutic applications and this work could serve as a template for future design of stimulus-responsive (ionic, redox, light) molecular switch for drug and gene delivery.

Compensated Arrhenius formalism applied to a conductivity study in poly(propylene glycol) diacrylate monomers.

The temperature dependence of the ionic conductivity is studied in a series of poly(propylene glycol) diacrylate monomers. The experimental data are analyzed by means of the approach recently proposed by Petrowsky et al. [J. Phys. Chem. B. 113, 5996 (2009)10.1021/jp810095g]. This so-called compensated Arrhenius formalism (CAF) approach takes into account the influence of the dielectric permittivity on the exponential prefactor in the classical Arrhenius equation. The experimental data presented in this paper show a good agreement with the CAF; this means that the exponential prefactor is principally dielectric permittivity dependent. The compensated data revealed two conduction processes with different activation energies; they correspond to low and high temperature ranges, respectively.

Mediation of acetylcholine's excitatory actions in central neurons.

In experiments on the hippocampus in situ (in rats under urethane), neither cyclic GMP nor H-8 (an antagonist of cyclic nucleotide-dependent kinases) had much effect on CA1/CA3 population spikes or on the excitatory action of ACh. This is further evidence against the idea that cyclic nucleotides play a major role as cholinergic second messengers. On the other hand, the results of tests with a PKC antagonist sphinganine are in keeping with some involvement of PKC in cholinergic actions. (Another PKC antagonist, H-7, proved to be a very powerful excitant, probably via disinhibition). Preliminary experiments on CA1 neurons in hippocampal slices (by single electrode voltage clamp), confirmed previous reports that carbachol depresses A- and C-type K currents, as well as inward Ca2+ currents; though the latter effect was sometimes mainly due to frequency-dependent inactivation of Ca currents. It is suggested that a single, primary muscarinic action, the acceleration of phosphinositide turnover, may account for a variety of secondary effects: on the one hand, via activation of PKC, a number of possible PKC-mediated actions, such as block of the slow AHP; on the other, via IP3 formation, a block of IM and a rise in cycloplasmic free Ca2+ that may cause inactivation of both Ca2(+)-inward currents, and Ca2(+)-dependent GKs.

PFG NMR measurements of flow through porous media: effects of spatial correlations of the magnetic field and the velocity field.

Used for a long time for diffusion studies, PFG NMR techniques are now widely used to study flow through porous media. We discuss here the effects of the magnetic field inhomogeneities and the finite gradient pulse duration in this case. We propose a statistical model based on spatial correlations of the magnetic field and velocity field and as far as we can, we draw practical conclusions on the PFG NMR measurements conditions.

A comparative study of the activity of a new agent, indapamide, in essential arterial hypertension.

A single-blind crossover trial was carried out in 38 elderly, hospitalised patients with essential hypertension to compare the hypotensive activity of 5 mg. indapamide daily with 100 mg. chlorthalidone daily. After initial treatment for 10 days with placebo, patients received treatment for 45 days with either indapamide or chlorthalidone and were then crossed over to the alternative drug for a similar period. Potassium supplementation was necessary in 25 of the patients receiving chlorthalidone, but was precribed as a precautionary measure in only 1 patients whilst on indapamide. Results showed that there were significant drops in blood pressure following both active medications, but that the percentage reduction in diastolic pressure was greater after indapamide. Indapamide also proved more effective than chlorthalidone in controlling the patients' subjective and functional symptoms of their hypertension. In an overall assessment of the effectiveness of both drugs, indapamide was judged to be better tolerated as well as more effective than chlorthalidone in 18 of the 38 patients, whilst chlorthalidone was preferred in only 7 instances.

Pulsed field gradient NMR measurements of probability distribution of displacement under flow in sphere packings.

In this work we used the PFG NMR displacement technique to investigate the transport of water particles under flow through a model porous media. Using different sizes of sphere for monodisperse glass sphere packings, we measured the probability distribution of displacement for mean displacements ranging from 0.08 to 7.3 times the characteristic length of the porous media. We observed, therefore, the transition between the velocity probability distribution and the Gaussian-shaped distribution of classical dispersion.

Group therapy for pathological gamblers: a cognitive approach.

This study evaluated the efficacy of a group cognitive treatment for pathological gambling. Gamblers, meeting DSM-IV criteria for pathological gambling, were randomly assigned to treatment (N=34) or wait-list control (N=24) conditions. Cognitive correction techniques were used first to target gamblers' erroneous perceptions about randomness, and then to address issues of relapse prevention. The dependent measures used were the DSM-IV criteria for pathological gambling, perceived self-efficacy, gamblers' perception of control, desire to gamble, and frequency of gambling. Post-treatment results indicated that 88% of the treated gamblers no longer met the DSM-IV criteria for pathological gambling compared to only 20% in the control group. Similar changes were observed on all outcome measures. Analysis of data from 6-, 12- and 24-month follow-ups revealed maintenance of therapeutic gains. Recommendations for group interventions are discussed, focusing on the cognitive correction of erroneous perceptions toward the notion of randomness.

Toxicity assessment of total dissolved solids in effluent of Alaskan mines using 22-h chronic Microtox and Selenastrum capricornutum assays.

In order to overcome limitations associated with the Daphnia assay, we have explored two alternative assays, the 22-h chronic Microtox test and the 3-day S. capricornutum test, as substitutes. During this study, we compared the two assays using both a simple TDS standard solution and field water samples from two Alaskan mines. Using EC20 values, our results suggest that simple TDS standard solutions are not representative of environmental water samples of equivalent TDS concentrations. When comparing assays, our results showed that the 22-h Microtox assay was more reproducible and sensitive to effluent waters than the algal assay. Principle component analysis indicated that the 22-h Microtox test was generally more sensitive to nickel, ammonia and chloride while the S. capricornutum growth test appeared sensitive to cadmium levels.

Observations on the preferential biodegradation of selected components of polyaromatic hydrocarbon mixtures.

The capacity of the naphthalene degrading enzyme (NAH) system of Pseudomonas fluorescens 5R and a number of other NAH system bacterial isolates to degrade mixtures of polyaromatic hydrocarbons (PAHs) and heterocyclic compounds were examined. It was found that all the examined organisms displayed similar patterns of preferential compound degradation when presented with the same mixture. Using strains that possess portions of the NAH system, this preferential degradation was localized to the activity of naphthalene dioxygenase. Comparisons of the first-order rates of compound degradation with the structures of the mixture components indicated that increased deviation from the base structure of naphthalene led to slower disappearance. Structural features that were found to decrease the rate of compound degradation include an increase in the number of methyl substituents and an increase in the size of a substituent.

[Detection of pulmonary embolisms by recording of the variations of thoracic impedance at each lung]. / Ddtection des embolies pulmonaires par l'enregistrement des variations d'impédance thoracique à poumon séparé.

It is possible to record changes of volume caused by variations of the blood supply to each lung by measuring the transthoracic electrical impedance. A theoretical study was performed beforehand to define the variations of the impedance of the deep-lying structures. The form, number and distribution of the electrodes were determined by experiments on a model so that only variations of the impedance of the pulmonary parenchyma, and not of the mediastinum, were recorded. In this way the origins of the signals recorded were known. The validity of the method was tested on patients having undergone pneumonectomy and on patients with defects of pulmonary perfusion. Using the data obtained during the preceding experimental studies it was possible to defect perfusion defects caused by pulmonary embolism. Five cases of pulmonary embolism, confirmed by angiography and lung scan, of varying severity and chronicity, are reported. The amplitude of the impedance curve was reduced on the affected side, the difference of amplitude between the two being related to the degree of vascular amputation.

[Reconstruction of the external ear]. / La reconstruction du pavillon auriculaire.

The authors after a short morphological description of the microtia, expose the surgical evolution which had led to the actual auricular reconstruction technique, using a costal cartilage framework. This technique requiring several steps is exposed in the typical case of microtia. It is the preferential method. The difficult reconstructions due to the poor quality of the skin are exposed by degree of complexity: in these cases, tissue expansion, fascia temporalis superficialis can be useful and finally auricular prostheses, attached to bone-integrated implants, can be recommended. The functional surgery of the middle ear is also replaced in the context of the auricular reconstruction which is done around 8 years old.

Use of new synthetic talc as reinforcing nanofillers for polypropylene and polyamide 6 systems: thermal and mechanical properties.

New layered synthetic nanotalc prepared at a lab-scale by a conventional hydrothermal process and commercial natural fine talc were used in order to establish a comparative study in terms of their contributions on the improvement of the final properties of two different polymers: a nonpolar polyolefin matrix and a polyamide. All samples were prepared by melt extrusion in a co-rotating microcompounder. The surface properties of talc - surface energy and isoelectric point - were probed. The particles' crystalline structure and the distribution/dispersion within the polymer matrix were performed using transmission electron microscopy and X-ray diffraction. The effect of talc particles on the crystallinity, the thermal and mechanical properties was highlighted as a function of the surface properties of talc. In the case of talc-filled PP systems, it seems that the incorporation of both natural and synthetic talc greatly improves the thermal stability of polypropylene matrix. The highest elastic modulus was obtained in presence of highly nucleating natural talc. Oppositely, the best ductility was observed for the synthetic talc-filled PP systems. For PA6/talc nanocomposites, a remarkable improvement in the dispersion of talc layers was shown and a significant increase in Young's modulus was determined due to the closer affinity between the hydrophilic nanotalc lamellae and the polar PA6 matrix.

Anoxia reversibly suppresses neuronal calcium currents in rat hippocampal slices.

Intracellular recording from CA1 neurons confirmed that short periods of anoxia (95% N2 + 5% CO2 for 2-4 min) have a hyperpolarizing action, caused by a rise in K conductance. After blockage of K channels with extracellular Cs+ and tetraethylammonium (or intracellular Cs+), large inward currents of Ca were evoked by depolarizing pulses: transient currents at a holding potential near -70 mV, and more sustained ones near -50 mV. Both types of Ca current were much reduced or fully suppressed after 1-3 min of anoxia, but they largely (or fully) recovered within 1-10 min of starting reoxygenation.

Hypoxic changes in hippocampal neurons.

1. Reversible effects of brief periods of anoxia (replacing 95% O2-5% CO2 with 95% N2-5% CO2 for 2-4 min) were studied in CA1 neurons in hippocampal slices (from Sprague-Dawley rats), kept in an interface-type chamber at 33.5 degree. 2. The predominant voltage change during anoxia (N2) was a hyperpolarization, accompanied by a marked fall in resistance and excitability; synaptic potentials were also depressed, especially inhibitory postsynaptic potentials (IPSPs). 3. In voltage-current (V-I) plots, the N2-evoked hypolarization had a reversal potential below -90mV, even when recording with 2 M KCl electrodes and after substituting 90% of medium Cl- with isethionate. The accompanying fall in input resistance (RN) is therefore probably caused by an increase in K conductance (in agreement with previous reports). There was evidence that anomalous rectification enhances the fall in RN but limits the hyperpolarization. 4. These effects of anoxia were not fully blocked by any of the K-channel antagonists tested, including Cs, TEA, 4-AP, quinine and apamin. 5. Intracellular injections of Ca chelators caused a variable depression of N2-evoked reductions in RN. 6. It is unlikely that N2 activates ATP-sensitive K channels as tolbutamide enhanced rather than depressed the hyperpolarization and fall in RN. 7. When early depletion of cellular ATP was prevented by incubation in creatine (25 mM for greater than 1 h), even longer anoxic periods produced only minor changes in potential, RN, and synaptic transmission. 8. It was concluded that activation of K conductance by a rise in cytosolic-free Ca2+ is the most plausible of several possible underlying mechanisms.

Changes in membrane currents of hippocampal neurons evoked by brief anoxia.

1. Effects of anoxia (2-4 min of 95% N2-5% CO2) on membrane currents of CA1 neurons were studied by single-electrode voltage clamp in hippocampal slices (from Sprague-Dawley rats) kept in an interface-type chamber at 33.5 degree. 2. When recording with KCl electrodes at a holding potential (VH) near-70 mV, anoxia evoked a slow outward current [0.18 +/- 0.06 (SE) nA], accompanied by a conductance increase ( + 46 +/- 20%, mean +/- SE). The difference current evoked by N2 had a reversal potential near-100 mV. It was much smaller in presence of 2-4 mM extracellular Cs, and any remaining outward current was abolished by 10 mM tetraethylammonium (TEA). Only inward currents were observed when recording with CsCl electrodes. 3. Inward relaxations evoked by large hyperpolarizing pulses from VH less than or equal to - 70 mV (Q-type) were not significantly depressed by anoxia (-1.5 +/- 6.0%). 4. Some voltage-dependent outward currents (evoked by 200-ms depolarizing pulses) were depressed during anoxia: 1) a fast-inactivating (A-like) current, obtained at VH less than or equal to -70 mV and suppressed by 200 microM 4-AP, was reduced by 25.6 +/- 7.3% (n = 5); 2) a slower, noninactivating (C-like) current, suppressed by TEA, was reduced by 52 +/- 7.2% (n = 16). Neither of these currents (1 or 2) was observed when recording with 2- to 3-M CsCl electrodes; and 3) small (M-like) inward relaxations, observed at VH approximately -40 mV 5. Net inward currents could be evoked after blockage of GK with 10 mM TEA when recording with KCl electrodes or by recording with CsCl electrodes. At VH less than or equal to -70 mV, large, transient, and incompletely controlled currents were evoked by depolarizing pulses; at VH less than or equal to -50 mV, smaller and more persistent currents were evoked by depolarizing pulses (L-like), and transient currents (T-like?) were seen immediately after hyperpolarizing pulses. 6.L-type currents (at VH less than or equal to -50 mV) were nearly abolished after 1-2 min anoxia (by approximately 90%). This was equally true of the currents evoked by constant pulses or peak currents in I-V plots. After reoxygenation, recovery was biphasic, with a quick early phase (to 50-80% in 2 min) and then a much slower one (to 60-90% by 10-15 min).(ABSTRACT TRUNCATED AT 400 WORDS)

Laser Doppler velocimetry using a superheterodyne spectrum analyzer.

We present a superheterodyne optical spectrum analyzer where the frequency of the local oscillator changes linearly in time via an acoustooptic modulator. With this device we analyze the power spectrum of the light scattered by a rotating cylinder; a theoretical expression of the power spectrum shows that the spectrum width depends essentially on three different parameters: the angular velocity of the cylinder, the scattering angles, and the apparent linear dimensions of the illuminated area.