How useful is satellite positioning system (GPS) to track gait parameters? A review.

Over the last century, numerous techniques have been developed to analyze the movement of humans while walking and running. The combined use of kinematics and kinetics methods, mainly based on high speed video analysis and forceplate, have permitted a comprehensive description of locomotion process in terms of energetics and biomechanics. While the different phases of a single gait cycle are well understood, there is an increasing interest to know how the neuro-motor system controls gait form stride to stride. Indeed, it was observed that neurodegenerative diseases and aging could impact gait stability and gait parameters steadiness. From both clinical and fundamental research perspectives, there is therefore a need to develop techniques to accurately track gait parameters stride-by-stride over a long period with minimal constraints to patients. In this context, high accuracy satellite positioning can provide an alternative tool to monitor outdoor walking. Indeed, the high-end GPS receivers provide centimeter accuracy positioning with 5-20 Hz sampling rate: this allows the stride-by-stride assessment of a number of basic gait parameters--such as walking speed, step length and step frequency--that can be tracked over several thousand consecutive strides in free-living conditions. Furthermore, long-range correlations and fractal-like pattern was observed in those time series. As compared to other classical methods, GPS seems a promising technology in the field of gait variability analysis. However, relative high complexity and expensiveness--combined with a usability which requires further improvement--remain obstacles to the full development of the GPS technology in human applications.

Mechanisms of spindle positioning during "Caenorhabditis elgans" asymmetric cell division

Résumé : Le positionnement correct du fuseau mitotique est crucial pour les divisions cellulaires asymétriques, car il gouverne le contrôle spatial de la division cellulaire et assure la ségrégation adéquate des déterminants cellulaires. Malgré leur importance, les mécanismes contrôlant le positionnement du fuseau mitotique sont encore mal compris. Chez l'embryon au stade une-cellule du nématode Caenorhabditis elegans, le fuseau mitotique est positionné de manière asymétrique durant l'anaphase grâce à l'action de générateurs de force situés au cortex cellulaire, et dont la nature était jusqu'alors indéterminée. Ces générateurs de force corticaux exercent une traction sur les microtubules astraux et sont dépendants de deux protéines Gα et de leurs protéines associées. Cette thèse traite de la nature de la machinerie responsable pour la génération des forces de tractions, ainsi que de son lien avec les protéines Gα et associées. Nous avons combiné des expériences de coupure par faisceau laser du fuseau mitotique avec le contrôle temporel de l'inactivation de gènes ou de l'exposition à des produits pharmacologiques. De cette manière, nous avons établi que la dynéine, un moteur se déplaçant vers l'extrémité négative des microtubules, ainsi que la dynamique des microtubules, sont toutes deux requises pour la génération efficace des forces de tractions. Nous avons démontré que les protéines Gα et leurs protéines associées GPR-1/2 et LIN-5 interagissent in vivo avec LIS-1, un composant du complexe de la dynéine. De plus, nous avons découvert que les protéines Gα, GPR-1/2 et LIN-5 promeuvent la présence du complexe de la dynéine au cortex cellulaire. Nos résultats suggèrent un mécanisme par lequel les protéines Gα permettent le recrutement cortical de GPR-1/2 et LIN-5, assurant ainsi la présence de la dynéine au cortex. Conjointement avec la dynamique des microtubules, ce mécanisme permet la génération des forces de tractions afin d'obtenir une division cellulaire correcte. Comme les mécanismes contrôlant le positionnement du fuseau mitotique et les divisions cellulaires asymétriques sont conservés au cours de l'évolution, nous espérons que les mécanismes élucidés par ce travail sont d'importance générale pour la génération de la diversité cellulaire durant le développement. De plus, ces mécanismes pourraient être applicables à d'autres divisions asymétriques, comme celle des cellules souches, dont le disfonctionnement peut entraîner la génération de cellules cancéreuses. Abstract : Proper spindle positioning is crucial for asymmetric cell division, because it controls spatial aspects of cell division and the correct inheritance of cell-fate determinants. However, the mechanisms governing spindle positioning remain incompletely understood. In the Caenorhabditis elegans one-cell stage embryo, the spindle becomes asymmetrically positioned during anaphase through the action of as-yet unidentified cortical force generators that pull on astral microtubules and that depend on two Gα proteins and associated proteins. This thesis addresses the nature of the force generation machinery and the link with the Gα and associated proteins. By performing spindle-severing experiments following temporally restricted gene inactivation and drug exposure, we established that microtubule dynamics and the minus-end directed motor dynein are both required for generating efficient pulling forces. We discovered that the Gα proteins and their associated proteins GPR-1/2 and LIN-5 interact in vivo with LIS-1, a component of the dynein complex. Moreover, we uncovered that LIN-5, GPR-1/2 and the Gα proteins promote the presence of the dynein complex at the cell cortex. Our findings suggest a mechanism by which the Gα proteins enable GPR-1/2 and LIN-5 recruitment to the cortex, thus ensuring the presence of cortical dynein. Together with microtubule dynamics, this allows pulling forces to be exerted and proper cell division to be achieved. Because the mechanisms of spindle positioning and asymmetric cell division are conserved across evolution, we expect the underlying mechanism uncovered here to be of broad significance for the generation of cell diversity during development. Moreover, this mechanism could be relevant for other asymmetric cell divisions, such as stem cell divisions, whose dysfunction may lead to the generation of cancer cells.

Simultaneous Optical Recording in Multiple Cells by Digital Holographic Microscopy of Chloride Current Associated to Activation of the Ligand-Gated Chloride Channel GABA(A) Receptor.

Chloride channels represent a group of targets for major clinical indications. However, molecular screening for chloride channel modulators has proven to be difficult and time-consuming as approaches essentially rely on the use of fluorescent dyes or invasive patch-clamp techniques which do not lend themselves to the screening of large sets of compounds. To address this problem, we have developed a non-invasive optical method, based on digital holographic microcopy (DHM), allowing monitoring of ion channel activity without using any electrode or fluorescent dye. To illustrate this approach, GABA(A) mediated chloride currents have been monitored with DHM. Practically, we show that DHM can non-invasively provide the quantitative determination of transmembrane chloride fluxes mediated by the activation of chloride channels associated with GABA(A) receptors. Indeed through an original algorithm, chloride currents elicited by application of appropriate agonists of the GABA(A) receptor can be derived from the quantitative phase signal recorded with DHM. Finally, chloride currents can be determined and pharmacologically characterized non-invasively simultaneously on a large cellular sampling by DHM.

Analysis of micro- and nano-structures of the corneal surface of Drosophila and its mutants by atomic force microscopy and optical diffraction.

Drosophila melanogaster is a model organism instrumental for numerous biological studies. The compound eye of this insect consists of some eight hundred individual ommatidia or facets, ca. 15 µm in cross-section. Each ommatidium contains eighteen cells including four cone cells secreting the lens material (cornea). High-resolution imaging of the cornea of different insects has demonstrated that each lens is covered by the nipple arrays--small outgrowths of ca. 200 nm in diameter. Here we for the first time utilize atomic force microscopy (AFM) to investigate nipple arrays of the Drosophila lens, achieving an unprecedented visualization of the architecture of these nanostructures. We find by Fourier analysis that the nipple arrays of Drosophila are disordered, and that the seemingly ordered appearance is a consequence of dense packing of the nipples. In contrast, Fourier analysis confirms the visibly ordered nature of the eye microstructures--the individual lenses. This is different in the frizzled mutants of Drosophila, where both Fourier analysis and optical imaging detect disorder in lens packing. AFM reveals intercalations of the lens material between individual lenses in frizzled mutants, providing explanation for this disorder. In contrast, nanostructures of the mutant lens show the same organization as in wild-type flies. Thus, frizzled mutants display abnormal organization of the corneal micro-, but not nano-structures. At the same time, nipples of the mutant flies are shorter than those of the wild-type. We also analyze corneal surface of glossy-appearing eyes overexpressing Wingless--the lipoprotein ligand of Frizzled receptors, and find the catastrophic aberration in nipple arrays, providing experimental evidence in favor of the major anti-reflective function of these insect eye nanostructures. The combination of the easily tractable genetic model organism and robust AFM analysis represents a novel methodology to analyze development and architecture of these surface formations.

High-precision satellite positioning system as a new tool to study the biomechanics of human locomotion.

New Global Positioning System (GPS) receivers allow now to measure a location on earth at high frequency (5Hz) with a centimetric precision using phase differential positioning method. We studied whether such technique was accurate enough to retrieve basic parameters of human locomotion. Eight subjects walked on an athletics track at four different imposed step frequencies (70-130steps/min) plus a run at free pace. Differential carrier phase localization between a fixed base station and the mobile antenna mounted on the walking person was calculated. In parallel, a triaxial accelerometer, attached to the low back, recorded body accelerations. The different parameters were averaged for 150 consecutive steps of each run for each subject (total of 6000 steps analyzed). We observed a perfect correlation between average step duration measured by accelerometer and by GPS (r=0.9998, N=40). Two important parameters for the calculation of the external work of walking were also analyzed, namely the vertical lift of the trunk and the velocity variation per step. For an average walking speed of 4.0km/h, average vertical lift and velocity variation were, respectively, 4.8cm and 0.60km/h. The average intra-individual step-to-step variability at a constant speed, which includes GPS errors and the biological gait style variation, were found to be 24. 5% (coefficient of variation) for vertical lift and 44.5% for velocity variation. It is concluded that GPS technique can provide useful biomechanical parameters for the analysis of an unlimited number of strides in an unconstrained free-living environment.

Intravitreal ranibizumab for age-related macular degeneration - optical coherence tomography guided retreatment intervals and their intra- and inter-individual variability

PURPOSE:To determine whether the need for retreatment after an initial loading phase of 3 monthly intravitreal injections of ranibizumab shows an intra-individual regular rhythm and to what degree it varies between different patients.SETTING:Prospective mono-centre cohort study.METHODS:Prospective study with 42 patients with exudative age-related macular degeneration (AMD), treatment na?ve, giving informed consent. Loading dose of 3 monthly doses of ranibizumab (0,5mg), followed by a 12 months pro re nata (PRN) regimen according to early exudative signs on spectral domain optical coherence tomography (HD-OCT Cirrus Zeiss?, cube 512x126). The follow-up visits were intensified (week 4, 5, 6, 7, 8, 10, 12, 14, 16, 20, 24, etc after each injection) in order to detect exudative recurrences early, and injection followed within 3 days in cases of subretinal fluid, or intraretinal cysts, or central thickness increase of >50?m. Intervals were calculated between injections and the following recurrence was calculated for the 12 month follow-up with PRN treatment. Variability was expressed as standard deviation (SD). RESULTS Visual acuity (VA) improved from a mean ETDRS letter score of 61.6 (SD 10.8) at baseline to 68.0 (SD 10.2, +6.4 letters) at month 3 and increased further to 74.7 (SD 9.0, +13.1 letters from baseline) at month 12. The 15 patients who have completed the study by October 2010 showed maintenance of the VA improvement. Retinal thickness of the central foveal subfield improved from a mean value of 366?m(baseline) to 253?m(month 3), well maintained thereafter. Mean number of injections was 8.8 (SD 3.5) per 12 months of follow-up (after 3 loading doses), ranging from 0 to 12, with mean individual treatment-recurrence intervals ranging from 28 to >365 days (mean 58 days). Intraindividual variability of treatment-recurrence intervals, measured as SD of the individual intervals, was 7.1days as a mean value(range 1.7 ? 22.6 days) for the 33 patients with more than 1 injection during follow-up. SD was higher for longer intervals of an individual patient. It ranged within 20% of the mean intra-individual interval for 30 patients(91%) and within 15% for 21 patients(64%). The first interval was within 1 week of the mean intra-individual interval in 64% of patients and within 2 weeks in 89% of patients.CONCLUSIONS:The majority of AMD patients showed a relatively stable rhythm for PRN injections of intravitreal ranibizumab after initial loading phase, associated with excellent functional and anatomical results. The initial interval between last loading dose and first recurrence may have a predictive value for further need of treatment, therefore potentially facilitating follow-up and patient care.

Optical probing of sodium dynamics in neurons and astrocytes.

Changes in intracellular Na(+) concentration underlie essential neurobiological processes, but few reliable tools exist for their measurement. Here we characterize a new synthetic Na(+)-sensitive fluorescent dye, Asante Natrium Green (ANG), with unique properties. This indicator was excitable in the visible spectrum and by two-photon illumination, suffered little photobleaching and located to the cytosol were it remained for long durations without noticeable unwanted effects on basic cell properties. When used in brain tissue, ANG yielded a bright fluorescent signal during physiological Na(+) responses both in neurons and astrocytes. Synchronous electrophysiological and fluorometric recordings showed that ANG produced accurate Na(+) measurement in situ. This new Na(+) indicator opens innovative ways of probing neuronal circuits.

Heated Optical Fiber for Distributed Soil-Moisture Measurements: A Lysimeter Experiment

An Actively Heated Fiber Optics (AHFO) method to estimate soil moisture is tested and the analysis technique improved on. The measurements were performed in a lysimeter uniformly packed with loam soil with variable water content profiles. In the first meter of the soil profi le, 30 m of fiber optic cable were installed in a 12 loops coil. The metal sheath armoring the fiber cable was used as an electrical resistance heater to generate a heat pulse, and the soil response was monitored with a Distributed Temperature Sensing (DTS) system. We study the cooling following three continuous heat pulses of 120 s at 36 W m(-1) by means of long-time approximation of radial heat conduction. The soil volumetric water contents were then inferred from the estimated thermal conductivities through a specifically calibrated model relating thermal conductivity and volumetric water content. To use the pre-asymptotic data we employed a time correction that allowed the volumetric water content to be estimated with a precision of 0.01-0.035 (m(3) m(-3)). A comparison of the AHFO measurements with soil-moisture measurements obtained with calibrated capacitance-based probes gave good agreement for wetter soils [discrepancy between the two methods was less than 0.04 (m(3) m(-3))]. In the shallow drier soils, the AHFO method underestimated the volumetric water content due to the longertime required for the temperature increment to become asymptotic in less thermally conductive media [discrepancy between the two methods was larger than 0.1 (m(3) m(-3))]. The present work suggests that future applications of the AHFO method should include longer heat pulses, that longer heating and cooling events are analyzed, and, temperature increments ideally be measured with higher frequency.

Analysis and spatial modeling of the indoor radon Swiss data

The present research deals with an important public health threat, which is the pollution created by radon gas accumulation inside dwellings. The spatial modeling of indoor radon in Switzerland is particularly complex and challenging because of many influencing factors that should be taken into account. Indoor radon data analysis must be addressed from both a statistical and a spatial point of view. As a multivariate process, it was important at first to define the influence of each factor. In particular, it was important to define the influence of geology as being closely associated to indoor radon. This association was indeed observed for the Swiss data but not probed to be the sole determinant for the spatial modeling. The statistical analysis of data, both at univariate and multivariate level, was followed by an exploratory spatial analysis. Many tools proposed in the literature were tested and adapted, including fractality, declustering and moving windows methods. The use of Quan-tité Morisita Index (QMI) as a procedure to evaluate data clustering in function of the radon level was proposed. The existing methods of declustering were revised and applied in an attempt to approach the global histogram parameters. The exploratory phase comes along with the definition of multiple scales of interest for indoor radon mapping in Switzerland. The analysis was done with a top-to-down resolution approach, from regional to local lev¬els in order to find the appropriate scales for modeling. In this sense, data partition was optimized in order to cope with stationary conditions of geostatistical models. Common methods of spatial modeling such as Κ Nearest Neighbors (KNN), variography and General Regression Neural Networks (GRNN) were proposed as exploratory tools. In the following section, different spatial interpolation methods were applied for a par-ticular dataset. A bottom to top method complexity approach was adopted and the results were analyzed together in order to find common definitions of continuity and neighborhood parameters. Additionally, a data filter based on cross-validation was tested with the purpose of reducing noise at local scale (the CVMF). At the end of the chapter, a series of test for data consistency and methods robustness were performed. This lead to conclude about the importance of data splitting and the limitation of generalization methods for reproducing statistical distributions. The last section was dedicated to modeling methods with probabilistic interpretations. Data transformation and simulations thus allowed the use of multigaussian models and helped take the indoor radon pollution data uncertainty into consideration. The catego-rization transform was presented as a solution for extreme values modeling through clas-sification. Simulation scenarios were proposed, including an alternative proposal for the reproduction of the global histogram based on the sampling domain. The sequential Gaussian simulation (SGS) was presented as the method giving the most complete information, while classification performed in a more robust way. An error measure was defined in relation to the decision function for data classification hardening. Within the classification methods, probabilistic neural networks (PNN) show to be better adapted for modeling of high threshold categorization and for automation. Support vector machines (SVM) on the contrary performed well under balanced category conditions. In general, it was concluded that a particular prediction or estimation method is not better under all conditions of scale and neighborhood definitions. Simulations should be the basis, while other methods can provide complementary information to accomplish an efficient indoor radon decision making.

The dmf1/mid1 gene is essential for correct positioning of the division septum in fission yeast.

Little is known about the mechanisms that establish the position of the division plane in eukaryotic cells. Wild-type fission yeast cells divide by forming a septum in the middle of the cell at the end of mitosis. Dmf1 mutants complete mitosis and initiate septum formation, but the septa that form are positioned at random locations and angles in the cell, rather than in the middle. We have cloned the dmf1 gene as a suppressor of the cdc7-24 mutant. The dmf1 mutant is allelic with mid1. The gene encodes a novel protein containing a putative nuclear localization signal, and a carboxy-terminal PH domain. In wild-type cells, Dmf1p is nuclear during interphase, and relocates to form a medial ring at the cell cortex coincident with the onset of mitosis. This relocalization occurs before formation of the actin ring and is associated with increased phosphorylation of Dmf1p. The Dmf1p ring can be formed in the absence of an actin ring, but depends on some of the genes required for actin ring formation. When the septum is completed and the cells separate, Dmf1p staining is once again nuclear. These data implicate Dmf1p as an important element in assuring correct placement of the division septum in Schizosaccharomyces pombe cells.

Visualization of aqueous shunt position and patency using anterior segment optical coherence tomography.

PURPOSE: To describe the use of anterior segment optical coherence tomography (AS-OCT) to clarify the position and patency of aqueous shunt devices in the anterior chamber of eyes where corneal edema or tube position does not permit a satisfactory view. DESIGN: Noncomparative observational case series. METHODS: Four cases are reported in which aqueous shunt malposition or obstruction was suspected but the shunt could not be seen on clinical examination. The patients underwent AS-OCT to identify the position and patency of the shunt tip. RESULTS: In each case, AS-OCT provided data regarding tube position and/or patency that could not be obtained by slit-lamp examination or by gonioscopy that influenced management. CONCLUSIONS: AS-OCT can be used to visualize anterior chamber tubes in the presence of corneal edema that precludes an adequate view or in cases where the tube is retracted into the cornea. In such cases, AS-OCT is useful in identifying shunt patency and position, which helps guide clinical decision making.