Fluid evolution at the Variscan front in the vicinity of the Aachen thrust

Quartz-carbonate-chlorite veins were studied in borehole samples of the RWTH-1 well in Aachen. Veins formed in Devonian rocks in the footwall of the Aachen thrust during Variscan deformation and associated fluid flow. Primary fluid inclusions indicate subsolvus unmixing of a homogenous H(2)O-CO(2)-CH(4)-(N(2))-Na-(K)-Cl fluid into a H(2)O-Na-(K)-Cl solution and a vapour-rich CO(2)-(H(2)O, CH(4), N(2)) fluid. The aqueous end-member composition resembles that of metamorphic fluids of the Variscan front zone with salinities ranging from 4 to 7% NaCl equiv. and maximum homogenisation temperatures of close to 400A degrees C. Pressure estimates indicate a burial depth between 4,500 and 8,000 m at geothermal gradients between 50 and 75A degrees C/26 MPa, but pressure decrease to sublithostatic conditions is also indicated, probably as a consequence of fracture opening during episodic seismic activity. A second fluid system, mainly preserved in pseudo-secondary and secondary fluid inclusions, is characterised by fluid temperatures between 200 and 250A degrees C and salinities of < 5% NaCl equiv. Bulk stable isotope analyses of fluids released from vein quartz, calcite, and dolomite by decrepitation yielded delta D(H2O) values from -89 to -113 aEuro degrees, delta(13)C(CH4) from -26.9 to -28.9aEuro degrees (VPDB) and delta(13)C(CO2) from -12.8 to -23.3aEuro degrees (VPDB). The low delta D and delta(13)C range of the fluids is considered to be due to interaction with cracked hydrocarbons. The second fluid influx caused partial isotope exchange and disequilibrium. It is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the Stavelot-Venn massif. The metamorphic fluid was focused along major thrust faults of the Variscan front zone such as the Aachen thrust. A second fluid influx was introduced from formation waters in the footwall of the Aachen thrust as a consequence of progressive deformation. Mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics.

Upper Triassic to Cretaceous radiolaria from Nicaragua and northern Costa Rica - The Mesquito composite oceanic terrane

We propose a new terrane subdivision of Nicaragua and Northern Costa Rica, based on Upper Triassic to Upper Cretaceous radiolarian biochronology of ribbon radiolarites, the newly studied Siuna Serpentinite Mélange, and published 40Ar/39Ar dating and geochemistry of mafic and ultramafic igneous rock units of the area. The new Mesquito Composite Oceanic Terrane (MCOT) comprises the southern half of the Chortis Block, that was assumed to be a continental fragment of N-America. The MCOT is defined by 4 corner localities characterized by ultramafic and mafic oceanic rocks and radiolarites of Late Triassic, Jurassic and Early Cretaceous age: 1. The Siuna Serpentinite Mélange (NE-Nicaragua), 2. The El Castillo Mélange (Nicaragua/Costa Rica border), 3.The Santa Elena Ultramafics (N-Costa Rica) and, 4. DSDP Legs 67/84. 1. The Siuna Serpentinite Mélange contains, high pressure metamorphic mafics and Middle Jurassic (Bajocian-Bathonian) radiolarites in original, sedimentary contact with arc-metandesites. The Siuna Mélange also contains Upper Jurassic black detrital chert formed in a marginal (fore-arc?) basin shortly before subduction. A phengite 40Ar/39Ar -cooling age dates the exhumation of the high pressure rocks as 139 Ma (earliest Cretaceous). 2. The El Castillo Mélange comprises a radiolarite block tectonically embedded in serpentinite that yielded a diverse Rhaetian (latest Triassic) radiolarian assemblage, the oldest fossils recovered so far from S-Central America. 3. The Santa Elena Ultramafics of N-Costa Rica together with the serpentinite outcrops near El Castillo (2) in Southern Nicaragua, are the southernmost outcrops of the MCOT. The Santa Elena Unit (3) itself is still undated, but it is thrust onto the middle Cretaceous Santa Rosa Accretionary Complex (SRAC), that contains Lower to Upper Jurassic, highly deformed radiolarite blocks, probably reworked from the MCOT, which was the upper plate with respect to the SRAC. 4. Serpentinites, metagabbros and basalts have long been known from DSDP Leg 67/84 (3), drilled off Guatemala in the Nicaragua-Guatemala forearc basement. They have been restudied and reveal 40Ar/39Ar dated Upper Triassic to middle Cretaceous enriched Ocean Island Basalts and Jurassic to Lower Cretaceous depleted Island arc rocks of probable Pacific origin. The area between localities 1-4 is largely covered by Tertiary to Recent arcs, but we suspect that its basement is made of oceanic/accreted terranes. Earthquake seismic studies indicate an ill-defined, shallow Moho in this area. The MCOT covers most of Nicaragua and could extend to Guatemala to the W and form the Lower (southern) Nicaragua Rise to the NE. Some basement complexes of Jamaica, Hispaniola and Puerto Rico may also belong to the MCOT. The Nicoya Complex s. str. has been regarded as an example of Caribbean crust and the Caribbean Large Igneous Province (CLIP). However, 40Ar/39Ar - dates on basalts and intrusives indicate ages as old as Early Cretaceous. Highly deformed Jurassic and Lower Cretaceous radiolarites occur as blocks within younger intrusives and basalts. Our interpretation is that radiolarites became first accreted to the MCOT, then became reworked into the Nicoya Plateau in Late Cretaceous times. This implies that the Nicoya Plateau formed along the Pacific edge of the MCOT, independent form the CLIP and most probably unrelated with he Galapagos hotspot. No Jurassic radiolarite, no older sediment age than Coniacian-Santonian, and no older 40Ar/39Ar age than 95 Ma is known from S-Central America between SE of Nicoya and Colombia. For us this area represents the trailing edge of the CLIP s. str.

Assessing the Functionality and Biocompatibility of a Wireless Contact Lens Sensor for 24 hour-intraocular Pressure Monitoring in Volunteers: Preliminary Results

Purpose: In vitro studies in porcine eyes have demonstrated a good correlation between induced intraocular pressure variations and corneal curvature changes, using a contact lens with an embedded microfabricated strain gauge. Continuous 24 hour-intraocular pressure (IOP) monitoring to detect large diurnal fluctuation is currently an unmet clinical need. The aims of this study is to evaluate precision of signal transmission and biocompatibility of 24 hour contact lens sensor wear (SENSIMED Triggerfish®) in humans. Methods: After full eye examination in 10 healthy volunteers, a 8.7 mm radius contact lens sensor and an orbital bandage containing a loop antenna were applied and connected to a portable recorder. Best corrected visual acuity and position, lubrication status and mobility of the sensor were assessed after 5 and 30 minutes, 4, 7 and 24 hours. Subjective comfort was scored and activities documented in a logbook. After sensor removal full eye examination was repeated, and the registration signal studied. Results: The comfort score was high and did not fluctuate significantly, except at the 7 hour-visit. The mobility of the contact lens was minimal but its lubrication remained good. Best corrected visual acuity was significantly reduced during the sensor wear and immediately after its removal. Three patients developed mild corneal staining. In all but one participant we obtained a registration IOP curve with visible ocular pulse amplitude. Conclusions: This 24 hour-trial confirmed the functionality and biocompatibility of SENSIMED Triggerfish® wireless contact lens sensor for IOP-fluctuation monitoring in volunteers. Further studies with a range of different contact lens sensor radii are indicated.

Positional therapy for obstructive sleep apnea: an objective measurement of patients' usage and efficacy at home.

BACKGROUND: Positional therapy that prevents patients from sleeping supine has been used for many years to manage positional obstructive sleep apnea (OSA). However, patients' usage at home and the long term efficacy of this therapy have never been objectively assessed. METHODS: Sixteen patients with positional OSA who refused or could not tolerate continuous positive airway pressure (CPAP) were enrolled after a test night study (T0) to test the efficacy of the positional therapy device. The patients who had a successful test night were instructed to use the device every night for three months. Nightly usage was monitored by an actigraphic recorder placed inside the positional device. A follow-up night study (T3) was performed after three months of positional therapy. RESULTS: Patients used the device on average 73.7 ± 29.3% (mean ± SD) of the nights for 8.0 ± 2.0 h/night. 10/16 patients used the device more than 80% of the nights. Compared to the baseline (diagnostic) night, mean apnea-hypopnea index (AHI) decreased from 26.7 ± 17.5 to 6.0 ± 3.4 with the positional device (p<0.0001) during T0 night. Oxygen desaturation (3%) index also fell from 18.4 ± 11.1 to 7.1 ± 5.7 (p = 0.001). Time spent supine fell from 42.8 ± 26.2% to 5.8 ± 7.2% (p < 0.0001). At three months (T3), the benefits persisted with no difference in AHI (p = 0.58) or in time spent supine (p = 0.98) compared to T0 night. The Epworth sleepiness scale showed a significant decrease from 9.4 ± 4.5 to 6.6 ± 4.7 (p = 0.02) after three months. CONCLUSIONS: Selected patients with positional OSA can be effectively treated by a positional therapy with an objective compliance of 73.7% of the nights and a persistent efficacy after three months.

Zonation for 3D aquifer characterization based on joint inversions of multimethod crosshole geophysical data

Predictive groundwater modeling requires accurate information about aquifer characteristics. Geophysical imaging is a powerful tool for delineating aquifer properties at an appropriate scale and resolution, but it suffers from problems of ambiguity. One way to overcome such limitations is to adopt a simultaneous multitechnique inversion strategy. We have developed a methodology for aquifer characterization based on structural joint inversion of multiple geophysical data sets followed by clustering to form zones and subsequent inversion for zonal parameters. Joint inversions based on cross-gradient structural constraints require less restrictive assumptions than, say, applying predefined petro-physical relationships and generally yield superior results. This approach has, for the first time, been applied to three geophysical data types in three dimensions. A classification scheme using maximum likelihood estimation is used to determine the parameters of a Gaussian mixture model that defines zonal geometries from joint-inversion tomograms. The resulting zones are used to estimate representative geophysical parameters of each zone, which are then used for field-scale petrophysical analysis. A synthetic study demonstrated how joint inversion of seismic and radar traveltimes and electrical resistance tomography (ERT) data greatly reduces misclassification of zones (down from 21.3% to 3.7%) and improves the accuracy of retrieved zonal parameters (from 1.8% to 0.3%) compared to individual inversions. We applied our scheme to a data set collected in northeastern Switzerland to delineate lithologic subunits within a gravel aquifer. The inversion models resolve three principal subhorizontal units along with some important 3D heterogeneity. Petro-physical analysis of the zonal parameters indicated approximately 30% variation in porosity within the gravel aquifer and an increasing fraction of finer sediments with depth.

New magnetotelluric data trough the boundary between the Ossa Morena and Centroiberian Zones

The south-western part of the Iberian Peninsula, including the southern branch of the Iberian Massif, has recently been the subject of several magnetotelluric (MT) studies. This area is made up of three different tectonic terranes: the South Portuguese Zone (SPZ), the Ossa Morena Zone (OMZ) and the Central Iberian Zone (CIZ). The boundaries between these zones are considered to be sutures, which appear as high electrical conductivity anomalies in the MT surveys. The OMZ is characterised by a conductive layer at middle-lower crustal levels. To investigate the continuity of this conductive layer into the CIZ, a new MT profile was carried out. This 75-km long ENE profile goes through the boundary between the OMZ and the CIZ. The results of a two-dimensional magnetotelluric inversion revealed a high-conductivity anomaly in the transition OMZ/CIZ (the so-called Central Unit), which is interpreted as due to interconnected graphite along shear planes. High-conductivity anomalies appeared in the middle crust of the CIZ, whose geometry and location are consistent with the conductive layer previously found in the OMZ, thus confirming the prolongation of the conductive layer into the CIZ. The top of this layer correlated spatially with a broad reflector detected by a seismic profile previously acquired in the same area. This, together with other geological and petrological evidence, points to a common origin for both features.

Deep crustal electromagnetic structure of Bhuj earthquake region (India) and its implications

The existence of fluids and partial melt in the lower crust of the seismically active Kutch rift basin (on the western continental margin of India) owing to underplating has been proposed in previous geological and geophysical studies. This hypothesis is examined using magnetotelluric (MT) data acquired at 23 stations along two profiles across Kutch Mainland Uplift and Wagad Uplift. A detailed upper crustal structure is also presented using twodimensional inversion of MT data in the Bhuj earthquake (2001) area. The prominent boundaries of reflection in the upper crust at 5, 10 and 20 km obtained in previous seismic reflection profiles correlate with conductive structures in our models. The MT study reveals 1-2 km thick Mesozoic sediments under the Deccan trap cover. The Deccan trap thickness in this region varies from a few meters to 1.5 km. The basement is shallow on the northern side compared to the south and is in good agreement with geological models as well as drilling information. The models for these profiles indicate that the thickness of sediments would further increase southwards into the Gulf of Kutch. Significant findings of the present study indicate 1) the hypocentre region of the earthquake is devoid of fluids, 2) absence of melt (that is emplaced during rifting as suggested from the passive seismological studies) in the lower crust and 3) a low resistive zone in the depth range of 5-20 km. The present MT study rules out fluidsand melt (magma) as the causative factors that triggered the Bhuj earthquake. The estimated porosity value of 0.02% will explain 100-500 ohm·m resistivity values observed in the lower crust. Based on the seismic velocities and geochemical studies, presence of garnet is inferred. The lower crust consists of basalts - probably generated by partial melting of metasomatised garnet peridotite at deeper depths in the lithosphere - and their composition might be modified by reaction with the spinel peridotites.

Combined use of the GGSFT data base and on Board Marine Collected Data to Model the Moho Beneath the Powell Basin, Antarctica

The Powell Basin is a small oceanic basin located at the NE end of the Antarctic Peninsula developed during the Early Miocene and mostly surrounded by the continental crusts of the South Orkney Microcontinent, South Scotia Ridge and Antarctic Peninsula margins. Gravity data from the SCAN 97 cruise obtained with the R/V Hespérides and data from the Global Gravity Grid and Sea Floor Topography (GGSFT) database (Sandwell and Smith, 1997) are used to determine the 3D geometry of the crustal-mantle interface (CMI) by numerical inversion methods. Water layer contribution and sedimentary effects were eliminated from the Free Air anomaly to obtain the total anomaly. Sedimentary effects were obtained from the analysis of existing and new SCAN 97 multichannel seismic profiles (MCS). The regional anomaly was obtained after spectral and filtering processes. The smooth 3D geometry of the crustal mantle interface obtained after inversion of the regional anomaly shows an increase in the thickness of the crust towards the continental margins and a NW-SE oriented axis of symmetry coinciding with the position of an older oceanic spreading axis. This interface shows a moderate uplift towards the western part and depicts two main uplifts to the northern and eastern sectors.

Stratigraphie, morphodynamique, paléoenvironnements des terrains sédimentaires meubles à forte déclivité du domaine périglaciaire alpin

Dans le contexte d'un climat de plus en plus chaud, une étude « géosystémique » de la répartition du pergélisol dans l'ensemble d'un versant périglaciaire alpin, de la paroi rocheuse jusqu'au glacier rocheux, s'avère primordiale. S'insérant dans cette problématique, ce travail de thèse vise comme objectif général l'étude des versants d'éboulis situés à l'intérieur de la ceinture du pergélisol discontinu selon deux volets de recherche différents : une étude de la stratigraphie et de la répartition du pergélisol dans les éboulis de haute altitude et des processus qui lui sont associés ; une reconstitution de l'histoire paléoenvironnementale du domaine périglaciaire alpin pendant le Tardiglaciaire et l'Holocène. La stratigraphie et la répartition spatiale du pergélisol a été étudiée dans cinq éboulis des Alpes Valaisannes (Suisse), dont trois ont fait l'objet de forages profonds, grâce à la prospection géophysique de détail effectuée à l'aide de méthodes thermiques, de résistivité, sismiques et nucléaires. Les mesures effectuées ont permis de mettre en évidence que, dans les cinq éboulis étudiés, la répartition du pergélisol est discontinue et aucun des versants n'est intégralement occupé par du pergélisol. En particulier, il a été possible de prouver de manière directe que, dans un éboulis, le pergélisol est présent dans les parties inférieures du versant et absent dans les parties supérieures. Trois facteurs de contrôle principaux de la répartition du pergélisol déterminée au sein des éboulis étudiés ont été individualisés, pouvant agir seuls ou de manière combinée : la ventilation ascendante, l'augmentation de la granulométrie en direction de l'aval et la redistribution de la neige par le vent et les avalanches. Parmi ceux-ci, la relation ventilation-granulométrie semble être le facteur de contrôle principal permettant d'expliquer la présence de pergélisol dans les parties inférieures d'un éboulis et son absence dans les parties supérieures. Enfin, l'analyse de la structure des éboulis périglaciaires de haute altitude a permis de montrer que la stratigraphie du pergélisol peut être un élément important pour l'interprétation de la signification paléoclimatique de ce type de formes. Pour le deuxième volet de la recherche, grâce aux datations relatives effectuées à l'aide de l'utilisation conjointe de la méthode paléogéographique et du marteau de Schmidt, il a été possible de définir la chrono-stratigraphie du retrait glaciaire et du développement des glaciers rocheux et des versants d'éboulis des quatre régions des Alpes suisses étudiées (régions du Mont Gelé - Mont Fort, des Fontanesses et de Chamosentse, dans les Alpes Valaisannes, et Massif de la Cima di Gana Bianca, dans les Alpes Tessinoises). La compilation de toutes les datations effectuées a permis de montrer que la plupart des glaciers rocheux actifs étudiés se seraient développés soit juste avant et/ou pendant l'Optimum Climatique Holocène de 9.5-6.3 ka cal BP, soit au plus tard juste après cet évènement climatique majeur du dernier interglaciaire. Parmi les glaciers rocheux fossiles datés, la plupart aurait commencé à se former dans la deuxième moitié du Tardiglaciaire et se serait inactivé dans la première partie de l'Optimum Climatique Holocène. Pour les éboulis étudiés, les datations effectuées ont permis d'observer que leur surface date de la période entre le Boréal et l'Atlantique récent, indiquant que les taux d'éboulisation après la fin de l'Optimum Climatique Holocène ont dû être faibles, et que l'intervalle entre l'âge maximal et l'âge minimal est dans la plupart des cas relativement court (4-6 millénaires), indiquant que les taux d'éboulisation durant la période de formation des éboulis ont dû être importants. Grâce au calcul des taux d'érosion des parois rocheuses sur la base du volume de matériaux rocheux pour quatre des éboulis étudiés, il a été possible mettre en évidence l'existence d'une « éboulisation parapériglaciaire » liée à la dégradation du pergélisol dans les parois rocheuses, fonctionnant principalement durant les périodes de réchauffement climatique rapide comme cela a été le cas au début du Bølling, du Préboréal à la fin de l'Atlantique récent et, peut-être, à partir des années 1980. - In the context of a warmer climate, a « geosystemical » study of the permafrost distribution in a whole alpine periglacial hillslope, from the rockwall to the rockglacier, is of great importance. With respect to this problem, the general objective of this PhD thesis is the global study of talus slopes located within the alpine periglacial belt following two different research axes: the analysis of the internal structure and of the permafrost distribution of high altitude talus slopes and of the related processes; the reconstruction of the palaeoenvironmental history of the alpine periglacial belt during the Lateglacial and the Holocene. The stratigraphy and the permafrost distribution were studied in five talus slopes of the Valais Alps (Switzerland) with the analysis of borehole data (on three of the five talus slopes) and other methods of permafrost prospecting: Electrical Resistivity Tomography (ERT), Refraction Seismic Tomography (RST) and nuclear well logging. The collected data shows that, in all of the studied talus slopes, permafrost distribution is discontinuous and that neither of the hillslopes is integrally characterised by permafrost. In particular, this data proves by direct investigations that, in talus slopes, permafrost is present in the lower parts of the hillslope, whereas it is absent in the upper parts. Permafrost distribution in alpine talus slopes is depending of the combination of almost three controlling factors, whose respective importance is variable: the chimney effect, the increase of grain size downslope and the redistribution of snow by avalanches. Depending on the size of the talus and on topographical and geomorphological heterogeneities, various cases are possible: one dominant controlling factor or the combination of various factors. Nevertheless, it would be an error to consider each controlling factor independently, without considering their relationships. Between these controlling factors, the relationship chimney effect/grain size seems to be the most important factor controlling the presence of permafrost in the lowest part of periglacial talus slopes, and its absence in the upper parts. Finally, the analysis of the talus structure shows that the permafrost stratigraphy may be an important element of interpretation of the palaeoclimatic significance of an alpine talus slope. The second research axe focused on the establishment of a chronology of the Lateglacial glacier retreat and the dating of rockglaciers and talus slopes development in four studied regions of the Swiss Alps (Mont Gelé - Mont Fort, Fontanesses and Chamosentse regions, in the Valais Alps, and the Cima di Gana Bianca Massif, in the Ticino Alps). The compilation of the dates acquired through the combination of the palaeogeographical method and of the Schmidt hammer indicates that most of the investigated active rockglaciers started to evolve during the early phases of the Holocene or, at the latest, after the early-to-mid Holocene Climatic Optimum (ending around 6.3 ka cal BP). For the dated relict rockglaciers, most of them started to evolve in the second half of the Lateglacial, and probably became inactive at the beginning of the Holocene Climatic Optimum. For the investigated talus slopes, the relative dating carried out allowed to show that their surface date from the period included between the Boreal and the end of the Atlantic, pointing out that the rockwall retreat after the end of the Holocene Climatic Optimum was weak, and that the interval between maximal and minimal ages is in most cases relatively short (4-6 millennia). Therefore, the rockwall retreat during the development period of the talus slopes must has been considerable. Thanks to the calculation of rockwall erosion rates based on the volume of talus accumulations for four of the investigated hillslopes, it was possible to find evidences of the existence of "paraperiglacial rockfall phases" related to the permafrost degradation in rockwalls. These phases coincide with rapid climate warming periods, as at the beginning of the Bølling, during the Preboreal or, maybe, since 1980.

A new method to estimate the infilling of alluvial sediment of glacial valleys using a sloping local base level

A new method is used to estimate the volumes of sediments of glacial valleys. This method is based on the concept of sloping local base level and requires only a digital terrain model and the limits of the alluvial valleys as input data. The bedrock surface of the glacial valley is estimated by a progressive excavation of the digital elevation model (DEM) of the filled valley area. This is performed using an iterative routine that replaces the altitude of a point of the DEM by the mean value of its neighbors minus a fixed value. The result is a curved surface, quadratic in 2D. The bedrock surface of the Rhone Valley in Switzerland was estimated by this method using the free digital terrain model Shuttle Radar Topography Mission (SRTM) (~92 m resolution). The results obtained are in good agreement with the previous estimations based on seismic profiles and gravimetric modeling, with the exceptions of some particular locations. The results from the present method and those from the seismic interpretation are slightly different from the results of the gravimetric data. This discrepancy may result from the presence of large buried landslides in the bottom of the Rhone Valley.

Automatic Tracer-Dilution Method Used for Stage-Discharge Ratings and Streamflow Hydrographs on Small Iowa Streams, HR-285, 1990

An automatic system was designed to concurrently measure stage and discharge for the purpose of developing stage-discharge ratings and high flow hydrographs on small streams. Stage, or gage height, is recorded by an analog-to-digital recorder and discharge is determined by the constant-rate tracer-dilution method. The system measures flow above a base stage set by the user. To test the effectiveness of the system and its components, eight systems, with a variety of equipment, were installed at crest-stage gaging stations across Iowa. A fluorescent dye, rhodamine-WT, was used as the tracer. Tracer-dilution discharge measurements were made during 14 flow periods at six stations from 1986 through 1988 water years. Ratings were developed at three stations with the aid of these measurements. A loop rating was identified at one station during rapidly-changing flow conditions. Incomplete mixing and dye loss to sediment apparently were problems at some stations. Stage hydrographs were recorded for 38 flows at seven stations. Limited data on background fluorescence during high flows were also obtained.

Data Acquisition and Computer Plotting of Delamtect Data, HR-269, 1985

The overall system is designed to permit automatic collection of delamination field data for bridge decks. In addition to measuring and recording the data in the field, the system provides for transferring the recorded data to a personal computer for processing and plotting. This permits rapid turnaround from data collection to a finished plot of the results in a fraction of the time previously required for manual analysis of the analog data captured on a strip chart recorder. In normal operation the Delamtect provides an analog voltage for each of two channels which is proportional to the extent of any delamination. These voltages are recorded on a strip chart for later visual analysis. An event marker voltage, produced by a momentary push button on the handle, is also provided by the Delamtect and recorded on a third channel of the analog recorder.

Pacemaker therapy in patients with neurally mediated syncope and documented asystole: Third International Study on Syncope of Uncertain Etiology (ISSUE-3): a randomized trial.

BACKGROUND: The efficacy of cardiac pacing for prevention of syncopal recurrences in patients with neurally mediated syncope is controversial. We wanted to determine whether pacing therapy reduces syncopal recurrences in patients with severe asystolic neurally mediated syncope. METHODS AND RESULTS: Double-blind, randomized placebo-controlled study conducted in 29 centers in the Third International Study on Syncope of Uncertain Etiology (ISSUE-3) trial. Patients were ≥40 years, had experienced ≥3 syncopal episodes in the previous 2 years. Initially, 511 patients, received an implantable loop recorder; 89 of these had documentation of syncope with ≥3 s asystole or ≥6 s asystole without syncope within 12 ± 10 months and met criteria for pacemaker implantation; 77 of 89 patients were randomly assigned to dual-chamber pacing with rate drop response or to sensing only. The data were analyzed on intention-to-treat principle. There was syncope recurrence during follow-up in 27 patients, 19 of whom had been assigned to pacemaker OFF and 8 to pacemaker ON. The 2-year estimated syncope recurrence rate was 57% (95% CI, 40-74) with pacemaker OFF and 25% (95% CI, 13-45) with pacemaker ON (log rank: P=0.039 at the threshold of statistical significance of 0.04). The risk of recurrence was reduced by 57% (95% CI, 4-81). Five patients had procedural complications: lead dislodgment in 4 requiring correction and subclavian vein thrombosis in 1 patient. CONCLUSIONS: Dual-chamber permanent pacing is effective in reducing recurrence of syncope in patients ≥40 years with severe asystolic neurally mediated syncope. The observed 32% absolute and 57% relative reduction in syncope recurrence support this invasive treatment for the relatively benign neurally mediated syncope. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00359203.

Étude des sédiments quaternaires, de la molasse et sa tectonique, dans le Grand Lac (Léman) à partir de données sismiques 2D et 3D

RESUME L'Institut de Géophysique de l'Université de Lausanne a développé au cours de ces dernières années un système d'acquisition de sismique réflexion multitrace à haute résolution 2D et 3D. L'objectif de cette thèse était de poursuivre ce développement tout améliorant les connaissances de la géologie sous le lac Léman, en étudiant en particulier la configuration des grands accidents sous-lacustres dans la Molasse (Tertiaire) qui forme l'essentiel du substratum des formations quaternaires. En configuration 2D, notre système permet d'acquérir des profils sismiques avec une distance inter-CDP de 1,25 m. La couverture varie entre 6 et 18 selon le nombre de traces et la distance inter-tir. Le canon à air (15/15 eu. in.), offre une résolution verticale de 1,25 ni et une pénétration maximale de 300 m sous le fond de l'eau. Nous avons acquis au total plus de 400 km de sections 2D dans le Grand Lac et le Haut Lac entre octobre 2000 et juillet 2004. Une campagne de sismique 3D a fourni des données au large d'Evian sur une surface de 442,5 m sur 1450 m, soit 0,64 km2. La navigation ainsi que le positionnement des hydrophones et de la source ont été réalisés avec des GPS différentiels. Nous avons utilisé un traitement sismique conventionnel, sans appliquer d'AGC et en utilisant une migration post-stack. L'interprétation du substratum antéquaternaire est basée sur l'identification des sismofaciès, sur leurs relations avec les unités géologiques adjacentes au lac, ainsi que sur quelques données de forages. Nous obtenons ainsi une carte des unités géologiques dans le Grand Lac. Nous précisons la position du chevauchement subalpin entre la ville de Lausanne, sur la rive nord, et le bassin de Sciez, sur la rive sud. Dans la Molasse de Plateau, nous avons identifié les décrochements de Pontarlier et de St. Cergue ainsi que plusieurs failles non reconnues jusqu'ici. Nous avons cartographié les accidents qui affectent la Molasse subalpine ainsi que le plan de chevauchement du flysch sur la Molasse près de la rive sud du lac. Une nouvelle carte tectonique de la région lémanique a ainsi pu être dressée. L'analyse du substratum ne montre pas de failles suggérant une origine tectonique de la cuvette lémanique. Par contre, nous suggérons que la forme du creusement glaciaire, donc de la forme du lac Léman, a été influencée par la présence de failles dans le substratum antéquaternaire. L'analyse des sédiments quaternaires nous a permis de tracer des cartes des différentes interfaces ou unités qui les composent. La carte du toit du substratum antéquaternaire montre la présence de chenaux d'origine glaciaire dont la profondeur maximale atteint la cote -200 ni. Leur pente est dirigée vers le nord-est, à l'inverse du sens d'écoulement actuel des eaux. Nous expliquons cette observation par l'existence de circulations sous-glaciaires d'eau artésienne. Les sédiments glaciaires dont l'épaisseur maximale atteint 150 ni au centre du lac ont enregistré les différentes récurrences glaciaires. Dans la zone d'Evian, nous mettons en évidence la présence de lentilles de sédiments glaciolacustres perchées sur le flanc de la cuvette lémanique. Nous avons corrélé ces unités avec des données de forage et concluons qu'il s'agit du complexe inférieur de la pile sédimentaire d'Evian. Celui-ci, âgé de plus de 30 000 ans, serait un dépôt de Kame associé à un lac périglaciaire. La sismique réflexion 3D permet de préciser l'orientation de l'alimentation en matériel détritique de l'unité. La finesse des images obtenues nous permet également d'établir quels types d'érosion ont affecté certaines unités. Les sédiments lacustres, dont l'épaisseur maximale imagée atteint plus de 225 m et sans doute 400 ni sous le delta du Rhône, indiquent plusieurs mécanismes de dépôts. A la base, une mégaturbidite, épaisse d'une trentaine de mètres en moyenne, s'étend entre l'embouchure de la Dranse et le delta du Rhône. Au-dessus, la décantation des particules en suspension d'origine biologique et détritique fournit l'essentiel des sédiments. Dans la partie orientale du lac, les apports détritiques du Rhône forment un delta qui prograde vers l'ouest en s'imbriquant avec les sédiments déposés par décantation. La structure superficielle du delta a brutalement évolué, probablement à la suite de l'évènement catastrophique du Tauredunum (563 A.D.). Sa trace probable se marque par la présence d'une surface érosive que nous avons cartographiée. Le delta a ensuite changé de géométrie, avec notamment un déplacement des chenaux sous-lacustres. Sur l'ensemble de nos sections sismiques, nous n'observons aucune faille dans les sédiments quaternaires qui attesterait d'une tectonique postglaciaire du substratum. ABSTRACT During the last few years the institute of Geophysics of the University of Lausanne cleveloped a 2D and 3D high-resolution multichannel seismic reflection acquisition system. The objective of the present work was to carry on this development white improving our knowledge of the geology under Lake Geneva, in particular by studying the configuration of the large accidents affecting the Tertiary Molasse that makes up the basement of most Quaternary deposits. In its 2D configuration, our system makes it possible to acquire seismic profiles with a CDP interval of 1.25 m. The fold varies from 6 to 18 depending on the number of traces and the shooting interval. Our air gun (15/15 cu. in.) provides a vertical resolution of 1.25 m and a maximum penetration depth of approximately 300 m under water bottom. We acquired more than 400 km of 2D sections in the Grand Lac and the Haut Lac between October 2000 and July 2004. A 3D seismic survey off the city of Evian provided data on a surface of 442.5 m x 1450 m (0.64 km2). Ship's navigation as well as hydrophone- and source positioning were carried out with differential GPS. The seismic data were processed following a conventional sequence without .applying AGC and using post-stack migration. The interpretation of the pre-Quaternary substratum is based on sismofacies, on their relationships with terrestrial geological units and on some borehole data. We thus obtained a map of the geological units in the Grand Lac. We defined the location of the subalpine thrust from Lausanne, on the north shore, to the Sciez Basin, on the south shore. Within the Molasse de Plateau, we identified the already know Pontarlier and St Cergue transforms Fault as well as faults. We mapped faults that affect subalpine Molasse as well as the thrust fault plane between alpine flysch and Molasse near the lake's south shore. A new tectonic map of the Lake Geneva region could thus be drawn up. The substratum does not show faults indicating a tectonic origin for the Lake Geneva Basin. However, we suggest that the orientation of glacial erosion, and thus the shape of Lake Geneva, vas influenced by the presence of faults in the pre-Quaternary basement. The analysis of Quaternary sediments enabled us to draw up maps of various discontinuities or internal units. The top pre-Quaternary basement map shows channels of glacial origin, the deepest of them reaching an altitude of 200 m a.s.l. The channel's slopes are directed to the North-East, in opposite direction of the present water flow. We explain this observation by the presence of artesian subglacial water circulation. Glacial sediments, the maximum thickness of which reaches 150 m in the central part of the lake, record several glacial recurrences. In the Evian area, we found lenses of glacio-lacustrine sediments set high up on the flank of the Lake Geneva Bassin. We correlated these units with on-land borehole data and concluded that they represent the lower complex of the Evian sedimentary pile. The lower complex is aider than 30 000 years, and it could be a Kame deposit associated with a periglacial lake. Our 3D seismic reflexion survey enables us to specify the supply direction of detrital material in this unit. With detailed seismic images we established how some units were affected by different erosion types. The lacustrine sediments we imaged in Lake Geneva are thicker than 225 m and 400 m or more Linder the Rhone Delta. They indicate several depositional mechanisms. Their base is a major turbidite, thirty meters thick on average, that spreads between the Dranse mouth and the Rhone delta. Above this unit, settling of suspended biological and detrital particles provides most of the sediments. In the eastern part of the lake, detrital contribution from the Rhone builds a delta that progrades to the west and imbricates with the settling sediments. The shallow structure of the Rhone delta abruptly evolved, probably after the catastrophic Tauredunum event (563 A.D.). It probably coincides with an erosive surface that we mapped. As a result, the delta geometry changed, in particular associated with a displacement of water bottom channels. In all our seismic sections, we do not observe fault in the Quaternary sediments that would attest postglacial tectonic activity in the basement.

Ambulatory blood pressure monitoring in the elderly hypertensive patient.

In this retrospective analysis, we assessed the usefulness of ambulatory blood pressure monitoring in the evaluation of elderly hypertensive patients. Thirty-eight untreated and 31 treated hypertensives aged 70 years or more had a systolic blood pressure greater than or equal to 160 mmHg and/or a diastolic blood pressure greater than or equal to 95 mmHg in the clinic. All 69 patients underwent blood pressure monitoring during their customary daily activities using a portable semi-automatic blood pressure recorder (Remier M2000). The mean of all blood pressures obtained with this device was taken as the ambulatory recorded blood pressure. Recorded blood pressures were greater than or equal to 160 mmHg systolic and greater than or equal to 90 mmHg diastolic in 17 untreated and 17 treated patients. In these patients, the introduction of antihypertensive therapy, or its modification, markedly reduced blood pressure during a 4-8 month follow-up. A further 21 untreated and 14 treated patients had recorded blood pressures of less than 160/90 mmHg. The treatment status of these patients was left unchanged for 4-8 months of follow-up. Nevertheless, office blood pressure in these groups, with no change in treatment, decreased significantly during the observation period. At the last visit to the outpatient clinic, there was no significant difference in blood pressure between the four subgroups of patients. Thus, ambulatory blood pressure monitoring appears to be useful in the elderly hypertensive patient in detecting those patients whose blood pressure is elevated only in the clinic. Blood pressure profiles obtained outside the clinic may therefore be useful in making therapeutic decisions in the aged hypertensive.