The tectonically controlled emplacement of a vertically sheeted gabbro-pyroxenite intrusion: Feeder-zone of an ocean-island volcano (Fuerteventura, Canary Islands)

The Miocene PX1 gabbro-pyroxenite pluton, Fuerteventura, Canary Islands, is a 3.5 x 5.5 km shallow-level intrusion (0.15-0.2 GPa and 1100-1120 degrees C), interpreted as the feeder-zone to an ocean-island volcano. It displays a vertical magmatic banding expressed in five 50 to 100 metre-wide NNE-SSW trending alkaline gabbro sequences alternating with pyroxenites. This emplacement geometry was controlled by brittle to ductile shear zones, generated by a regional E-W extensional tectonic setting that affected Fuerteventura during the Miocene. At a smaller scale, the PX1 gabbro and pyroxenite bands consist of metre-thick differentiation units, which suggest emplacement by periodic injection of magma pulses as vertical dykes that amalgamated, similarly to a sub-volcanic sheeted dyke complex. Individual dykes underwent internal differentiation following a solidification front parallel to the dyke edges. This solidification front may have been favoured by a significant lateral/horizontal thermal gradient, expressed by the vertical banding in the gabbros, the fractionation asymmetry within individual dykes and the migmatisation of the wall rocks. Pyroxenitic layers result from the fractionation and accumulation of clinopyroxene +/- olivine +/- plagioclase crystals from a mildly alkaline basaltic liquid. They are interpreted as truncated differentiation sequences, from which residual melts were extracted at various stages of their chemical evolution by subsequent dyke intrusions, either next to or within the crystallising unit. Compaction and squeezing of the crystal mush is ascribed to the incoming and inflating magma pulses. The expelled interstitial liquid was likely collected and erupted along with the magma flowing through the newly injected dykes. Clinopyroxene mineral orientation - as evidenced by EBSD and micro X-ray tomography investigations - displays a marked pure-shear component, supporting the interpretation of the role of compaction in the generation of the pyroxenites. Conversely, gabbro sequences underwent minor melt extraction and are believed to represent crystallised coalesced magma batches emplaced at lower rates at the end of eruptive cycles. Clinopyroxene orientations in gabbros record a simple shear component suggesting syn-magmatic deformation parallel to observed NNE-SSW trending shear zones induced by the regional tensional stress field. This emplacement model implies a crystallisation time of 1 to 5 years for individual dykes, consistent with PX1 emplacement over less than 0.5 My. A minimum amount of approximately 150 km(3) of magma is needed to generate the pluton, part of it having been erupted through the Central Volcanic Centre of Fuerteventura. If the regional extensional tectonic regime controls the PX1 feeder-zone initiation and overall geometry, rates and volumes of magma depend on other, source-related factors. High injection rates are likely to induce intrusion growth rates larger than could be accommodated by the regional extension. In this case, dyke intrusion by propagation of a weak tip, combined with the inability of magma to circulate through previously emplaced and crystallised dykes could result in an increase of non-lithostatic pressure on previously emplaced mushy dyke walls; thus generating strong pure-shear compaction within the pluton feeder-zone and interstitial melt expulsion. These compaction-dominated processes are recorded by the cumulitic pyroxenite bands. (C) 2010 Elsevier B.V. All rights reserved.

Transcatheter stent-valve implantation in a stenotic pulmonary conduit via a sub-xyphoidian access

Patients who develop a severe stenosis in biological pulmonary conduits previously implanted for pulmonary outflow trunk reconstructions are treated either by surgical re-replacement, or by transcatheter stent-valve implantation through a femoral vein access. A catheter-based sub-xyphoidian access through the right ventricle for stent-valve positioning in a pulmonary conduit has rarely been proposed. We describe the case of a 20-year-old man who underwent a pulmonary trunk reconstruction for a congenital pulmonary valve dysplasia and a few years later developed a stenosis in the pulmonary conduit. He was successfully treated with a 23 mm Edwards Sapien stent-valve implantation in pulmonary position, through an unusual right ventricular, sub-xyphoidian access and without contrast medium injections and pleura opening.

Sub-cortical and brainstem sites associated with chemo-stimulated increases in ventilation in humans.

We investigated the neural basis for spontaneous chemo-stimulated increases in ventilation in awake, healthy humans. Blood oxygen level dependent (BOLD) functional MRI was performed in nine healthy subjects using T2 weighted echo planar imaging. Brain volumes (52 transverse slices, cortex to high spinal cord) were acquired every 3.9 s. The 30 min paradigm consisted of six, 5-min cycles, each cycle comprising 45 s of hypoxic-isocapnia, 45 s of isooxic-hypercapnia and 45 s of hypoxic-hypercapnia, with 55 s of non-stimulatory hyperoxic-isocapnia (control) separating each stimulus period. Ventilation was significantly (p<0.001) increased during hypoxic-isocapnia, isooxic-hypercapnia and hypoxic-hypercapnia (17.0, 13.8, 24.9 L/min respectively) vs. control (8.4 L/min) and was associated with significant (p<0.05, corrected for multiple comparisons) signal increases within a bilateral network that included the basal ganglia, thalamus, red nucleus, cerebellum, parietal cortex, cingulate and superior mid pons. The neuroanatomical structures identified provide evidence for the spontaneous control of breathing to be mediated by higher brain centres, as well as respiratory nuclei in the brainstem.

HIV disclosure and nondisclosure among migrant women from sub-Saharan Africa living in Switzerland.

No study to date has focused specifically on the reasons for and against disclosure of HIV-positive status among sub-Saharan migrant women. Thirty HIV-positive women from 11 sub-Saharan countries living in French-speaking Switzerland participated in semi-structured individual interviews. The reasons women reported for disclosure or nondisclosure of their HIV serostatus were classified into three categories: social, medical, and ethical. The women identified the stigma associated with HIV as a major social reason for nondisclosure. However, this study identifies new trends related to disclosure for medical and ethical reasons. Being undetectable played an important role in the life of sub-Saharan migrant women, and analysis revealed their medical reasons for both disclosure and nondisclosure. Disclosure to new sexual partners occurred when women had a more positive perception about HIV and when they believed themselves to be in a long-term relationship. Women reported nondisclosure to family members when they did not need help outside the support provided by the medical and social fields. The results on ethical reasons suggested that challenging stigma was a reason for disclosure. Since the women' perceptions on HIV changed when they came to see it as a chronic disease, disclosure occurred in an attempt to normalize life with HIV in their communities in migration and to challenge racism and discrimination. Our findings can help health providers better understand the communication needs of sub-Saharan migrant women with respect to HIV/AIDS and sexuality and offer them adequate disclosure advice that takes into account migration and gender issues.