Aluminous hydrous magnesium silicate as a lower-mantle hydrogen reservoir: a role as an agent for material transport.

The potential for storage of a large quantity of water/hydrogen in the lower mantle has important implications for the dynamics and evolution of the Earth. A dense hydrous magnesium silicate called phase D is a potential candidate for such a hydrogen reservoir. Its MgO-SiO2-H2O form has been believed to be stable at lower-mantle pressures but only in low-temperature regimes such as subducting slabs because of decomposition below mantle geotherm. Meanwhile, the presence of Al was reported to be a key to enhancing the thermal stability of phase D; however, the detailed Al-incorporation effect on its stability remains unclear. Here we report on Al-bearing phase D (Al-phase D) synthesized from a bridgmanite composition, with Al content expected in bridgmanite formed from a representative mantle composition, under over-saturation of water. We find that the incorporation of Al, despite smaller amounts, into phase D increases its hydrogen content and moreover extends its stability field not only to higher temperatures but also presumably to higher pressures. This leads to that Al-phase D can be one of the most potential reservoirs for a large quantity of hydrogen in the lower mantle. Further, Al-phase D formed by reaction between bridgmanite and water could play an important role in material transport in the lower mantle.

Incorporation mechanism of Fe and Al into bridgmanite in a subducting mid-ocean ridge basalt and its crystal chemistry.

The compositional difference between subducting slabs and their surrounding lower-mantle can yield the difference in incorporation mechanism of Fe and Al into bridgmanite between both regions, which should cause heterogeneity in physical properties and rheology of the lower mantle. However, the precise cation-distribution has not been examined in bridgmanites with Fe- and Al-contents expected in a mid-ocean ridge basalt component of subducting slabs. Here we report on Mg0.662Fe0.338Si0.662Al0.338O3 bridgmanite single-crystal characterized by a combination of single-crystal X-ray diffraction, synchrotron 57Fe-Mössbauer spectroscopy and electron probe microanalysis. We find that the charge-coupled substitution AMg2+ + BSi4+ ↔ AFe3+(high-spin) + BAl3+ is predominant in the incorporation of Fe and Al into the practically eightfold-coordinated A-site and the sixfold-coordinated B-site in bridgmanite structure. The incorporation of both cations via this substitution enhances the structural distortion due to the tilting of BO6 octahedra, yielding the unusual expansion of mean bond-length due to flexibility of A-O bonds for the structural distortion, in contrast to mean bond-length depending reasonably on the ionic radius effect. Moreover, we imply the phase-transition behavior and the elasticity of bridgmanite in slabs subducting into deeper parts of the lower mantle, in terms of the relative compressibility of AO12 (practically AO8) and BO6 polyhedra.

A new high-pressure strontium germanate, SrGe2O5.

The Sr-Ge-O system has an earth-scientific importance as a potentially good low-pressure analog of the Ca-Si-O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO3 high-pressure perovskite phase is the first Ge-based transparent electronic conductor make the Sr-Ge-O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high-pressure strontium germanate, SrGe2O5. Single crystals of this compound crystallized as a co-existent phase with SrGeO3 perovskite single crystals in the sample recovered in the compression experiment of SrGeO3 pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium-oxygen framework layers stacked along [001], with Sr atoms located at the 12-coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO6 octahedra and between GeO6 octahedra and GeO4 tetrahedra. The present SrGe2O5 is thus isostructural with the high-pressure phases of SrSi2O5 and BaGe2O5. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO6 and GeO4 polyhedra to cation substitution at the Sr site are much less than that of the SrO12 cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.

Extracorporeal membrane oxygenation for respiratory failure: comparison of venovenous versus venoarterial bypass.

PURPOSE: This study compared the respiratory status before and during extracorporeal membrane oxygenation (ECMO) in patients receiving venovenous (VV) and venoarterial (VA) ECMO to evaluate the choice of ECMO in patients with respiratory failure. METHOD: Between January 2003 and December 2007, 16 patients with respiratory failure required ECMO. Venovenous bypass and VA bypass were used in 9 cases (VV group) and 7 cases (VA group), respectively. The respiratory status before and during ECMO was compared between the two groups. RESULTS: The percentage of patients requiring renal replacement therapy prior to ECMO use was significantly higher in the VA group than in the VV group. There were no significant differences between the two groups in PaO(2)/FIO(2), AaDO(2), pulmonary compliance, and the lung injury score prior to ECMO use. These parameters gradually improved in both groups; however, no significant intergroup differences were seen for up to 96 h after ECMO introduction. There was also no significant difference between the two groups in ECMO removal rate (VV group: 56%, VA group: 43%). CONCLUSION: These results suggest that VV ECMO is comparable to VA ECMO, and can maintain sufficient respiratory support when VV ECMO is introduced to respiratory failure patients lacking evidence of renal and/or heart failure.

The effect of a temporary inferior vena cava filter in the treatment of deep vein thrombosis in critically-ill patients.

We studied the clinical courses of patients with deep vein thrombus (DVT) who underwent insertion of temporary inferior vena cava filters (tIVCF) and evaluated the effectiveness of the tIVCF. From January 2003 to March 2008, tIVCF were placed in 12 patients with a diagnosis of DVT in the Intensive Care Unit (ICU) of Gunma University Hospital. The mean age of the patients was 52 +/- 16 years (range, 18-82). Eight were medical patients who had not undergone any prior surgery, and 4 were postoperative patients, including 3 with a malignancy. The diagnosis of DVT was made using enhanced computed tomography. The Toray Neuhaus Protect catheter (6Fr, Toray Medical, Tokyo) was used as a tIVCF in all 12 patients. We evaluated the clinical course of the patients before and after placement of a tIVCF and studied their prognosis. DVT occurred on 15 +/- 9 days after surgery or admission to hospital. Pulmonary thromboembolism (PTE) was detected in 7 patients prior to the placement of a tIVCF, 3 of whom required cardiopulmonary resuscitation. The mean duration of tIVCF placement was 18 +/- 9 days; no episodes of PTE occurred after tIVCF placement. DVT completely or almost completely disappeared during the period of tIVCF placement; subsequently, tIVCFs were successfully removed in 10 patients (83%). A permanent IVCF was placed in only 1 patient, and the tIVCF was removed in the remaining patient because of suspected catheter infection. There were 2 complications related to tIVCF placement: infection at the insertion site and suspected catheter infection. tIVCF placement could prevent the occurrence of PTE without provoking life-threatening complications. The results suggest that tIVCF is useful in the prevention of PTE in patients with DVT.

[Successful management of a man with fulminant myocarditis using percutaneous cardiopulmonary support].

Fulminant myocarditis is a fetal disease characterized by a distinct viral prodrome, sudden onset of severe hemodynamic compromise, and marked myocardial inflammation. One possible therapy to improve the poor prognosis of such patients may be the implantation of circulatory support systems that allow myocardial recovery. We report here successful management of a patient with fulminant myocarditis using percutaneous cardiopulmonary support (PCPS), intra-aortic balloon pump (IABP), and continuous hemodiafiltration (CHDF). A 37-year-old Japanese man suddenly experienced cardiopulmonary dysfunction shortly after general fatigue, and was diagnosed as having fulminant myocarditis. PCPS was immediately initiated because catecholamine infusion and IABP were not enough to support circulation. Although severe dyskinesis was observed on his admission, cardiac function recovered twelve days after PCPS initiation with ejection fraction from 16% to 73%. Renal and hepatic failure also recovered with the improvement of cardiac function. We describe our clinical experiences in cardiogenic shock after acute fulminant myocarditis and discuss therapeutic guidelines for the use of PCPS, with its management and complications.

Benefits of the laryngeal mask for airway management during electroconvulsive therapy.

Accumulation of carbon dioxide (CO2) can disturb systemic hemodynamics and increase the seizure threshold in patients receiving electroconvulsive therapy (ECT). The purpose of this study was to investigate the effects of the laryngeal mask on blood gas, hemodynamics, and seizure duration during ECT under propofol anesthesia. Ventilation was assisted using either a face mask (n=23) or laryngeal mask (n=23) and 100% oxygen. There was no significant difference in PaO2 between the two groups. PaCO2 was greater in the face mask group than the laryngeal mask group at 3 minutes (54 +/- 11 mm Hg, 41 +/- 8 mm Hg, respectively) and 5 minutes (52 +/- 11 mm Hg, 43 +/- 15 mm Hg, respectively) after electrical stimulation (p<0.01). Mean blood pressure was higher than the corresponding preanesthesia value at 1 to 5 minutes after electrical stimulation in the face mask group and at 1 to 3 minutes after electrical stimulation in the laryngeal mask group. Mean seizure duration in the face mask group was significantly shorter than that in the laryngeal mask group (33 +/- 11 seconds, 42 +/- 10 seconds, respectively p<0.01). The change in PaCO2 was minor in the laryngeal mask group compared with the face mask group and seizure duration was longer in the laryngeal mask group. Laryngeal mask may be suitable for airway management during ECT anesthesia, especially when fitting a face mask is difficult.