Linear stability analysis and nonlinear simulations of convective dissolution in an inclined porous layer between impermeable surfaces

Convective dissolution can occur in porous media when a given solute dissolves in a host layer from above and increases the density of the host solution. Buoyancy-driven fingering can then develop, which increases the transfer flux of the solute. We investigate here numerically the properties of this convective dissolution when the porous host layer is inclined by an angle θ relative to the horizontal direction. We consider an incompressible flow in porous media governed by Darcy's law, driven by density gradients associated with the concentration of the dissolving solute. The model problem focuses on the case of a very long (infinite) tilted porous layer limited by two parallel impermeable surfaces. A linear stability analysis and nonlinear simulations are performed using the Boussinesq approximation. A vorticity-stream function formulation is adopted to solve the two-dimensional hydrodynamic field through the finite element method. We find that the inclination of the interface decreases the growth rate of the instability and the range of unstable wavenumbers, delaying or even suppressing the onset of the fingering instability. Moreover, it introduces a drift velocity on the perturbations, which is characterized here in both the linear stability analysis and the nonlinear simulations.

Exon 3-deleted growth hormone receptor isoform is not related to worse bone mineral density or microarchitecture or to increased fracture risk in acromegaly

PURPOSE

Acromegaly is a cause of secondary osteoporosis and is associated with increased risk of vertebral fractures (VFs). The influence of exon 3-deleted isoform of growth hormone receptor (d3-GHR) on bone microarchitecture has not been studied in acromegaly.

AIM

The aim of this study was to analyze the associations between d3-GHR isoform and bone mineral density (BMD), bone microarchitecture, and VFs in acromegaly patients.

METHODS

Consecutive acromegaly patients treated at a single reference center were included. BMD was analyzed using dual-energy X-ray absorptiometry (DXA) and bone microarchitecture was analyzed by high-resolution peripheral quantitative computed tomography (HR-pQCT). The presence of moderate to severe VFs was assessed by thoracic and lumbar X-ray. GHR genotyping was analyzed by PCR, and full-length isoform of GHR (fl-GHR) was represented by a 935-bp fragment and d3-GHR by a 532-bp fragment.

RESULTS

Eighty-nine patients were included [56 females; median age at diagnosis: 43 years (17-78)]. Disease was uncontrolled in 63% of patients. At least one d3-GHR allele was present in 60% of patients. Frequency of active disease (p = 0.276) and hypogonadism (p = 1.000) was not different between patients with fl-GHR and those with at least one d3-GHR. There was no difference in any DXA or HR-pQCT parameters between patients with fl-GHR and those with d3-GHR. Significant VFs were observed in 14% of patients, but there was no difference in frequency between patients with fl-GHR and those with at least one d3-GHR allele (p = 0.578).

CONCLUSIONS

Presence of d3-GHR was not associated with worse BMD or bone microarchitecture or with higher frequency of significant VFs.

Impact of the radical prostatectomy surgical technique and surgeon experience on freedom from cancer recurrence

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Background: We have shown a direct relation between positive margin (PM), morbidity outcomes and surgeon volume, technique after radical prostatectomy (RP). Significant variation occurs even among high volume providers. Our aim was to analyze the surgeon effects on cancer control after RP. Methods: We evaluated 8196 consecutive cT1–3NxMx naive men who underwent RP by one of 76 surgeons within 4 institutions between 1987 and 2003. We calculated the 5-yr probability of recurrence (BCR, PSA elevation >0.4 ng/ml × 2 or initiation of secondary therapy for a PSA rise) for each surgeon assuming a log-logistic survival distribution. A meta-analysis controlling for case mix: PSA, Gleason score, stage, PM and surgical expertise (i.e. cumulative number of surgeries performed) to evaluate for differences in BCR rates between surgeons was performed. We applied the I-square statistic to determine what proportion of the variation represented genuine differences v. chance alone. Results: 33 surgeons performed > 40 RP with 17 surgeons having > 100 procedures during the study period. BCR events were recorded in 1361 patients. The overall 5-yr freedom from BCR with 2524 patients remaining at risk was 80% (79%, 81%) . Extracapsular extension, seminal vesicle invasion, nodal metastasis, PM, Gleason score and PSA were independent predictors of BCR. The surgical volume also correlated independently with BCR. Importanntly we found significant variability on freedom from BCR between high volume surgeons. The I-squared statistic from the meta-analysis was 0.63. That is, approximately 63% of the difference in BCR rates among surgeons can be explained by genuine differences in surgical skill and approach, and approximately 37% is compatible with chance alone. For a sensitivity analysis, we repeated the analysis excluding surgeons who performed less than 100 procedures. In this sub-analysis, the I-squared statistic remained very significant at 0.48. Conclusions: Our data shows that in men treated by RP, the BCR outcomes of men are not exclusively determined by the biology and stage of prostate cancers (explained in most models), but to the surgical skill. Clinical trials evaluating BCR outcomes must prove equivalency among providers so that results are not biased by them.

No significant financial relationships to disclose.

[Secondary biliary cirrhosis in a patient with histiocytosis X]

Histiocitose X or Histiocytosis of the Langerhans cells represents a complex spectrum of clinical alterations, resulting from infiltration by anomalous histiocytes of various organs, including the skin, bones, lungs, lymphatic ganglia and liver. Liver disease is rare and the mechanism by which lesions appear is unknown. Cholestasis results from phenomena of sclerosant colangitis, which affects the intrahepatic ducts, or from proliferation of histiocytic cells in the periportal areas. Some patients develop biliar cyrrhosis. The authors present the clinical case of a 62-year-old female patient, hospitalized for chronic cholestasis, diabetes and gallstone in the main bile duct. She had metastatic lesions of the hypophysis and bones, the biopsies of which revealed infiltration by histiocytic cells. Endoscopic Retrograde Colangiopancreatography (E.R.C.P.) revealed dilatation of intrahepatic bile ducts and stenosis of left hepatic duct. A histological study of the hepatic biopsy showed chronic cholestasis and areas of fibrosis, without infiltration by histiocytic granulomas, which were observed in the medular biopsy and in the thyroid nodule cytology.

Endosonography in the diagnosis of "blue rubber bleb nevus syndrome": an uncommon cause of gastrointestinal tract bleeding

Blue rubber bleb nevus syndrome is a rare condition characterized by the presence of multiple angiomatic lesions of the skin. These are associated with similar lesions in other organs, namely in the gastrointestinal tract, causing anemia through chronic bleeding. We describe the case of a 72-year-old woman with microcytic anemia. A barium study revealed irregular lacunae in the distal esophagus. A subsequent endoscopy showed blue nodular lesions similar to angiomas of the esophagus and stomach fundus. Endosonography confirmed its angiomatic nature. Exploration of other organs, using magnetic resonance and cranial computed tomography, did not reveal the presence of this type of lesion. In physical examination, two angiomatic lesions were observed on the face and lips, respectively. These were blue in color and compressible, leaving an empty wrinkled sac that rapidly refilled, typical of angiomas.

Synchronic signet ring carcinoma and adenocarcinoma complicating extensive and long-standing ulcerative colitis

We report the case of a 38 year-old woman with extensive ulcerative colitis (UC) for 9 years that had consistently been under close endoscopic surveillance. She had had two previous severe attacks requiring hospital admission, with good response to intravenous steroids. In the last relapse, a total colonoscopy demonstrated extensive lesions of UC throughout the entire colon. Multiple biopsies taken every 3 cm revealed only low-grade dysplasia and lesions characteristic of UC. Due to medical therapy failure, the patient was submitted for proctocolectomy. Pathological examination of the resected specimen showed a signet ring carcinoma and a synchronic adenocarcinoma in the sigmoid colon, both undetected by colonoscopy and biopsies. The issue of surveillance in patients with extensive and long-standing UC is discussed.

Modeling spiral Ca2+ waves in single cardiac cells: role of the spatial heterogeneity created by the nucleus

Excitation-contraction coupling in cardiomyocytes is known to rely on the Ca(2+)-induced Ca2+ release mechanism. This autoamplification process is also very apparent when voltage-clamped or Ca(2+)-overloaded myocytes exhibit fast-propagating Ca2+ waves. Although most of the fronts are planar, some adopt a spiral shape, revealing additional characteristics about the excitability and structure of the cardiac cell (P. Lipp and E. Niggli, Biophys. J. 65: 2272-2276, 1993: J. Engel, M. Fechner, A. Sowerby, S. Finch, and A. Stier, Biophys. J. 66: 1756-1762, 1994). Using a previously developed model for Ca2+ oscillations and waves (A. Goldbeter, G. Dupont, and M.J. Berridge, Proc. Natl. Acad. Sci. USA 87: 1461-1465, 1990; G. Dupont and A. Goldbeter, Biophys. J. 67: 2191-2204, 1994), we study by numerical simulations different conditions in which spiral Ca2+ waves can occur as a result of the spatial heterogeneity created by the nucleus in a system with geometry resembling that of a myocyte. A region of the cell lacking Ca2+ pools, acting as an obstacle able to break the propagation of planar waves, suffices to initiate a spiral wave; however, this region must be properly placed with respect to the pacemaker. An obstacle behaving as a barrier to diffusion is also able to create the initial bending that can lead to the spiral wave. We study how the occurrence of spiral Ca2+ waves in single cardiomyocytes is influenced by factors such as the stimulus location and the position, shape, and dimensions of the obstacle to planar wave propagation.

[Pulmonary valve endocarditis caused by Streptococcus bovis]

The authors report a case of isolated infective endocarditis of the pulmonary valve due to Streptococcus bovis in a 62-year-old male presented with delayed fever of unknown origin. There were no predisposing factors such as i.v. drug abuse or congenital heart disease. The clinical course was complicated with an epidose of pulmonary emboli occurring after the onset of treatment. The patient responded to the appropriate antibiotics without requiring valve surgery. The association of Streptococcus bovis endocarditis and bacteremia with colonic neoplasia has been reported in the literature. In this case the evaluation of the colon was negative.