Evidence Of Constriction Research Articles

Strain partitioning in the Moine Nappe, northernmost Scotland

Abstract Extreme strain in the form of flattening or constriction during noncoaxial shear in ductile shear zones provides a record of ductile thrust system dynamics and the overall tectonic evolution. Within the Moine Nappe in northern Scotland, between the Ben Hope and Moine thrusts, the Strathan Conglomerate displays apparent strain partitioning with extreme flattening (e.g., laterally extensive sheets of deformed pebbles with aspect ratios of 134:113:1 and 88–92% estimated thinning) adjacent to the overlying Ben Hope Thrust and extreme constriction (e.g., rods with aspect ratios of 21:4:1 and estimated extension of 1000%) lower in the nappe package. We demonstrate that partitioning of strain is between its intensity and how deformation is manifested. Field, microstructural, and crystallographic orientation data from this study indicate that both areas were deformed by WNW-directed noncoaxial shear and coaxial flattening under amphibolite-facies conditions. Adjacent to the Ben Hope thrust, flattening was pervasive during nonco-axial shear, whereas beneath and within the Moine Nappe package, polyphase folding dominated. There, early, large-scale folds (F2) rotated into the transport direction. Subsequent transport-parallel (F3) folds and tubular sheath folds formed on the F2 limbs and were dismembered to form rods. No evidence of constriction is observed; instead, pervasive noncoaxial shear was accompanied by minor flattening under decreasing temperature conditions. Thus, these S-tectonites in the Moine Nappe are the result of concentrated flattening of pebbles into sheets during WNW-directed shear, whereas the L-tectonites result from heterogeneously distributed shear and folding, coupled with minor flattening, which produced rods without constriction.

P1501 Huge lateral wall ventricular pseudoaneurysm complicating a silent myocardial infarction

Abstract Introduction Mechanical complications of acute myocardial infarction (AMI) are mainly ventricular septal rupture (VSR), free wall rupture, and ischemic mitral regurgitation. If the patient survives the acute phase, negative remodeling starts to occur leading to aneurysm or pseudoaneurysm formation. Case report A 44-year-old male patient, smoker with a past medical history of hypertension, diabetes mellitus and no past cardiac history except for recurrent pericardiocentesis of hemorrhagic pericardial effusion in another hospital since 3 months with no available data, presented to our medical facility complaining of dyspnea grade III with no orthopnea or paroxysmal nocturnal dyspnea that started 4 months ago and progressed gradually with no history of any acute events. He was hemodynamically stable with no audible murmurs and clear chest auscultation. Transthoracic echocardiography (TTE) showed reduced left ventricular (LV) systolic function (ejection fraction 40%) with accidentally discovered large lateral wall ventricular pseudoaneurysm containing a large mural thrombus (Panels A and B) and a small pericardial effusion with no evidence of constriction or tamponade. Cardiac Computed tomography (CT) confirmed the presence of large ventricular pseudoaneurysm with mural thrombus lining the wall of the aneurysm (Panels C and D). Invasive coronary angiography (CA) revealed a total occlusion of the left circumflex artery (LCx) and non significant lesions in the remaining coronaries. The patient refused to have surgery and he was discharged on anti-ischemic, anti-failure measures and anti-coagulation with close follow-up. Conclusion Bedside echocardiography is still the mainstay procedure for diagnosis of mechanical complications following AMI and other imaging modalities such as cardiac CT and cardiac magnetic resonance (CMR) are new diagnostic tools for confirming the diagnosis and planning for further interventions. Although rare, mechanical complications of AMI should always be considered in every ischemic patient. Abstract P1501 Figure. Echo and CT images

Evidence for constriction and Pliocene acceleration of east‐west extension in the North Lunggar rift region of west central Tibet

AbstractThe active north trending North Lunggar rift in west central southern Tibet exposes an extensional metamorphic core complex bounded by an east dipping low‐angle normal fault. Apatite and zircon (U‐Th)/He thermochronology and thermal modeling of the North Lunggar rift document a minimum timing for rift inception at >10 Ma and rapid footwall exhumation between 5 and 2 Ma. Miocene footwall cooling and exhumation rates were initially slow to moderate at <50°C Ma−1 and <1 mm a−1, followed by increased Pliocene rates as high as >400°C Ma−1 and 4–10 mm a−1. Footwall isotherms were significantly compressed during rapid exhumation resulting in an elevated transient geothermal gradient between 50 and 90°C km−1. The minimum magnitude of horizontal extension for the North Lunggar rift is 8.1–12.8 km; maximum is 15–20 km, less in the south at ~10 km. Mean Pliocene extension rate is 1.2–2.4 mm a−1 in the ~120° direction. Results for the North Lunggar rift are similar in magnitude, rate, and orientation of slip to the kinematically linked Lamu Co dextral strike‐slip fault to the north. This suggests a state of constrictional strain during Pliocene time along this stretch of the Bangong‐Nujiang suture from which the Lamu Co fault emanates. The onset of extension in this region may be explained by crustal thickening and gravitational orogenic collapse, followed by accelerated rifting resulting from localized crustal stretching and increased magmatic activity, potentially driven by the position and northward extent of underthrusting Indian lithosphere.

MR imaging findings in 76 consecutive surgically proven cases of pericardial disease with CT and pathologic correlation

To describe findings of patients with surgically confirmed pericardial disease on state of the art MR sequences. Retrospective review was performed for patients who underwent pericardiectomy and preoperative MR over a 5 year period ending in 2009. Patients' records were reviewed to confirm the diagnosis of chronic recurrent pericarditis, constrictive pericarditis, or pericardial tumor. MR imaging findings of pericardial thickness, IVC diameter, presence or absence of pericardial or pleural effusion, pericardial edema, pericardial enhancement, and septal "bounce" were recorded. Patients with constriction had a larger IVC diameter (3.1 ± 0.4 cm) than patients with recurrent pain and no constriction (2.0 ± 0.4 cm). Mean pericardial thickness for the 16 patients with chronic recurrent pericarditis but no evidence of constriction was 4.8 ± 2.9 mm. Mean pericardial thickness for patients with constriction was 9.2 ± 7.0 cm with calcification, and 4.6 ± 2.1 cm without calcification. 94% of patients with chronic recurrent pericarditis had gadolinium enhancement of the pericardium, while 76% of patients with constriction had pericardial enhancement. Septal "bounce" was present in 19% of chronic recurrent pericarditis cases and 86% of constriction cases. 5 patients had a pericardial neoplasm, 1 of which was not identified preoperatively. State of the art MR techniques can identify significant and distinct findings in patients with chronic recurrent pericarditis, constrictive pericarditis, and pericardial tumors.

Retracted: Isolated Subacute Effusive and Nonconstrictive Epicarditis Masquerading as a Right Atrial Mass

Epicarditis (visceral pericardial inflammation) is a very unique and rare diagnosis. It is almost always associated with parietal pericardial involvement and may occur in medical conditions such as viral, bacterial (mycobacterial) infections and uremia or postoperatively in the setting of cardiac surgery. Frequently, no etiology is found. Most cases are associated with constrictive physiology, and patients present with symptoms and signs of right-sided heart failure. Effusive epicarditis is often present, and the clinical features may easily be confused with those of pericardial effusion with tamponade. We report a unique case of isolated subacute effusive and nonconstrictive epicarditis mimicking a right atrial mass in a 72-year-old patient who was diagnosed with nonmetastatic gastric adenocarcinoma. Our case is unique for several reasons: inflammation was limited to the epicardium (very few cases have been described to date); the patient was asymptomatic, with no clinical or echocardiographic evidence of constriction (this represents a novel finding, explained in part by the more limited extent of inflammation, with no significant fibrotic component and no parietal pericardial involvement); and this is the first report of epicarditis occurring in association with a malignancy, which we hypothesize may represent an inflammatory paraneoplastic process.

Comment on Point:Counterpoint “The muscle metaboreflex does/does not restore blood flow to contracting muscles”

The following letters are in response to the Point:Counterpoint series “The muscle metaboreflex does/does not restore blood flow to contracting muscles” that appeared in the January issue (vol. 100: 357–361, 2006; ). To the Editor : This letter

Vigabatrin Retinopathy in an Irish Cohort: Lack of Correlation with Dose

The anticonvulsant vigabatrin (VGB) causes irreversible visual-field constriction in 19-92% of patients. It is unclear whether this correlates with dosing, and the natural history of the retinopathy remains obscure. We conducted a retrospective analysis of patients receiving long-term VGB to examine whether toxicity is related to the daily dose, duration of therapy, or cumulative dose. Information from 93 patients taking long-term, stable VGB therapy was analyzed. We recorded data on patient demographics, VGB dosing, and all visual-field assessments. We used the mean redial degrees (MRD) from the right eye to compare the amount of constriction with the dose of VGB. The mean number of assessments was two (range, 1-6). Of patients having more than one assessment (n = 65), the mean follow-up time was 2.4 years (range, 0.7-5.6 years); in 52.7%, visual-field constriction developed. Male and female patients were affected equally. We found no correlation between the average MRD and either the maximum dose of VGB taken, the duration of exposure, or the cumulative dose. The shortest exposure time to development of constriction was 1.1 years. All patients with normal fields on initial assessment continued to have normal fields on follow-up. Most patients who had evidence of constriction on initial assessment and remained taking VGB showed no progression on follow-up. One patient had a substantial recovery of vision after discontinuation of VGB. Development of visual constriction in patients receiving prolonged, standard doses of VGB does not depend on the daily dose, duration of exposure, or cumulative dose. Other contributing factors were not identified. Our data suggest that field defects may develop within the first few years of therapy and possibly remain stable thereafter.

Localization and function of early cell division proteins in filamentous Escherichia coli cells lacking phosphatidylethanolamine.

Escherichia coli cells that contain the pss-93 null mutation are completely deficient in the major membrane phospholipid phosphatidylethanolamine (PE). Such cells are defective in cell division. To gain insight into how a phospholipid defect could block cytokinesis, we used fluorescence techniques on whole cells to investigate which step of the cell division cycle was affected. Several proteins essential for early steps in cytokinesis, such as FtsZ, ZipA, and FtsA, were able to localize as bands to potential division sites in pss-93 filaments, indicating that the generation and localization of potential division sites was not grossly affected by the absence of PE. However, there was no evidence of constriction at most of these potential division sites. FtsZ and green fluorescent protein (GFP) fusions to FtsZ and ZipA often formed spiral structures in these mutant filaments. This is the first report of spirals formed by wild-type FtsZ expressed at normal levels and by ZipA-GFP. The results suggest that the lack of PE may affect the correct interaction of FtsZ with membrane nucleation sites and alter FtsZ ring structure so as to prevent or delay its constriction.

Toxoplasma gondii: an ultrastructural study of host-cell invasion by the bradyzoite stage.

The invasion of Toxoplasma gondii tachyzoites and bradyzoites was followed in bovine kidney cells via electron microscopy. The process of invasion differed between bradyzoites and tachyzoites. In the early stages of entry there was evidence of localised formation of membrane projections in the host cell adjacent to the parasite. Parasite reorientation and rhoptry release appeared to be necessary for invasion; however, the tight junction could not be clearly discerned and there was no evidence of constriction or of any membrane shedding from the parasite. The resulting parasitophorous vacuole was smaller than the tachyzoite vacuole and parasites were frequently found to lie immediately under the host cell membrane. The vacuole was rapidly adapted by the release and formation of an intra-phagosomal membrane network, while the parasitophorous vacuole formed a relationship with host-cell endoplasmic reticulum.

Predictors of constrictive pericarditis after tuberculous pericarditis.

To identify features which predict the subsequent development of constrictive pericarditis from acute or subacute tuberculous (TB) pericarditis. Tertiary referral centre, chest hospital. The records of 16 consecutive patients in whom acute or subacute TB pericarditis was diagnosed between 1988 and 1990 at a chest hospital were reviewed. These records included a follow up of at least 12 months. During a follow up of 14.2 (12-30) months, 8 patients had constrictive pericarditis diagnosed by cardiac catheterisation or by inspection at the time of operation (group A). There was no evidence of constriction in the other eight patients (group B). There was no significant difference between the two groups in the type or duration of symptoms of TB pericarditis before admission or the volume and characteristics of pericardial fluid obtained at hospital admission. Clinical features of cardiac tamponade on admission correlated closely with the subsequent development of constrictive pericarditis requiring pericardectomy (7/8 v 2/8; P = 0.01), despite the fact that the signs of tamponade resolved completely after pericardiocentesis. The findings suggest that cardiac tamponade in the early clinical stage of TB pericarditis is the most predictive factor of subsequent constrictive pericarditis. The degree of fibrosis of pericardium when treatment starts may be the most important determinant of whether or not constriction develops.

Effects of rapid volume expansion on the right filling pressures after prosthetic valve surgery

The effects of rapid intravascular volume expansion were studied in 12 patients, 4 to 14 years after single prosthetic heart valve replacement. The data observed showed a statistically significant mean difference before and after volume expansion of right atrial mean pressure and right ventricular end diastolic and pulmonary capillary pressures. However, right atrial and pulmonary capillary pressures equilibration was not detected. The right atrial pressure form showed abnormal variations during inspiration. Dip and plateau right ventricular diastolic pressure configuration was recorded in 6 patients after expansion, was absent in 2 and questionable in 4. A deep Y descent with an M-shaped right atrial pressure form was recorded in all 12 patients. The explanation for these phenomena is unclear. Thus, in the absence of pressure equilibration and clinical evidence of constriction, the abnormalities recorded during rapid volume expansion should be cautiously interpreted.

Pericarditis as a manifestation of histoplasmosis during two large urban outbreaks.

During two histoplasmosis outbreaks in Indianapolis 45 patients presented with pericarditis. The pericarditis occurred as a late complication in individual patients and during the outbreak. Risk factors for this complication included young age, immunocompetence, and male sex in persons between 20 and 39 years old. Intrathoracic adenopathy was present in 66% of cases. Since cultures were uniformly negative, including pericardial fluid or tissue from nine patients, serologic studies provided the basis for diagnosis. Although the course was usually benign, nine patients presented with tamponade and another with constrictive pericarditis. Prompt response to antiinflammatory medications and failure to identify H. capsulatum in the pericardial fluid or tissue support a noninfectious, inflammatory mechanism for this complication. Of 20 patients reexamined 1 year later, none had evidence of constriction but three had pericardial thickening by echocardiography. Histoplasmosis should be considered in patients with pericarditis from endemic areas, particularly when associated with intrathoracic adenopathy.

Constrictive Pericarditis Following Aortocoronary Bypass Surgery

A 61-year-old man had progressive dys pnea along with signs and symptoms sug gesting severe right heart failure following aortocoronary bypass surgery. He was ini tially treated with indomethacin, digoxin, and furosemide, but with no major change in his condition. Four months after opera tion the patient presented with clinical find ings compatible with the postpericardiotomy syndrome and hemodynamic evidence of constriction. Pericardiectomy resulted in a marked improvement in his functional ca pacity. The possible mechanism for peri cardial constriction following open heart surgery is discussed.

The Role of Surgery in Tuberculous Pericarditis

To define the role of surgery in the treatment of tuberculous pericarditis, 62 consecutive patients treated for this condition were reviewed. Medical therapy alone achieved satisfactory results in less than one-third of the patients. One-half of the patients eventually required pericardiectomy for symptoms of recurrent cardiac tamponade or evidence of constriction. A favorable response to medical therapy alone could not be predicted. The results of surgery were excellent if operation was performed prior to constriction. In our opinion, all reasonable-risk patients with tuberculous pericarditis would benefit by prompt surgical intervention following institution of chemotherapy.