Home About us Contact
|
Home About us Contact | ||
|
|
||
Critical Structures (critical + structure)
Selected AbstractsCatheter Ablation of Long-Lasting Persistent Atrial Fibrillation: Critical Structures for TerminationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2005MICHEL HAÏSSAGUERRE M.D. Background: The relative contributions of different atrial regions to the maintenance of persistent atrial fibrillation (AF) are not known. Methods: Sixty patients (53 ± 9 years) undergoing catheter ablation of persistent AF (17 ± 27 months) were studied. Ablation was performed in a randomized sequence at different left atrial (LA) regions and comprised isolation of the pulmonary veins (PV), isolation of other thoracic veins, and atrial tissue ablation targeting all regions with rapid or heterogeneous activation or guided by activation mapping. Finally, linear ablation at the roof and mitral isthmus was performed if sinus rhythm was not restored after addressing the above-mentioned areas. The impact of ablation was evaluated by the effect on the fibrillatory cycle length in the coronary sinus and appendages at each step. Activation mapping and entrainment maneuvers were used to define the mechanisms and locations of intermediate focal or macroreentrant atrial tachycardias. Results: AF terminated in 52 patients (87%), directly to sinus rhythm in 7 or via the ablation of 1,6 intermediate atrial tachycardias (total 87) in 45 patients. This conversion was preceded by prolongation of fibrillatory cycle length by 39 ± 9 msec, with the greatest magnitude occurring during ablation at the anterior LA, coronary sinus and PV-LA junction. Thirty-eight atrial tachycardias were focal (originating dominantly from these same sites), while 49 were macroreentrant (involving the mitral or cavotricuspid isthmus or LA roof). Patients without AF termination displayed shorter fibrillatory cycles at baseline: 130 ± 14 vs 156 ± 23 msec; P = 0.002. Conclusion: Termination of persistent AF can be achieved in 87% of patients by catheter ablation. Ablation of the structures annexed to the left atrium,the left atrial appendage, coronary sinus, and PVs,have the greatest impact on the prolongation of AF cycle length, the conversion of AF to atrial tachycardia, and the termination of focal atrial tachycardias. [source] Introduction to Flap Movement: Reconstruction of Five Similar Nasal Defects Using Different FlapsDERMATOLOGIC SURGERY, Issue 2005Elbert H. Chen MD Background. There are several options for closure of a given surgical defect after tumor extirpation is confirmed. Flap reconstruction is one of these options. Objective. The purpose of this article is to introduce the three basic types of flap movement: advancement, rotation, and transposition. Methods. Five similar defects located on the nasal sidewall were repaired, each using a different flap design. Results. The optimal flap design for a given defect on a particular patient is based on the answers to a series of questions: Where is the available tissue reservoir? How can tissue be mobilized from the reservoir to cover the defect? How do the resulting tension vectors affect critical structures? Where are the final incision lines? Conclusion. Many factors must be evaluated before determining a method of reconstruction. Flap reconstruction requires a thorough understanding of anatomy and tissue movement. [source] Retrograde amnesia and the volume of critical brain structuresHIPPOCAMPUS, Issue 8 2003M.D. Kopelman Abstract There are many controversies concerning the structural basis of retrograde amnesia (RA). One view is that memories are held briefly within a medial temporal store ("hippocampal complex") before being "consolidated" or reorganised within temporal neocortex and/or networks more widely distributed within the cerebral cortex. An alternative view is that the medial temporal lobes are always involved in the storage and retrieval (reactivation) of autobiographical memories (multiple trace theory). The present study used quantitative magnetic resonance imaging (MRI) in 40 patients with focal pathology/volume loss in different sites, to examine the correlates of impairment on three different measures of RA. The findings supported the view that widespread neural networks are involved in the storage and retrieval of autobiographical and other remote memories. Brain volume measures in critical structures could account for 60% of variance on autobiographical memory measures (for incidents and facts) in diencephalic patients and for 60,68% of variance in patients with frontal lesions. Significant correlations with medial temporal lobe volume were found only in the diencephalic group, in whom they were thought to reflect thalamic changes, but not in patients with herpes encephalitis or hypoxia in whom the temporal lobes were particularly implicated. The latter finding fails to support one of the main predictions of multiple trace theory, as presently expounded. © 2003 Wiley-Liss, Inc. [source] On the Fracture Toughness of Advanced MaterialsADVANCED MATERIALS, Issue 20 2009Maximilien E. Launey Abstract Few engineering materials are limited by their strength; rather they are limited by their resistance to fracture or fracture toughness. It is not by accident that most critical structures, such as bridges, ships, nuclear pressure vessels and so forth, are manufactured from materials that are comparatively low in strength but high in toughness. Indeed, in many classes of materials, strength and toughness are almost mutually exclusive. From a fracture-mechanics perspective, the ability of a microstructure to develop toughening mechanisms acting either ahead or behind the crack tip can result in resistance-curve (R-curve) behavior where the fracture resistance actually increases with crack extension; the implication here is that toughness is often developed primarily during crack growth and not for crack initiation. Biological materials are perfect examples of this; moreover, they offer microstructural design strategies for the development of new materials for structural applications demanding combinations of both strength and toughness. [source] Interplanner variability in carrying out three-dimensional conformal radiation therapy for non-small-cell lung cancerJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 3 2008S Everitt Summary This study evaluated the variability among six radiation therapy planners in planning radiation treatment for four patients with lung cancer using two treatment protocols. The interplanner variability for target conformity and homogeneity was smaller than the variability among the patients and planning approaches. The same was found for the dose volume indices achieved for most critical structures, indicating that interplanner variability is not likely to be an important source of variation in radiotherapy studies if concise treatment protocols are followed. [source] Multicentre quality assurance of intensity-modulated radiation therapy plans: A precursor to clinical trialsJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 5 2007MJ Williams Summary A multicentre planning study comparing intensity-modulated radiation therapy (IMRT) plans for the treatment of a head and neck cancer has been carried out. Three Australian radiotherapy centres, each with a different planning system, were supplied a fully contoured CT dataset and requested to generate an IMRT plan in accordance with the requirements of an IMRT-based radiation therapy oncology group clinical trial. Plan analysis was carried out using software developed specifically for reviewing multicentre clinical trial data. Two out of the three plans failed to meet the prescription requirements with one misinterpreting the prescription and the third failed to meet one of the constraints. Only one plan achieved all of the dose objectives for the critical structures and normal tissues. Although each centre used very similar planning parameters and beam arrangements the resulting plans were quite different. The subjective interpretation and application of the prescription and planning objectives emphasize one of the many difficulties in carrying out multicentre IMRT planning studies. The treatment prescription protocol in a clinical trial must be both lucid and unequivocally stated to avoid misinterpretation. Australian radiotherapy centres must show that they can produce a quality IMRT plan and that they can adhere to protocols for IMRT planning before using it in a clinical trial. [source] Herpes simplex virus type 1 dysregulates anti-fungal defenses preventing monocyte activation and downregulating toll-like receptor-2MICROBIOLOGY AND IMMUNOLOGY, Issue 12 2008Claudio Cermelli ABSTRACT We investigated the interplay occurring between pathogens in the course of dual infections, using an in vitro model in which the THP-1 monocytic cell line is first infected with HSV-1 and then exposed to Ca or Cn. These three pathogens share some pathogenic features: they cause opportunistic infections, target macrophages and are neurotropic. Here, we show that HSV-1-infected THP-1 cells exhibited augmented phagocytosis against the two opportunistic fungi but reduced capability to counteract fungal infection: the better ingestion by monocytes was followed by facilitated fungal survival and replication. Reduced IL-12 production was also observed. Cytofluorimetric analysis showed that HSV-1-infected monocytes exhibit: (i) downregulated TLR-2 and TLR-4, critical structures in fungal recognition; (ii) reduced expression of CD38 and CD69, known to be important markers of monocyte activation; and (iii) enhanced expression of apoptosis and necrosis markers, in the absence of altered cell proliferation. Overall, these findings imply that HSV-1 infection prevents monocyte activation, thus leading to a significant dysfunction of the monocyte-mediated anti- Candida response; HSV-1 induced apoptosis and necrosis of monocytes further contribute to this impairment. [source] Temporary Intermaxillary Fixation using Individualized Acrylic Splints Permits Image,Data-Based Surgery of the Lower Jaw and OropharynxTHE LARYNGOSCOPE, Issue 8 2004Jürgen Hoffmann MD Abstract Objectives/Hypothesis: Image,data-based surgical navigation is used as a helpful device in the operating room to localize critical structures with a high degree of accuracy. It also enables physicians to plan therapeutic performance. Because it relies on preoperatively acquired computed tomography (CT) or magnetic resonance imaging (MRI) data, there is restricted access for navigation of surgical instruments in areas that show motion uncorrelated with radiologic data. Thus, in the case of moveable structures, for example the lower jaw, navigational procedures could not yet be applied. Study Design: We introduce a new technique using individualized intermaxillary splints that fix the mandible in a reproducible aboccluded position at the time of image-data acquisition and surgery. Methods: Different manufacturing processes were investigated. The feasibility of uni- and bilateral intermaxillary splints was studied under clinical conditions in four patients during different procedures in the mandibular and oropharyngeal regions. Results: The manufacturing of the splints showed was easily performed in a short time. With bilateral fixation, there was a high anatomic target precision of 1.6 to 2.3 mm. Conclusions: The use of bilateral intermaxillary splints that fix the patient's mandible in a reproducible aboccluded position permits an image,data-based navigated surgical approach to the oropharyngeal and mandibular regions. [source] Formation of Trichlorinated Dibenzo- p -dioxins from 2,4-Dichlorophenol and 2,4,5-Trichlorophenolate: A Theoretical StudyCHEMPHYSCHEM, Issue 11 2006Ernesto Suárez Abstract The reaction of the 2,4,5-trichlorophenolate anion with 2,4-dichlorophenol to afford trichlorinated dibenzo- p -dioxins (T3CDDs) is investigated at the B3LYP/6-31+G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d)+ZPVE(B3LYP/6-31+G(d)) levels of theory. The first stage of the process corresponds to the formation of a predioxin, which can evolve through four different routes. Two of them lead directly to the products 2,3,7-T3CDD and 1,3,8-T3CDD, and the other two afford different predioxin-type intermediates, which in turn can evolve through all or some of the four routes to give new predioxins or T3CDD. Consequently, the theoretical results obtained show plainly the complex chemistry implied in the formation of dioxins from chlorophenols via anionic mechanisms by disclosing all the critical structures through which the system evolves, thus allowing assessment of the viability of the different mechanistic routes and the accessible products. The statistical thermodynamics treatment at 1 atm and 298.15, 600, 900, and 1200 K indicates that at higher temperatures, the Gibbs energy barrier for the formation of the initial predioxin is clearly the rate-determining step for the whole process, but at lower temperatures the Gibbs energy barrier for this step is similar to those for its evolution into 2,3,7-T3CDD. This result is in contrast with previous proposals that the closure of the central ring is the rate-limiting step. Finally, according to our results the rate constant for the formation of polychlorinated dibenzo- p -dioxins increases with the temperature, in agreement with the experimental observation that the conversion of trichlorophenols increases when going from 600 to 900 K in the gas phase in the absence of catalysts, and with DFT molecular dynamics results. [source] | |||||||||||||