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Biomedical subjects

A Moreo

Publications and source records attributed to A Moreo.

At least 19 recordsLinked to original sources
PubMed2001

Colossal effects in transition metal oxides caused by intrinsic inhomogeneities.

The influence of quenched disorder on the competition between ordered states separated by a first-order transition is investigated. A phase diagram with features resembling quantum-critical behavior is observed, even using classical models. The low-temperature paramagnetic regime consists of coexisting ordered clusters, with randomly oriented order parameters. Extended to manganites, this state is argued to have a colossal magnetoresistance effect. A scale T(*) for cluster formation is discussed. This is the analog of the Griffiths temperature, but for the case of two competing orders, producing a strong susceptibility to external fields. Cuprates may have similar features, compatible with the large proximity effect of the very underdoped regime.

Journal Article↗
PubMed2001

Safety, feasibility, and diagnostic accuracy of accelerated high-dose dipyridamole stress echocardiography.

Protocols for dipyridamole stress testing have evolved in the last 16 years in the neverending quest of optimal diagnostic accuracy and user friendliness. Higher dipyridamole dose in a shorter infusion time provides higher sensitivity, but concern over safety is still controversial. An accelerated high-dose (0.84 mg/kg in 6 minutes without atropine) dipyridamole stress test was performed on 1,295 patients in 2 echocardiographic laborotories: Institute of Clinical Physiology of Pisa and Niguarda Hospital of Milan. During testing, there were no deaths and no patients had ventricular fibrillation. Major adverse reactions occurred in 3 cases (1 every 431 studies): 1 myocardial infarction, 1 brief cardiac asystole, and 1 transient ischemic attack. Overall feasibility was 97%. In 66 patients with normal function at rest who were evaluated off therapy, with coronary angiography performed independently of test results, the accelerated high-dose protocol showed a sensitivity of 85% (confidence interval [CI] 73% to 92%) and a specificity of 93% (CI 83% to 97%) for angiographically assessed coronary artery disease (quantitatively assessed diameter reduction > or = 50%). Diagnostic accuracy of the accelerated high dose was 89% (CI 79% to 95%). Thus, accelerated high-dose dipyridamole stress echocardiography was reasonably safe and well tolerated. This protocol is especially appealing for its excellent diagnostic accuracy coupled with the short imaging time and no need for drug cocktails.

Aged↗
PubMed2001

Resistivity of Mixed-Phase Manganites.

The resistivity rho(dc) of manganites is studied using a random resistor-network, based on phase separation between metallic and insulating domains. When percolation occurs, both as chemical composition or temperature vary, results in good agreement with experiments are obtained. Similar conclusions are reached using quantum calculations and microscopic considerations. Above the Curie temperature, it is argued that ferromagnetic clusters should exist in Mn oxides. Small magnetic fields induce large rho(dc) changes and a bad-metal state with (disconnected) insulating domains.

Journal Article↗
PubMed2000

Giant cluster coexistence in doped manganites and other compounds

Computational studies of models for manganese oxides show the generation of large coexisting metallic and insulating clusters with equal electronic density, in agreement with the recently discovered micrometer-sized inhomogeneities in manganites. The clusters are induced by disorder on exchange and hopping amplitudes near first-order transitions of the nondisordered strongly coupled system. The random-field Ising model illustrates the qualitative aspects of our results. Percolative characteristics are natural in this context. The conclusions are general and apply to a variety of compounds.

Journal Article↗
PubMed2000

Magnetic domains and stripes in a spin-fermion model for cuprates

Monte Carlo simulations applied to a model of interacting fermions and classical spins show the existence of antiferromagnetic spin domains and charge stripes upon hole doping. The stripes have a filling of approximately 1/2 hole per site, and they separate spin domains with a pi phase shift among them. The observed stripes run either along the x or y axes. No particular boundary conditions or external fields are needed to stabilize these structures. When magnetic incommensurate peaks are observed at momentum pi(1,1-delta), charge incommensurate peaks appear at (0,2delta). The charge fluctuations responsible for the stripe formation also induce a pseudogap in the density of states.

Journal Article↗
PubMed2000

Incorrect echocardiographic diagnosis in patients with mechanical prosthetic valve dysfunction: correlation with surgical findings.

PURPOSE: To identify the rate of occurrence and type of incorrect echocardiographic diagnoses in patients with mechanical valve prostheses. PATIENTS AND METHODS: We studied 170 consecutive patients (73 women and 97 men) with a total of 208 prostheses who underwent surgery for mitral (n = 136) or aortic (n = 72) valve dysfunction between January 1991 and December 1997. Preoperative echocardiographic data were compared with surgical findings. Any major discrepancy between the echocardiographic reports and surgery was judged to be unconfirmed when the preoperative echocardiographic diagnosis was not confirmed at surgery, but the prosthesis was found to be dysfunctioning; and was judged to be erroneous when the preoperative echocardiographic diagnosis was not confirmed, and surgical inspection failed to reveal any other prosthetic abnormality. RESULTS: There were 25 (12%) diagnostic errors. Of the 136 mitral prostheses, there were 9 unconfirmed diagnoses of paravalvular regurgitation (6 had a fibrous tissue overgrowth, 1 had a thrombus with fibrous tissue overgrowth, 1 had endocarditis vegetations, and 1 had a ball variance) and 5 erroneous diagnoses. Eleven diagnostic errors were made in the 72 aortic prostheses: there were 9 unconfirmed diagnoses (paravalvular regurgitation was diagnosed as transvalvular in 7, and transvalvular regurgitation as paravalvular in 2 cases), and 2 erroneous diagnoses. CONCLUSIONS: Although echocardiography has gained great credibility among clinicians, special care should be taken when assessing patients in whom prosthetic valve dysfunction is suspected.

Aged↗
PubMed2000

Left ventricular performance in chronic mitral regurgitation: temporal response to valve repair and prognostic value of early postoperative echocardiographic parameters.

BACKGROUND: The temporal response of the left ventricle due to the relief of volume loading after mitral valve repair, and the prognostic value of early changes in left ventricular size and function, are not fully documented. The purpose of this study was to analyze the evolution of left ventricular performance after surgery, and to evaluate how early postoperative echocardiographic parameters compare with late ventricular function. METHODS: We studied 58 patients with chronic degenerative mitral regurgitation using echocardiography, before, and 9 +/- 3 days and 38 +/- 6 months after mitral valve repair. RESULTS: Between the preoperative and early postoperative study, left ventricular end-diastolic and left atrial size, and ejection fraction decreased, whereas left ventricular end-systolic dimension did not change. Between the early and late postoperative study left ventricular end-systolic size decreased significantly, there was a further decrease in left ventricular end-diastolic dimension and a significant increase in ejection fraction; left atrial size did not change. Multivariate analysis showed that preoperative and early postoperative ejection fraction, and the early postoperative reduction in diastolic dimension were the best predictors of late left ventricular function. CONCLUSIONS: In patients with chronic degenerative mitral regurgitation, the greatest reduction in end-diastolic dimension occurs within 2 weeks of the reversal of volume overload; a significant reduction in end-systolic dimension with an increase in ejection fraction occurs later. In our experience, early postoperative echocardiographic measurements of left ventricular size and function can provide important prognostic information.

Adolescent↗
PubMed1999

Phase separation scenario for manganese oxides and related materials

Recent computational studies of models for manganese oxides have revealed a rich phase diagram, which was not anticipated in early calculations in this context performed in the 1950s and 1960s. In particular, the transition between the antiferromagnetic insulator state of the hole-undoped limit and the ferromagnetic metal at finite hole density was found to occur through a mixed-phase process. When extended Coulomb interactions are included, a microscopically charged inhomogeneous state should be stabilized. These phase separation tendencies, also present at low electronic densities, influence the properties of the ferromagnetic region by increasing charge fluctuations. Experimental data reviewed here by applying several techniques for manganites and other materials are consistent with this scenario. Similarities with results previously discussed in the context of cuprates are clear from this analysis, although the phase segregation tendencies in manganites appear stronger.

Journal Article↗
PubMed1999

The limitations of echocardiography in the overall diagnosis of the morphological lesions associated with infective endocarditis: comparison of echocardiographic and surgical findings.

Echocardiography is commonly accepted as the method of choice for the non-invasive diagnosis of vegetations and other lesions associated with infective endocarditis. To assess the accuracy of echocardiography in the overall diagnosis of the morphological cardiac lesions we retrospectively analyzed and compared the preoperative echocardiographic data with the surgical findings of 120 consecutive cases operated for infective endocarditis. Transthoracic echocardiography (TTE) was used in 60 cases (51 with native and 9 with prosthetic valves), both TTE and transesophageal echocardiography (TEE) in 50 (26 with native and 24 with prosthetic valves) and only TEE in 10 patients who underwent emergency surgery. The echocardiographic diagnosis was correct in all the cases, but incomplete in 26 (16 with native and 10 with prosthetic valves). Most of the incomplete diagnoses occurred regarding vegetations, perforations of the valvular leaflets and perivalvular abscesses. There were no differences between aortic or mitral valves (14/66 vs 11/60; p = ns), native or prosthetic (16/79 vs 10/37; p = ns), TTE or TEE (13/60 vs 13/60; p = ns); however, TEE was performed in more complex cases and in severely ill patients. In six of the incomplete diagnoses, echocardiography preceded surgery by one week or more, and in six the mistakes were not confirmed by the reviewer. In conclusion, our study suggests that an echocardiographic diagnosis of endocarditis may be correct but sometimes incomplete. In patients without prosthetic valves who have a technically-adequate transthoracic echocardiogram, transesophageal echocardiography is not indispensable but should be chosen from time to time. However, the patients with endocarditis and no contraindication to the transesophageal procedure should undergo both transesophageal and transthoracic echocardiography before surgery in order to obtain as much and the most definite information possible. An echocardiographic study should be repeated just before any surgical procedures in patients with active endocarditis. Finally, it needs to be emphasized that the training and clinical judgement of the operator performing the study are important elements determining the results of echocardiographic study.

Adult↗
PubMed1997

Dipyridamole thallium-201 imaging very early after uncomplicated acute myocardial infarction in patients treated with thrombolytic therapy.

The aim of this study was to assess the safety and prognostic value of dipyridamole 201T1 imaging very early after acute myocardial infarction in patients treated with thrombolytic therapy. Fifty-two consecutive patients with an uncomplicated clinical course underwent quantitative planar dipyridamole 201T1 imaging 2 5 days after acute myocardial infarction. The patients were followed for 14 +/- 7 months after discharge. No major complications occurred during the test. Of the 30 patients with redistribution, five (16.6%) developed in-hospital unstable angina as against none of the 22 patients without redistribution. During follow-up, a total of live late cardiac events were observed: two deaths and two cases of unstable angina in the group with reversible defects and one reinfarction in the group with fixed defects. The 1-year actuarial probability of being free of cardiac events was, respectively, 66 +/- 10% and 94 +/- 5% in the patients with and without redistribution (P < 0.01). In conclusion, in patients treated with thrombolysis, dipyridamole-201T1 imaging very early after uncomplicated acute myocardial infarction is a feasible and safe test. Patients with fixed defects appear to be at low risk and may be candidates for early discharge; the presence of redistribution identifies a subgroup of patients who may benefit from further careful clinical evaluation.

Adult↗