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Biomedical subjects

J L Vega

Publications and source records attributed to J L Vega.

At least 19 recordsLinked to original sources
PubMed2004

Collisional line shapes for low frequency vibrations of adsorbates on a metal surface.

The dynamics of atoms or molecules adsorbed on a metal surface, and excited by collisions with an atomic beam, are treated within a theory that includes energy dissipation into lattice vibrations by means of a frequency and temperature dependent friction function. The theory provides dynamic structure factors for energy transfer derived from collisional time correlation functions. It describes the relaxation of a vibrationally excited atom or molecule within a model of a damped quantum harmonic oscillator bilinearly coupled to a bath of lattice oscillators. The collisional time correlation function is generalized to include friction effects and is applied to the vibrational relaxation of the frustrated translation mode of Na adsorbed on a Cu(001) surface, CO on Cu(001), and CO on Pt(111), following excitation by collisions with He atoms. Results for the frequency shift and width of line shapes versus surface temperature are in very good agreement with experimental measurements of inelastic He atom scattering. Our interpretation of the experimental results provides insight on the relative role of phonon versus electron-hole relaxation.

Journal Article↗
PubMed2004

Hamiltonian theory for vibrational line shapes of atoms adsorbed on surfaces.

The vibrational motions of atomic adsorbates on surfaces can be probed by helium atom scattering. The experimental observable is the dynamic structure factor, which shows an inelastic peak around the vibrational frequency of the isolated adsorbates known as the frustrated translational or T-mode peak. In this paper we develop a theory for the line shape of this peak, as well as for its temperature-dependent shift and broadening, based on a Hamiltonian equivalent of the generalized Langevin equation. The theory can be used to infer physical parameters of the adatom-surface interaction, such as the friction coefficient, the barrier height to diffusion, and the anharmonicity parameter. Numerical simulations are used to ascertain the range of validity of the theory, which is also generalized to describe multidimensional systems and to include quantum corrections. We compare the theoretical predictions for the shift and broadening with experimental results for the Na/Cu(001) system, showing quantitative agreement within experimental resolution.

Journal Article↗
PubMed2001

[Clinical profile and prognosis of patients with endocarditis and periannular pseudoaneurysms].

INTRODUCTION AND OBJECTIVES: Little information is available on the clinical profile and prognosis of patients with endocarditis and periannular pseudoaneurysms because the presence of pseudoaneurysm itself is considered an indication albeit not an evidence-based indication, for surgery. METHODS: We followed 18 patients (11 males, mean age: 5 +/- 4) with endocarditis and pseudoaneurysm diagnosed by transesophageal echocardiography and/or at surgery over 14 +/- 5 months. RESULTS: Aortic (n = 14; 6 on native valve, 8 on prosthesis) was more frequent than mitral (n = 3; 3 prosthesis) or tricuspid location (n = 1). Auriculoventricular block developed in 6 patients, all with aortic pseudoaneurysm. The most frequently involved microorganisms were staphylococci (n = 5) and streptococci (n = 5). Abscesses were found in 5 patients. Pseudoaneurysm was not considered an indication for surgery. Eleven patients underwent surgery 5 died after surgery (45%), 1 had reinfection and 5 are asymptomatic. The remaining 7 patients received only medical treatment: two died (28%), one developed reinfection and 4 are asymptomatic. The size of the pseudoaneurysm remained stable after 24 months of follow-up in the 4 asymptomatic medically treated patients (maximal diameter: 21 +/- 5 at diagnosis versus 22 +/- 5 at latest follow-up; p = NS). CONCLUSIONS: We conclude that the presence of a pseudoaneurysm identifies a subset of endocarditis patients with a high mortality. Pseudoaneurysms are usually located in an aortic position and around prosthetic material. Medical treatment without surgery should be considered when no other surgical indications exist. Lastly the size of a pseudoaneurysm in medically treated patients does not increase over time

Adult↗
PubMed2000

Successful treatment of vasospastic angina with a coronary stent.

Calcium antagonists are the treatment of choice in vasospasm angina when no stenosis or mild stenosis are present. We present a case in which ergonovine echocardiography showed vasospasm of the right coronary artery despite optimal medical treatment. Stenting of a mild stenosis in that artery successfully controlled vasospasm and a pre-discharge ergonovine echocardiographic test was negative. The patient remains asymptomatic one year after stenting.

Angina Pectoris, Variant↗
PubMed1999

Clinical course, microbiologic profile, and diagnosis of periannular complications in prosthetic valve endocarditis.

Whether periannular extension of prosthetic valve endocarditis (abscesses, pseudoaneurysms, fistulas) is related to the etiologic agent, the clinical course and the prognosis is still unknown. Likewise, transesophageal echocardiographic accuracy in detecting periannular complications in prosthetic recipients remains unsettled. We retrospectively analyzed data from 87 patients with anatomically proven prosthetic valve endocarditis who underwent a transesophageal echocardiographic examination. Periannular complications (30 abscesses, 18 pseudoaneurysms, 8 fistulas; 8 with >1) were found in 46 patients; results were compared with the remaining 41 without complications. Transesophageal echocardiography correctly identified 27 abscesses (90%) and all pseudoaneurysms and fistulas. One diagnosis of pseudoaneurysm by echocardiography was not found at surgery. No statistical differences were found regarding age, sex, type of prosthesis (mechanical vs biologic), and etiologic agent. Periannular complications were more frequent in aortic location (70% vs 20% in mitral position; p <0.001) and in early (within 6 months after surgery) endocarditis (63% vs 38% in late endocarditis; p = 0.04). The same percentage of patients from both groups underwent surgery (98% with and 90% without complications). At discharge, 62% and 67% of patients were alive, respectively. Thus, periannular complications in prosthetic valve endocarditis are more frequent in aortic location and within 6 months after surgery. Neither the type of prosthesis nor the etiologic agent are related to the presence of periannular complications. Short-term prognosis in patients who underwent surgery is not affected by the presence of periannular complications.

Abscess↗
PubMed1999

Levy-nearest-neighbors Bak-Sneppen model.

We study a random neighbor version of the Bak-Sneppen model, where "nearest neighbors" are chosen according to a probability distribution decaying as a power law of the distance from the active site, P(x) approximately x-x(ac)(-omega). All of the exponents characterizing the self-organized critical state of this model depend on the exponent omega. As omega-->1 we recover the usual random nearest-neighbor version of the model. The pattern of results obtained for a range of values of omega is also compatible with the results of simulations of the original BS model in high dimensions. Moreover, our results suggest a critical dimension dc=6 for the Bak-Sneppen model, in contrast with previous claims.

Journal Article↗
PubMed1999

[The prognostic value of dobutamine echocardiography after an uncomplicated acute myocardial infarct].

BACKGROUND AND PURPOSE: The identification of patients at risk for future events after an infarction is mandatory. The aim of this study was to assess the prognostic value of dobutamine stress echocardiography after an uncomplicated myocardial infarction. METHODS: One hundred and twenty five patients (mean age 65 +/- 11 years, males 82%) underwent dobutamine-echo within ten days after an uncomplicated myocardial infarction. Four myocardial responses were identified: a) negative; b) sustained improvement of myocardial contractility; c) initial improvement followed by worsening, and d) worsening at a distance or in the infarcted zone. RESULTS: Mean follow-up was 7.4 +/- 4.6 months. An adverse outcome occurred in 47 patients: non cardiac death in 3, cardiac death in 6, myocardial infarction in 5, angina in 21, congestive heart failure in 2, and in 10 patients revascularization. Cox regression analysis showed that worsening of contractility was the best predictor for adverse events (p < 0.0001, relative risk 2.8; 95% confidence interval: 1.7-4.5). Non-smoking and previous angina were also predictors of adverse events (p = 0.003 and p = 0.04, respectively). Similar results were obtained after excluding the revascularized patients. CONCLUSIONS: Sustained improvement of contractility in the infarcted region is not a predictor of adverse events. Asynergy at a distance or in the infarcted region during dobutamine echocardiography within ten days after an uncomplicated myocardial infarction predicts adverse cardiac events during follow-up. Therefore, dobutamine echocardiography could be used for risk stratification after acute myocardial infarction.

Aged↗
PubMed1997

[Survey of residents on their satisfaction after obtaining a hospital post].

BACKGROUND: To evaluate the degree of satisfaction of the resident physicians in an university hospital by the election of the speciality and the hospital, after the takeover of the workplace and in the course of their period of residence. SUBJECTS AND METHODS: An anonymous questionnaire was distributed to the 164 residents of the hospital to know the concordance between the initial expectations of the residents and the degree of current satisfaction, about the specialty and the chosen hospital. RESULTS: 149 out of 164 residents (90.8%) answered the survey. In what is referring to the elected speciality, 57% (85 residents) expressed to be satisfied or very satisfied by their election; 22% (33 residents) felt indifferent, and 21% (31 residents) were unsatisfied or very unsatisfied. In what concerns to the chosen hospital, 43% (64 residents) were satisfied or very satisfied; 29% (43 residents) indifferent, and 28% (42 residents) were unsatisfied or very unsatisfied. With respect to the degree of satisfaction by the exercise of the profession at the moment of accomplishing the survey, 98% (143/149) of the residents answered, and of these, 30% (43 residents) expressed to be satisfied or very satisfied; 28% (40 residents), indifferent, and 42% (60 residents), unsatisfied or very unsatisfied. In the degree of satisfaction influenced in a statistically significant way the group of speciality chosen (medical, surgical or central services) after the examination and the moment of accomplishing the survey; the number of order of the residents examination; to have or not to have a speciality wished before of the residents examination, and the year of residence underway. CONCLUSIONS: The degree of satisfaction of the resident physicians by the election of the speciality and of the hospital is relatively low. This fact outlines the suitability of the election system of the specialty.

Adult↗
PubMed1997

Right ventricular asynergy during dobutamine-atropine echocardiography.

OBJECTIVES: We sought to analyze right ventricular contractility during dobutamine infusion in patients with right coronary artery disease and to elucidate whether the development of right ventricular asynergy aids in characterizing a right coronary artery stenosis. BACKGROUND: Clinical investigations are emphasizing the importance of right ventricular function in patients with coronary artery disease. Thus, prognosis of patients with inferior myocardial infarction is influenced by right ventricular function. This study describes the echocardiographic and electrocardiographic findings during dobutamine-atropine echocardiography in patients with right coronary artery disease. METHODS: We studied 31 patients with isolated right coronary artery disease and no previous myocardial infarction. Six patients with poor acoustic window were excluded (feasibility 80%). The remaining 25 patients underwent dobutamine-atropine echocardiography. A right coronary artery stenosis located before the origin of the right ventricular branches was considered proximal; otherwise, it was considered distal. RESULTS: Right ventricular asynergy during dobutamine-atropine testing developed in 17 patients (sensitivity 68%); 14 had proximal and 3 had distal right coronary artery disease. The following segments were involved: inferior (n = 17), lateral (n = 5) and outflow tract (n = 1). No patient showed anterior asynergy. All 17 patients had left ventricular asynergy as well. Ischemia-free time was 10.7 +/- 6.2 (mean +/- SD) min for the right ventricle and 8.9 +/- 5.2 min for the left ventricle (p < 0.05). Ischemic ST changes were recorded in 15 patients (in standard leads in 14 and in right precordial leads in 8). All patients with right precordial changes showed ST elevation and had right ventricular asynergy (sensitivity and specificity for right ventricular asynergy 47% and 100%, respectively). A control group of 25 patients with no right coronary artery disease (5 with no disease, 15 with left anterior descending and 5 with left circumflex coronary artery disease) underwent dobutamine echocardiography. Right ventricular asynergy developed in two patients with left anterior descending artery stenosis (specificity 92%); in both, the anterior wall was affected. CONCLUSIONS: Echocardiography during dobutamine infusion is a reliable technique for assessing right ventricular dysfunction in patients with right coronary artery disease. Right ventricular contractility can be assessed during dobutamine echocardiography in selected patients.

Aged↗
PubMed1995

Antibodies to hepatitis C virus: a cross-sectional study in patients attending a trauma unit or admitted to hospital for elective surgery.

OBJECTIVE: To assess the prevalence of hepatitis C virus (HCV) antibodies in patients attending a trauma unit or admitted to hospital for elective surgery, and to identify risk factors for acquiring HCV infection. DESIGN: A cross-sectional study. SETTING: The emergency room of a Department of Orthopaedic Surgery and a hospital for elective (non-digestive) surgery. PATIENTS: A study population of 1824 subjects (mean age 40.1 +/- 18.1 years) and sera from a control group of 4703 blood donors giving their first donation. INTERVENTIONS: Serum samples were screened for HCV antibodies by second-generation enzyme-linked immunosorbent assays and recombinant immunoblot assays. MAIN OUTCOME MEASURES: HCV serostatus and the relationship between anti-HCV-positivity and age, intravenous drug use, tattoos, blood transfusion, a history of hepatitis and exposure to a contact who had had hepatitis. RESULTS: The overall prevalence of anti-HCV antibodies was 2.85% in the study population and 0.5% among blood donors (chi 2 = 64.5; P < 0.0001). Anti-HCV-positivity was more common in men (3.8 versus 1.9%; P < 0.05) and in subjects with history of hepatitis (13.5 versus 2.0%; P < 0.001), exposure to a contact who had had hepatitis (12.5 versus 1.9%; P < 0.001), blood transfusion (7.8 versus 2.3%; P < 0.001), tattoos (36 versus 2.4%; P < 0.001) and intravenous drug use (85.7 versus 1.9%; P < 0.001). However, one third of subjects had no risk factors for HCV infection. The logistic regression analysis confirmed a statistically significant association (P < 0.05) between anti-HCV-positivity and intravenous drug use, tattoos, blood transfusion, a history of hepatitis and exposure to a contact who had had hepatitis. CONCLUSIONS: These results show almost a five-fold higher prevalence of anti-HCV among patients attending a trauma unit or admitted to hospital for elective surgery than among blood donors.

Adolescent↗
PubMed1994

Intrafamilial spread of hepatitis C virus infection.

We assessed the prevalence of antibodies to hepatitis C virus (anti-HCV) among 401 household contacts of 161 persons with chronic hepatitis C (index patients). None of the index patients had antibodies against HIV. The overall prevalence of anti-HCV was 3.2% (2.5% in the absence of previous parenteral exposure). Sexual partners had a seroprevalence of 4.7% and non-sexual contacts, 2.5%. Among non-sexual contacts, parents showed the highest rate (4.2%). The mean duration of exposure in the anti-HCV-positive sexual partners was 17.3 +/- 8.5 years, vis-à-vis 9.2 +/- 7.4 years in the anti-HCV-negative sexual partners. We conclude that there is little risk of HCV infection through household contact. Although the form of transmission is not well identified, the duration of sexual activity suggests that the time needed to become infected is long.

Adult↗
PubMed1993

Open mitral commissurotomy: fourteen- to eighteen-year follow-up clinical study.

From May 1974 to December 1978, 159 patients with mitral stenosis underwent open mitral commissurotomy at our institution. Follow-up data were complete in 96.8%, with a mean follow-up of 13.7 years (range, 14 to 18 years). Preoperatively, most patients (n = 94) were in functional class III or IV. Valve calcification was found in 18 patients (11.3%), left atrial thrombosis was found in 21 (13.2%), and the subvalvular apparatus was affected in 105 (66%). When a residual insufficiency was detected during the operation, a mitral annuloplasty was performed (n = 43). There was one hospital death (0.6%) and 15 late deaths (9.5%). Actuarial survival at 15-year and 18-year follow-up is 89.4% +/- 3% and 75.2% +/- 10.8%. Fifteen patients (9.7%) had a thromboembolic episode 1 to 189 months after operation (mean, 104.3 months). Eleven patients (7%) required reoperation 3 to 183 months after operation (mean, 110.1 months). Freedom from reoperation at 18-year follow-up was 91.9% +/- 2.7%. Event-free actuarial survival at 15-year and 18-year follow-up was 73.4% +/- 4.2% and 54.3% +/- 10.5%. Most patients (n = 131) are in class I or II. Open mitral commissurotomy represents a safe surgical alternative for treating mitral stenosis, allowing a complete removal of atrial thrombosis if present. This long-term follow-up clinical study encourages us to persist in this successful surgical repair of mitral stenosis.

Actuarial Analysis↗