124,732 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Enhanced reflex response to baroreceptor deactivation in subjects with tilt-induced syncope
No full textOBJECTIVES: We sought to evaluate whether changes in resting baroreflex control of heart rate are a distinctive feature of healthy subjects with a history of syncope prone to a positive tilt-test response.
BACKGROUND: The mechanisms involved in the pathogenesis of vasovagal syncope (VVS) are still poorly understood; in particular, the contribution of arterial baroreflex control of heart rate is matter of discussion.
METHODS: A passive tilt-table test was performed in 312 consecutive, otherwise healthy subjects (age 36 +/- 15 years) with unexplained syncope and 100 control subjects. At baseline, spontaneous baroreflex sensitivity (BRS; ms/mm Hg) and the baroreflex effectiveness index (BEI) were assessed using the sequence method.
RESULTS:
The study population showed normal baroreflex function. Tilt-induced VVS in 94 subjects who were younger than both the tilt-negative and control subjects (30 +/- 14, 38 +/- 15, and 37 +/- 14 years, respectively; p = 0.00005) showed greater BRS (17.4 +/- 9.8, 13.2 +/- 7.9, and 12.8 +/- 8.2 ms/mm Hg, respectively; p = 0.0001), but had a similar BEI (0.59 +/- 0.18, 0.56 +/- 0.19, and 0.58 +/- 0.2, respectively; p = NS). On Cox multivariate analysis, the occurrence of VVS during tilt was inversely related to age (hazard ratio 0.97; p = 0.0004) and directly related to the BRS slope of sequences, implying a baroreceptor deactivation (hazard ratio 1.05; p = 0.02), but not of sequences characterized by arterial baroreceptor stimulation.
CONCLUSIONS: Subjects with tilt-induced VVS showed greater resting BRS but had a normal BEI. The enhanced reflex tachycardic response to arterial baroreceptor deactivation at rest may represent a characteristic feature of subjects prone to tilt-induced VVS
Cardiac resynchronization therapy tailored by echocardiographic evaluation of ventricular asynchrony
No full textOBJECTIVES: The value of interventricular and intraventricular echocardiographic asynchrony parameters in predicting reverse remodeling after cardiac resynchronization therapy (CRT) was investigated.
BACKGROUND: Cardiac resynchronization therapy has been suggested as a promising strategy in patients with severe heart failure and left bundle branch block (LBBB), but the entity of benefit is variable and no criteria are yet available to predict which patients will gain.
METHODS: Interventricular and intraventricular mechanical asynchrony was evaluated in 20 patients (8 men and 12 women, 63 +/- 10 years) with advanced heart failure caused by ischemic (n = 4) or nonischemic dilated cardiomyopathy (n = 16) and LBBB (QRS duration of at least 140 ms) using echocardiographic Doppler measurements. Left ventricular end-diastolic volume index (LVEDVI) and left ventricular end-systolic volume index (LVESVI) were calculated before and one month after CRT. Patients with a LVESVI reduction of at least 15% were considered as responders.
RESULTS: Cardiac resynchronization therapy significantly improved ventricular volumes (LVEDVI from 150 +/- 53 ml/m(2) to 119 +/- 37 ml/m(2), p < 0.001; LVESVI from 116 +/- 43 ml/m(2) to 85 +/- 29 ml/m(2), p < 0.0001). At baseline, the responders had a significantly longer septal-to-posterior wall motion delay (SPWMD), a left intraventricular asynchrony parameter; only QRS duration and SPWMD significantly correlated with a reduction in LVESVI (r = -0.54, p < 0.05 and r = -0.70, p < 0.001, respectively), but the accuracy of SPWMD in predicting reverse remodeling was greater than that of the QRS duration (85% vs. 65%).
CONCLUSIONS: In patients with advanced heart failure and LBBB, baseline SPWMD is a strong predictor of the occurrence of reverse remodeling after CRT, thus suggesting its usefulness in identifying patients likely to benefit from biventricular pacing
Short term reverse remodeling predicts long term haemodynamic improvement after cardiac resynchronization therapy
No full textPrognostic significance of bioelectrical evaluation of body composition in chronic heart failure
No full textEchocardiographic characteristics of unaffected relatives of patients with familial and non-familial idiopathic dilated cardiomyopathy
No full textEfeito da virose do enrolamento da folha na composição química do vinho Cabernet Franc.
No full textForam comparados vinhos da cultivar Cabernet Franc (Vitis vinifera L.) provenientes de plantas sadias e atacadas pela virose do enrolamento da folha. O experimento foi realizado em Bento Gonçalves, RS, durante as safras de 1986, 1987, 1988, 1990 e 1991. O vinhedo foi instalado em 1982, sendo as videiras enxertadas sobre o porta-enxerto '101-14' e dispostas em 10 fileiras divididas por plantas sadias e plantas doentes. Os vinhos foram elaborados pelo processo de microvinificação a partir de 20kg de uva colhidos de maneira homogênea em toda a área. Os principais efeitos da virose na composição dos vinhos foram a diminuição do teor alcoólico, pH, cinzas, intensidade de cor e polifenóis totais. A virose também diminuiu o teor de acetato de etila e a soma de álcoois superiores. Quanto aos minerais, a virose determinou uma diminuição do K e Rb e um aumento nos teores de Ca e Mg
Shortened head-up tilting test guided by systolic pressure reductions in neurocardiogenic syncope
No full textBACKGROUND: Asymptomatic reductions in arterial pressure have been reported to occur before the onset of tilt-induced syncope. We investigated the predictive value of these reductions for a positive tilt result.
METHODS AND RESULTS: In a first study, 238 consecutive healthy subjects with unexplained syncope underwent a passive tilt table test. Finger systolic arterial pressure (SAP) recordings made it possible to calculate how many of the beat-to-beat SAP values during the first 15 minutes of tilt were lower than the lowest value recorded at baseline. Neurocardiogenic syncope was diagnosed in 73 subjects; 28 fainted after 15 minutes of tilt and experienced more pressure reductions than did the subjects with a negative test (328+/-400 versus 119+/-284; P<0.01). More than 14 SAP reductions during the first 15 minutes of tilt allowed us to predict a positive test with 93% sensitivity, 58% specificity, and positive and negative predictive values of 28% and 98%, respectively. In a second prospective study (80 consecutive subjects), the online analysis of this criterion by visually inspecting a Finapres monitor showed 80% sensitivity, 85% specificity, and positive and negative predictive values of 57% and 94%.
CONCLUSIONS: In healthy subjects with unexplained syncope, the evaluation of SAP reductions during the first 15 minutes of tilt is a marker of systolic pressure instability preceding syncope and constitutes a simple and good predictor of tilt outcome that could be used to guide test duration
Two-dimensional echocardiographic evaluation of aneurysms of the descending thoracic aorta.
No full textTo determine the ability of two-dimensional echocardiography (2-D echo) to detect aneurysms and dissections of the descending thoracic aorta (DTA), we studied 15 patients, five with proved DTA dissections (group A) and 10 with proved aneurysms without dissection (group B), using 2-D echo in three recording positions: precordial, suprasternal and a modified apical. The DTA was visualized in 14 of 15 patients (93%); in each patient in group A, an intimal flap was recognized (in two patients only by the apical approach and in one patient by all approaches). The DTA was visualized in nine of 10 patients in group B; in each patient, the internal dimension of the DTA was enlarged (25-43 mm/m2). In one group B patient, aortic dissection was erroneously suspected because spurious echoes were present in the lumen; in another patient, 2-D echo failed to demonstrate a thrombotic stratification in the enlarged lumen. We conclude that 2-D echo using all available approaches appears to be a reliable technique for evaluating dissections and aneurysms of the DTA.</jats:p
- …
