1,720,998 research outputs found
Mechanisms of coronary flow reserve impairment in human hypertension - An integrated approach by transthoracic and transesophageal echocardiography
No full textThe purpose of this study was to investigate the different mechanisms responsible for an impairment of coronary vasodilator capacity in hypertensive subjects by an integrated echocardiographic approach, including transesophageal Doppler echocardiography, which allows noninvasive monitoring of coronary flow velocity in the left anterior descending artery during pharmacological vasodilation. The study population consisted of 17 healthy control subjects and 33 hypertensive subjects: 10 without hypertrophy, 16 with mild to moderate hypertrophy, and 7 with severe left ventricular hypertrophy. Mean systolic and diastolic flow velocities were monitored basally (together with indexes of myocardial oxygen demand, such as heart rate, myocardial inotropism, and left Ventricular wall stress) and during infusion of low-dose (0.56 mg/kg per 4 minutes) and high-dose (0.84 mg/kg per 9 minutes) dipyridamole. Coronary reserve was assessed as the ratio of mean diastolic velocity after high-dose dipyridamole and basal diastolic velocity, and minimum coronary resistance as the ratio of diastolic blood pressure and diastolic velocity after high-dose dipyridamole. Compared with the control group, in all hypertensive groups, coronary reserve was similarly decreased (3.54+/-0.84 versus 2.59+/-0.42, 2.29+/-0.46, and 2.43+/-0.71; P<.01) and minimum resistance increased (0.56+/-0.15 versus 0.75+/-0.31, 0.75+/-0.19, and 0.78+/-0.21 mm Hg . s(-1). cm(-1); P=NS). These results confirm that coronary reserve in hypertensive individuals is reduced even before the occurrence of left ventricular hypertrophy. The reduction in coronary reserve depends on both an increase in resting coronary flow and an impairment in maximal vasodilator capacity. An increase in resting flow is dependent on higher heart rate and wall stress in hypertensive subjects without ventricular hypertrophy and on increased myocardial mass in hypertensive subjects with hypertrophy. Hypertensive subjects with ventricular hypertrophy also demonstrated a significantly blunted response to low-dose dipyridamole
Transesophageal echocardiography in myocardial ischemia: a review.
No full textThis article reviews established as well as emerging fields in the application of transesophageal echocardiography (TEE) in the investigation of myocardial ischemia. TEE already has a well defined and established role in stress echocardiography in patients with poor transthoracic acoustic window, and in the detection of intraoperative myocardial ischemia in cardiac and noncardiac surgery. The evaluation of right ventricular ischemia and infarction and the assessment of coronary flow reserve (CFR) are relatively new fields in the application of TEE and the potential of this technique has not yet been fully evaluated. The evidence collected and reviewed in this article is still preliminary but it presupposes a significant role of TEE in the diagnosis and pathophysiological assessment of myocardial ischemia
Cerebral Blood Flow Response to Nifedipine and Captoril in Hypertensive Patients: a Transcranial Doppler Study
No full textEchocardiographic Evaluation of Neoplastic Infiltration of the Heart and Great Vessels: Preliminary Experience with Panoramic and Omniplane Probes
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Hypertension and Left Ventricular Hypertrophy Further Impair Utilization of the Reduced Coronary Reserve in Patients with Coronary artery Stenosis
No full textLeft ventricular hypertrophy (LVH) predisposes to an increased infarct size after coronary occlusion in dog. Aim of the study was to investigate the impact of the coexistence of LVH secondary to hypertension and coronary stenosis on the coronary vasodilator capacity in man. Coronary flow velocity in left anterior descending artery (LAD) was monitored by Transesophageal-Doppler at baseline and during low- and high-dose of iv. Dipyridamole (0.56mg/Kg/4min followed after 2min by 0.28mg/Kg/2min) in 56 patients, divided as follows: 19 normal controls (N Group), 21 pts with hypertension, LVH and no CAD (LVH Group), and 16 pts with moderate LAD artery stenosis (≤ 75%) [10 without LVH (LAD Group) and 6 with LVH secondary to hypertension (LAD + LVH Group)]. All pts had Dipyridamole Echo test negative for left ventricular asynergy. Blood pressure and left ventricular mass were similar in N vs LAD pts, and in LVH vs LAD + LVH. Mean total coronary flow velocity was measured from Doppler recordings. Coronary reserve was computed as the ratio of high-dose Dipyridamole to Basal flow velocity. Minimum coronary resistance and the percent of coronary reserve recruited after low-dose Dipyridamole were also computed.ResultsBaseline coronary flow velocity was 29±6 cm/sec in N, and significantly higher in LVH and CAD (39±11 and 41±11, respectively, p<0.01). Coronary flow velocity after high-dose Dipyridamole was 92±18 in N, and significantly lower only in LAD + LVH (68±16, p<0.05). Coronary reserve was 3.3±0.7 in N, and significantly reduced in all pts subgroups (2.4±0.4, 2.2±0.6, 2.3±0.4 in LVH, LAD, LAD + LVH; P<0.01 vs N). Percent of coronary reserve recruited after low-dose Dipyridamole was 94±8% in N, 91±11% in LAD, and lower in LVH (79±11%, P<0.01 vs N) and in LAD + LVH (69±10%, P<0.05 vs LVH). Compared to N, minimum coronary resistance was significantly higher in LVH (p<0.05) and LAD + LVH (p<0.01) (0.94±0.2 vs 1.20±0.3 and 1.40±0.4 mmHg/ml/min, respectively); it was also higher in LAD + LVH than in LAD alone (1.07±0.2 mmHg/ml/min, p<0.05).ConclusionsCoronary reserve is similarly reduced in pts with LVH secondary to hypertension, LAD stenosis alone, or LVH + LAD stenosis. Coexistence of hypertensive LVH with LAD stenosis is associated. compared to LAD stenosis alone, with significantly higher minimum coronary resistance and a hindered utilization of the reduced coronary reserve
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