1,721,076 research outputs found
Attuali campi di applicazione, nel settore dell’illuminazione, nei quali l’utilizzo dei LED risulta vantaggioso
No full textCardiovascular reflexes mediated by sympathetic afferent fibers
No full textIn this paper the experimental evidence supporting the hypothesis that excitatory sympathetic reflexes may participate in the tonic control of the cardiovascular system is discussed. Positive feedback pressor sympathetic reflexes can be obtained with physiological distensions of the descending thoracic aorta in conscious dogs with all nerves intact in absence of any pain reaction. These excitatory reflexes interact with supraspinal regulatory mechanisms, inhibitory in nature. A massive excitation of cardiac sympathetic afferents, produced by intracoronary injections of bradykinin, also elicits a pressor reflex, without pain reactions. In the absence of anesthesia and recent surgery, the cardiovascular excitatory reflexes, subserved by sympathetic afferent fibers, can easily prevail. We suggest that negative and positive feedback mechanisms interact continuously to achieve the most adequate neural cardiovascular control
Impact of Fast Interface States on Effective Mobility of Heavily-Doped MOSFET's.
No full textEds G. Baccarini and M. Rudan , Editions Frontieres, France
Granger causality in cardiovascular variability series: comparison between model-based and model-free approaches
No full textA linear model-based (MB) approach for the evaluation of Granger causality is compared to a nonlinear model-free (MF) one. The MB method is based on the identification of the coefficients of a multivariate linear regression via least-squares procedure. The MF technique is grounded on the concept of local prediction and exploits the k-nearest-neighbors approach. Both the methods optimize the multivariate embedding dimension but MF technique is more parsimonious since the number of components taken from each signal can be different. Both methods were applied to the variability series of heart period (HP), systolic arterial pressure (SAP) and respiration (R) recorded during spontaneous and controlled respiration at 15 breaths/minute (SR and RC15) in 19 healthy humans. Both MB and MF methods revealed the increase of HP predictability during RC15 and the unmodified causality from SAP to HP and from R to HP during RC15, thus suggesting that nonlinear methods are not superior to the linear ones in assessing predictability and causality in healthy humans
Effects of sympathetic activation and regular periodic breathing on complexity of heart period variability
No full textSummary Background. Heart rate exhibits different levels of complexity which are probably related to the neural autonomic modulation. Aim of the study. The aim is to analyze the effect of the sympathetic activation and of a regular periodical external input on the complexity of heart period. Methods. Fifteen healthy young subjects were recorded at rest during spontaneous breathing, during head-up tilt, and at rest during controlled breathing at different rates (10, 15, and 20 breaths/min). The minimum of corrected conditional entropy (CCE) was used to measure complexity (the higher the minimum, the larger the complexity). Spectral indexes in low and high frequency (LF and HF) bands were calculated as well. Results. CCE minimum was significantly lower during tilt and controlled respiration at 10 breaths/min compared to rest during spontaneous breathing, while LF/HF ratio was larger during tilt but smaller during controlled respiration at 10 breaths/min. During faster respiratory rates CCE minimum and the LF/HF were unchanged. No significant correlation was detected between the CCE minimum and the mean or variance of the heart period. CCE minimum was correlated with LF/HF ratio only at rest and during tilt. Conclusions. These results indicate that complexity of heart period is not related to its mean or variance, does not depend only on regularity of respiration, and is affected by interventions capable of entraining different regulatory mechanisms and reducing the number of temporal scales involved on heart period regulation
Testing the presence of non stationarities in short heart rate variability series
No full textThe study proposes a test to evaluate stationarity over short beat-to-beat variability series of heart period (about 300 samples). This test checks the steadiness of mean and variance (i.e. a restricted form of weak stationarity). Artificial series, in which changes of the mean and variance are simulated, are utilized to set the analysis parameters and to evaluate the performance of the method. Next, the test is applied to beat-to-beat series variability series of heart period derived from humans at rest, during controlled respiration at different breathing rates (10, 15 and 20 breaths/minute) and during 80° head-up tilt. The application proves the difficulty to find stationary periods in short term recordings of heart period variability and prompts for an assessment of the effect of non stationarities on traditional linear and non linear indexes assuming stationarity as a requirement
Lack of association between prodromes nausea and vomiting and specific electrocardiographic patterns of acute myocardial infarction
No full textWe conducted an observational study on 164 patients consecutively admitted to our coronary care unit in order to evaluate the predictive role of cardiac prodromes nausea and vomiting, in distinguishing a particular electrocardiographic pattern (Q wave versus non-Q wave and localisation) of an acute myocardial infarction. Patients with the prodromes made up 47.0% of all Q wave myocardial infarction and 59.4% in those without Q wave myocardial infarction. Furthermore, patients had nausea and vomiting in 25.0% of all Q wave myocardial infarction and in 31.2% of all non-Q wave infarction. No significant differences were found in the patients who experienced nausea and vomiting in the localisation (anterior versus inferior) of myocardial infarction. Our findings indicate that the cardiac prodromes of nausea and vomiting do not play any particular role in predicting a specific electrocardiographic pattern of acute myocardial infarction
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
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