Internal avalanches in a pile of superconducting vortices

Using an array of miniature Hall probes, we monitored the spatiotemporal variation of the internal magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. We found that a sizable fraction of the increase in the local vortex population occurs in abrupt jumps. The size distribution of these avalanches presents a power-law collapse on a limited range. In contrast, at low temperatures and low fields, huge avalanches with a typical size occur and the system does not display a well-defined macroscopic critical current.Comment: 5 pages including 5 figure

Flux-line entanglement as the mechanism of melting transition in high-temperature superconductors in a magnetic field

The mechanism of the flux-line-lattice (FLL) melting in anisotropic high-T_c superconductors in ${\bf B}\parallel {\bf \hat{c}}$ is clarified by Monte Carlo simulations of the 3D frustrated XY model. The percentage of entangled flux lines abruptly changes at the melting temperature T_m, while no sharp change can be found in the number and size distribution of vortex loops around T_m. Therefore, the origin of this melting transition is the entanglement of flux lines. Scaling behaviors of physical quantities are consistent with the above mechanism of the FLL melting. The Lindemann number is also evaluated without any phenomenological arguments.Comment: 10 pages, 5 Postscript figures, RevTeX; changed content and figures, Phys. Rev. B Rapid Commun. in pres

Patient Management of Hypertensive Subjects without and with Diabetes Mellitus Type II

The description of blood pressure (BP) curve has evolved to include several noninvasively determined parameters, such as aortic stiffness, BP variability, wave reflections, and pulse pressure amplification. These techniques are likely to improve the efficacy of assessing pulsatile arterial hemodynamics and changes in arterial stiffness. The goal for future antihypertensive treatments should not only reduce steady BP, but also control pulsatile pressure and modify the stiffness gradient between central and peripheral arteries, which is frequently elevated. These changes have the potential to reduce residual cardiovascular risk but also to define drug strategies adapted to the needs of individual hypertensive subjects. © 2016 Elsevier Inc

Arterial stiffness and central hemodynamics in treated hypertensive subjects according to brachial blood pressure classification

BACKGROUND: International recommendations have classified brachial blood pressure (BP) in subgroups enabling better cardiovascular risk stratification. Central BP is an independent predictor of cardiovascular risk, differing from brachial BP through the predominant influence of arterial stiffness and wave reflections. Central BP has never been studied in relation to international guidelines for brachial BP classification. METHODS: In 580 chronically treated hypertensive subjects we measured: carotid-femoral pulse wave velocity (PWV), carotid artery augmentation index (AI) and carotid blood pressures, using applanation tonometry and pulse wave analysis, and using brachial BP for carotid pressure wave calibration. RESULTS: For each given brachial value, carotid systolic blood pressure (SBP) and PP were significantly lower than the corresponding brachial SBP and PP. This pressure amplification was significantly lower in the 'optimal' and 'normal' BP ranges (6.8-7.4 mmHg) than in the higher BP ranges (10.1-11.3 mmHg), mainly depending on heart rate (HR) and PWV levels. PWV gradually increased as a function of brachial BP classification and was a significant predictor of this classification independently of age, drug treatment, atherosclerotic lesions and even mean BP. Finally, PWV was a highly sensitive marker of the effective BP control throughout all decades of age. CONCLUSION: Under chronic antihypertensive therapy, central BP does not strictly parallel the corresponding brachial BP classification, depending on differences in aortic stiffness and HR. Whether aortic PWV might predict the brachial BP classification and/or the presence of effective BP control, as suggested in this study, needs further confirmation. © 2008 Lippincott Williams & Wilkins, Inc

Arterial stiffness in hypertension and function of large arteries

BACKGROUND Arterial stiffness-typically assessed from non-invasive measurement of pulse wave velocity along a straight portion of the vascular tree between the right common carotid and femoral arteries-is a reliable predictor of cardiovascular risk in patients with essential hypertension. METHODS We reviewed how carotid-femoral pulse wave velocity increases with age and is significantly higher in hypertension (than in age- and gender-matched individuals without hypertension), particularly when hypertension is associated with diabetes mellitus. RESULTS From the elastic aorta to the muscular peripheral arteries of young healthy individuals, there is a gradual but significant increase in stiffness, with a specific gradient. This moderates the transmission of pulsatile pressure towards the periphery, thus protecting the microcirculatory network. The heterogeneity of stiffness between the elastic and muscular arteries causes the gradient to disappear or be inversed with aging, particularly in long-standing hypertension. CONCLUSIONS In hypertension therefore, pulsatile pressure transmission to the microcirculation is augmented, increasing the potential risk of damage to the brain, the heart, and the kidney. Furthermore, elevated pulse pressure exacerbates end-stage renal disease, particularly in older hypertensive individuals. With increasing age, the elastin content of vessel walls declines throughout the arterial network, and arterial stiffening increases further due to the presence of rigid wall material such as collagen, but also fibronectin, proteoglycans, and vascular calcification. Certain genes, mainly related to angiotensin and/or aldosterone, affect this aging process and contribute to the extent of arterial stiffness, which can independently affect both forward and reflected pressure waves. © American Journal of Hypertension, Ltd 2020. All rights reserved

Added value of aortic pulse wave velocity index for the detection of coronary heart disease by elective coronary angiography

Background: Non-invasive tests leading to elective coronary angiography (CAG) have low diagnostic yield for obstructive coronary heart disease (CHD). Aortic stiffness, an independent predictor of CHD events can be easily measured by pulse wave velocity (PWV). We aimed at retrospectively evaluating the diagnostic accuracy PWV index to detect CHD in consecutive patients with suspected CHD that underwent CAG. Method: In population of 86 healthy patients with available PWV data, a theoretical PWV was derived. In different population of 62 individuals who underwent CAG for suspected CHD, PWV index was calculated as index [(measured PWV–theoretical PWV)/theoretical PWV]. Logistic regression and comparisons between ROC curves were used to add value of CAG indication performance of PWV index. Results: Out of 62, seventeen patients presented obstructive CHD and 22 patients had non-obstructive CHD. PWV index and severity of CHD were positively correlated (p < 0.0001). After applying several models that included classical CHD predictor, the higher performance to detect abnormal CAG was obtained with the combined classifier PWV index/carotid plaque with 87% sensitivity, 93% specificity, 0.92 accuracy and 0.31 threshold. To detect obstructive CAG, individual classifier PWV index presents 94% sensitivity, 91% specificity, 0.95 accuracy and 0.46 threshold. Conclusion: PWV index is individualized approach that optimizes CHD diagnostic strategies and thus might be clinically useful for reducing the rate of unnecessary invasive CAG. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group

Increased Pulse Pressure Amplification in Treated Hypertensive Subjects With Metabolic Syndrome

Background: Brachial pulse pressure (PP) is physiologically higher than central PP. This PP amplification, which protects the heart from increased afterload, is related to the progressive increase of arterial stiffness along the vascular tree and subsequent changes in pressure wave reflections. The PP amplification increases with high heart rate (HR), which is observed in subjects with metabolic syndrome (MS). The objective of this study was to investigate whether PP amplification is affected by MS and is related to cardiovascular (CV) risk. Methods: In 613 subjects treated for hypertension (41% with MS) pulse wave analysis was used to investigate carotid blood pressure (BP), pressure wave reflections from carotid augmentation index (AI), and arterial stiffness from aortic pulse wave velocity (PWV). The CV risk was estimated from standard Framingham equations. Results: Pulse pressure amplification, HR, and PWV, but not AI, were increased in subjects with MS compared to control subjects without MS with the same age, gender, and mean arterial pressure. The difference in PP amplification between the two groups disappeared after adjustment for both HR and PWV. The AI was the main predictor of PP amplification, representing 28% and 19% of its total variance in subjects without and with MS, respectively. The CV risk for coronary, but not for cerebral, mortality was related to PP amplification. Conclusions: Although PWV is increased in treated hypertensive subjects with MS, compared to control, PP amplification is increased due to the effect of increased HR and attenuated pressure wave reflections. The observed relation of increased PP amplification with organ-specific CV risk needs further investigation. © 2007 American Journal of Hypertension, Ltd