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Aortic Valve Endothelium Mechanobiology
Published in Juhyun Lee, Sharon Gerecht, Hanjoong Jo, Tzung Hsiai, Modern Mechanobiology, 2021
Rachel L. E. Adams, Craig A. Simmons
The fluid mechanics of flowing blood, referred to as hemodynamics, fluctuates in magnitude and velocity depending on cardiac output and local vessel geometry. At the cellular level, the endothelium is subjected to laminar blood flow, of which the tangential component of the frictional force is called wall shear stress (WSS). Shear stress in the aortic valve cannot be directly measured; rather, it is calculated from known local parameters, such as velocity, viscosity, and geometry. The aortic valve experiences different hemodynamics throughout the cardiac cycle, and the leaflets are exposed to different stresses on their opposite sides; as a result, shear stress values are temporally and spatially dynamic and are consequently challenging to calculate.
Syncope: Physiology, Pathophysiology and Aeromedical Implications
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
David A. Low, Christopher J. Mathias
Syncope (or fainting) is defined as a transient loss of postural tone and/or consciousness due to transient global cerebral hypoperfusion (Moya et al., 2009). The regulation of blood pressure and thus maintenance of cerebral blood flow within normal limits are critical in preserving adequate cerebral oxygenation and ensuring consciousness (van Lieshout et al., 2003). Neural and non-neural mechanisms must ensure effective and rapid return of blood to the heart and continued delivery to the brain, particularly in the upright posture, where the anatomical positions of the brain and the heart and the hydrostatic gradient imposed by gravitational stress result in about 70 per cent of the body’s blood volume being located below the heart (Rowell, 1993). A precipitous decrease in blood pressure may lead to inadequate cerebral perfusion, potentially causing reduced physical and/or mental capacity and syncope. Moreover, a syncopal episode may lead to injury through loss of postural tone and to seizures as a result of cerebral hypoxia. Furthermore, if the syncopal attack and the cerebral hypoperfusion continue to be unresolved, irreversible damage can occur. The cardiovascular system has to monitor and regulate blood pressure continuously through the autonomic modulation of the heart and circulation that plays a key role in determining and integrating haemodynamic adjustments.
Pulsatile flow of thixotropic blood in artery under external body acceleration
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Louiza Cheffar, Abdelhakim Benslimane, Djamel Sadaoui, Adel Benchabane, Karim Bekkour
Hemodynamics is an area of science concerned with the dynamics of blood flow and explains the physical laws that govern the flow of blood in the blood vessels through which the flow occurs. Simulation of blood flow in the arterial network system will provide a better understanding of the physiology of human body. Hence, detailed knowledge of blood flow is a fundamental key concept in the understanding of cardiovascular system and in the detection of arterial diseases. However, the effects of thixotropy in terms of the viscosity ratio μr, external acceleration characterized by the parameter Ag, the pressure ratio e and the frequency fb on the flow variables are investigated. The corresponding flow variables namely: velocity and wall shear stress have been analyzed and discussed.
Impact of sedentarism due to the COVID-19 home confinement on neuromuscular, cardiovascular and metabolic health: Physiological and pathophysiological implications and recommendations for physical and nutritional countermeasures
Published in European Journal of Sport Science, 2021
Marco Narici, Giuseppe De Vito, Martino Franchi, Antonio Paoli, Tatiana Moro, Giuseppe Marcolin, Bruno Grassi, Giovanni Baldassarre, Lucrezia Zuccarelli, Gianni Biolo, Filippo Giorgio di Girolamo, Nicola Fiotti, Flemming Dela, Paul Greenhaff, Constantinos Maganaris
During exercise, sheer stress and other hemodynamic stimuli induce positive effects on the peripheral circulation, favouring vasodilation, proliferation of blood vessels and an anti-atherogenic phenotype. Inactivity inevitably goes in the opposite direction. According to Boyle et al. (2013) a reduction of physical activity to <5000 steps/day for only a few days impairs flow-mediated vasodilation. Preliminary data from our group suggest that 10 days of bed rest induces, in healthy young subjects, an impaired microvascular function, as shown by a blunted blood flow increase during passive leg movement of one leg (an index of nitric oxide [NO]-mediated vasodilation [Gifford & Richardson, 2017]) (Zuccarelli et al., 2020), and by a less pronounced reactive microvascular hyperaemia following a transient ischaemia, in association with signs of impaired NO metabolism (Porcelli et al., 2020).