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Chapter 19 Blood Flow Measurement
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
A limb or organ will swell if the venous return is occluded, due to the inflow of arterial blood (see figure 19.12). Venous flow can be occluded by using a pressure cuff that is inflated well above venous pressure, but below systolic arterial pressure. The volume change will give a measure of the blood volume of the limb or organ, and the rate of change of volume gives a measure of the arterial blood flow. This is the basis of venous occlusion plethysmography. It avoids the problem of volume changes resulting from the net difference between arterial and venous flows by reducing the venous flow to zero. However, the technique does have to make some assumptions. The assumptions underlying the technique are that occlusion of the venous return does not affect the arterial supply, that the resulting increase in venous pressure does not reduce the arterial flow rate, that the swelling of the tissue in question is equal to the increase in the blood volume and that the venous occlusion is only applied for a limited period.
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
During prolonged orthostatic stress, additional adjustments are mediated by the humoral limb of the neuroendocrine system. In response to decreases in effective blood volume, increases in activity of the vasopressin and renin-angiotensin-aldosterone systems occur that further augment sympathetic nerve activity and preserve effective blood volume (Rowell, 1993). Other non-neural mechanisms that assist with the maintenance of blood pressure during orthostatic stress are the skeletal muscle pump (such as during muscular contraction) and the thoracoabdominal respiratory pump (for example, the lowering and raising of the ribcage and diaphragm). These mechanisms serve to increase venous return to the heart and attenuate pooling in the dependent veins.
Cardiovascular System:
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
The larger veins in the legs lie close to the skeletal muscle beds and can be compressed with skeletal muscle contraction. This compression pushes the venous blood forward toward the heart (and the valves prevent the backflow when the muscles relax). This is referred to as the skeletal muscle pump, and it is a factor in encouraging venous return. Other factors that aid in venous return include the respiratory suction (the negative pressure created on inspiration) and the diastolic suction (created during isovolumic relaxation); these help create a pressure gradient between the veins and the right atrium.
Eccentric exercise improves myocardial oxygen supply/demand balance with decelerating aortic diastolic pressure decay: The acute and chronic studies
Published in European Journal of Sport Science, 2023
Kaname Tagawa, Song-Gyu Ra, Toru Yoshikawa, Seiji Maeda
Hashimoto and Ito (2017) demonstrated that increased aortic diastolic pressure decay modulates the relationship between increased aortic stiffness and decreased SEVR in patients diagnosed with hypertension. Aortic diastolic pressure decay explains the relationship between changes in aortic stiffness and SEVR following RE in young men (Tagawa et al., 2019). In these young men, it was observed that ECC bicep curls decelerated aortic decay without change in its stiffness (as assessed with aortic PWV). Although aortic stiffness may not be involved in the deceleration of aortic decay, an improved aortic decay may involve the Valsalva maneuver. Although the pumping action of the muscle causes an increase in venous return (Laughlin, Korthuis, Duncker, & Bache, 2011), the Valsalva maneuver decreases it due to an elevated intrathoracic pressure (Little, Barr, & Crawford, 1985). An elevated intrathoracic pressure is 3.4-fold higher during CON than ECC exercise (Lentini, McKelvie, McCartney, Tomlinson, & MacDougall, 1993). Therefore, favourable muscle pumping action and intrathoracic pressure during ECC exercise may improve venous return as compared with CON exercise. This phenomenon may lead to decelerated aortic diastolic pressure decay.
Characterization of the structural configuration and tensile properties of medical bandages
Published in The Journal of The Textile Institute, 2022
Yasamin Haririan, Azita Asayesh
Bandages can be classified based on their function to light support bandages, conforming bandages, orthopedic bandages, and compression bandages. Light support bandages, which are also called short or minimal stretch bandages, are used to prevent the formation of oedema and give support in the management of mild sprains and strains. Conforming bandage are types of elastic bandages that conforms well to body contours and permits free movement of limbs and joints. Orthopedic bandages are used under plaster casts to provide padding and prevent discomfort (Horrocks & Anand, 2000). Compression bandages are generally applied to reduce edema and facilitate venous return in limbs with varying degrees of venous incompetence. Compression bandages can be subdivided into four groups according to the levels of sub-bandage pressure that they are required to deliver: light compression bandage, moderate compression bandage, high compression bandage, and extra high compression bandage. The pressure exerted by the compression bandage to the limb is determined by the Laplace equation (Equation (1)), in which the applied pressure by the bandages is directly proportional to the tension and number of layers being applied, but inversely proportional to the circumference of the limb and the width of the bandage (Anand et al., 2010). where P: sub-bandage pressure (mmHg),
Monitoring calf circumference: changes during prolonged constrained sitting
Published in Ergonomics, 2022
Laura Rigby, Mona Frey, Kara-lyn Alexander, Diana De Carvalho
Many aspects of sitting may contribute to cardiovascular disease risk. These include lack of movement (which negatively impacts efficient pumping of blood back to the heart) and flexion points at the hips and knees (which can mechanically restrict venous return). Uninterrupted leg bending for 3 hours has been shown to result in reduced popliteal artery blood flow and mean shear rate in a lab-based study involving 12 young healthy participants (Walsh et al. 2017). Additionally, a study requiring participants to sit for 3 hours without moving showed a decrease in shear stress and superficial femoral artery flow-mediated dilation (FMD) (Thosar et al. 2015). A decrease in FMD can reduce the elasticity of the artery walls and impact blood flow. Increasing arterial wall stiffness can increase blood pressure and chances of developing cardiovascular disease. Chester, Rys, and Konz (2002) also found that sitting increased hydrostatic pressure and resulted in poor blood flow and circulation. Poor venous return can cause fluid to filter out of the vasculature and into tissue spaces, resulting in swelling and is measurable as an increase in calf circumference (Vena et al. 2017). Fluid accumulation in the lower limbs can have detrimental implications for the cardiovascular health of individuals, thus justifying the monitoring of calf circumference during sitting.