Haemodynamics: flow, pressure and resistance
Neil Herring, David J. Paterson in Levick's Introduction to Cardiovascular Physiology, 2018
Venous pressure depends very much on the position of the vein relative to heart level, because of gravity (Figure 8.2). Moreover, since the vein wall is thin and collapsible, the crosssectional profile and volume change markedly with pressure (Figure 8.22). This results in large changes in peripheral venous blood volume with changes in body posture. When venous pressure is below zero (atmospheric pressure), as in a hand above heart level, the vein collapses into a dumb-bell shaped profile, and flow is confined to the narrow marginal channels. At a transmural pressure of +1 mmHg, the vein assumes a narrow elliptical cross section. As pressure rises towards 10 mmHg, the elliptical profile becomes progressively rounder. These changes in profile enable peripheral veins to accommodate a large volume of blood in response to relatively small changes in pressure. The maximum distensibility (compliance) occurs at ~4 mmHg and is ~100 mL/mmHg for the human systemic venous system. This is some 50 times greater than arterial compliance.
High-altitude protection
Nicholas Green, Steven Gaydos, Hutchison Ewan, Edward Nicol in Handbook of Aviation and Space Medicine, 2019
Cardiovascular effects: Central venous pressure increased, impeding venous return and cardiac output.Blood pools in extremities and reduces circulating blood volume.May lead to loss of consciousness (pressure breathing syncope) if pressure breathing is maintained for more than a few minutes.Lower limb counter-pressure applied using anti-G trousers will limit pooling of blood in capacitance vessels of legs helping to maintain cardiac output.
Hygiene
Barbara Smith, Linda Field in Nursing Care, 2019
The use of compression stockings, or surgical stockings, reduces the incidence of deep vein thrombosis, which can be caused by immobility or restricted mobility. They are recommended to be used after surgery and patients are advised to wear them as much as possible. One of the main reasons people are advised to wear these is to prevent deep vein thrombosis and pulmonary embolism from occurring. Compression stockings are also prescribed as part of the treatment of venous ulcers, leg oedema and low blood pressure. Middle-aged and older people undergoing surgery or those on prolonged bedrest are usually prescribed compression stockings. The stockings are used as part of a patient’s treatment and are intended for use for a specified amount of time. Relatively fit patients may wear the stockings for only a few hours, but other patients may be advised to wear them for several days or weeks (NHS Choices, 2018; National Institute for Health and Care Excellence, 2018b).
Mechanistic links between systemic hypertension and open angle glaucoma
Published in Clinical and Experimental Optometry, 2022
Ying-kun Cui, Li Pan, Tim Lam, Chun-yi Wen, Chi-wai Do
In contrast, the blood supply to an organ is generally regulated by the perfusion pressure. The perfusion pressure is defined as the difference between arterial and venous pressure. The higher the perfusion pressure, the greater the blood flow to the organ and the less likely the organ becomes ischaemic. In most cases, the pressure outside the vein is considered to be atmospheric,39 as shown in Figure 1A. Nevertheless, under certain circumstances, the tissue outside the vein could exert pressure on the vein. For example, whilst standing, there is blood pooling in the veins of the lower limbs due to gravity. To facilitate blood return to the heart, the skeletal muscle contracts, enhancing blood circulation in the presence of one-way venous valves.40
Catecholamine-induced reverse takotsubo cardiomyopathy
Published in Baylor University Medical Center Proceedings, 2019
Shivani Bhat, Hashim Gazi, Victor Mwansa, Lovely Chhabra
A repeat examination was remarkable for tachycardia (heart rate 116 beats/min), hypotension (blood pressure 80/46 mm Hg), diaphoresis, and tachypnea (respiratory rate 21 breaths/min). Central venous pressure was 10 mm Hg, and mean arterial pressure was 68 mm Hg. Laboratory results showed elevated aspartate and alanine aminotransferases and a normal coagulation profile. The patient’s serial troponin levels increased from <0.01 ng/L to 4.04 ng/L in 5 hours. A transthoracic echocardiogram showed severe left ventricular systolic dysfunction (ejection fraction of 20%) and mid to basal ballooning with preserved apical contractility (Figure 2). Antithrombotic therapy was not administered due to ongoing hemoptysis and thus supportive therapy along with steroids was continued. Unenhanced computerized tomography of the chest, abdomen, and pelvis was remarkable for bilateral ground-glass opacities in the upper pulmonary lobes and dense opacities in the lower pulmonary lobes.
Mathematical modeling of the Fontan blood circulation supported with pediatric ventricular assist device
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Ekaterina Rubtsova, Aleksandr Markov, Sergey Selishchev, Jamshid H. Karimov, Dmitry Telyshev
The Fontan circulation has significant shortcomings regarding normal circulation. First, it is an increased pressure in the venous section. Due to absence of the pulmonary ventricle, blood goes directly from the systemic veins to the pulmonary artery; as a result, accumulating reservoirs disappear from the system. Pressure in the systemic veins and in the pulmonary artery is equalized. The venous pressure becomes abnormally high, the systemic veins are stretched and blood begins to stagnate. At the same time, the pressure in pulmonary arteries is not high enough. In addition, with exclusion of the pulmonary ventricle from the circulation, one of the system’s natural pumps disappears. As a result, venous return to the systemic ventricle falls, which, according to the Frank-Starling mechanism, causes a decrease in a stroke volume (SV), and so blood flow rate in the system decreases. The Fontan circulation creates suboptimal circulatory condition and alters function of the cardiovascular system. Nevertheless, when adequately managed and post-procedure guided patients can lead a normal lifestyle.
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