Nature of Flow of a Liquid
Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos in McDonald's Blood Flow in Arteries, 2022
One of the most recent invasive methods for measuring coronary blood flow in humans and calculating the dimensionless variable coronary flow reserve (CFR) is with the intracoronary Doppler flow wire (Doucette et al., 1992; Nichols et al., 2015). In a large majority of experimental and clinical studies, CFR is measured and used as a flow-derived index of stenosis severity (Feldman et al., 1979b) or microvascular function/dysfunction (Kothawade and Bairey Merz, 2011; Sara et al., 2015). In clinical studies the most frequently used pressure-derived index to assess stenosis severity, the fractional flow reserve (FFR) (Pijls et al., 1996; Koo, 2014; Coughlan et al., 2017) has long been considered the gold standard for this purpose, despite the fact that the FFR assesses solely epicardial stenosis severity and aims to estimate coronary flow impairment in the coronary circulation. CFR reflects abnormalities in both the epicardial coronary artery and the coronary microvasculature but is less established than FFR. It is now recognized that both tools may provide insight into the pathophysiological substrate of ischemic heart disease and that particularly combined FFR and CFR measurements have the potential to provide a comprehensive insight into the multilevel involvement of ischemic heart disease. The review by Stegehuis et al. (2018) discusses the diagnostic and prognostic characteristics, as well as future implications of the combined assessment of FFR and CFR pressure and flow measurements as parameters for inducible ischemic heart disease (IHD) (see Chapter 14). Since an error is introduced by the intravascular Doppler flow wire on peak flow velocity measurements (Chodzynski et al., 2016), some investigators have derived and used CFR obtained using noninvasive positron emission tomography (PET) or other methods including CMR with high-fidelity intracoronary arterial micromanometry to measure coronary blood flow (Hwang et al., 2017). It is frequently overlooked that FFR is a coronary artery pressure-derived index of coronary blood flow impairment and may be inferior to the coronary artery flow-derived index (van de Hoef et al., 2015). Also, CFR can give information about both macro- and microvascular circulations, while FFR gives information of only the macrocirculation and on the severity of coronary stenosis. This subject is of intense interest in the assessment of patients considered for urgent stenting (see Chapter 14). Hemodynamic factors that tend to affect the magnitude of blood flow disturbances include velocity, viscosity and density of the blood. For example, an increased blood velocity or a reduction of blood viscosity would increase the intensity of turbulence. The pulsatile nature of blood flow may also lead to flow instability. The effects of unsteady flow on the transition from laminar to turbulent flow have been evaluated by several investigators (Hale et al., 1955; Parker, 1977), but an understanding of the stability of unsteady flow, even in tube flow, is still poor (Parker, 1977; Chahed et al., 1991). Lesions that produce a partial obstruction to flow or an irregularity of the vessel wall would augment flow disturbances. The normal aortic and pulmonary valves also cause flow disturbances because the valvular leaflets act as natural projections into the stream of flow (Sabbah and Stein, 1979). Fluttering of the free margin of the leaflets may also contribute to the disturbances. Several anatomic and hematologic factors affect the character of blood flow in the cardiovascular system. Anatomic factors that tend to diminish disturbances of flow at branches of vessels include branch-to-trunk-area ratios less than 1.0 (Walburn et al., 1979) and acute angles of branching (Roach, 1977b). Arterial tapering (Walburn and Stein, 1981) and vessel distensibility (Stein et al., 1980) also diminish disturbances. Hematological factors that minimize disturbances include a normal concentration of RBCs and deformability of the RBCs (Stein et al., 1975; Sabbah and Stein, 1976).
Motion of blood in the venous system—novel findings
Dinker B. Rai in Mechanical Function of the Atrial Diastole, 2022
In certain disease conditions there are subtle changes that take place in hemodynamics continuously in the human body and that may not reflect any change in the venous or arterial pressures. In such situations physicians are completely at a loss to understand the ongoing events of patients. CVID is one such situation in the venous system. A patient in a state of shock or in cardiac arrest in which no arterial pressures can be recorded are classic examples of inadequacies of dependency on pressure monitoring of the arterial system. Arterial pressure is dependent upon positive pressure measurement and applicable only to the arterial limb of the circulatory system. In the venous limb circulation is in collapsible tubes and operated by negative pressure. The circulatory system consists of the heart and arterial, capillary, and venous limbs and they operate as one system. A common parameter has to be found and used to understand the hemodynamics of the whole system. This study is an attempt to find an alternative parameter applicable to the whole system as circulation of blood is the sign of life and its main functional feature. Maintaining a particular average velocity in the whole system is a necessity for the “milieu interior” of the body and is dependent upon a coordinated function of all four limbs. Understanding this aspect and getting a grip on the measurement of velocity as a parameter to know the changes in hemodynamics can help in the diagnosis, treatment, and prognosis of the various diseases of cardiac, arterial, capillary, and venous origin. It also may be an important parameter of the future. This study is based on the direct measurement of velocity of the blood, which may prove to be a better parameter in the future and open new doors in this direction.
Infertility Diagnosis and Treatment
Sujoy K. Guba in Bioengineering in Reproductive Medicine, 2020
Hemodynamics is closely related to tissue oxygenation and so a study of the tissue oxygen levels gives valuable information not only about the circulation but also regarding tissue metabolism. By drawing blood, the blood oxygenation level may be obtained by in vitro analysis but the data does not correctly reflect the tissue oxygenation. The latter parameter can be better obtained by inserting into the tissue needle type Polarographie electrodes. When diffusion into a microelectrode of a particular molecular species is the rate-determining step in an electrochemical reaction, the electrical current-voltage relationship of the electrode gives the concentration of the molecular species. This is the basic principle of polarography. Oxygen sensing Polarographie probe comprises of an electrolytic cell with gold, platinum or copper cathode separated from a silver anode by an insulating material. Electrical continuity between the anode and the cathode is established by electrolytic gel. Tissue oxygen permeates into the gel across a thin gas permeable membrane. A potential of about 0.8 V is applied between the anode and cathode. Current flowing is proportional to the amount of oxygen which is reduced at the cathode with the formation of silver oxide at the anode. The oxygen reduced is proportional to the oxygen diffusing in, which in turn bears a direct relationship to the tissue oxygen concentration.
The role of exercise hemodynamics in assessing patients with chronic heart failure and left ventricular assist devices
Published in Expert Review of Medical Devices, 2019
Aaron Koshy, Thomas Green, Anet Toms, Sophie Cassidy, Stephan Schueler, Djordje Jakovljevic, Guy A MacGowan
ABSTRACT Introduction: Chronic heart failure is characterized by reduced exercise capacity. Invasive exercise hemodynamics are not routinely performed unless patients undergo transplant or left ventricular assist devices (LVAD) assessment, though now with readily available noninvasive devices, exercise hemodynamics are easily obtained. Our contention is that this is a valuable opportunity to acquire a more accurate measure of cardiac status in heart failure. Exercise hemodynamic measures such as cardiac power output can be carried out cheaply and effectively. Recent studies have highlighted the added value of exercise hemodynamics in prognostication of heart failure, and their role in assessing myocardial recovery in LVADs. Areas covered: In this review, we explore the literature available on Medline until 2019 focusing on resting and exercise hemodynamics alongside the methods of assessment (invasive and noninvasive) in heart failure with reduced ejection fraction and patients with implanted LVADs. Expert opinion: Hemodynamics measured both at rest and exercise are expected to play a significant role in the work up of transplant and LVAD patients. Furthermore, there is the potential to utilize noninvasive assessment in a complimentary fashion to support patient selection and improve the monitoring of response to treatment across the full cohort of heart failure patients.
Mechanical circulatory support devices: methods to optimize hemodynamics during use
Published in Expert Review of Medical Devices, 2017
Ben Bow Chung, Gabriel Sayer, Nir Uriel
ABSTRACT Introduction: Mechanical circulatory support (MCS) is an increasingly utilized mode of therapy in the management of advanced heart failure, both as bridge to heart transplantation and destination therapy. As MCS becomes more prevalent, it is ever more important to understand the complex hemodynamics of these devices, as well as the strategies for hemodynamic optimization. Areas covered: This review provides an overview of hemodynamics in the normal human heart and the failing heart. We discuss the various short-term mechanical circulatory support devices and their hemodynamic consequences. We will then discuss the differences between left ventricular assist devices, and the impact of these differences on hemodynamics. We will describe the strategies for hemodynamic optimization using echocardiographic and invasive ramp studies. Finally, we will discuss the impact of speed changes with exercise and discuss future directions for advancements in MCS therapies. Expert commentary: We advocate for a deeper understanding of the hemodynamics underpinning MCS devices. We also recommend the more widespread use of ramp studies for speed optimization, which have been well validated across a number of different left ventricular assist device types.
Hemodynamic impact of cerebral aneurysm endovascular treatment devices: coils and flow diverters
Published in Expert Review of Medical Devices, 2014
Leonid Goubergrits, Jens Schaller, Ulrich Kertzscher, Thies Woelken, Moritz Ringelstein, Andreas Spuler
Coils and flow diverters or stents are devices successfully used to treat cerebral aneurysms. Treatment aims to reduce intra-aneurysmal flow, thereby separating the aneurysmal sac from the blood circulation. The focus and this manuscript combining literature review and our original research is an analysis of changes in aneurysmal hemodynamics caused by endovascular treatment devices. Knowledge of post-treatment hemodynamics is a path to successful long-term treatment. Summarizing findings on hemodynamic impact of treatment devices, we conclude: coiling and stenting do not affect post-treatment intra-aneurysmal pressure, but significantly alter aneurysmal hemodynamics through flow reduction and a change in flow structure. The impact of treatment devices on aneurysmal flow depends, however, on a set of parameters including device geometry, course of placement, parent vessel and aneurysm geometry.