About this Research Topic
Breakthroughs in Physics and Engineering have helped us to advance the understanding of human physiology, and have made it more quantitative for the purpose of medical assessment. Herein, we are providing a quantitative format of Cardiovascular Physiology and its Medical Assessment, based on Physics and Engineering perspective. This consists of the following processes:
1. Bioelectrical Process in the Heart, in which electrical activity is initiated in the SA node, and the impulse spreads throughout the atria via specialized internodal pathways, to the atrial myocardial contractile cells and the atrioventricular node. From the AV node the electrical impulse spreads through the bundle of His, bundle branches, and Purkinje fibers to myocardial contractile cells in the ventricles, causing ventricular contractility for initiating LV ejection. This bioelectrical activity is characterized by ECG, and its signal processing enables cardiac diagnostics.
2. Contraction Process of the Heart Myocardium, causing the development of stress in the left ventricular wall by which the intra-ventricular pressure rises adequately to be able to promote LV ejection. To quantify this process, the LV can be modelled as an ellipsoidal chamber, and its wall stress described by a cardiac contractility index formulated in terms of the maximum rate of change of LV systolic wall stress (σ) normalized to intra-LV pressure (P), as d(σ/P)/dtmax or dσ*/dtmax , where σ* = σ /P, in terms of the maximal flow rate from the ventricle (cardiac output) normalized to myocardial volume (or mass). This index is easily measured non-invasively, from echocardiography or magnetic resonance imaging. It can be employed by us to detect heart failure.
3. Intra-Ventricular Blood Flow Analysis, by means of the governing equations of fluid flow, by which we can determine the flow patterns of velocity and pressure distribution in the LV, and thereby show how adequate pressure is generated to open the aortic valve. For this purpose, we can use the vector flow mapping (VFM) technique to generate flow velocity vector fields, by post-processing the colour Doppler echo images. In systolic flow patterns, it can be seen that LV contraction produces recirculating flow patterns and directed flow towards the aortic valve. However, in heart failure subjects, the abnormal recirculating flow patterns, formed during isovolumic contraction, are seen to remain until the end of the systolic phase, whereby the peak flow rate out of LV is reduced.
4. Blood Flow into the Aorta and Pulse Wave Propagation, by which we can determine the pulse wave propagation velocity in terms of the aortic constitutive property to characterize arteriosclerosis. We can also carry out analysis of blood flow into the aorta, in terms of aortic flow rate & pressure and aortic elasticity & flow resistance, to yield the differential equation for pressure in terms of the aortic inflow. Then by carrying out the Doppler Echocardiographic determination of aortic inflow, we can solve the differential equation for aortic pressure, and non-invasively obtain this very useful aortic pressure-time profile.
5. Blood Flow in the Coronary Vasculature, causing myocardial perfusion and contractility. For this purpose, the blood flow in curved coronary and obstructed arteries can be carried out by CFD modeling of the Navier-Stokes equations to determine flow patterns, wall shear stress and wall pressure gradient in imaging-based coronary arterial models. By doing CFD analysis of coronary artery models constructed from CT imaging, we can determine the wall shear stress and wall pressure gradient at critical sites of a coronary artery, based on which we can assess its being prone to atherosclerosis and plaque formation.
6. Cardiac Perfusion Analysis to compute Intra-Myocardial Blood Flow velocity and pressure patterns. For this purpose, we can carry out myocardial perfusion SPECT imaging, prescribe the myocardial conductivity, and then do intra-myocardial flow analysis to determine the blood pressure and velocity distributions in myocardial segments. In this way, we can quantify decreased blood flow in ischemic areas of the myocardium.
7. Patient-Specific Simulation of Coronary Bypass Grafting, to alleviate the effects of diminished coronary blood flow and myocardial perfusion. This enables us to determine the ideal method and geometry of distal anastomosis of the coronary bypass graft with the stenosed coronary artery.
This Research Topic encourages submissions across all these domains of cardiovascular physiology, to provide a comprehensive characterization of cardiovascular physiology, which can be employed as a learning resource and in courses in both engineering and medical schools at universities.
Keywords: cardiovascular disease, medical imaging, signal processing, medical informatics, hemodynamics
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