Table 2. Summary of hemodynamic parameters and their implication.
| Parameter | Definition | Physiological implication | Note |
|---|---|---|---|
| Flow velocity or flow rate (m/s) | The distance propagated by blood flow divided by the time it takes to go through this distance | Related to the severity of the stenosis; decreases with age; lower in hypertension patients | Precisely segments the interactive geometrical boundaries of the vessels |
| PWV (m/s) | The speed at which a pulse wave traveled along a vessel; usually several times quicker than the blood flow velocities | A marker of vascular stiffness; mirrors the overall compliance of vessels; assists in the interpretation of specific sites of focal diseases, such as atherosclerotic plaque and aneurysms | Boundary layer analysis of small-scale vascular velocity profile; correlated to temporal resolution |
| WSS (Pa) | Friction and shear stress imposed by tangential liquid and viscosity along blood vessel wall | Demonstrated endothelial function; correlated to vascular disorders, such as arteriosclerosis and the stability of plaque | Depends on the contour of the wall boundary; may be an underrated attribute for several reasons: finite partial -volume effect, low space resolution, digital derivation of the flow distribution |
| KE (mJ) | The energy needed to accelerate a certain number of blood volume from a quiescent state to a certain velocity; the energy existed in the flow of the blood accompany motion | Tracks cardiac function; diastolic pressure; assesses LV and RV dysfunction | Difference in KE should not only be attributed to a decrease in stroke volume |
| TKE (mJ) | A measure of energy loss in disturbed flow; represents the energy transformed into heat because of turbulence flow | Blood flow becomes turbulent in local narrows because of aortic valves stenosis or aortic coarctation; higher TKE with similar flow velocities indicates a more serious stenosis situation | The sensitivity is affected by VENC; mitigated by a multipoint approach with 3 different VENCs per direction |
| Vorticity (s−1) | Local rotation of blood particles; derivative quantity of the velocity field; a measurement of velocity gradients in different spaces can describe the vortex flow | Related to cardiac function, especially diastolic dysfunction; evaluates complicated congenital intracardiac malformations; high vorticity values correlated with a high risk of atherosclerosis | The precise position and appearance of the vortices in the cardiac cycle should be considered; depends on chamber geometry; increased vorticity could result in viscous energy loss |
| Pressure gradient (mmHg) | Differences in pressure between chambers or vessels; related to changes in blood momentum | Evaluates the temporal and spatial distribution of different pressure gradients through a large vascular segment or a cardiac chamber | Avoid issues caused by noise |
| Components of dynamic ventricular flow (%) | Including direct flow, retained inflow, delayed ejection flow, and residual volume | Can detect LV reconstruction and dysfunction | Sensitive to noise and systematic errors |
PWV, pulse wave velocity; WSS, wall shear stress; TKE, turbulent kinetic energy; KE, kinetic energy; VENC, velocity encoding; LV, left ventricular; RV, right ventricular.