BIOENGINEERING FLUID DYNAMICS

Introduction to Course aims and contents. Definition of fluid and main fundamental physical quantities. Absolute and relative pressure. Rheology: Newtonian and non-Newtonian fluids, blood rheology. Hydrostatics: fundamental law for incompressible fluid, pressure force on plane and curved surfaces. Application to prosthetic heart valves. Kinematics: velocity and acceleration, unsteady, steady and uniform flow, flow rate, mass conservation principle, average velocity. Dynamics: Reynolds and Womersley numbers; laminar and turbulent regimes; Poiseuille flow in a pipe; flow resistance in laminar flows: series and parallel pipes; application to human systemic circulation; Womersley flow in rigid pipes: analytical solution, analysis of pulsatile effects, application to human circulation; one-dimensional flows and total head definition; total head conservation equation; flow energy continuous and local dissipations; momentum conservation equation; pump head and power in hydraulic circuits. Heart valve stenosis: definition and etiology; fluid dynamic model of the flow through a nozzle, vena contracta and contraction coefficient; transvalvular pressure drop in stenotic valves: maximum drop and recovery effect; net pressure drop: quasi-steady model; intertial effects on transvalvular flow: partial and complete net pressure drop models. Hemodynamics of prosthetic heart valves, in vitro tests of valve systolic and diastolic performance, European standards; fundamentals of local flow dynamics in proximity of a prosthesis. Heart valve insufficiency: definition and etiology; Laplace law; fluid dynamic indexes of insufficiency severity; potential flows, absorbing point flow; PISA method for insufficiency graduation. Vascular stenosis: definition, fluid dynamic model, evaluation of transtenotic pressure drop. In vitro pulsatile mock loop at HER Laboratory: description and use in laboratory sessions.