Physiological flow impedance as a fluid mechanical field variable

The concept of impedance for biological flows (respiration, circulation, etc.) was originally introduced to relate pressure and flow rate in a lumped-parameter framework. Such an approach enables the pressure to be calculated from the flow rate (or vice-versa) at discrete locations with no information about the flow between these points. Another restriction is that the impedance relations are generally based on fluid-flow models in long tubes and the end effects are neglected. The authors have developed an alternative approach by solving the equations of motion in geometries and under conditions relevant to different sections of the respiratory system. Thus, they have obtained field descriptions which provide analytical expressions for pressure and flow rate as functions of space and time. From these expressions, the authors synthesize a field description for impedance.<>