Effect of flow on the resistance of modelled femoral artery stenoses.

An accurate model of the pressure-flow relationship of a stenosis is necessary for the correct interpretation of haemodynamic measurements. Modelled femoral artery stenoses were tested in vitro and the pressure drop: flow ratio (resistance) was most accurately represented by a fixed component (Rf) combined with a variable component (Rv) that increased linearly with flow (Q) such that Rv = SvQ. For stenoses of 68-94 per cent area, Rf increased from 3.2 to 77.7 milliperipheral resistance units (mPRU), while Sv increased from 0.009 to 0.578 mPRU ml-1 min and Rv was dominant for physiological flow rates. It was concluded that the approximation of a significant stenosis to a fixed resistance is incorrect.