Lessons from in vitro models of small, irregular, multiple and tunnel-like stenoses relevant to clinical stenoses of valves and small vessels.

This review examines data on the accuracy of the simplified Bernoulli equation for quantitation of pressure drops across small, irregular, multiple and tunnel-like stenoses. This information is drawn from in vitro models of such cardiovascular stenoses and explores the limits of this simplification as they affect accuracy in special situations. Within the physiologic range, discrete small and irregular stenoses present no problems for the measurement of pressure drops using the simplified Bernoulli equation. Multiple side by side orifices of different dimension also give reasonable data using this approach. Tunnel-like stenoses of very small diameter and finite length produce underestimation of the true pressure drop through the stenosis when the simplified Bernouli equation is used. This underestimation is primarily due to neglect of the energy consumed by viscous friction in this situation. These considerations are especially pertinent to the problem of measuring pressure gradients across coronary vessels to assess their clinical significance as well as the adequacy of angioplasty and other intravascular interventional techniques. Because this area needs further exploration, some discussion of in vitro models as such as included.