OVERESTIMATION OF FLOW VELOCITY THROUGH LEAKS IN MECHANICAL VALVE PROSTHESES AND THROUGH SMALL ORIFICES BY CONTINUOUS-WAVE DOPPLER

The reliability of continuous-wave Doppler flow velocity measurements through small regurgitant lesions, such as in prosthetic leakage, has not been systematically analyzed. To evaluate the accuracy of continuo us-wave Doppler in prosthetic valve leakage and small orifices in an i n vitro, steady-flow model-flow velocities through the leaks of twelve intact mechanical prostheses and through six circular nozzles (area 0 .5 to 20 mm(2)) were measured at pressure drops between 30 and 105 mm Hg. These results were compared with those predicted by the modified B ernoulli equation. Laser Doppler anemometry of flow velocities through the nozzles was also performed. Despite high correlation, there was s ubstantial overestimation of Bernoulli predicted velocities by echo Do ppler in the prosthetic leaks (mean +12.3% +/- 9.4%; range 90.3% to 14 3.4%). In the nozzles less than or equal to 10 mm(2), but not in the l argest (20 mm(2)) nozzle, there was also overestimation of the Bernoul li predicted velocities (mean +6.2% +/- 2%). Laser Doppler anemometry of flow velocities through the nozzles showed slightly lower values th an predicted by the Bernoulli equation. Thus, continuous-wave echo Dop pler overestimates flow velocities through small orifices. This appare ntly is, at least in part, due to transit time effects and should be t aken into account when using echo Doppler in small (<10 mm(2)) orifice s, such as in mild to moderate regurgitant lesions and prosthetic valv e leakage.