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

A systematic evaluation of the accuracy of continuous wave echo Dopple r measurements across prosthetic valve leakages and regurgitant lesion s has not been performed. Continuous echo Doppler velocity measurement s in an in vitro, steady flow model, across the leaks of 12 intact mec hanical prostheses and across six circular nozzles (area, 0.5-20 mm(2) ) at pressure drops between 30 and 105 mm Hg were analyzed and compare d to the velocities predicted by the modified Bernoulli equation. Lase r Doppler anemometry of flow velocities through the nozzles was perfor med in addition. Despite excellent correlation, there was substantial overestimation of ''Bernoulli predicted''-velocities by echo Doppler i n the prosthetic leaks (mean +12.3 +/- 9.4 %; range, 90.3-143.4 %). Al so in nozzles less than or equal to 10 mm(2), but not in those greater than or equal to 20 mm(2), an overestimation of the ''Bernoulli predi cted''-velocities was observed (mean +6.2 +/- 2 %). Laser Doppler anem ometry of flow velocities through the nozzles showed slightly lower va lues than predicted by the Bernoulli equation. This effect apparently is due to transit time effects leading to spectral broadening and shou ld be taken into account when using echo Doppler measurements in very small (< 10 mm(2)) orifices, such as mild to moderate regurgitant lesi ons and prosthetic valve leakage.