CURRENT STATUS OF FLOW CONVERGENCE FOR CLINICAL-APPLICATIONS - IS IT A LEANING TOWER OF PISA

Spatial appreciation of flow velocities using Doppler color how mappin g has led to quantitative evaluation of the zone of flow convergence p roximal to a regurgitant orifice. Based on the theory of conservation of mass, geometric analysis, assuming a series of hemispheric shells o f increasing velocity as flow converges on the orifice-the so-called p roximal isovelocity surface area (PISA) effect-has yielded methods pro mising noninvasive measurement of regurgitant flow rate. When combined with conventional Doppler ultrasound to measure orifice velocity, reg urgitant orifice area, the major predictor of regurgitation severity, can also be estimated. The high temporal resolution of color M-mode ca n be used to evaluate dynamic changes in orifice area, as seen in many pathologic conditions, which enhances our appreciation of the pathoph ysiology of regurgitation, The PISA methodology is potentially applica ble to any restrictive orifice and has gained some credibility in the quantitative evaluation of other valve pathology, particularly mitral and tricuspid regurgitation, and in congenital heart disease, Although the current limitations of PISA estimates of regurgitation have tempe red its introduction as a valuable clinical tool, considerable efforts in in vitro and clinical research have improved our understanding of the problems and limitations of the PISA methodology and provided a fi rm platform for continuing research into the accurate quantitative ass essment of valve regurgitation and the expanding clinical role of quan titative Doppler color how mapping.