Potential limitations of center-line pulsed Doppler recordings: an in vitro flow visualization study

In this study an in vitro model that permits visualization of the flow velocity profile has been used to determine if duplex pulsed Doppler recordings made with a small sample volume in the center line of the vessel can determine the severity of a stenosis in the 38% to 75% range of cross-sectional area reduction. Because most Doppler instruments measure the maximum peak frequency and the extent of spectral broadening, observations in the flow model included changes in the center-line maximum velocity and the location and intensity of flow disturbances. The results showed that center-line measurements of maximum velocity (equivalent to peak Doppler frequency) were directly related to the severity of the stenosis as long as the recordings were made from within the throat to about 1.5 to 3 tube diameters downstream, depending on the shape of the stenosis. However, flow disturbances (equivalent to spectral broadening) did not always occur in the center line of the vessel. Stenoses greater than 50% area reduction produced turbulence across the entire vessel in the region 4.5 to 7.5 diameters downstream. The turbulent period started just before peak systole and extended to just less than half the pulse cycle. In the more proximal zone a forward flow jet was present in the central part of the vessel, and reverse flow was present in the outer region. The interfacial layer between these two regions is subjected to high shear rates that resulted in the formation of waves and vortices.(ABSTRACT TRUNCATED AT 250 WORDS)