Variability of flow patterns in the normal carotid bifurcation.

One hundred and nine carotid bifurcations of 56 healthy subjects were examined by means of a Doppler color flow imaging (DCFI) system. Flow separation was found in 102 (93.6%) bifurcations. Different patterns of the spatial and temporal distribution of flow separation zones could be distinguished: separated flow was either restricted to the proximal external (5.9%), the internal (34.3%) or both carotid arteries (40.2%). In 11.8% zones of secondary flow extended from the internal into the external carotid artery around the flow divider, and in 7.8% the distribution was diffuse. The maximum of reversed flow signals occurred immediately after the systolic peak (73%) but lasted for highly variable intervals throughout the cardiac cycle. This demonstration of the unexpectedly various spatial and temporal patterns of secondary flow phenomena contrasts with concepts from in vitro flow studies. This information about conditions in vivo must be considered in investigations of early atherosclerosis in the human carotid bifurcation.