The importance of taper proximal and distal to Y-bifurcations in arteries.

Changes in luminal cross-sectional area from human cerebral arteries, porcine renal arteries and human aorto-iliac junctions were found to be both significant and gradual. Proximal to the flow divider, luminal cross-sectional area increased by 10.8 +/- 5.7% for the human aorto-iliac and 94.5 +/- 5.0% for the cerebrals. Distal to the flow divider, the summed luminal area of the two daughter branches decreased by 36.4 +/- 4.0% for the cerebrals and 15.9 +/- 5.2% for the renals. Taper was defined as the ratio of the area change to the vessel length over which the change occurred. Positive taper corresponded to a narrowing in cross-section while negative taper represented an expansion in luminal area. All taper values were significantly different from zero (t-test, P < 0.05). Arterial ellipticity was examined from the ratio of lateral and antero-posterior diameters of cross-sections in the parent trunk from human aorto-iliacs and porcine renal arteries. We have shown that ellipticity begins one parent-tube diameter from the apex of the bifurcation in both samples studied. These large changes in luminal area and taper, which have been overlooked previously, have significant implications for the propagation of flow and pressure waves as well as for flow patterns.