Spiral systolic blood flow in the ascending aorta and aortic arch analyzed by echo-dynamography.

Using echo-dynamography, systolic blood flow structure in the ascending aorta and aortic arch was investigated in 10 healthy volunteers. The blood flow structure was analyzed based on the two-dimensional (2D) and 1D velocity vector distributions, changing acceleration of flow direction (CAFD), vorticity distribution, and Doppler pressure distribution. To justify the results obtained in humans, in vitro experiments were done using straight and curved tube models of 20mm diameter. The distribution of the CAFD showed a spiral staircase pattern along the flow axis line. In addition, the changes in the velocity profile in the short-axis direction, 2D distribution of the vorticity, and velocity vector distribution on the aortic cross-section plane, all confirmed the presence of systolic twisted spiral flow rotating clockwise toward the peripheral part of the ascending aorta. The rotation cycle of this spiral flow correlated inversely with the maximum velocity of the aortic flow, so that this cycle was shorter in early systole and longer in late systole. The model experiments showed similar results. The spiral flow seemed to be produced by several factors: (i) anterior shift of the direction of ejected blood flow due to the anterior displacement of the projection of the aorta; (ii) accelerated high pressure flow ejected antero-upward; (iii) inertia resistance at the peripheral boundary of the sinus of Valsalva; and (iv) reflection caused by the concave spherical structure of the inner surface of the basal part of the aorta. Because the main spiral flow axis line nearly coincided with the center line of the aorta, it is concluded that the occurrence of the spiral flow plays an important role in maintaining the blood flow direction passing through the cylindrical curved aortic arch and thus in keeping the most effective ejection as well as in dispersing the shear stress in the aortic wall.