Hydrodynamics of Aortic Blood Flow

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Abstract
A thermistor was used to record the temperature at regular intervals across the aortic diameter of dogs during the continuous infusion of cold indicator solution at various upstream locations. The results showed that the indicator mixed across the greater part of the diameter of the aorta in the ascending portion and proximal half of the arch but maintained a more streamlined pattern in the distal portion of the arch and descending thoracic aorta. These observations were confirmed by cineangiography. When two thermistors were located in different positions in the aortic root, and when cold saline was injected suddenly in their vicinity, the temperatures recorded by the two thermistors equalized immediately following the onset of systole. Sound waves also were detected during the systolic interval in the ascending but not in the descending aorta. These findings are consistent with the presence of disturbed, but not necessarily turbulent flow in the ascending aorta; and with predominantly streamlined, but not necessarily completely laminar flow in the descending portion. The factors producing disturbed flow in the aortic root and the transition of flow to a more streamlined pattern in the descending portion are discussed in hydrodynamic terms. It is postulated that during systole the blood ejected into the aorta separates from a slower moving boundary layer near the walls and at the edges of the valve cusps. This separation produces disturbed flow and mixing in the entering jet. While the thin layer adjacent to the walls as well as stagnant areas behind the valves do not fully mix with the central stream, they represent a relatively small proportion of the total aortic blood flow. Additional mixing is produced by the prominent backflow in early diastole and by the branchings of the coronary and brachiocephalic arteries.

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