Comparison of Numerical Simulations and Ultrasonography Measurements of the Blood Flow through Vertebral Arteries

Vertebral arteries are a system of two blood vessels through which blood is carried to the rear region of the brain. This region of the human body has to be very well supplied with blood. Blood is delivered to the brain through carotid arteries as well. Due to their position and shape, vertebral arteries are a special kind of blood vessels. They have their origin at a various distance from the aortic ostium, can branch off at different angles, and have various lengths, inner diameters and spatial shapes. The above-mentioned variations are connected with inter-patient differences in the human anatomy. In the upper part of vertebral arteries, there is a marked arch curvature, owing to which turning the head is not followed by obliteration of these vessels. Contrary to other arteries, vertebral arteries join at their ends to form one vessel, a comparatively large basilar artery. This junction can be characterized by a varied geometry as well. For individual geometrical configurations of the vertebral artery system, there are also differences in the diameter of the left and right artery. All the abovementioned differences result from a unique individual anatomical structure and do not follow from any pathology (Daseler & Anson 1959; Jozwik & Obidowski 2008; Jozwik & Obidowski 2010). Some symptoms occurring in patients may suggest that the cause of an ailment lies in an incorrect blood supply to the rear region of the brain, and thus in an incorrect blood flow through vertebral arteries. The direct cause of such a phenomenon can result from arterial occlusion. The ultrasonography is employed to check the flow correctness. It is rather difficult to conduct this imaging procedure, but if it is performed by an experienced specialist, then the results obtained can be considered reliable. It happens, however, that the measured values of the maximum and minimum velocity in the left and right artery, which characterize the blood flow, differ significantly. Hence, the diagnosis of arteriosclerosis in these vessels is well based. It can be an indication for a surgical procedure (Mysior 2006). A significantly large percentage of cases diagnosed in such a way are not related to changes in the artery structure, and thus surgery would be irrelevant. If a structure and a shape of vertebral arteries, their individual variations are considered, then differences in the blood flow and a lack of relation between these differences and artery diameters can result from flow phenomena only.