Blood hammer phenomenon in human aorta: Theory and modeling

This paper contains the results of computing of a blood pressure and a flow speed in a human aorta in a diastolic phase of a heart cycle. The model is based on the one-dimensional flow approach. The blood hammer effect means abrupt increasing of pressure in a blood vessels due to the sharp changes in flow speed. The closing of aortic valve at the proto-diastole phase causes such blood hammer. We consider an aorta as a simple cylindrical conduit with elastic walls. The aortic valve and the bifurcation were located in the opposite ends of the conduit. The analysis of possible types of blood hammer effect in the "conduit-blood" system was performed. The lifelike initial and boundary conditions for the problem were proposed. We found a strong peak of pressure during the first third of diastole at the normal closure of the aortic valve. We observed the minor fluctuations of pressure in the later part of diastole too. Blood flow speed also has minor oscillations during the diastole. Such results are typical under the complete blood hammer effect condition. An abnormal long valve closure causes an incomplete blood hammer effect. In that case the calculated oscillations of the flow speed had higher intensity without strong pressure peak. The Fourier spectra of pressure fluctuations are located in the range of 16-87 Hz, that is nearby to known frequencies of the second heart sound produced by aortic valve.