Structure and adaptation of arteries to pulsatile flow: The case of the ascending aorta

Purpose: The objectives are: (i) assess the development of the impedance of some arteries during the first decades of life; (ii) determine the influence of pulse rate in arterial impedance; (iii) compare the structure of some arterial segments with optimized structures with respect to blood flow; and (iv) explain the elongation of the ascending aorta throughout life in healthy subjects. Methods: A model of the arterial network previously developed by the authors, together with data of lengths, diameters, and distensibilities of arterial segments reported in the literature were used. The impedances of the aorta and carotid artery were calculated based on that model. Similarly, the impedances of various arteries corresponding to heart rates of 65 bpm and 120 bpm were calculated. Values observed in arterial segments were compared with the respective optimal values from the viewpoint of hemodynamic performance. This allowed drawing conclusions on the arterial segments that might be critical with regard to hemodynamics. Results: It was found that in healthy people impedances of the aorta and the carotid artery decrease markedly with age especially during body growth. It was also found that impedances of the main arteries do not significantly change with heart rate, even if sharp changes in arterial distensibility are observed. With respect to optimal flow performance, it was found that scaling between diameters of branching arteries is generally close to optimality, while the corresponding length scaling is far from optimality. It was also found that the ascending aorta and aortic arch are among those arterial segments whose lengths are much smaller than the optimum values. An explanation is offered for the age associated elongation of the aorta in healthy people. Conclusions: In healthy subjects, the human arterial system continues to optimize its performance at least until the age of 60.