Submitted on June 12, 2006
Accepted on February 6, 2007
Development of systemic arterial mechanical properties from infancy to adulthood interpreted by four-element windkessel models
Roberto Burattini1* and Paola Oriana Di Salvia2
1 Department of Electromagnetics and Bioengineering, Polytechnic University of Marche, Ancona, Italy; Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, Washington, United States
2 Department of Electromagnetics and Bioengineering, Polytechnic University of Marche, Ancona, Italy
* To whom correspondence should be addressed. E-mail: r.burattini{at}univpm.it.
Aortic impedance data of infants, children and adults (age range 0.8 to 54 yr), previously reported by others, were interpreted by means of three alternative four-element windkessel models: W4P, W4S and IVW. The W4P and W4S, are derived from the three-element windkessel (W3) by connecting an inertance, L, in parallel or in series, respectively, with the aortic characteristic resistance, Rc. In the IVW, L is connected in series with a viscoelastic windkessel (VW). The W4S and IVW (same input impedance) fitted the data best. The W4S, however, suffers from the assumption that Rc is part of total peripheral resistance, Rp. The IVW model offers a new paradigm for interpretation of resistive properties in terms of viscous (Rd) properties of vessel wall motion, distinguished from Rp. Results indicated that rapid reduction of Rd/Rp during early development is functional to modulation of decay time constant, 
d, of pressure in diastole, such that normalization over heart period (d/T) is independent of body size. Estimates of C vs. age were fitted by a bell-shaped curve with a maximum at 30 yr. With BW factored out by normalization, the C/BW data scattered about a bell-shaped curve centred at 66 mmHg. Inertance was significantly higher in paediatric patients than in adults, in accordance with a lower cross sectional area of the vasculature, commensurate to a lower CO. Changes of arterial properties appear functional to control the ratio of pulsatile power to active power and keep arterial efficiency as high as 97% in infants and children.
