Age-Related Changes of Arterial Mechanical Properties in Rats: Analysis Using Exponentially Tapered T-Tube Model

This study was designed to explore the changes of mechanical properties in the rat's arterial system at different ages by using the exponentially tapered T-tube model. Long-Evans male rats at the ages of 6, 12, and 18 months were anesthetized and thoractomized. Rats at the ages of 6, 12, and 18 months were individually referred to as young, adult, and middle-aged rats. The pulsatile pressure and flow signals in the ascending aorta were measured by a high-fidelity pressure sensor and electromagnetic flow probe, respectively. Model parameters, such as aortic characteristic impedance, vascular tapering index, wave transit time, and arterial load compliance, were inferred from the aortic pressure and flow signals to describe the pulsatile nature of blood flows in the vasculature. The static hemodynamic condition in those animals with different ages was characterized by (i) no change in cardiac output and (ii) a decrease in heart rate, arterial blood pressure, as well as total peripheral resistance. As for the pulsatile nature of the arterial system, the wave transit time remained unaltered, indicating there was no change in the aorta's distensibility of rats at those three different ages. The arterial load compliance, which describes the buffering nature of a hollow vessel, also remained unchanged. On the contrary, there was a significant fall in aortic characteristic impedance in those age-related rats. The decline of aortic characteristic impedance without a significant change in arterial distensibility suggests that lumen growth of the aorta and large arteries may occur in rats up to middle age.