Does the Augmentation Index of Pulse Waves Truly Increase With Progression of Atherosclerosis? An Experimental Study With Hypercholesterolemic Rabbits

Recently, the central augmentation index (AIx) has been reported to show a nonlinear correlation with age. We investigated whether the AIx of the central artery changes with the progression of atherosclerosis in Kurosawa and Kusanagi-hypercholesterolemic (KHC) rabbits. We simultaneously recorded pressure and flow waves in the ascending aorta in normal and KHC rabbits aged 10−12, 22−24, and 34−36 months, under pentobarbital anesthesia. The systolic, diastolic, and mean arterial pressures and total peripheral vascular resistance were significantly higher in KHC rabbits than in their age-matched controls. The systolic pressure of the KHC rabbits increased with age. Additionally, the AIx of the KHC rabbits was significantly higher than that of their age-matched controls, although the AIx did not show a significant age-dependent increase in either of the two rabbit groups. However, the development of atherosclerotic lesions progressed markedly in KHC rabbits, and the early and late (pulse pressure [PP]) systolic waves increased progressively in amplitude with age in the KHC rabbits. On the other hand, no significant differences were seen in the normal and KHC rabbits’ cardiac output (CO), stroke volume (SV), or heart rate (HR) at any age, nor did the two strains show significant age-related changes in these variables. Aortic compliance (SV/PP) was significantly lower in the 22−24- and 34−36-month-old KHC rabbits than in their age-matched controls, and decreased with age in the KHC rabbits. Although the progression of atherosclerosis stiffened the aortic wall, it did not affect the AIx. This was partly the result of the decreased distensibility of the wall, in which the pressure waves used to determine AIx were measured.