Increased carotid artery stiffness decreases measured carotid-femoral pulse wave velocity and effects the estimation of age dependency of aortic stiffness

Carotid-femoral pulse wave velocity (PWVcf) is promoted as a clinical marker of aortic stiffness and is a measure utilising two sites where the pulse can be obtained non-invasively. PWVcf calculation requires subtraction of the heart-to-carotid pulse transit time from the heart-to-femoral pulse transit time. This implies that an independent increase in carotid stiffness (PWVc) will decrease PWVcf. This study aims to quantify the effect of age dependent increase in PWVc on PWVcf compared to the age dependent increase in aortic stiffness, determined as aortic PWV (PWVa). Comparison was made by using data from previous studies reporting increase in stiffness with age of the carotid artery1 (PWVc=0.0009×age2-0.0465×age+6.2 m/s), femoral artery2 (PWVf=0.0443×age+7.18 m/s), and PWVcf3 (PWVcf=0.001×age2-0.017×age+5.49 m/s). Using these values and average distances for aortic, carotid, and femoral arterial lengths, PWVa was calculated as a function of age (PWVa=0.0016×age2-0.0711×age+5.43 m/s). Comparison of PWVa and PWVcf demonstrates that the age dependency of PWV (m/s/year) is not the same when determined from PWVcf and PWVa. From 20 to 55 years, PWVcf overestimates the age dependency of PWVa by an average of 29%. From 55 to 90 years, PWVcf underestimates age dependency of PWVa by an average of 17%. These findings suggest that increased carotid stiffness can compromise the potential prognostic power of PWVcf measurements.