Stiffness parameter β

Abstract

Stiffness parameter β (stiffness β) is calculated from carotid diameter, distension and local carotid pressure as an index of blood pressure-independent blood vessel elasticity suitable for measuring distensibility of the carotid artery. This value is also measured in the ascending aorta and descending thoracic aorta. Among the indices for measuring distensibility of the carotid artery, stiffness β offers good intra- and inter-observer reproducibility, showing a coefficient of variation within 10%. Measurement values differ depending on whether the vascular pulsation is measured by the ultrasonic RF-tracking method or the M-mode method, and whether vessel diameter is measured as the media-adventitia (outer vessel wall) distance or lumen-intima (inner vessel wall) distance. Also, since slight differences in pulsation width are seen depending on the apparatus used, comparison of the apparatus and measurement method in a unified manner is desirable. Outer vessel wall distance of the common carotid artery correlates more closely with age than does inner wall vessel distance, so measuring the distance to the adventitia would be more appropriate to evaluate arterial stiffness. There is a strong correlation between cardio-ankle vascular index (CAVI) and stiffness β using transesophageal echography of the descending thoracic aorta. The correlating CAVI with stiffness β of the common carotid artery is not as large as that of the aorta. Most recent studies of stiffness β have focused on indicators of early changes in arteriosclerosis, such as stiffness β in the aorta of pre-hypertensive patients decreasing with improvements in exercise and lifestyle habits. Appropriate stiffness is necessary for blood vessels to maintain good blood flow to the periphery. However, arterial stiffness increases with age. Stiffness β, as an indicator of stiffness, is used to measure early changes in local arteriosclerosis, and abnormalities in carotid arteries represent a risk factor for ischemic cerebrovascular disease.