Correction of carotid intima-media thickness for adaptive dependence on tensile stress: implication for cardiovascular risk assessment

Abstract

Purpose: Early artery wall-thickening detected by ultrasound-assessed increased carotid intima-media thickness (IMT) may reflect atherosclerosis or represent an adaptive response to keep homeostasis tensile stress that is related inversely to wall thickness by Laplace's equation. We attempted to discriminate between both mechanisms by correcting IMT for its inverse association with tensile stress.

Methods: Common carotid IMT and lumen diameter (D) where determined in 40 healthy controls and 119 never-treated asymptomatic patients with >or=1 traditional cardiovascular risk factor. The cross-sectional area (CSA) was calculated as pi x IMT x (IMT + D). Tensile stress was approximated by [mean blood pressure x (D/2 x IMT)], and wall shear stress by [(blood viscosity) x 4 x (mean blood velocity/D)]. Inverse regression line relating IMT and tensile stress in controls (p < 0.001) was used as a reference to determine in an individual at-risk patient the IMT deviation, defining DeltaIMT from the regression line of controls at the measured patient's tensile stress.

Results: DeltaIMT correlated positively with age (p < 0.05), body mass index (p < 0.05), blood pressure (p < 0.001), and glucose (p < 0.001). In multivariate analysis, DeltaIMT was independently associated with age (p < 0.01), male gender (p < 0.001), and blood pressure (p < 0.001). IMT showed positive association with age (p < 0.001) but not with other risk factors. Also, DeltaIMT, like CSA, correlated positively with tensile stress (p < 0.001) and negatively with wall shear stress (p < 0.05, p < 0.01), whereas IMT correlated negatively with tensile stress (p < 0.001) but not with wall shear stress.

Conclusion: Correcting IMT for adaptive association with tensile stress may give more strength to carotid evaluation for assessing cardiovascular risk.