QJM vol. 97 no. 11 © Association of Physicians 2004; all rights reserved.
Mathematical estimation of the potential effect of vascular remodelling/dilatation on B-mode ultrasound intima-medial thickness
From the Departments of 1Epidemiology and 2Biostatistics, University of Arkansas for Medical Sciences College of Public Health, 3AP Calculus, Little Rock Christian Academy, 4 Department of Biostatistics, University of North Carolina at Chapel Hill, 5 Department of Pathology, Louisiana State University Health Science Center, New Orleans, and 6Departments of Internal Medicine, Physiology, and Biophysics, University of Arkansas for Medical Sciences, USA
Received 2 February 2004 and in revised form 30 June 2004
Background: Arterial diameter changes are known to impact wall thickness, but the clinical relevance of the changes is unclear.
Aim: To use known mathematical relationships to estimate anticipated changes in arterial wall thicknesses occurring with enlargement of atherosclerotic regions.
Design: Mathematical relationships between a cylinder's diameter and its wall thickness were used to calculate the theoretical effect of diameter enlargement on the thickness of an atherosclerotic wall.
Methods: Equating the wall areas of two cylinders, one of smaller diameter than the other, allowed estimation of the degree of thickening that would be needed to maintain intima-medial thickness (IMT) after arterial remodelling. The difference in cylinder diameters was based on arterial diameter enlargement reported with atherosclerosis progression. Thus, the calculated wall changes estimate arterial changes which could go undetected if only IMT is measured by ultrasound.
Results: The expected IMT change for diameter enlargement is not a linear function of the diameter change, but varies depending upon initial size (diameter and IMT). Thus a 0.6 mm arterial diameter enlargement would be expected to cause a 0.039–0.235 mm change in IMT, depending on artery size. The estimated IMT change is similar to that associated with major atherosclerotic risk factors.
Discussion: The level of vascular remodelling reported with atherosclerosis could have a measurable impact on IMT, suggesting that indicators incorporating both diameter and IMT may be better disease indicators than IMT alone. Arterial diameters, as well as IMT, should be obtained in ultrasound studies of atherosclerosis.
Address correspondence to Dr M.L. Eigenbrodt, Department of Epidemiology, UAMS College of Public Health, 4301 W. Markham, Slot 820, Little Rock, Arkansas 72205, USA. e-mail: eigenbrodtmarshal{at}uams.edu