Histomechanics of arteries due to altered mechanical forces

Abstract

Mechanical forces such as shear stress and pressure affect the cells of the arterial wall. Large arteries seek to maintain an optimal shear stress of 1.5 Pa and a circumferential stress of 100 kPa; when conditions such as pressure and flow are altered, the vessel undergoes both acute and long-term changes in an attempt to restore normalcy. In response to reduced flow, the vessel constricts acutely and the wall thickens; increased flow causes dilation and the wall's thickness decreases. In contrast, increased pressure, or the pathological condition known as hypertension, induces wall thickening while maintaining a relatively constant lumen diameter. Since mechanical forces affect the blood vessel at the cellular level, histology becomes a convenient and useful tool in visualizing gross morphological changes and molecular changes in the cell. Quantitative histology endeavors to analyze and quantify parameters of interest from histological images. Current quantitative histological methods, however, are not objective and often rely on the user selection the region of interest to be measured. Consequently, a semi-automatic image analysis system was created using MetaMorph (MM), an image analysis software package, and Visual Basic (VB)5.0. By writing code in VB, MM's capabilities were extended to perform novel measurements including circumferential measurements of wall thickness and radial and circumferential gradients of elastin and collagen in the vessel wall. Other parameters of interest that were measured included lumen diameter and average wall thickness.