MECHANICAL PROPERTIES OF ACTIVE AND PASSIVE RAT MIDDLE CEREBRAL ARTERIES

摘要

Cerebral arteries play an important role in the regulation of cerebral blood flow through autoregulation, a well established phenomenon which is caused by a combination of myogenic, neuronal and metabolic mechanisms. Myogenic reactivity is the ability of the vascular smooth muscle cells (SMC) to contract in response to stretch or to an increase in transmural pressure (TMP), and to dilate in response to a decrease in TMP. It is this active constriction of arteries within the autoregulatory range that prompts studies of not just passive mechanical properties, but also active mechanical properties. Passive properties provide an understanding of the behavior of the extracellular matrix components of arteries (i.e. collagen and elastin); but, in order to understand how the artery behaves in vivo, it is necessary to understand the mechanical properties with smooth muscle cell activation. Mechanical properties might also be altered if the vessel is diseased or damaged. Ischemia has been shown to reduce vascular tone, which might lead to brain tissue damage during stroke Therefore studying the mechanical properties of vessels in disease states to determine if they are able to adequately take part in controlling local blood flow is also important. This study utilizes in vitro pressure-diameter data to characterize the active (pressure-induced SMC activation) and passive (papaverine-induced) mechanical properties of ischemic, contralateral to ischemic and sham-operated rat middle cerebral arteries (MCA). Parameters calculated from the MCA pressure-diameter data include a stiffness parameter, β, an incremental elastic modulus, E_(inc-p), and a modified incremental modulus, E_(inc-a), that accounts for smooth muscle cell activation at different pressure levels.