The biaxial active mechanical properties of the porcine primary renal artery.

The mechanical response of arteries under physiological loads can be delineated into passive and active components. The passive response is governed by the load-bearing constituents within the arterial wall, elastin, collagen, and water, while the active response is a result of vascular smooth muscle cell (SMC) contraction. In muscular blood vessels, such as the primary renal artery, high SMC wall content suggests an elevated importance of the active response in determining overall vessel behavior. This study is a continuation of our previous investigation, in which a four-fiber constitutive model of the passive response of the primary porcine renal artery was identified. Here we focus on the active response of this vessel, specifically in the case of maximal SMC contraction, and develop a constitutive model of the active stress-stretch relations. The results of this study demonstrate the existence of biaxial active stress in the vessel wall, and suggest the active mechanical response is a critical component of renal arterial performance.