Model of geometrical and smooth muscle tone adaptation of carotid artery subject to step change in pressure

Recent experimental studies have shown significant alterations of the vascu lar smooth muscle (VSM) tone when an artery is subjected to an elevation in pressure. Therefore, the VSM participates in the adaptation process not on ly by means of its synthetic activity (fibronectins and collagen) or prolif erative activity (hypertrophy and hyperplasia) but also by adjusting its co ntractile properties and its tone level. In previous theoretical models des cribing the time evolution of the arterial wall adaptation in response to i nduced hypertension, the contribution of VSM tone has been neglected. In th is study, we propose a new biomechanical model for the wall adaptation to i nduced hypertension, including changes in VSM tone. On the basis of Hill's model, total circumferential stress is separated into its passive and activ e components, the active part being the stress developed by the VSM. Adapta tion rate equations describe the geometrical adaptation (wall thickening) a nd the adaptation of active stress (VSM tone). The evolution curves that ar e derived from the theoretical model fit well the experimental data describ ing the adaptation of the rat common carotid subjected to a step increase i n pressure. This leads to the identification of the model parameters and ti me constants by characterizing the rapidity of the adaptation processes. Th e agreement between the results of this simple theoretical model and the ex perimental data suggests that the theoretical approach used here may approp riately account for the biomechanics underlying the arterial wall adaptatio n.