The role of venous capacity active changes in the control of cardiac output: a computer simulation study

The role of active changes in venous capacity during short-term cardiovascular homeostasis is analyzed through a mathematical model of the baroreflex system. The main biophysical factors included in the model are: dependence of cardiac output on atrial pressure and on the arterial afterload; static sigmoidal response of the baroreceptors; action of feedback reflex mechanisms on heart rate, systemic arterial resistance, systemic venous unstressed volume and systemic venous compliance. Computer simulations were performed to investigate the interaction among the aforementioned mechanisms, and the specific role of venous capacity active changes, in vagotomized subjects under conditions of cardiovascular stress. The obtained results indicate that the mechanism regulating venous capacity plays a pivotal role in maintaining adequate values of circulatory filling pressure and cardiac output in the early phase following acute blood volume changes