Cardiovascular Function Integration
- Blood flow exiting the heart must ultimately equal the blood flow entering the heart at a single value of Right Atrial Pressure (RAP). Consequently, the cardiac output must be equal to the venous return at a single value for the RAP in any physiological or pathological scenario. Given this rule, the intersection of the cardiac function curve and the vascular function curve provides the equilibrium point of the entire cardiovascular system. Below we consider two perturbations of the cardiovascular system and discuss how overlapped cardiac and vascular function curves can help predict and understand the changes to the to cardiac output, venous return, and right atrial pressure
- Transfusion of a large fluid volume into the circulation results in a right-ward shift of the vascular function curve due to the increase in total blood volume and thus "Mean Systemic Pressure". As is clear, the equilibrium point of the cardiovascular system is now significantly shifted upward and to the right. Consequently, the cardiac output and venous return to the heart increase as well as the RAP.
- Increased SNS tone rotates the cardiac function curve counter-clockwise due to its boosting of the heart's contractility and heart rate. Additionally, SNS stimulation reduces venous vascular compliance and thus causes venoconstriction which increases the "Mean Systemic Pressure", shifting the vascular function curve to the right. The combined effect of these changes is a substantial increase in the cardiac output and venous return without a large change in the RAP.