The overall objective of my research plan is to obtain quantitative understanding of the mechanism (s) by which the cardiovascular system regulates cardiac output. I view the cardiovascular system in a largely lumped fashion consisting of a pump, the right and left hearts and lungs, connected to a conduct system, the systemic vascular bed which mechanically interact with each other. Multiple neuro-humoral controllers within the body can modify the characteristics of the hearts and lung pump as well as the systemic vascular bed in order to maintain homeostasis of the entire system when a disturbance occurs. The first objective of this proposal is to quantitatively evaluate the role of several naturally occurring vasoactive substances as well as the carotid sinus baroreceptor reflex has on modifying the various parameters of the entire systemic vascular bed. The major effort will be focused on changes in capacity as well as the resistive parameters of the entire systemic vascular bed. The second objective of this proposed research will be to further decompose the entire systemic vascular bed into parallel flow channels. As a first step the systemic vascular bed will be subdivided into two major subdivisions. I will measure the changes in capacity and resistive parameters of each of these major subdivisions caused by the carotid sinus baroreceptor reflex.