-  GUYTON DIAGRAM -

The venous return curve graphically represents the characteristics of blood flow from the venous capacitance beds to the right heart.  The x-intercept of the venous return curve is the mean circulatory pressure which is determined by the patient's 'volume status' as well as venous compliance.  The slope of the venous return curve represents the resistance to venous return.  The cardiac function curve describes blood flow as a function of right atrial pressure and its slope is determined by overall cardiac performance.  The intersection of the two curves represents the 'operating point' of the cardiovascular system; this point defines the central venous pressure and cardiac output for a given physiological state.

A graphical method of assessing the relationship between right atrial pressure [or central venous pressure] and cardiac output as a function of both venous return and cardiac function.