A novel, graphical means of relating changes of thoracic volume and intra-thoracic pressure [as a function of pulmonary, chest wall and airway mechanics] to alterations in cardiac function and venous return.

The two most prominent mechanical mediators of heart-lung interaction are changes in thoracic volume and intra-thoracic pressure.  These are depicted on the Campbell Diagram laying into the page [on the x,z axes].  The Guyton Diagram remains on the x, y axes.  Because the x-intercept of the cardiac function curve assumes intra-thoracic pressure, changes in intra-thoracic pressure are represented by parallel shifts in the cardiac function curve.  The distending pressure or 'trans-mural' pressure of the right atrium is defined by the central venous pressure minus the intra-thoracic pressure.