Figure 3.

The method to calculate the pulmonary blood volume variation. Panels A and B show the instantaneous blood flow (filled circles) and cross sectional area (open circles) throughout the cardiac cycle in the pulmonary artery and in the sum of the pulmonary veins, respectively. Panel C shows the flow difference between the pulmonary artery and the sum of the pulmonary veins. Panel D shows the integral of the graph in Panel C, thus showing the cumulative pulmonary blood volume variation during the cardiac cycle.