Pulmonary Vascular Volume. Pulmonary vascular volume for control (Panel B) and tamponade (Panel D) cases. With 1000 ml effusion, the mean pulmonary vascular volume increases by 20.8% due to compressed ventricles. Two increases in pulmonary volume take place in a cardiac cycle, namely, one due to RV ejection in systole (labeled S) and the other due to pulmonary venous reversal flow at end of diastole (labeled D) from the left atrium. Effusion limits pulmonary venous return, resulting in lower volume excursion per cardiac cycle and accumulation of blood in the pulmonary vasculature. Left heart atrioventricular interaction is observed with distinct systolic and diastolic venous return phases, the diastolic/systolic volume ratio smaller than in control. With respiration shown in Panels A-B, mean pulmonary blood is maximum on inspiration due to higher RV inflow and lower LA outflow.