Fig. 2. Phasic flow tracings of vena cava blood flow, pulmonary artery blood flow, and aortic blood flow. Positive-pressure inspiration induces successively a decrease in vena cava blood flow ( 1 ), a decrease in pulmonary artery blood flow ( 2 ), and a decrease in aortic blood flow ( 3 ). From Morgan et al. 31 ; used with permission.