Changes in inferior vena cava blood flow at increased negative intrathoracic pressure

An increase in the negative intrathoracic pressure had practically no effect on the mean blood flow in the posterior vena cava and femoral vein in cats and healthy volunteers, because instantaneous (phasic) values of the venous blood flow increased during inspiration, while during expiration they decreased to a lower extent than during natural respiration. These phasic changes in the venous blood flow were due to changes not only in intrathoracic, but also in transdiaphragmatic pressure.