Figure 3.

The physiology of respiratory-induced flow and pressure changes during positive pressure ventilation without additional respiratory effort. The inspiratory rise in intrathoracic pressure is transmitted, at least in part, to the pericardium and causes increased transmural pressure across the RV wall, plethora within the IVC and compression of the SVC. The RV stroke volume immediately falls. Concurrently, the pulmonary vasculature is compressed, forcing blood into the LV causing an initial increase in LV stroke volume. After the pulmonary transition time, the LV receives less blood and its stroke volume falls. This effect is exaggerated in states of low circulating volume and attenuated in the overloaded system or when either ventricle is failing. PP pulse pressure, IVC D inferior vena cava diameter, SVC D superior vena cava diameter.