Figure 8. Techniques and mechanisms of cardiac massage. Conventional closed-chest compressions generate forward blood flow via 1 or both of the mechanisms depicted in the top 2 panels, known as the heart pump and the chest pump models, respectively (A and B). Several alternative methods of cardiac massage have been studied. Load-distributing band CPR (C) raises intrathoracic pressure and, with it, systolic pressure via the chest pump model. Active compression decompression (D) was designed to augment venous blood return via increased negative intrathoracic pressure, which may be improved with an impedance threshold device. Interposed abdominal counterpulsation (E) may augment perfusion by increasing diastolic aortic pressure or by several other proposed mechanisms.