Blood Flow Maintenance by Cardiac Massage During Cardiopulmonary Resuscitation: Classical Theories, Newer Hypotheses, and Clinical Utility of Mechanical Devices
Highlights
- According to this alternative theory, blood flow does not occur by direct cardiac compression, but rather by a thoracic pump mechanism. Increased intrathoracic pressure during compression forces blood from the thoracic vessels into the systemic circulation, with the heart acting as a conduit and not as a pump. The compression leads to a uniform pressure rise within the whole intrathoracic compartment, and retrograde venous flow is inhibited by the collapse of veins at the thoracic inlet and by venous valvular closure as well. This theory requires the mitral valve to remain open throughout the whole cardiac cycle, and ventricular sizes to show minimal changes during CPR (View Highlight)
- Shaw et al.4 introduced the concept of “lung pump” (View Highlight)
- In this model, the heart is part of a pump that is composed of three components: an inlet valve, a compression chamber, and an outlet valve. The inlet valve is represented by the pulmonary valve, the compression chamber by the lung vasculature and the left atrial and ventricular chambers, and the outlet valve by the aortic valve. As a result, the heart is neither a pump nor a passive conduit as described by the cardiac or thoracic pump hypotheses, but rather an essential part of a larger pumping system. (View Highlight)
- during the late stages of resuscitation, a thoracic pump mechanism might be the major determinant of forward blood flow because of a relatively stiff myocardium. (View Highlight)
- The cardiac pump theory is likely to be the main mechanism during the initial phases of CPR. The contribution of the thoracic pump mechanism probably increases during resuscitation, becoming relevant in prolonged CPR (View Highlight)