Blood flow maintenance by cardiac massage during cardiopulmonary resuscitation: Classical theories, newer hypotheses, and clinical utility of mechanical devices

Abstract

The mechanisms by which closed chest cardiac massage produces and maintains blood flow during cardiopulmonary resuscitation are still debated. To date, two main theories exist: the ''cardiac pump'', which assumes that blood flow is driven by direct cardiac compression and the ''chest pump'', which hypothesizes that blood flow is caused by changes in intrathoracic pressure. Newer hypotheses including the ''atrial pump'', the ''lung pump'', and the ''respiratory pump'' were also proposed. We reviewed studies supporting these different theories as well as the clinical evidences on the utility of mechanical devices proposed to optimize cardiopulmonary resuscitation, in view of their pathophysiological assumptions with regard to the underlying theory. On the basis of current evidence, a single theory is probably not sufficient to explain how cardiac massage produces blood flow. This suggests that different simultaneous mechanism might be involved. The relative importance of these mechanisms depends on several factors, including delay from collapse to starting of resuscitation, compression force and rate, body habitus, airway pressure, and presenting electrocardiogram. The complexity of the physiologic events occurring during cardiopulmonary resuscitation, together with the need of adequate training for a correct and prompt utilization of mechanical devices, might also partially explain the disappointing results of these devices in most clinical studies.

Right-to-Left Shunts Occur During Cardiopulmonary Resuscitation: Echocardiographic Observations

“…Right-to-left shunt occurring during CPR is presumed to be due to a hemodynamic phenomenon generated by chest compressions, which comprise repetitive compressions of the sternal area. Chest compressions increase intrathoracic pressure and/ or compress the cardiac chambers by nonselectively pressing intrathoracic structures, including the heart, which generates blood flow (15)(16)(17), thus creating new circulatory physiology that is different from that of a normal heartbeat. According to a report on hemodynamic measurements taken during CPR, the peak values of aortic pressure and right atrial pressure are similar during chest compression (18).…”

Changes in Peripheral Arterial Blood Pressure After Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) in Non-traumatic Cardiac Arrest Patients

“…impedance threshold device). It is however possible that it is the sum of different simultaneous mechanisms that produces the forward blood ow (24,25).…”

Combination of cardiac and thoracic pump theories in rodent cardiopulmonary resuscitation: a new method of three-side chest compression

“…The competing concepts as to whether the heart is a pump or a conduit have caused much controversy. As a result, the mechanism of chest compression is often explained by the lung pump theory, in which the heart works as a part of the larger pumping system with the lungs [4, 8]. Our work was not conducted to separately investigate this point.…”

“…Two different mechanisms of chest compression have been proposed: cardiac pump theory and thoracic pump theory [4–7]. Cardiac pump refers to a pump delivering the blood by directly squeezing the heart between the spine and the sternum, while the thoracic pump theory relates the heart to a passive conduit in which blood is forced away from the thorax when the intrathoracic pressure exceeds extravascular pressure during chest compression.…”

“…These competing concepts of whether the heart is a pump or a conduit have caused much controversy. The mechanism of chest compression is often explained by the lung pump theory, in which the heart works as a part of the larger pumping system with the lungs [4, 8]. Rudikoff [7] measured pressures in “the heart pump” in dogs, including the left ventricle, aorta, right atrium, and pulmonary artery, which were identical and equal to the intrathoracic pressure estimated by an esophageal balloon catheter.…”