The traditional concept of cardiopulmonary resuscitation (CPR) is that the heart is squeezed between the sternum and the spine during external cardiac massage to create a pressure gradient that forces blood from the heart to the periphery. Although the heart may actually be squeezed in some persons by this maneuver, a newer view of CPR holds that closed-chest compression produces a generalized rise in intrathoracic pressure that is applied to the pulmonary vascular bed as well as the heart. Thus, the heart does not serve primarily as a pump during external cardiac massage but instead acts as a conduit for blood from the lungs. Furthermore, flow into extrathoracic vessels depends on their tendency to remain open or to collapse: forward flow occurs across the head during CPR because a pressure gradient is developed between the carotid artery and the more compressible jugular vein. These ideas have potential clinical implications and greatly increase our understanding of the physiology of CPR.
(JAMA 244:1366-1370, 1980)
Luce JM, Cary JM, Ross BK, Culver BH, Butler J. New Developments in Cardiopulmonary Resuscitation. JAMA. 1980;244(12):1366-1370. doi:10.1001/jama.1980.03310120052029