Which of the following is NOT a mechanism of forward blood flow?

The correct choice identifies a mechanism of forward blood flow that is not recognized or established in medical physiology. Forward blood flow during cardiopulmonary resuscitation (CPR) is primarily achieved through various means that effectively create pressure gradients within the thoracic cavity to facilitate blood circulation.

Cardiac pump theory explains how compressions directly squeeze the heart chambers to eject blood during CPR. Thoracic theory, on the other hand, describes how compressions increase intrathoracic pressure, pushing blood out of the heart and into circulation. The lung theory is less commonly referred to in this context, but it relates to the role of the lungs in ventilation and perfusion balance during CPR efforts.

In contrast, while "arterial theory" might suggest a focus on arteries' role in blood flow, it is not established as a specific mechanism influencing forward flow during CPR. It does not reflect a recognized physiological process within the context of resuscitation techniques and practices, making this choice the appropriate one to identify as not being a mechanism of forward blood flow.