Cardiac Pump Theory

Cardiac pump theory refers to a proposed mechanism of how cardio-pulmonary resuscitation (CPR) works. Cardiac pump theory asserts that the action of chest compressions in CPR moves the heart to make it pump blood throughout the body. An alternative model, thoracic pump theory, suggests that compression of the chest area rather than the heart itself causes blood circulation. Both effects probably occur in CPR.

CPR Background

• CPR keeps someone whose breathing and/or heart has stopped alive. Its purpose is to help the patient breathe and maintain blood circulation. If the patient has stopped breathing, the rescuer checks the airway, pinches the patient's nose and covers the mouth with his own, and breathes into the patient's lungs. The rescuer gives two such rescue breaths. Then, the rescuer places both hands on the patient's chest and pushes down about one and a half inches and releases pressure, pushing 30 times in about 20 seconds. The rescuer repeats the two rescue breaths and the pumping until the patient revives or help arrives. The 2005 American Heart Association guidelines for CPR recommend the 30:2 (compressions:breaths) for all unresponsive patients.

Cardiac Pump Theory

• In CPR, the aid giver pushes down on the patient's chest, directly above the heart. Cardiac pump theory asserts that compressing the heart between the sternum (chest bone) and the spine pushes the blood in the heart to the rest of the body. Releasing the pressure allows the heart chambers and other blood vessels to refill. Rapidly repeating the compression and release causes the blood to move throughout the vital organs.

Thoracic Pump Theory

• According to the thoracic pump theory, the chest compressions of CPR put pressure on the whole chest cavity to circulate blood, particularly to the brain. In this model, the heart acts primarily as a passageway for the blood. The theory developed from observing conscious patients with a ventricular fibrillation, who could maintain consciousness by forcibly coughing, with data published in 1976 in the Journal of the American Medical Association. The American Heart Association (AHA) guidelines say that cough-CPR lacks usefulness for unconscious patients, yet agree with the mechanics of the theory.

Both Theories Have Validity

• A study in dogs by clinical researcher George W. Maier in the July 1984 issue of Circulation provided the groundwork for the standard procedure for CPR. It also provided a basis for understanding that both theories contribute to blood circulation during CPR. The rapid chest compressions, or "high impulse CPR," pump both the heart and the whole chest cavity to circulate blood. However, the focus of the pressure in the compressions of CPR remains the heart.

Effective CPR in Light of Both Theories

• The AHA guidelines lists the following reasons CPR may not work in a given case:

  • Time delays between cardiac event and CPR
  • Excessive breathing into the patient's lungs, decreasing cardiac output
  • Too few compressions before giving up or stopping to give breath
  • Slow and shallow compressions

  The rule of thumb according to the AHA: "Push hard, push fast, allow full chest recoil after each compression, and minimize interruptions in chest compressions." CPR can cause rib fractures, but it saves a life. AHA plans to publish revised guidelines in 2010.