CPR, or cardiopulmonary resuscitation, restarts the circulatory system in an indirect manner. It does this by supporting the heart with oxygen until an electrical shock from a defibrillator is administered to the heart.
When a person’s heart stops, this is called cardiac arrest. The heart may stop for a variety of reasons, most often due to a disturbance in the electrical rhythm within the heart itself. This is caused by a heart attack or lack of adequate blood flow through the coronary arteries due to a blockage. When a blockage occurs, part of the heart muscle gets irritable and starts to die. In an attempt to compensate, the heart’s electrical system starts to send out random impulses trying to trigger a regular rhythm to produce proper contractions of the heart muscle. These irritable impulses, called ventricular fibrillation, make the heart’s beating look like it is a mass of shaking jelly. Because the heart is no longer beating efficiently, the heart’s muscle is not receiving oxygenated blood during this time. By performing CPR, we can artificially oxygenation the heart muscle until a defibrillator arrives.
CPR is performed by compressing rhythmically on the person’s chest to squeeze the heart between the breastbone or sternum and the spine. A series of compressions are alternated with breathing into the person’s mouth. The compressions then circulate the oxygenated blood around the body to the brain and heart tissues to keep them viable. This is critical for defibrillation. If a heart is going to accept an electrical shock, it must be properly oxygenated. An example of this is a group of people in an auditorium for a speech. No one will be able to pay attention to the speech if they haven’t been nourished with food first.
The only thing that is going to help the heart get going again is a defibrillator. Contrary to popular belief, a defibrillator doesn’t actually “restart” the heart either, rather, it stops the irritable impulses of ventricular fibrillation and allows the heart’s natural rhythm to start again, hence the name “de-fibrillator” or defibrillator. A defibrillator’s electrical pads are applied to a patient’s chest and an electric current is sent through the heart muscle in two different directions. This shock can be equated to blowing a whistle in the crowded auditorium full of people who are all talking to each other while the speaker is trying to address them. When the whistle is blown, the audience stops talking and pays attention so the speaker can begin talking properly and be heard.
So one can see how CPR doesn’t actually “restart” the circulatory system but provides support for the whole system until a defibrillator is able to shock the heart. The shock then halts the irritable rhythm that is not providing for adequate circulation of oxygenated blood and allows the heart to restart itself.
