Host: How exactly does CPR help a cardiac arrest victim?

Robert O'Connor: Well the CPR has been around for about 40 or 50 years and we are really now starting to understand how the mechanics of it work and I think we are still far from completely understand it but what we do now is that when someone suffers sudden cardiac arrest, they have enough of an oxygen reservoir in their lungs that we don't need to breathe for them and chest compressions are far more important.

In fact, if you interrupt compressions to breathe for the person it exacts a huge price in terms of blood flow. The pressure, the blood pressure that you have been able to initiate and maintain with chest compressions is suddenly lost when you interrupt. So our thinking now is it's very important to keep your hands on the chest and just keep compressing.

There is also some evidence that there is a pass of gas exchange with chest compressions. In other words, there is some breathing that it really occurs, so that you really don't have to perform rescue breathing until the cardiac arrest has been going on for several minutes. So my advice to any bystander is don't worry about rescue breathing, just start with chest compressions and don't stop until help gets there.

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