Since 2008, the American Heart Association has recommended that when someone sees a person go into cardiac arrest, chest compression alone should be started. But Iwami said the matter was controversial, and the study was conducted to determine whether chest compression alone is effective.
Sayre said that if chest compressions are started almost immediately, there is enough air in the victim's lungs to supply oxygen to the body.
Availability of an automated external defibrillator (AED) -- a portable device that delivers an electric shock to restart the heart -- is crucial to the patient's survival, he said. AEDs are available in public areas in the United States and in other countries including Japan.
"It's the combination that makes a big difference," he said.
"Doing something is always better than doing nothing," Sayre added. "So, if you see someone collapse, start pushing hard and fast on the center of their chest."
Another expert, Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, noted that the majority of the people who suffered bystander-witnessed cardiac arrests during the study period did not receive any type of CPR or public access defibrillation.
That highlights "the critical need for global improvement in individuals trained and willing to perform chest compression-only CPR and increased access to automatic external defibrillator devices," he said.
Iwami agreed. "We should implement programs to increase the number of lay rescuers who can at least perform chest compressions and use an AED," he said.
However, in certain cases, traditional CPR is still preferable. For infants and children, for instance, t
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