This photograph, taken in the 1950's, depicts Dr. C. Park, Anesthesia Resident, Baltimore City Hospital; Capt. Martin McMahon, Chief, Baltimore Fire Department Ambulance Service and Dr. Peter Safar, Chief, Department of Anesthesia, Baltimore City Hospital, performing one of the earliest resusucitation studies using CPR. Dr. Safar's research in the 1950's and 1960's was supported by the US Army.

This figure shows documentation of resuscitation methods on volunteers who were sedated and paralyzed by drugs. They had a natural airway, without tracheal tube. The volunteers were health professionals, as this one, Dr. Felix Steichen. He is being ventilated by Dr. Safar. The rescuers waiting to perform the new mouth-to-mouth methods were laypersons, being instructed only with a brief live demonstration.

This figure shows a professional ambulance rescuer (Captain Martin McMahon, Chief of the Baltimore Fire Department Ambulance Service) performing the then taught chest-pressure arm-lift method of artificial ventilation on curarized volunteer Dr. Felix Steichen. These methods produced no air exchange in the majority of subjects.

This figure shows Dr. Safar performing backward tilt of the head and direct mouth-to-mouth ventilation, producing large tidal volumes, monitored by calibrated pneumograph on the chest. Oxygenation was monitored by ear oximeter. Blood gas levels were maintained normal during 30 minutes of direct mouth-to-mouth ventilation by untrained rescuers.