Various types of chest compressions may be performed on a patient during a single resuscitation event. In embodiments one or more compression time parameters may be changed during the event, potentially optimizing blood flow for one side of the patient's heart, then the other. In some embodiments the event includes one or more prolonged compressions interposed between other compressions, potentially enabling the blood to reach to more remote locations than otherwise. In embodiments, a CPR chest compression machine includes a compression mechanism configured to perform successive compressions to the patient's chest, and a driver configured to drive the compression mechanism accordingly. In embodiments, a CPR metronome issues prompts for compressions accordingly.