What Is Cardiopulmonary Resuscitation?

Cardiopulmonary resuscitation, universally abbreviated CPR, is an emergency procedure that substitutes external chest compressions and assisted ventilation for the pumping and gas exchange functions lost during cardiac arrest. Its purpose is to sustain enough blood flow to the brain and myocardium to preserve viability until a perfusing rhythm can be restored, usually by defibrillation or by treatment of a reversible cause. CPR does not itself restart the heart, but it buys the time in which definitive treatment can work.

The modern technique dates to 1960, when closed-chest compression was combined with mouth-to-mouth ventilation and external defibrillation into a single sequence. Two mechanical explanations for the resulting flow coexist: the cardiac pump theory, in which the heart is squeezed between sternum and spine, and the thoracic pump theory, in which compression raises intrathoracic pressure and drives blood out through vessels held open by differing collapsibility. Both are relevant to device design, because they predict different optimal compression waveforms and different responses to airway pressure.

Compression Mechanics and Quality Metrics

Blood flow during CPR is a strong function of compression depth, rate, chest recoil, and the fraction of time compressions are actually being delivered. The 2025 American Heart Association guidelines for adult basic life support specify a rate of 100 to 120 compressions per minute and a depth of at least 5 centimeters in adults, with full recoil between compressions and interruptions kept as short as possible. Even performed well, CPR generates only about a quarter to a third of normal cardiac output, so small degradations in technique translate directly into lost perfusion pressure. Coronary perfusion pressure, the difference between aortic and right atrial pressure during the relaxation phase, is the physiologic quantity that best predicts return of spontaneous circulation, and it decays within seconds when compressions pause.

Instrumentation and Feedback

Because compression quality degrades with rescuer fatigue and is poorly self-assessed, measurement has become part of the procedure. Accelerometer-based pucks placed on the sternum integrate acceleration twice to estimate displacement and report depth and rate in real time, and defibrillator pads double as transthoracic impedance sensors that detect ventilation and chest motion. Studies comparing compression quality on scene against quality during ambulance transport, such as an analysis of compression quality during ground transport, show measurable declines once a moving vehicle is involved, which motivated mechanical piston and load-distributing band devices. End-tidal carbon dioxide capnography provides a second, independent signal: a sudden rise often marks the return of spontaneous circulation, and a persistently low value indicates poor flow.

Defibrillation and the Chain of Survival

CPR is one link in a sequence that also includes early recognition, rapid emergency medical services activation, prompt defibrillation, and post-arrest care. Automated external defibrillators analyze the surface electrocardiogram for ventricular fibrillation or pulseless ventricular tachycardia and deliver a biphasic truncated exponential shock, a waveform that achieves defibrillation at lower delivered energy than the older monophasic designs. Filtering compression artifact out of the ECG so that rhythm analysis can proceed without pausing compressions remains an active signal processing problem. The 2025 guidelines executive summary also incorporates opioid antagonist administration into the basic life support algorithm, reflecting the changing epidemiology of out-of-hospital arrest.

Applications

Cardiopulmonary resuscitation and its supporting technology appear in a range of settings, including:

• Out-of-hospital emergency response by bystanders and emergency medical services
• In-hospital rapid response and code teams
• Public access defibrillation programs in airports, schools, and stadiums
• Design and validation of mechanical compression devices and feedback sensors
• Manikin-based simulation training with instrumented performance scoring
• Drone and dispatcher-assisted delivery of defibrillators to arrest locations