Cardiopulmonary Resuscitation (CPR) is a life-saving technique designed to manually maintain blood flow and oxygen delivery to the brain and other organs when a person’s heart has stopped beating. This procedure simulates the function of the heart and lungs to sustain life until professional medical help can arrive. Chest compressions are the mechanical action at the core of CPR, creating an artificial circulation. High-quality CPR relies on a precise cycle of compression and release, which is fundamental to maximizing the chance of survival.
The Primary Goal of Chest Compressions
The mechanical purpose of chest compressions is to create an artificial cardiac output by physically squeezing the heart and increasing pressure within the chest cavity. When a rescuer presses down on the center of the chest, the heart is compressed between the sternum (breastbone) and the spine. This compression phase, sometimes called artificial systole, forces blood out of the ventricles and into the body’s circulation. This action propels oxygenated blood through the aorta to the brain and other vital organs, acting as a temporary external pump. For compressions to be effective, they must be delivered at an adequate depth, typically between 2 and 2.4 inches (5 to 6 cm) for an adult, and at a rate of 100 to 120 compressions per minute.
Why Full Recoil is Essential for Cardiac Filling
The compression phase is only half of the life-saving cycle; the release phase, known as full recoil, is equally important. Full chest recoil allows the chest wall to spring back completely to its normal, uncompressed height. This complete return creates a momentary drop in pressure within the chest cavity, establishing a negative intrathoracic pressure. This negative pressure acts like a vacuum, drawing deoxygenated blood from the body’s veins back into the heart’s chambers, a process called venous return or preload. Without adequate venous return, the heart chambers will not fill sufficiently with blood between compressions.
Furthermore, the heart muscle itself receives its blood supply primarily during this relaxation phase. The coronary arteries are perfused when the pressure in the aorta is higher than the pressure inside the relaxed ventricles. Allowing full recoil maximizes the time and pressure gradient for this coronary artery perfusion, which is necessary for the heart muscle to recover and potentially resume a normal rhythm.
Physical Consequences of Incomplete Recoil
Failing to allow for full chest recoil is often referred to as “leaning” on the chest between compressions. This error has negative physiological consequences that severely reduce the effectiveness of CPR. When the chest does not fully return to its neutral position, the pressure within the chest cavity remains artificially high. This sustained positive intrathoracic pressure actively impedes the flow of blood from the veins back into the heart. The reduction in venous return means the heart’s chambers are not allowed to fully refill, resulting in an insufficient volume of blood, or preload, for the next compression to eject. Consequently, the cardiac output generated by each subsequent compression drops significantly, even if the compression depth and rate are otherwise correct.
Incomplete recoil also directly compromises the Coronary Perfusion Pressure (CPP), which is the pressure gradient that drives blood flow into the heart muscle itself. A lower CPP makes it harder for the heart to sustain itself and reduces the likelihood of achieving a return of spontaneous circulation. Additionally, maintaining partial pressure on the chest increases the physical strain on the rescuer, leading to earlier fatigue.