During CPR, what happens during the recoil of the chest between compressions?

During CPR, the recoil of the chest between compressions creates a vacuum effect in the thoracic cavity. This negative pressure helps draw blood back towards the heart, allowing for better venous return. As the chest wall rises after each compression, the pressure inside the thoracic cavity decreases relative to the atmospheric pressure outside the body. This reduction in pressure facilitates the return of blood from the body's peripheral veins into the right atrium of the heart.

Understanding this process is crucial for effective CPR, as it emphasizes the importance of allowing full chest recoil after each compression. If the chest does not fully recoil, the vacuum effect diminishes, leading to less blood returning to the heart and ultimately reducing the efficacy of chest compressions.