During expiration, which of the following actions occurs?

During expiration, the diaphragm relaxes, which leads to a decrease in the volume of the thoracic cavity. As the diaphragm returns to its resting position, the pressure within the thoracic cavity increases relative to atmospheric pressure. This pressure difference forces air out of the lungs, resulting in expiration.

The relaxation of the diaphragm is a passive process during normal expiration. It is key in driving air out of the lungs as there is no active muscular contraction required. Understanding this process is crucial for EMTs, as it is fundamental to the mechanics of breathing and vital for assessing respiratory function in patients.