During expiration, what happens to the pressure in the thoracic cavity?

During expiration, the pressure in the thoracic cavity increases. This process occurs as the diaphragm and intercostal muscles relax, leading to a decrease in the volume of the thoracic cavity. According to Boyle's Law, when the volume of a closed system decreases, the pressure within that system increases.

As the lungs contract during expiration, air is expelled from the lungs due to this increased pressure relative to atmospheric pressure. This pressure change is essential for moving air out of the lungs and facilitating proper ventilation. The mechanics of breathing depend heavily on the relationship between thoracic pressure and lung volume changes, highlighting the importance of pressure dynamics in respiratory physiology.

In normal physiological function, the pressure does not remain constant or decrease during expiration; rather, it actively increases to drive air out of the lungs.