What occurs during normal breathing cycles regarding the change in intrapleural pressure?

During normal breathing cycles, intrapleural pressure changes significantly, particularly during inspiration and expiration. As the diaphragm and intercostal muscles contract during inhalation, the volume of the thoracic cavity increases, leading to a decrease in intrapleural pressure. This negative pressure facilitates the drawing of air into the lungs.

When expiration occurs, the muscles relax, the volume of the thoracic cavity decreases, and intrapleural pressure returns to its resting levels, which is less negative due to the elastic recoil of the lungs and the thorax. This cyclic change—decreasing during inspiration and returning during expiration—reflects the dynamic nature of the intrapleural space as it responds to respiratory mechanics. Thus, the correct understanding of intrapleural pressure dynamics during the breathing cycle is that it decreases with inspiration and then returns to a higher level during expiration.