What happens to intrapleural pressure during expiration?

During expiration, the intrapleural pressure changes in response to the movements of the thoracic cavity and lungs. While inhaling, the diaphragm and intercostal muscles contract, expanding the thoracic cavity, which causes intrapleural pressure to become more negative. During expiration, these muscles relax, and the elastic recoil of the lungs results in a decrease in the volume of the thoracic cavity. This process increases the pressure in the pleural space, making it less negative than during inhalation.

However, it is important to note that intrapleural pressure does not actually become positive during normal expiration; instead, it returns to a value that is less negative than during inhalation. This return is part of the normal respiratory cycle. Therefore, the correct interpretation during expiration is that the intrapleural pressure stabilizes or returns to a more neutral state compared to the extreme negative values achieved during inhalation.