The pleural cavity in healthy individuals is a potential space and is under negative pressure. Its main purpose is to allow the lungs to fully adhere to the chest wall, and the lubricating fluid present serves to prevent too much friction between the lungs and chest wall during deep inhalation, which could cause pain. For various reasons, such as a ruptured lung bulla or trauma to the chest wall, a certain amount of air can enter the pleural cavity, leading to pain in patients. Due to the presence of pleurisy, friction occurs between the lungs and chest wall—particularly between the lower chest wall and the lungs—causing intense pain during deep inhalations. If a large volume of air is present, it can prevent the lungs from fully expanding, potentially leading to symptoms of breathing difficulties or an obstructed exhalation.