What happens to the lung if intrapleural pressure is excessively decreased?

When intrapleural pressure is excessively decreased, the pressure difference between the intrapleural space and the alveoli becomes too great, leading to a condition often referred to as pneumothorax or lung collapse. The lungs are normally kept inflated due to a slight negative pressure in the pleural cavity, which allows the lungs to expand when the thoracic cavity expands during inhalation. If the intrapleural pressure drops excessively, perhaps due to air entering the pleural space, the negative pressure that keeps the lungs inflated can no longer hold. This leads to the lung unable to maintain its expanded state and subsequently collapsing.

A collapse results in decreased lung volume and impaired gas exchange, highlighting the crucial role of intrapleural pressure in maintaining lung integrity. Therefore, it is essential for the intrapleural pressure to remain slightly negative for the lungs to stay expanded and functioning correctly.