What is the total pressure a lung exerts while breathing out?

The total pressure a lung exerts while breathing out is called the expiratory pressure. It is the sum of the elastic recoil pressure of the lung parenchyma, the pressure due to the contraction of the respiratory muscles, and the pressure due to the flow of air through the airways.

During expiration, the respiratory muscles relax, allowing the elastic recoil of the lung parenchyma to draw the lungs back to their resting position. This creates a negative pressure in the pleural space, which draws air out of the lungs. The expiratory pressure is the pressure that is required to overcome the elastic recoil of the lungs and the resistance of the airways.

The expiratory pressure is typically lower than the inspiratory pressure, as the respiratory muscles are not working as hard to expel air from the lungs as they are to draw air in. The expiratory pressure is also affected by the lung volume, as the elastic recoil of the lung parenchyma is greater at higher lung volumes.