Question

Which of the following is true of the pulmonary pressures?

-Intrapleural pressure is always positive so that the pleural membranes remain in contact.
-Because of pneumothorax, intrapleural pressure equilibrates with atmospheric pressure. Without the positive force of alveolar pressure pushing the lung outward, the lung collapses due to elastic recoil forces.
-The difference between intra-alveolar pressure and atmospheric pressure is the pressure gradient that drives ventilation.
-An increase in transpulmonary pressure creates a larger collapsing pressure across the lungs, which is accompanied by the contraction of the lungs (alveoli).

Answer 1

The true statement about pulmonary pressures is that the difference between intra-alveolar pressure and atmospheric pressure creates the pressure gradient that drives ventilation. Intrapleural pressure is always negative in a healthy respiratory system, not positive, and an increase in transpulmonary pressure expands, not contracts the lungs.

Step-by-step explanation:

The statement that relates to the pulmonary pressures is: 'The difference between intra-alveolar pressure and atmospheric pressure is the pressure gradient that drives ventilation.' This is true because intra-alveolar pressure changes during breathing and always equilibrates with atmospheric pressure, facilitating the movement of air in and out of the lungs. Intrapleural pressure, on the other hand, is always negative relative to intra-alveolar pressure, maintaining a pressure gradient that keeps the lungs expanded against the chest wall.

In contrast, the statement about intrapleural pressure being always positive is incorrect. In reality, intrapleural pressure is negative during the normal breathing cycle. In the case of pneumothorax, intrapleural pressure does equilibrate with atmospheric pressure, but this is a pathological condition, and the positive force described is not alveolar pressure but atmospheric pressure preventing the lung's collapse. Lastly, an increase in transpulmonary pressure actually expands the lungs rather than causing them to contract, as it represents the difference between the intrapleural and intra-alveolar pressures.