Under normal conditions in the pleural cavity, what type of pressure exists?

Under normal conditions in the pleural cavity, what type of pressure exists?

• A. Positive
• B. Negative
• C. Zero
• D. None

Answer: (B)

The pleural space is normally under a slight suction, meaning intrapleural pressure is negative compared with atmospheric pressure. This subatmospheric pressure comes from the opposing elastic forces: the chest wall tends to expand outward while the lungs tend to recoil inward. That suction keeps the lungs pressed against the chest wall, creating a transpulmonary pressure that keeps the airways open and allows effortless inflation. In practical terms, intrapleural pressure at rest is about -5 cm H2O and becomes more negative during inspiration. If this pressure rose to zero or became positive, the suction would be lost and the lungs could collapse, which is what happens in a pneumothorax where the pleural space equilibrates with atmospheric pressure.

The pleural space is normally under a slight suction, meaning intrapleural pressure is negative compared with atmospheric pressure. This subatmospheric pressure comes from the opposing elastic forces: the chest wall tends to expand outward while the lungs tend to recoil inward. That suction keeps the lungs pressed against the chest wall, creating a transpulmonary pressure that keeps the airways open and allows effortless inflation. In practical terms, intrapleural pressure at rest is about -5 cm H2O and becomes more negative during inspiration. If this pressure rose to zero or became positive, the suction would be lost and the lungs could collapse, which is what happens in a pneumothorax where the pleural space equilibrates with atmospheric pressure.