The pressure of pleural fluid is sub-atmospheric. According to reference (1), it exists as a thin film under sub-atmospheric pressure, in the range of 5 cm water pressure. This means the pressure is lower than atmospheric pressure. Reference (2) further indicates that this pressure is even lower at the lung apex compared to the base.
In summary:
- Pleural fluid pressure is less than atmospheric pressure.
- It typically measures around -5 cm of water pressure (relative to atmospheric).
- The pressure varies within the pleural space, being more negative at the apex of the lung than at the base.
