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4 out of 5

The intrapleural pressure is negative both during inspiration and expiration because:

A Intrapulmonary pressure is always negative

B Thoracic cage and lung’s opposite recoil.

C Transpulmonary pressure determines the negativity

D Surfactant prevents the lungs to collapse

Ans. B Thoracic cage and lung’s opposite recoil.

I. Pleural pressure is the pressure of the fluid in the narrow space between the lung pleura and the chest wall pleura. This is normally a slightly negative pressure.

II. The normal pleural pressure at the beginning of inspiration is about —5 cmH2OQ, which is the amount of suction that is required to hold the lung open to their resting level.

III. Then, during inspiration, expansion of the chest cage pulls the surface of the lungs with still greater force and creates a more negative pressure of about —7.5 cmH2O.