Under what condition is plateau pressure measured?

• A. During peak inspiratory flow
• B. During No Air Flow
• C. During Expiration
• D. During Coughing

Answer: (B)

Plateau pressure is the pressure in the alveoli when there is no gas flow, measured during an inspiratory hold at the end of a successful breath. This pause lets airway pressure equilibrate and removes the pressure drop across the airways due to resistance, so the value reflects the elastic recoil of the lungs and chest wall (lung compliance). That’s why it’s measured with no flow.

If you measure during peak inspiratory flow, the reading includes resistance in the airways and tubing and doesn’t isolate the elastic recoil. Expiration and coughing involve ongoing flow and dynamic changes, making them unsuitable for plateau pressure measurement.