Which mechanism ends inspiration when a pressure limit is reached and commonly serves as a safety feature?

• A. Exhalation
• B. Volume Limit
• C. Pressure Limit
• D. Pressure Cycling

Answer: (D)

In pressure-based cycling, inspiration ends when airway pressure reaches a preset limit. The ventilator uses this pressure threshold as the trigger to switch from inspiration to expiration, so the flow stops as soon as that limit is hit. This mechanism acts as a safety feature by capping peak airway pressure to protect against barotrauma.

Exhalation is simply the phase that follows inspiration, not the trigger that ends it. A volume limit ends inspiration when a target tidal volume is delivered, which is a different criterion and not tied to a pressure threshold. A pressure limit is the safety value set to prevent excessive pressure, but the action that terminates inspiration is the pressure cycling itself—the switch triggered by reaching that limit.