What happens to ventilator graphics when flow is inadequate?

• A. Concave pressure-time curve on inspiration
• B. Convex pressure-time curve on inspiration
• C. Flat flow-volume loop
• D. Steep inspiratory slope

Answer: (A)

When flow is inadequate, the patient’s own inspiratory effort dominates because the ventilator can’t deliver air fast enough. That mismatch shows up on the inspiratory portion of the pressure-time graph as a scooped or concave shape—the pressure rises more slowly at first and bends inward rather than forming a smooth, straight rise. This concave inspiratory curve reflects trouble meeting demand due to limited flow.

The other patterns don't fit this situation: a convex inspiratory limb implies rapid pressurization or good flow, not under-delivery; a flat flow-volume loop would indicate essentially no inspiratory flow, which isn’t the case with inadequate but present flow; a steep inspiratory slope suggests quick pressurization with adequate or sufficient flow.