On a static PV curve for ARDS, recruitment is associated with which inflection point?

• A. Lower inflection point
• B. Upper inflection point
• C. Midpoint
• D. No inflection point

Answer: (A)

In ARDS, recruitment shows up on a static PV curve as a change in how the lung volume responds to pressure—specifically where the curve shifts from a flat, low-volume region to a steeper, more compliant region. The lower inflection point is that pressure threshold where the collapsed alveoli begin to open and contribute to a larger increase in volume for each increment in pressure. Below this point, most units are unrecruited and the curve climbs slowly; once you pass it, recruitment accelerates and compliance improves. The upper inflection point marks where further pressure causes overdistension, not recruitment, so it isn’t associated with recruitment. The midpoint isn’t a defined marker for recruitment, and no inflection point would imply no recruitment. Therefore, recruitment is associated with the lower inflection point.