Dynamic compliance measures how easily the lungs and airways together expand during an actual breath, factoring in airway resistance as well as lung stiffness.
Normal — similar to static in healthy lungs.
Mildly reduced.
Moderately reduced — stiffness or resistance.
Severely reduced — check for resistance vs. stiff-lung cause.
Given: Vt 500 mL, peak 30, PEEP 5 cmH₂O.
Because it's taken while air is moving, it includes airway resistance.
Static compliance isolates lung and chest-wall stiffness using plateau pressure. Dynamic compliance uses peak pressure, so it also reflects airway resistance. A widening gap between the two points to an airway resistance problem.
Roughly 50–100 mL/cmH₂O in healthy lungs, usually a little lower than static compliance because of airway resistance.
When dynamic compliance drops much more than static, the problem is increased airway resistance — bronchospasm, secretions, or a kinked or narrow tube — rather than stiff lungs.
Because it depends on airflow and resistance, which vary with bronchial tone, secretions, and patient effort, it fluctuates more than the flow-independent static value.