Define residual volume of air

Residual volume (RV) is the amount of air that remains in a person’s lungs after maximum exhalation. In other words, this is the volume of air that we can’t possibly get out of our lungs, meaning that the lungs are never completely empty of air. Otherwise, they would collapse as the tissue sticks together. On average, a person’s RV is about a liter and doctors can run special tests to find a person’s RV, as it can indicate lung health.