The catheter–tubing–transducer column is a spring: it has a natural frequency and a damping coefficient. An optimally damped trace is faithful — sharp upstroke, clear dicrotic notch. Overdamped (air bubble, kink, clot, low flush pressure) is slurred, loses the notch, and reads a falsely low systolic / high diastolic. Underdamped (stiff or long tubing) overshoots and rings, reading a falsely high systolic. Use the fast-flush square-wave test to tell them apart, and watch the measured pressure diverge from the true pressure.