Overview
The ASD example allows interatrial redistribution that buffers the modeled ventricular volume-loading response to respiration. It does not remove every respiratory effect from every measured pressure.
With tamponade plus the large ASD example, atrial redistribution suppresses respiratory ventricular filling and pulse-pressure variation, even if net shunt flow is small. Tamponade and transmitted thoracic pressure remain; this exception is not proof that the effusion is safe.