Which atrium's activity is reflected by the PAOP waveform?

The PAOP (Pulmonary Artery Occlusion Pressure) waveform specifically reflects the left atrial pressure. This is because the PAOP indirectly measures left atrial pressure by occluding a pulmonary artery branch with a balloon-tipped catheter, which provides an estimate of the left atrial filling pressure under normal hemodynamic conditions.

When measuring PAOP, the catheter is positioned in the pulmonary artery, and when the balloon is inflated, it blocks the flow in that segment of the artery, creating a pressure gradient that allows for analysis of the pressures on the left side of the heart. Since PAOP is primarily indicative of the left atrium's activity, it is used to assess left ventricular function and fluid status of the patient.

Understanding the context allows one to appreciate why the other options do not apply: the right atrium does not directly influence the PAOP, nor does the measurement reflect both atrial activities simultaneously. Thus, the correct interpretation is that the activity reflected in the PAOP waveform is solely that of the left atrium.