Pulmonary capillary wedge pressure is obtained by:

• A. Measuring pressure in the right atrium
• B. Inserting a catheter into the pulmonary artery and wedging to measure downstream pressure
• C. Placing the catheter in the aorta
• D. Measuring in the left ventricle during systole

Answer: (B)

Pulmonary capillary wedge pressure is obtained by inserting a balloon-tipped catheter into the pulmonary artery and advancing it until the balloon is wedged in a small distal branch. When the balloon is inflated and flow is occluded, the pressure measured beyond the balloon reflects the pressure in the left atrium (and thus left-sided filling pressures). This is because the occluded catheter sits in a stagnant column of blood that communicates with the left heart but is isolated from the right heart and systemic arteries.

This technique is typically used during right heart catheterization with a Swan-Ganz catheter to estimate left atrial pressure, which helps assess conditions like left heart failure or mitral valve disease. Normal PCWP is roughly 6–12 mmHg; higher values indicate elevated left-sided pressures, while lower values suggest hypovolemia or low left-sided filling pressures.

Other options would measure different pressures: measuring in the right atrium gives right atrial pressure; placing the catheter in the aorta yields systemic arterial pressure; measuring in the left ventricle during systole reflects LV systolic pressure, not PCWP.