An indirect measure of left atrial pressure, obtained by occluding a pulmonary artery branch
Expansion
Inflating the balloon of a pulmonary artery catheter occludes flow in that branch, creating a static column of blood continuous with the left atrium. The measured pressure therefore approximates left atrial pressure and hence left ventricular end-diastolic pressure.
Normal is about 6 to 12 mmHg.
Raised in left ventricular failure, mitral stenosis or regurgitation, and fluid overload. Pulmonary oedema becomes likely above about 18 to 20 mmHg, once hydrostatic pressure overwhelms plasma oncotic pressure.
Normal despite pulmonary oedema indicates a permeability problem rather than a pressure problem, that is acute respiratory distress syndrome. This distinction was the classic use of the measurement.
Accuracy requires the catheter tip in West zone 3, where the pulmonary vein remains open. Pulmonary artery catheters are now used far less often, since large trials showed no mortality benefit and less invasive tools have replaced them.