Final answer:
A pulmonary artery catheter cannot be used to obtain Left ventricular pressure, as it is not placed in the left side of the heart.
Step-by-step explanation:
The question asks which parameter cannot be obtained by placing a pulmonary artery catheter (PAC). The PAC can be used to measure several hemodynamic variables within the heart and pulmonary circulation. Specifically, it can measure the Right atrial pressure (central venous pressure), Right ventricular pressure, Pulmonary artery pressure, and Cardiac output. However, it cannot directly measure the Left ventricular pressure because the catheter is not placed in the left side of the heart due to the risk of systemic embolization and because the pressure in the left heart can be significantly higher than in the right, posing a risk of catheter-related complications.