This came up in Question 19 from the second paper of 2007.
The awesomeness of the PA catheter is discussed in greater detail elsewehere.
Appropriate zone positioning is also discussed.
To maintain a column of blood between the pressure transducer and the left atrium, the balloon has to be below the atrium. This means you have to send the catheter tip into Wests Zone 3 when you are floating it .
Tests which suggest appropriate Zone 3 positioning of the PAC
This a full-text version of the seminal paper from 1970:
Swan HJ, Ganz W, Forrester J, Marcus H, Diamond G, Chonette D (August 1970). "Catheterization of the heart in man with use of a flow-directed balloon-tipped catheter". N. Engl. J. Med. 283 (9): 447–51.
A manufacturer (Edwards) offers some free information about the PA catheter on their product page.
The PA catheter section from The ICU Book by Paul L Marino (3rd edition, 2007) is a valuable read.
Armstrong, Ehrin J., James M. McCabe, and Melvin D. Cheitlin. "Pulmonary artery catheterization in the intensive care unit: just numbers floating by?."Archives of internal medicine 171.12 (2011): 1110-1111.
Additionally, UpToDate has an article on PA catheter positioning.
They in turn reference an article from Lung, which I cannot provide a full-text link to.
Summerhill EM, Baram M. Principles of pulmonary artery catheterization in the critically ill. Lung 2005; 183:209.