esophageal mannometry&PH study

Hi all,
I have been introduced to assist esophageal manometry and PH study. It is facinating and I am really keen to learn more about this study, however, I have found very hard to find a book on this subject for nurses. Do you know any book dedicated for nurses on this subject and how can I order to buy it? I need your help! By the way, I am asking you from New Zealand! I must know either title of the book or author and publisher's name. I am looking forward to hearing from you.

warm regards,

Erica