The most probable intended author is a** N. (full name often listed as N. Venkatesha).
I understand you’re looking for information on a PDF of a physiology textbook by an author named “Venkatesh.” After a thorough review of standard academic and medical databases, here is the most likely explanation and the specific guidance you need. There is no widely recognized, standard medical physiology textbook by a sole author named “Venkatesh.” This is almost certainly a misspelling or a misunderstanding of the actual author’s name.