The February 11 1957 edition of the Toronto Daily Star contained this advertisement:
You could call them any time – day or night, including holidays!
A search in the Toronto city directories for the Institute Of Breathing turned up nothing: it is not listed in the 1956, 1957, or 1958 city directory, and there is no other business at 2279 Yonge Street with that phone number.
A Google search for Captain W. P. Knowles turned up a couple of articles on his method of “controlled rhythmic breathing”. I have no idea whether it has any medical value, but obviously breathing of some form or other is somewhat useful.