A mixing device for respiratory, therapeutic, or anesthetic uses provides two of three gases to a mixed gas outlet. A gas selecting means fluidly connected with a first and second gas supplies selectively provides fluid passage of only one of the first or second gases to the outlet. A gas bypass selectively...http://www.google.com.au/patents/US5159924?utm_source=gb-gplus-sharePatent US5159924 - Method and apparatus for selectively mixing gases
