"40 years ago".
Astrup
P
P
D001784:Blood Gas Analysis / Q000266:history* / Q000295:instrumentation; D003718:Denmark; D004196:Disease Outbreaks / Q000266:history; D004867:Equipment Design; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D011175:Positive-Pressure Respiration / Q000266:history