A cannula for introducing medical instruments into an anatomical cavity includes an elongate tubular body defining a lumen and a valve protruding distally from the tubular body for preventing fluid flow through the lumen when medical instruments are withdrawn from the anatomical cavity into the tubular...http://www.google.com.au/patents/US5752970?utm_source=gb-gplus-sharePatent US5752970 - Cannula with distal end valve
