A TROCAR catheter assembly employs a regulated gas flow between a catheter and the inner wall of a cannula sleeve in which the catheter moves. Annular grooves are formed in the wall of the sleeve and the grooves are connected to a source of gas which produces a pressure differential which causes gas...http://www.google.com/patents/US5300047?utm_source=gb-gplus-sharePatent US5300047 - Trocar cannula and catheter
