Disclosure is made of an improvement in the T-shaped tracheal stents and in the tracheal cannulas of the prior art, permitting one to conveniently have a complete and unitary unit including a closure member affixed to the device of the invention. Unidirectional retention sleeves are also described, which...http://www.google.es/patents/US5184610?utm_source=gb-gplus-sharePatente US5184610 - Tracheal cannulas and stents
