Tubular medical instrument having a flexible sheath with cuffs

A tubular medical instrument comprising:

• an elongated flexible sheath for insertion into a body cavity of a human body;
• a radially expansible main cuff having a doubled back section on an outer peripheral surface of one end of the flexible sheath and also having outer surfaces which, when said sheath is inserted in the body cavity, are normally in contact with a wall surface of the body cavity when the main cuff is expanded, means for supplying air to said main cuff to expand same, said outer surfaces, when said main cuff is expanded in said body cavity, being continuously deformed in a first direction upon movement of said sheath in said body cavity in a second opposite direction corresponding to that in which the flexible sheath is inserted into the body cavity, without involving substantial slippage;
• a radially expansible auxiliary cuff mounted on a portion of the outer peripheral surface of the flexible sheath which is close to the main cuff and is opposite to said one end of the flexible sheath with respect to the main cuff;
• said doubled back section riding on the auxiliary cuff as the main cuff is being deformed in the first direction during the insertion of the flexible sheath;
• and
• means for supplying air to said auxiliary cuff to expand same to separate the outer surfaces of the main cuff from the wall surface of the body cavity and to push the doubled back section away from the auxiliary cuff into an original position of the doubled back section with respect to the main cuff.