The diaphragm (or accessing means) 38 preferably is equipped with a hole (or changing means) 39 through its thickness through which a guide wire, a needle, or other object of relatively small diameter can pass. [0043] When a guide wire or a needle is passed through the hole 39, the resilience of the diaphragm 38 presses the inner wall of the hole 39 sealingly against the outer surface of the guide