loose loop to a tear patch 297 the thread then extends from the shunt as depicted at 299 through for example a suitable opening in the diametrically opposed wall of the central member 292 thus the thread 298 is used as the means for aiding the insertion of the shunt where gentle pulling does not tear the patch 297 to initiate the splitting action when the shunt is to be removed forceps or other appropriate instruments are placed against the shunt and a greater pulling force is applied to tear the patch 297 and cause the thread 298 to slice through the shunt wall much in the manner that the thin ribbon in a gum pack severs the enclosing plastic wrapper to expose the gum fig1 depicts a further alternative embodiment of the invention wherein a further coil structure is employed in a shunt 300 more particularly thin flexible wire springs or coils 302 304 are laminated with a coating of a flexible elastomer material generally as previous depicted in fig1 a 16b to form an impervious central member 305 and generally tapered end members 306 308 the end members are formed with openings 301 303 a choker tube 310 is formed with a wall of the central member 304 at generally a midpoint and extends generally normal therefrom threads are secured to respective facing ends of the coils 302 304 are passed through the choker tube 310.