Vascular prosthesis

A vascular prosthesis intended to act as a substitute blood vessel comprises a porous corrugated tube (1) of textile material presenting a pattern of a series of axially disposed markings (3,4 or 5) on the corrugations (2) so disposed that the appearance of the pattern changes when the prosthesis is extended. The change in the appearance of the pattern as the tube is extended provides an indication to the user when the prosthesis has been extended to the desirable extent.

The subject of this invention is a vascular prosthesis of the type 
comprising a porous tube made of textile material formed with 
circumferential corrugations intended to act as a substitute blood vessel 
in a human or an animal body. 
In placing a vascular prosthesis in position in a human or animal body it 
is extremely desirable that the graft should not be twisted. To this end 
it is known to provide on the graft at least one line of contrasting 
colour so that any twist in the graft becomes readily apparent. However, 
there is another consideration relating to the fitting of a graft. That is 
that the amount by which the graft is extended axially beyond its 
unstressed condition should be maintained within a predetermined limit. If 
the graft is not stretched far enough there may be an increased resistance 
presented to the flow of blood through the graft because of interference 
presented by the corrugations. If the graft is stretched too much the 
pores may be extended to a point where there is a danger of haemorrhage 
occurring at the junction between the graft and the host tissue before 
there has been time for the build up of tissue on the walls of the graft 
or the sutures at the junction may be pulled out of the host tissue if 
excessive stretch as a result of excessive tension in the graft itself. 
It is an object of the present invention to provide an indicating means on 
the graft which will indicate to the surgeon who is implanting the graft 
not only whether the graft is straight but also when the correct amount of 
extension has been attained. 
A vascular prosthesis according to the invention comprises a corrugated 
tube of textile material characterized by presenting a pattern of a series 
of separate axially disposed markings on the corrugations, the disposition 
of the markings being such that when the prosthesis is extended to about 
the predetermined correct degree of extension whereby to increase the 
angle between opposite sides of each corrugation the observed pattern of 
markings along the prosthesis changes to provide a signal that the correct 
degree of extension has been attained. 
In one construction, on each crest and/or in each trough, there is provided 
a short axial line, so disposed that when the prosthesis is extended to 
the predetermined proper extent the individual lines are in alignment and 
show gaps between adjacent lines the projected lengths of which to an 
observer are a readily discernible proportion of the length of each line. 
Preferably the proportion is a proportion of equality i.e. the lengths of 
the gaps appear to be the same as the lengths of the individual lines thus 
providing a dashed line from one end of the prosthesis to the other with 
the lengths of lines and spaces all equal. 
Alternatively the prosthesis may be marked with spaced circumferential 
lines each of which forms a short arc on the surface of the prosthesis, 
the axial positioning and spacing of the lines being such that when the 
prosthesis is extended by the desirable amount the arcs when viewed from 
one side of the prosthesis are spaced in a predetermined relation to one 
another, once again preferably equi-distantly from one another. 
The arcs may be so positioned that when the prosthesis is in the unstressed 
state the arcs appear in groups of closely spaced lines and when the 
prosthesis is extended to the desirable extent the radially projected 
lengths of the gaps between all the arcs become equal to an observer. 
In a still further alternative arrangement the markings are in the form of 
geometrical shapes which in the unstressed state of the prosthesis have 
one form and when the prosthesis is extended change to another readily 
distinguishable geometrical shape. For example the prosthesis may bear 
marks which appear as diamonds or ellipses when the prosthesis is 
unextended and which appear as squares or circles respectively when the 
prosthesis is extended to the desirable extent.

In the drawings 1 denotes the prosthesis formed with corrugations 2. In 
FIGS. 1, 2 and 3, the numeral 3 denotes axially orientated lines marked on 
the tube constituting the prosthesis while in FIGS. 4, 5 and 6, the 
numeral 4 denotes arcuate lines marked on the tube constituting the 
prosthesis. In FIGS. 7, 8 and 9 the numeral 5 indicates squares marked on 
the tube constituting the prosthesis. 
Referring first to the construction of FIGS. 1, 2 and 3, the prosthesis 
appears as illustrated in FIG. 2 with the lines marked thereon indicating 
a more or less continuous line or at least with gaps between adjacent 
lines much smaller than the lengths of the lines themselves. When the 
prosthesis is extended to the most desirable extend for use as a graft the 
angle between the sides of each corrugation is increased so that the 
radially projected length of each line or each space as the case may be as 
seen by an observer is changed to show a dashed line along the length of 
the prosthesis in which the individual lines and spaces are of equal 
length. 
In the construction of FIGS. 4, 5 and 6, the unextended prosthesis appears 
as in FIG. 5 with the lines appearing in groups in which the spacing is 
irregular. When the prosthesis is extended to the desirable extend for use 
as a graft once again the projected distance between adjacent lines is 
changed because of the change in angularity of the surface carrying the 
lines and they appear all equi-spaced in an axial direction. 
In the construction of FIGS. 7, 8 and 9 the unextended prosthesis appears 
in FIG. 7 with the squares appearing as transversely orientated diamonds. 
When the prosthesis is extended to the desirable extent the diamond shapes 
appear as squares or quasi-squares.