Catheter having sections of variable torsion characteristics

A flexible catheter comprises at least one resilient, flexible, tubular layer in telescoping relation with, and bonded to, a tubular wire sheath. A first catheter section includes the wire strands at a first angle to each other. A second catheter section includes the wire strands at a second angle to each other, with the second angle being different from the first angle so that the physical characteristics of the first and second catheter sections are different.

BACKGROUND OF THE INVENTION 
In Stevens U.S. Pat. Nos. 3,485,234 and 3,585,707, tubular products such as 
catheters are disclosed which comprise an extruded plastic coating having 
a tubular, braided wire sheath disposed tightly about a plastic coating in 
telescoping relation therewith. A second, extruded layer of plastic is 
then applied over the braided sheath. 
Such a catheter having a braided sheath increases the torsional stiffness 
of the catheter, so that torque may be better transmitted to typically the 
distal tip thereof with manipulation from the proximal catheter end. Such 
a characteristic is desirable to facilitate advancement, for example of an 
intravascular catheter through the branching blood vessel system of a 
patient. As the catheter is advanced, the surgeon may rotate the proximal 
end, and, by the invention of the Stevens patents, the distal end more 
accurately follows the desired rotational movement imparted to the 
catheter by the surgeon. 
In some uses, it would be desirable for certain portions of the catheter to 
have more or less torsional rigidity than other portions of the catheter. 
For example, it might be desirable for the distal tip of the catheter to 
be very soft and pliable, with a low torsional rigidity, while an 
intermediate section of the catheter should have greater amounts of 
torsional rigidity to permit the transfer of torque to the tip area from 
the distal end. 
On the other hand, it may be desirable for a catheter to have high torque 
at its tip but low longitudinal stiffness or "pushability". On the other 
hand, other sections such as the hub may desirably have high "pushability" 
or longitudinal rigidity, but with less torsional rigidity. Other sections 
of the catheter may desirably have intermediate properties in terms of 
torsional and longitudinal rigidity or stiffness. 
By this invention, varying sections of the catheter may have varying 
torsional and longitudinal rigidity, in accordance with many different, 
desired, predetermined plans. This may be accomplished by variation of the 
relationships of the strands in the flexible, tubular, braided wire sheath 
provided to the catheter, to provide catheters with varying properties as 
may be desired. 
DESCRIPTION OF THE INVENTION 
This invention relates to a flexible catheter which comprises at least one 
resilient, flexible tubular layer in telescoping relation with and bonded 
to a tubular, wire sheath made of generally helically disposed, crossing 
wire strands. 
In accordance with this invention, a first section of the catheter has such 
crossing wire strands which define a first angle to each other. A second 
section of the catheter has crossing wire strands of the sheath which 
define at least one second angle to each other. The second angle is 
different from the first angle, with the result that the physical 
characteristics of the first and second catheter sections are different. 
Particularly, in this circumstance the torsional and longitudinal rigidity 
of the respective catheter sections will vary. 
Preferably, at least one second angle of crossing strands of a second 
section is at least 5 and preferably 10 to 40 degrees different from the 
first angle of the first section. If desired, a plurality of second 
sections may be present, the second sections defining strands having 
different second angles from each other. Alternatively, only a single 
second section with a single, second strand angle may be present. 
It is generally preferred for the strands of a section to each define 
substantially similar angles to the catheter axis although if desired the 
angle of one of the set of helical strands in the sheath may define a 
substantially different angle to the catheter axis than the other set of 
helical strands in the same portion of the sheath. 
Such tubular wire sheath of braided form is well known, having two sets of 
generally helically disposed strands which cross each other in engaging 
relation and weave in and out, over and under each other. Alternatively, 
the sets of crossing strands may be of purely helical configuration, with 
a first set and a second set of strands each defining a cylinder in their 
helical paths, with the second set of strands positioned inside the first 
set in telescoping relation therewith, without weaving or braiding of the 
crossing fibers. One set of strands defines a clockwise helix, and the 
other set a counterclockwise helix, so that the respective strands cross 
each other in straight manner, and bonded together. 
Such tubular wire sheaths may be made on conventional and commercially 
available wire braiding machines or the like. The desired tubular, braided 
wire sheath may be made on a conventional wire braider, making use of a 
process controller of a design readily made by those skilled in the art to 
cause the "braid pitch" (the angle between the crossing braid strands) to 
be modified along the various sections of the braid that correspond to the 
first and second sections of the catheter. If desired, this may be 
accomplished by forming the braid on the flexible, tubular layer to bring 
them into bonded relation, or the braid may be applied by sliding it over 
the flexible, tubular layer. 
The nonbraided crossing wire cylinders may have the strands of the two sets 
separately and sequentially wound on the flexible tubular layer, if 
desired, or such a sheath may be preformed. In any case, typically, an 
outer plastic or rubber layer is provided to enclose the tubular wire 
sheath and to facilitate the bonding of the sheath to the rest of the 
catheter. 
In one preferred embodiment, the catheter of this invention may have a 
distal end and a proximal end, the strand angle of the tubular wire sheath 
of a first catheter section at the distal end being less than the 
corresponding strand angle of the wire sheath in a second catheter section 
which is spaced from the distal end by the first section. As a result of 
this, the first section can have lower torsional stiffness and greater 
longitudinal stiffness than the second section. 
Additionally, it may be preferred for the strands of the tubular wire 
sheath adjacent the proximal end to be substantially parallel to the axis 
of the catheter. This provides a section with high "pushability" resulting 
from a high longitudinal stiffness, compared with the rest of the 
catheter. At the same time, the torsional stiffness may be low. This can 
facilitate the ease with which the physician can insert the catheter into 
a blood vessel or the like. 
Typically, the catheter of the above specific type has strands of the 
braided wire sheath which all define substantially similar angles to the 
catheter axis in their respective sections. 
The strands of "wire" used herein may be metallic, such as stainless steel, 
or nonmetallic, such as nylon, carbon fibers, KEVLAR fibers, or the like 
and may be of any desired cross-sectional shape. Also the strand cross 
section may change in shape or size along the length of the catheter in a 
manner independent of the strand angle. 
Catheters in accordance with this invention may be manufactured by the 
technique as described in the previously cited Stevens patents. 
Additionally, any other conventional and desired method of manufacture may 
be used.

DESCRIPTION OF SPECIFIC EMBODIMENT 
Referring to the drawings, a catheter 10 in accordance with this invention 
is shown. The specific catheter is made in accordance with the above cited 
Steven patents, with an inner plastic extrusion 12 being extruded on a 
mandrel 14 such as a silver wire. Inner plastic extrusion 12 may be of any 
appropriate material which is desirably used for a catheter such as 
polyethylene, nylon, PVC, polyurethane, or silicone rubber. 
Either before or after curing inner extrusion 12 on mandrel 14, it may be 
placed into a conventional wire braiding machine to form a tubular, 
braided wire sheath 16 about the outer surface of inner extrusion 12. The 
braid may be laid down on inner extrusion 12 in the form of a set of 
counterrotating helical strands 18, 20, one of which set of strands 
rotates clockwise and the other counterclockwise. The braided strand 
arrangement may be conventional in configuration, except as otherwise 
taught herein. 
Adjacent the distal end or catheter tip 22 the counterrotating sets of 
strands 18, 20 are formed to have a strand angle 24 to each other of, in 
this specific embodiment, 38 degrees, as indicated by reference numeral 
24. Strand angle 24 is the angle that most closely faces in the direction 
of the catheter axis 23, rather than the side angle 25 which faces 
transversely thereto. It can also be seen that strands 18, 20 each have 
substantially identical angles to axis 23 in each section. 
A transitional area 27 is provided on the catheter, in which the braider 
machine is set to change the strand angle from the strand angle of 38 
degrees found in the tip section 22 to, in this specific embodiment, a 
strand angle 29 of 60 degrees in a second catheter section 26, as shown. 
Thus, second section 26 of the catheter has a lower longitudinal 
stiffness, and a higher torsional stiffness than tip section 22. Thus 
second section 26 permits the catheter to transmit torque well along its 
length, while tip section 22 is more yielding and resilient in terms of 
torque transmission. 
Second catheter section 2 typically encompasses a great majority of the 
length of the catheter. However, at proximal end 28, a flared hub 30 may 
be formed typically during a later process step after the removal of 
mandrel 14. A second transitional area 32 of the catheter may be provided 
in which the wire braiding machine is set to change the strand angle from 
60 degrees to parallel strand relation 34 in proximal end 28, as shown. 
The respective strand sections 34 are substantially parallel to catheter 
axis 23. 
The effect of this is to increase the longitudinal rigidity of the catheter 
in end 28, while the torsional stiffness is minimized. 
An outer plastic layer 40 may also be applied over tubular, braided wire 
sheath 16, as is conventional. 
While the above embodiment in accordance with this invention is shown, it 
is contemplated that many other embodiments and angular relationships 
between the strands and respective catheter sections may be utilized, to 
provide catheters of many and varying characteristics as may be desired. 
For example, a central catheter section may be provided between sections 
22 and 26, if desired, in which the strand angle is 45 degrees. A one inch 
transition section may be provided between the central section and tip 
section 22, and a three inch transition section may be provided between 
the central section and section 26. 
Also, the wire sheath 16 may be made of "memory wire" such as Nitnol brand 
wire. Such wire can assume a predetermined shape upon heating to a certain 
temperature (or sometimes by electrical stimulation). Thus the cool, 
straight catheter can be designed to form a desired curve after 
implantation. 
The above has been offered for illustrative purposes only, and is not 
intended to limit the scope of the invention of this application, which is 
as defined in the claims below.