U.S. patent application number 10/039134 was filed with the patent office on 2002-05-16 for biolelectrical cable having a low friction outer surface.
Invention is credited to Sass, Richard G..
Application Number | 20020058980 10/039134 |
Document ID | / |
Family ID | 23646087 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020058980 |
Kind Code |
A1 |
Sass, Richard G. |
May 16, 2002 |
Biolelectrical cable having a low friction outer surface
Abstract
A bioelectrical cable comprising a conductor-insulator portion
including conductive wires set into an insulating medium and an
outer layer having a low friction outer surface. In one preferred
embodiment, the outer layer is made of polymeric material having
tetrafluoroethylene end groups. The low friction outer surface may
permit easier cable removal, when cable replacement is
warranted.
Inventors: |
Sass, Richard G.; (Portland,
OR) |
Correspondence
Address: |
Richard G. Sass
16125 SW 72nd Avenue
Portland
OR
97224
US
|
Family ID: |
23646087 |
Appl. No.: |
10/039134 |
Filed: |
January 3, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10039134 |
Jan 3, 2002 |
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09415534 |
Oct 8, 1999 |
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Current U.S.
Class: |
607/116 |
Current CPC
Class: |
A61N 1/05 20130101 |
Class at
Publication: |
607/116 |
International
Class: |
A61N 001/05 |
Claims
1. A bioelectrical cable comprising: (a) a conductor-insulator
portion including conductive wires set into an insulating medium;
and (b) an outer layer having a low friction outer surface.
2. The cable of claim 1 wherein said outer layer is made of
polymeric material having tetrafluoroethylene end groups.
Description
RELATED PATENT APPLICATIONS
[0001] The present application is a divisional of U.S. patent
application Ser. No. 09/415,534, filed Oct. 8, 1999.
BACKGROUND OF THE INVENTION
[0002] The present invention is a bioelectrical cable that is more
biocompatible than currently available bioelectrical cables.
[0003] Bioelectrical cables include cardiac implant cables,
neuro-stimulus cables and any cable designed to apply an electric
charge to body tissue or to supply a device which applies such a
charge.
[0004] Bioelectrical stimulus cables must meet a number of
challenging criteria. For example, a cardiac implant cable
typically stretches from a subcutaneous fat deposit through the rib
cage to a cardiac implant such as a pacemaker. The cable is
continuously perturbed by the beating of the heart. It must not,
however, become fatigued by this constant flexure to the point
where a substantial number of the cable fibrils break. (A fibril is
a thin wire used in a cable.) Not only does a broken fibril not
conduct electricity to the implant but it also may work its way
through the insulating layers of the cable and make harmful contact
with body tissue. A bioelectrical stimulus cable must also be
completely biocompatible. That is, the exterior of the cable must
be made of biocompatible materials and the constant flexure caused
by movement of the patient or his organs must not cause a rupture
that would lead to the release of materials that are not
biocompatible.
[0005] Heretofore, the general approach to the production of this
type of cable has been to produce a tight helix so each fibril
would experience only a small part of the total cable flexure. One
problem with a tight helix is that it places a restriction on the
number of independent leads that can be included in the cable. If
more leads could be included in a cable, however, more purposes
could be served with respect to an implant. For example, a single
cardiac implant may function as both a pacemaker and as a
defibrillator and may require a set of leads to power the pacemaker
and a separate set of leads to power the defibrillator when it is
needed. Additionally, a set of control leads may be necessary to,
for example, adjust the operation of the pacemaker and the
defibrillator.
[0006] Another problem encountered in the use of bioelectrical
stimulus cables is the formation of scar tissue about the cable. It
is occasionally necessary to replace a bioelectrical stimulus
cable. Removing the old cable can provide a difficult challenge to
the surgeon performing the replacement if considerable scar tissue
has grown about and adhered itself to the cable, as is typical.
SUMMARY OF THE INVENTION
[0007] The present invention is a bioelectrical cable comprising a
conductor-insulator portion including conductive wires set into an
insulating medium and an outer layer having a low friction outer
surface. In one preferred embodiment, the outer layer is made of
polymeric material having tetrafluoroethylene end groups. The low
friction outer surface may permit easier cable removal, when cable
replacement is warranted.
[0008] The foregoing and other objectives, features, and advantages
of the invention will be more readily understood upon consideration
of the following detailed description of the invention, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0009] FIG. 1 is a greatly expanded transverse cross-sectional view
of a bioelectrical stimulus cable according to the present
invention.
[0010] FIG. 2 is a greatly expanded longitudinal cutaway view of
the bioelectrical stimulus cable of FIG. 1.
[0011] FIG. 3 is a still more greatly expanded cross-sectional view
of a single insulated lead of the bicelectrical stimulus cable of
FIG. 1.
[0012] FIG. 4 is a greatly expanded transverse cross-sectional view
of an alternative preferred embodiment of a bioelectrical stimulus
cable according to the present invention.
[0013] FIG. 5 is a greatly expanded longitudinal cutaway view of
the bioelectrical stimulus cable of FIG. 3
[0014] FIG. 6 is a still more greatly expanded cross-sectional view
of a single coaxial lead of the bioelectrical stimulus cable of
FIG. 4.
[0015] FIG. 7 is a still more greatly expanded cross-sectional view
of a single insulated lead of a bioelectrical stimulus cable
identical with that of FIG. 1 except that it includes the insulated
leads shown in FIG. 7.
[0016] FIG. 8 is a greatly expanded transverse cross-sectional view
of a cable for treating congestive heart failure.
[0017] FIG. 9 is a greatly expanded longitudinal cutaway view of
the cable of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] Referring to FIGS. 1 and 2, a preferred embodiment of a
bioelectrical stimulus cable 10 according to the present invention
has a diameter of 3 mm (119 mils). At its center is a central lumen
12 preferably made of polyurethane or silicone and having an inner
diameter of 0.45 mm (0.018") and an outer diameter of 0.96 mm
(0.038"). The central lumen 12 performs at least two important
functions. First, it may accommodate a guide wire during the
insertion process. Second, it adds rigidity to the cable.
[0019] Arranged about central lumen 12 are thirteen insulated leads
20, each having a diameter of 0.22 mm (0.0087"). In an alternative
embodiment fillers, each also having a diameter of 0.22 mm
(0.0087"), are interspersed with a reduced number of leads 20.
Referring to FIG. 2, the leads 20 are wrapped about central lumen
12 in a "lazy" helix having a lay length of between 10 mm (0.4")
and 15 mm (0.6"). Such an arrangement is necessary when so many
leads are used, thirteen leads being considerably more than is
typically available in prior art cables.
[0020] FIGS. 4, 5 and 6 show an alternative embodiment 29 having a
central filler 12' rather than tube 12 and twenty coaxial insulated
leads 30 twisted counter to leads 20. Each coaxial lead 30 has a
central conductor 32 that is 40 .mu.m in diameter and is made from
four 20 .mu.m (0.8 mil) strands of silver plated CS95, available
from Phelps Dodge of Inman, S.C., that have been stranded and
twisted together. Central conductor 32 is covered with a 38 .mu.m
(1.5 mil) thick coating 36 of fluorinated ethylene propylene (FEP).
This, in turn, is covered with a shield 38 made of 20 .mu.m (0.8
mil) strands of CS95 that collectively provide 90% minimum
coverage. A 13 .mu.m (0.5 mil) wall 39 of polyurethane surround the
coaxial lead 30, which has a 50 ohm impedance. The provision of
coaxial leads 30 permits a far greater total bandwidth for the
transmission of instrumentation data than is currently available in
bioelectrical stimulus leads.
[0021] Referring to FIG. 3, each of the insulated leads 20,
includes seven strands or fibrils 22, each of which is a 40 .mu.m
(1.57 mil) strand of MP35N, an alloy that is frequently used in
cardiac cables due to its durability and biocompatibility. MP35N is
widely available from several different suppliers. Alternatively,
one of the fibrils 22 is a drawn filled tube (DFT) with walls of
MP35N filled with silver. Immediately surrounding each group of
fibrils 22 is a bimaterial coat 24, having an interior coating 26
that is 25.4 .mu.m (1 mil) thick and is made of ethylene
tetrafluoroethylene (ETFE). An outer elastomeric coating 28 of coat
24 is 25.4 .mu.m (1 mil) thick and may be made of polyurethane.
Because ETFE has a higher melting temperature than polyurethane,
ETFE interior coating 26 may be coated with melted polyurethane,
without melting any of the ETFE.
[0022] Referring to FIG. 7, an alternative preferred embodiment
includes leads 20', in place of leads 20. Each lead 20' is made of
seven strands 21' of 12.7 .mu.m (0.5 mil) thick fibrils 23 of
MP35N. Lead 20' is even more resilient and wear resistant than lead
20. The use of the smaller diameter fibrils imparts superior
physical characteristics to cable 20' due to the inherently greater
flexibility and freedom from incusions of these fibrils 23.
[0023] Coat 24 is an important part of the present invention. The
principal problem that should be avoided in cardiac cables is that
of fibrils 22 breaking from extended fatigue. The breaking of a
fibril, however, does not typically occur in a single
undifferentiated step. Rather, the fibril first develops a sharp
bend or kink through extended wear. After the kink is formed a
break typically occurs fairly rapidly. If a fibril does not kink it
is far less likely to ever break. ETFE is a rigid mater al that
holds the fibrils so that they remain straight and unbent. ETFE is
also a low friction material, so that each set of fibrils 22 may
slide with respect to the interior surface of coating 26, thereby
avoiding internal strain. Elastomeric coating 28 provides
cushioning between neighboring leads 20 and helps to prevent fibril
kinking and fatigue by absorbing the shock caused by the heart
beats.
[0024] Surrounding insulated leads 20 is a 500 .mu.m (0.02")
tubular wall 50 of elastomeric insulating material, such as
silicone or polyurethane. Wall 50 is elastomeric or spongy enough
to dampen the vibrations caused by the beating of the heart yet
thick and substantial enough to help prevent kinking of the fibrils
22. Outside of wall 50 is a 100 .mu.m (0.004") tubular polyester
fiber braid 52. This braid imparts tensile strength to cable 10 not
only because of its own tensile strength but also because when it
is pulled it contracts radially, squeezing the interior portions of
cable 10 and thereby increasing the overall tensile strength of
cable 10.
[0025] Finally, at the radial exterior of cable 10 is a 127 .mu.m
(0.005") polyurethane or silicone wall 60. Preferably, this wall is
made of polyurethane with TFE end groups, to create a low friction
surface. A low friction surface 64 may be helpful when removing
cable 10 from a patient as is sometimes necessary. In addition, the
surface 64 may be ribbed or otherwise textured with a 10 micron
order of magnitude three dimensional structure designed to
encourage healthy tissue growth about the cable and to prevent the
growth of scar tissue. Interlinked holes within the range of 2-150
microns in diameter have been found to be an effective structure
for encouraging the growth of healthy tissue. In one preferred
embodiment surface 64 is textured with interlinked holes in this
size range. In an additional preferred embodiment the radially
outermost portion of cable 10 is separable from the portion
containing the leads 20, so that the lead containing portion may be
replaced without removing surface 64 which may be retained by body
tissue.
[0026] Referring to FIGS. 8 and 9 a bioelectrical stimulus cable
110 designed for the treatment of congestive heart failure includes
eight insulated leads 20' (shown in greater detail in FIG. 7), each
of which can be usec either for the transmission of power or for
the transmission of sensor data or control data. In the treatment
of congestive heart failure it is typically desirable to stimulate
the heart at a number of different sites. The presence of eight
leads, each of which could be used for power transmission in cable
110, permits flexibility in meeting these requirements.
[0027] Leads 20' are wound helically about a central silicone rod
112 that has a diameter of 333 .mu.m (13 mils). Surrounding leads
20' is a tube of silicone having a wall thickness of 0.33 mm (13
mils). Exterior to this tube is another tube 116 having a wall
thickness of 127 .mu.m (5 mils) being made of 80% polyurethane and
20% silicone. The entire cable 110 has a diameter of 1.65% mm (65
mils) as opposed to 3 mm for cable 10. This reduced diameter is
desirable in a cable for the treatment of congestive heart
failure.
[0028] The terms and expressions which have been employed in the
foregoing specification are used therein as terms of description
and not of limitation, and there is no intention, in the use of
such terms and expressions, of excluding equivalents of the
features shown and described or portions thereof, it being
recognized that the scope of the invention is defined and limited
only by the claims which follow.
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