U.S. patent application number 11/412767 was filed with the patent office on 2007-11-01 for intraluminal guidance system using bioelectric impedance.
This patent application is currently assigned to Medtronic Vascular, Inc.. Invention is credited to Alan Oliver Carney.
Application Number | 20070255270 11/412767 |
Document ID | / |
Family ID | 38229754 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070255270 |
Kind Code |
A1 |
Carney; Alan Oliver |
November 1, 2007 |
Intraluminal guidance system using bioelectric impedance
Abstract
A system using bioelectric impedance to guide a flexible
elongate transluminal device through an occlusion in a vessel. The
device can be a guidewire or a device for performing an
atherectomy, discectomy, ablation or similar technique. The device
includes a first electrode disposed on a distal portion of the
device. A second electrode is disposed in electric contact with the
patient separate from the first electrode. An electric current is
supplied between the first and second electrodes and a voltage drop
is measured between the first and second electrodes. The voltage
drop is converted to bioelectric impedance. Based on the impedance
measurement, a clinician can determine if the device is approaching
the vessel wall, permitting the clinician to redirect the device
away from the vessel wall.
Inventors: |
Carney; Alan Oliver; (Menlo,
IE) |
Correspondence
Address: |
MEDTRONIC VASCULAR, INC.;IP LEGAL DEPARTMENT
3576 UNOCAL PLACE
SANTA ROSA
CA
95403
US
|
Assignee: |
Medtronic Vascular, Inc.
Santa Rosa
CA
|
Family ID: |
38229754 |
Appl. No.: |
11/412767 |
Filed: |
April 27, 2006 |
Current U.S.
Class: |
606/35 |
Current CPC
Class: |
A61B 17/320758 20130101;
A61B 2017/00026 20130101; A61B 2017/22042 20130101; A61B 2017/22094
20130101; A61B 2017/22044 20130101 |
Class at
Publication: |
606/035 |
International
Class: |
A61B 18/04 20060101
A61B018/04 |
Claims
1. A guidance system for crossing an occlusion in a patient's
vessel, the system comprising: a first flexible elongate element
adapted for transluminally approaching and crossing the occlusion,
the first elongate element having a first electrode disposed
adjacent a distal end thereof, the first electrode electrically
connectable to the patient; a second electrode electrically
connectable to the patient, wherein the second electrode is a skin
electrode or the second electrode is disposed on a balloon, the
balloon mounted on a flexible elongate catheter adapted for
transluminal insertion into the vessel; an electric power source
connectable to the first and second electrodes and adapted to
provide an electric current thereto; and an impedance monitor
connectable to the first and second electrodes and adapted to
determine a bioelectric impedance there between.
2-4. (canceled)
5. The system of claim 1, wherein the first elongate element is a
guidewire
6. The system of claim 1, wherein the first elongate element is an
ablation device.
7. The system of claim 6, wherein the power source provides power
to the ablation device.
8. The system oft claim 7, wherein the impedance monitor is coupled
to a shut-off switch that shuts off power to the ablation device
when the impedance drops below a predetermined value.
9. The system of claim 1, wherein the current provided by, the
power source is an alternating current with a frequency in the
range of 1 kHz to 500 kHz.
10. The system of claim 1, wherein the impedance monitor is coupled
to an alarm that sounds when the impedance drops below, a
predetermined value.
11. The system oft claim 1, wherein the first elongate element is
an atherectomy device comprising a rotatable cutting head wherein
the first electrode is disposed on the cutting head.
12. The system of claim 11, wherein the impedance monitor is
coupled to a shut-off switch that stops the cutting head frown
rotating when the impedance drops below a predetermined value.
13. The system of claim 1, wherein the first elongate element is an
atherectomy device comprising a rotatable cutting head, further
comprising a guidewire disposed within the cutting head, wherein
tire first electrode is disposed on the guidewire.
14. A method for guiding a device through an occlusion in a
patient's vessel, the method comprising the steps of: delivering a
flexible elongate element transluminally to the occlusion, wherein
a first electrode is disposed on a distal portion of the elongate
element; advancing the elongate element into the occlusion;
providing a second electrode separate from the first electrode and
in electrical contact with the patient, wherein the second
electrode is a skin electrode or the second electrode is disposed
on a balloon, the balloon mounted on a flexible elongate catheter
adapted for transluminal insertion into the vessel; providing an
electric power source coupled to the first and second electrodes;
activating the power source to provide an electric current between
the first and second electrodes; measuring a voltage drop between
the first and second electrodes; and calculating a bioelectric
impedance based on the voltage drop between the first and second
electrodes.
15-17. (canceled)
18. The method of claim 14, wherein the step of activating the
power source to provide a current between the first and second
electrodes takes place in a pulsed sequence.
19. The method of claim 18, wherein the impedance is calculated
each time a current is provided between the first and second
electrodes.
20. The method of claim 14, further comprising the step of
advancing the elongate element through the occlusion as the current
is applied between the first and second electrodes.
21. The method of claim 14, further comprising, prior to advancing
the elongate element into the occlusion, the steps of: positioning
the first electrode in electrical contact with the vessel adjacent
the occlusion; measuring a voltage drop between the first electrode
and the second electrode; and calculating a predetermined
bioelectric impedance value based on the voltage drop between the
first second electrodes.
22. The method of claim 14, further comprising the step of
directing the elongate element away from the vessel wall when the
calculated impedance reaches a predetermined bioelectric impedance
value.
23. The method of claim 14, wherein an alarm is triggered when the
calculated impedance reaches a predetermined bioelectric impedance
value.
24. The method of claim 14, wherein the elongate element is a
guidewire.
25. The method of claim 14, wherein the elongate element is an
atherectomy device.
26. The method of claim 25, wherein the atherectomy device includes
a cutting head that rotates as the atherectomy device is advanced
through the occlusion.
27. The method of claim 26, wherein a shut-off switch stops the
rotation of the cutting head when the impedance reaches a
predetermined level.
28. The method of claim 14, wherein the elongate element is a laser
ablation device.
29. The method of claim 23, wherein the power source provides power
to the laser ablation device, and wherein a shut-off switch off
power to the laser ablation device when the impedance reaches a
predetermined level.
Description
FIELD OF THE INVENTION
[0001] The disclosure relates generally to a guidance system for
use in a patient's vessel, and more particularly, to a system for
guiding an intra-luminal device through an arterial chronic total
occlusion (CTO) using bioelectric impedance.
BACKGROUND OF THE INVENTION
[0002] Stenotic lesions may comprise a hard, calcified substance
and/or a softer thrombus material, each of which forms on the lumen
walls of a blood vessel and restricts blood flow there through.
Intra-luminal treatments, such as balloon angioplasty, stent
deployment, atherectomy, and thrombectomy are well known and have
proven effective in the treatment of such stenotic lesions. These
treatments often involve the insertion of a therapy catheter into a
patient's vasculature, which may be torturous and may have numerous
stenoses of varying degrees throughout its length. In order to
place the distal, treatment portion of a catheter within the
treatment site, a steerable guidewire is typically introduced and
tracked from an incision, through the vessels, and across the
lesion. Then, a catheter, e.g., a balloon catheter, perhaps
carrying a stent, can be tracked over the guidewire to the
treatment site. Ordinarily, the distal end of the guidewire is
quite flexible so that as it is directed, or steered through the
lumen, it can find its way through the turns of the typically
irregular passageway without perforating or otherwise damaging the
vessel wall.
[0003] In some instances, the extent of occlusion of the lumen is
so severe that the lumen is completely or nearly completely
obstructed, leaving virtually no passageway for the guidewire. Such
a condition may be described as a total occlusion. If this
occlusion persists for a long period of time, the lesion is
referred to as a chronic total occlusion or CTO. Furthermore, in
the case of diseased blood vessels, the lining of the vessels may
be characterized by the prevalence of atheromatous plaque, which
may form total occlusions. The extensive plaque formation of a
chronic total occlusion typically has a fibrous cap surrounding
softer plaque material. This fibrous cap may present a surface that
is difficult to penetrate with a conventional guidewire, and the
typically flexible distal tip of the guidewire may be unable to
cross the lesion.
[0004] Thus, for treatment of total occlusions, guidewire having
stiffer distal tips have been employed to recanalize a total
occlusion. However, blood vessels are not straight and fluoroscopic
visualization of the natural path through an occlusion is poor
because there is little or no flow of radiographic contrast through
the occlusion. Therefore, simply using a stiffer guidewire to push
through an occlusion increases the risk that the guidewire tip will
penetrate the vessel wall.
[0005] Atherectomy is another established treatment for occlusions.
Atherectomy procedures typically involve inserting a cutting or
ablating device through the access artery, e.g. the femoral artery
or the radial artery, and advancing it through the vascular system
to the occluded region, and rotating the device at high speed via a
drive shaft to cut through or ablate the plaque over the wire. The
removed plaque or material can then be suctioned out of the vessel
or be of such fine diameter that it is cleared by the
reticuloendothelial system. Atherectomy devices also present the
danger of unwanted perforation of a vessel wall by the material
removal device. This can occur when the material removal device
improperly engages the vessel wall, for example when the material
removal device is not oriented substantially parallel to the axis
of the vessel. In this situation, the material removal device, e.g.
cutter or abrasive ablator, may improperly engage the vessel wall
and cause unwanted damage thereto. Other ablation and discectomy
devices also present the danger of damage to a vessel wall.
[0006] Thus, there is a need for a device and method to reduce the
risk of damage to a vessel wall when a guidewire or a device for
performing an atherectomy, discectomy, ablation or similar
procedure is crossing an occlusion.
[0007] Electrical impedance is the opposition to the flow of an
alternating current, which is the vector sum of ohmic resistance
plus additional resistance, if any, due to induction, to
capacitance, or to both. Bioelectric impedance is known, e.g., for
use in measuring body fat composition. For example, bathroom scales
may include means to measure body fat composition using bioelectric
impedance. According to this technique, a person's body fat is
measured by determining the impedance of the person's body to
electrical signals, and calculating the percent body fat based upon
the measured impedance and other variables, such as height, weight,
age, and sex.
[0008] Bioelectric impedance is typically determined by supplying a
harmless electric current through at least two separated electrodes
that contact portions of a body, and measuring a voltage across the
body portion. This voltage is measured either (1) via the same
electrodes through which current is supplied, or (2) via one or
more distinct pairs of voltage-measuring electrodes. The
bioelectric impedance is then readily calculated from the current
and the measured voltage. The calculated bioelectric impedance may
be compared to an expected value or range of common or known
values, or it may be compared to one or more bioelectric impedance
values previously measured in, and calculated for the same
patient.
BRIEF SUMMARY OF THE INVENTION
[0009] The present disclosure is a system that uses bioelectric
impedance to guide an elongate intraluminal device through an
occlusion in a vessel. The device can be a medical guidewire or a
therapeutic catheter for performing an angioplasty, atherectomy,
discectomy, ablation or similar procedure. The device includes an
electrode disposed on a distal portion of the device. A second
electrode is disposed separately of the first electrode, either on
the same device or on a separate device. For example, the second
electrode may be mounted on a skin electrode or on a balloon of a
catheter. The system provides an electric power source and an
impedance monitor for connection to the first and second
electrodes.
[0010] During use of the above system to guide an elongate device
through a vessel occlusion in a patient, a first electrode is
disposed adjacent the occlusion targeted for crossing. A second
electrode is spaced apart from the first electrode and disposed in
electrical contact with the patient's tissue, e.g., against the
wall of the occluded or another vessel. The second electrode may be
a skin electrode in contact with the patient's skin. As the
elongate device is advanced through the occlusion, an electric
current is supplied between the first and second electrodes and a
voltage drop is measured between the first and second electrodes.
The voltage drop is converted arithmetically to a calculated
bioelectric impedance. By comparing the measured/calculated
bioelectric impedance to a known, e.g., expected standard or
previously measured impedance, a clinician can determine whether
the device is approaching the vessel wall and posing a risk of
perforating the wall. With this information, the clinician can halt
advancement of the device, and possibly redirect the device away
from the vessel wall.
BRIEF DESCRIPTION OF DRAWINGS
[0011] The foregoing and other features and advantages of the
disclosure will be apparent from the following description of the
disclosure as illustrated in the accompanying drawings. The
accompanying drawings, which are incorporated herein and form a
part of the specification, further serve to explain the principles
of the disclosure and to enable a person skilled in the pertinent
art to make and use the disclosure. The drawings are not to
scale.
[0012] FIG. 1 is a partial cut-away view of a vessel including an
occlusion and illustrating a system in accordance with an
embodiment of the present disclosure.
[0013] FIG. 2 illustrates the system as shown in FIG. 1, with the
introduction of a microcatheter.
[0014] FIG. 3 illustrates the system as shown in FIG. 2, with the
introduction of a guidewire.
[0015] FIG. 4 illustrates the system as shown in FIG. 3, with the
guidewire advanced into the occlusion.
[0016] FIG. 5 is a partial cut-away view of the system of FIGS. 1-4
illustrating a schematic representation of equipment outside of the
vessel.
[0017] FIG. 6 is a side view of a steerable guidewire of the
present disclosure.
[0018] FIG. 7 is a partial cut-away view of a vessel including an
occlusion and illustrating another embodiment in accordance with
the present disclosure.
[0019] FIG. 8 is a cross-section of a vessel including an occlusion
and showing another embodiment in accordance with the present
disclosure.
[0020] FIG. 9 is a plan view of a patient illustrating another
embodiment in accordance with the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Specific embodiments of the present disclosure are now
described with reference to the figures, where like reference
numbers indicate identical or functionally similar elements. The
terms "distal" and "proximal" are used in the following description
with respect to a position or direction relative to the treating
clinician. "Distal" or "distally" are a position distant from or in
a direction away from the clinician. "Proximal" and "proximally"
are a position near or in a direction toward the clinician.
[0022] The present disclosure is directed to a system and method
for guiding an elongate medical device, such as a guidewire or
catheter for performing an angioplasty, atherectomy, dissection, or
ablation, through an occlusion in a patient's vessel. Although the
present description relates to crossing an occlusion in a blood
vessel, such as an arterial stenosis, the invention is not so
limited, and may be applicable for providing guidance during
crossing of other blockages in other passageways in a patient. A
blood vessel 10 with an occlusion 12 blocking blood flow through it
is shown in FIGS. 1-4. A balloon catheter 14 with a balloon 16 near
its distal end is advanced through the vasculature to a position
proximal to occlusion 12, as shown in FIG. 1. Catheter 14 and
balloon 16 can be made of materials known to those skilled in the
art. In an embodiment of the present disclosure, balloon 16
includes a second, ring electrode 18 disposed about its periphery.
Optionally, a micro-catheter 20 is advanced through catheter 14
such that a distal portion of micro-catheter 20 extends from a
distal end of catheter 14, as shown in FIGS. 2 and 3. A guidewire
22 may be advanced through balloon catheter 14 and optional
micro-catheter 20 and extends into occlusion 12, as shown in FIGS.
3 and 4. Although FIG. 1 shows balloon 16 inflated for clarity of
the illustration, balloon 16 is typically advanced through blood
vessel 10 in an uninflated condition. Balloon 16 is inflated prior
to advancing guidewire through occlusion 12. Thus, balloon 16 need
not be inflated until after the step shown in FIG. 3, although it
can be inflated at anytime after being advanced through blood
vessel 10 to the position shown in FIG. 1. Further, although FIGS.
1-4 show balloon 16 with ring electrode 18, any suitable device can
be equipped with an electrode, provided that the electrode can be
maintained in electrical contact with the wall of the vessel during
crossing of the occlusion. For example, a second guidewire could be
used with an electrode disposed thereon and placed against the wall
of the vessel. Alternatively, the second electrode may be
positionable in electrical contact with the patient's tissue in a
different vessel, or outside of the patient's vascular system, or
outside the patient's body, viz. a skin electrode as will be
discussed below with respect to electrode 50.
[0023] Referring to FIG. 6, guidewire 22 includes a tip 24 with a
first electrode 26 disposed thereon. Guidewire 22 in FIG. 6 is
shown as a steerable guidewire. Any guidewire suitable for crossing
an occlusion may be used, as would be apparent to those skilled in
the art. Guidewire 22 can be fabricated from materials as known to
those skilled in the art. Electrode 26 may be an electrically
conducting electrode and can be fabricated from a variety of
conductive materials known in the art, including stainless steel,
copper, silver, gold, platinum and alloys and combinations
thereof.
[0024] Referring to FIG. 5, an electrically conductive lead 28
communicates with electrode 26, as by an insulated wire (not shown)
within guidewire 22, and lead 28 extends outside of the body to an
electric power source 32. An electrically conductive lead 30
communicates with ring electrode 18, as by an insulated or
otherwise electrically isolated wire (not shown) within catheter
14, and lead 30 extends outside the body to an electrical impedance
monitor 34. Power source 32 and impedance monitor 34 are connected
together externally or they may be combined in an integral device.
Power source 32 and impedance monitor 34, in conjunction with leads
28, 30 and electrodes 18, 26 form a complete electrical circuit
that includes a portion of a patient's body extending between
electrodes 18, 26. The materials that define the portion of a
patient's body in the electrical circuit will be discussed in
detail below.
[0025] Power source 32 generates a harmless electric current
through lead 28 between electrodes 26 and 30. The current may be a
pulsed and/or alternating current and the selected alternating
frequency may be in the range of 1 kHz to 500 kHz or other suitable
frequencies known to those of skill in the art of bioelectric
impedance. Ring electrode 18 may be fabricated from a variety of
conductive materials known in the art, including stainless steel,
copper, silver, gold, platinum and alloys and combinations thereof.
In an alternative embodiment of the disclosure, a smaller, viz.,
non-ring shaped electrode or a plurality of electrodes may be
disposed on balloon 16, provided such that that the electrode(s)
may be brought into electrical contact with the wall of vessel 10,
as by inflating balloon 16 into apposition with the vessel
wall.
[0026] In practice, as guidewire 22 is advanced through occlusion
12, power source 32 generates an electric current through leads 28,
30 and through the patient's tissue between electrodes 18, 26. The
current can be pulsed in a suitable range of pulse frequencies as
may be determined by those of skill in the art of bioelectric
impedance. While current is flowing through electrodes 18, 26, a
corresponding resistance or voltage drop is measured between
electrodes 18, 26. The voltage drop is arithmetically converted to
an impedance measurement at impedance monitor 34. Impedance monitor
34 may include logic resources, such as a microprocessor, and/or
memory resources, such as a RAM or DRAM chip, configured to
analyze, store and display bioelectric information derived from
electrodes 18, 26. For example, impedance monitor 34 may include a
voltage-current converting circuit, an amplifying circuit, an A/D
converting circuit, and an impedance arithmetic operation section.
Impedance monitor 34 may further include, or may be coupled to, a
display device 34d, such as a cathode ray tube, liquid crystal
display, plasma display, flat panel display or the like.
[0027] Occlusions 14 are generally made of atherosclerotic plaques.
Although atherosclerotic plaques may vary, they contain many cells;
mostly these are derived from cells of the wall that have divided
wildly and have grown into the surface layer of the blood vessel,
creating a mass lesion. Plaques also contain cholesterol and
cholesterol esters, commonly referred to as fat, that lie freely in
the space between the cells and within the cells themselves. A
large amount of collagen is present in the plaques, particularly in
advanced plaques of the type which cause clinical problems.
Additionally, human plaques contain calcium to varying degrees,
hemorrhagic material including clot and grumous material composed
of dead cells, fat and other debris. Plaques also contain about
10-20% water. This general composition of atherosclerotic plaques
results in a relatively high electrical resistance (and
correspondingly high bioelectric impedance), as compared to more
lean body tissue, such as vessel wall 10.
[0028] Thus, when electrode 26 located on tip 24 of guidewire 22 is
disposed generally at the center of occlusion 12, the electric
current from power source 32 passes through the relatively high
resistance atherosclerotic plaque of occlusion 12 before reaching
the relatively lower resistance wall of vessel 10. The current then
travels through the wall of vessel 10 to ring electrode 18. If tip
24 of guidewire 22 goes off-course such that it becomes closer to
the wall of vessel 10, then the current travels a shorter distance
through less thickness of the relatively high resistance
atherosclerotic plaque of occlusion 12 before reaching the wall of
vessel 10. Ultimately, if tip 24 approaches the wall of vessel 10,
the current passes through very little of the relatively high
resistance atherosclerotic plaque of occlusion 12 before reaching
vessel 10. Thus, the impedance detected between electrodes 18, 26
and displayed at impedance monitor 34 will decrease if tip 24
approaches the wall of vessel 10.
[0029] A clinician may stop the advancement of, and/or attempt to
redirect guidewire 22 away from the wall of vessel 10 when the
bioelectric impedance drops below a certain threshold value. Such a
threshold value may be measured and calculated by measuring
bioelectric impedance in undiseased vessel tissue adjacent target
occlusion 12, using the system of the disclosure prior to advancing
guidewire 22 into occlusion 12. Alternatively, a bioelectric
impedance threshold value for comparison during crossing of
occlusion 12 may be a value that may be predicted by an experienced
clinician, or a value that a large number of similar patients are
known to have in common, or a value that is otherwise available,
e.g., from a printed or electronic reference source. The
clinician's reaction to the bioelectric impedance reaching a low
limit may prevent tip 24 of guidewire 22 from piercing vessel 10.
Impedance monitor 34 may further include an alarm 34a such that
when the impedance reaches a predetermined limit, the alarm is
activated, thereby alerting the clinician that the impedance has
reached the predetermined limit.
[0030] FIG. 7 shows another embodiment of the present disclosure
which is similar to the embodiment shown in FIGS. 1-6 except that
an atherectomy device 36 is advanced through balloon catheter 14
into occlusion 12. Atherectomy device 36 includes a cutting head 38
that is rotated at high speed, e.g., via a drive shaft to cut or
ablate a passageway through the plaque of occlusion 12. The removed
plaque or material may be suctioned out of the vessel as is known
to those skilled in the art. A first electrode 44 is disposed on
cutting head 38. An electric current is provided through electrodes
18, 44 and a voltage drop is measured between electrodes 18, 44, in
the same manner as described above with respect to the embodiment
of FIGS. 1-6 (the power source, impedance monitor, and leads are
not shown). The measured voltage drop is converted to impedance by
the impedance monitor. Based on the calculated impedance, it can be
determined if cutting head 38 is too close to the wall of vessel
10. In such a case, advancement of atherectomy device 36 may be
halted and/or cutting head 38 may be redirected away from the wall
of vessel 10. In any of the embodiments wherein the device for
crossing occlusion 12 is power-assisted, impedance monitor 34 may
further include a shut-off switch 34s such that when the impedance
reaches a predetermined low limit, power to the device is shut-off.
For example, power to atherectomy device 36 may be shut-off by
switch 34s such that cutting head 38 stops rotating, thereby
preventing cutting head 38 from damaging vessel 10.
[0031] FIG. 8 is an alternative embodiment of atherectomy device 36
shown in FIG. 7. An atherectomy device 36a of FIG. 8 includes a
guidewire 40 disposed through and extending slightly beyond a
cutting head 38a. A first electrode 42 is disposed at the distal
tip of guidewire 40. Atherectomy device 36a functions in the same
manner as the device of FIG. 7, except that the electrode is
disposed in a different position.
[0032] In an alternative to the embodiments described with respect
to FIGS. 1-8, balloon 16 with ring electrode 18 is not required.
Instead, a second, skin electrode 50 may be placed externally on
the patient's chest, as shown in FIG. 9. In this embodiment, if one
of first electrodes 26, 42 or 44 is in occlusion 12, not near the
wall of vessel 10, then the impedance between first electrodes 26,
42 or 44 and skin electrode 50 may be safely above the bioelectric
impedance threshold low limit and the clinician can continue
advancing guidewire 22, atherectomy device 36, 36a, or a device for
performing laser ablation, discectomy, or other similar procedures.
When guidewire 22, atherectomy device 36, 36a, or a device for
performing laser ablation, discectomy, or other similar procedures
approaches the wall of vessel 10, the impedance between first
electrodes 26, 42 or 44 and skin electrode 50 may approach the
bioelectric impedance threshold low limit, and optionally providing
an audible or visual signal to the clinician. When a signal is
detected, the clinician may be alerted, for example, by impedance
monitor 34, to indicate that the device crossing occlusion 12 may
need to be redirected away from the wall of vessel 10. Upon
examination, the clinician may determine that the device has safely
passed through occlusion 12 and electrode 26, 42, or 44 may have
contacted the wall of vessel 10 distal to occlusion 12.
[0033] Impedance monitor 34 may include display device 34d, alarm
34a, and shut-off switch 34s, as described with respect to the
embodiment shown in FIG. 5. While the embodiment with skin
electrode 50 is described in conjunction with the detection of any
bioelectric impedance value indicating to the clinician that the
device may be approaching the vessel wall, the embodiments may be
interchangeable. For example, when using ring electrode 18 on
balloon 16, a low value of impedance may not be detected between
electrode 26, 42, or 44 and ring electrode 18 when guidewire 22 is
near the center of occlusion 12. Factors such as the frequency of
the current provided by power source 32 and the location of ring
electrode 18, for example, may be adjusted so that the device
functions in the "go/no-go" manner. Similarly, skin electrode 50
may be used in the embodiments described in FIGS. 1-8 such that
changes in the measured bioelectric impedance may apprise the
clinician of the anatomical location of the device in the patient,
instead of providing information regarding the distance of the
device from a surrounding vessel wall.
[0034] While various embodiments of the present disclosure have
been described above, it should be understood that they have been
presented by way of illustration and example only, and not
limitation. It will be apparent to persons skilled in the relevant
art that various changes in form and detail can be made therein
without departing from the spirit and scope of the disclosure.
Thus, the breadth and scope of the present disclosure should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the appended claims and
their equivalents. It will also be understood that each feature of
each embodiment discussed herein, and of each reference cited
herein, can be used in combination with the features of any other
embodiment. All patents and publications discussed herein are
incorporated by reference herein in their entirety.
* * * * *