U.S. patent application number 11/889294 was filed with the patent office on 2007-11-29 for heated catheter used in cryotherapy.
This patent application is currently assigned to CSA Medical, Inc.. Invention is credited to Jennifer B. Cartledge, Mark H. Johnston.
Application Number | 20070276360 11/889294 |
Document ID | / |
Family ID | 38336992 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070276360 |
Kind Code |
A1 |
Johnston; Mark H. ; et
al. |
November 29, 2007 |
Heated catheter used in cryotherapy
Abstract
Disclosed is a cryosurgical catheter which is heated in order to
prevent its freezing within the lumen of an endoscope. The catheter
is to be used with an endoscope to perform cryoablation on an
internal tissue; e.g., the esophagus. Electric conductivity to
produce heat employs an electrical conductive coating on the
catheter. Also, disclosed is a fitting for use with a catheter
comprising both a connection for receiving gas and an electrical
connection.
Inventors: |
Johnston; Mark H.;
(Lancaster, PA) ; Cartledge; Jennifer B.;
(Clemson, SC) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W.
SUITE 1100
WASHINGTON
DC
20036
US
|
Assignee: |
CSA Medical, Inc.
Baltimore
MD
|
Family ID: |
38336992 |
Appl. No.: |
11/889294 |
Filed: |
August 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10352266 |
Jan 27, 2003 |
7255693 |
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11889294 |
Aug 10, 2007 |
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10106985 |
Mar 26, 2002 |
7025762 |
|
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11889294 |
Aug 10, 2007 |
|
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|
09477839 |
Jan 5, 2000 |
6383181 |
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11889294 |
Aug 10, 2007 |
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09050150 |
Mar 30, 1998 |
6027499 |
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11889294 |
Aug 10, 2007 |
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60047484 |
May 23, 1997 |
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Current U.S.
Class: |
606/21 |
Current CPC
Class: |
A61B 18/02 20130101;
A61B 2018/00101 20130101; A61B 2018/0212 20130101; A61B 18/08
20130101 |
Class at
Publication: |
606/021 |
International
Class: |
A61B 18/02 20060101
A61B018/02 |
Claims
1. A catheter for cryogenically treating a desired area, the
catheter comprising: an elongated, flexible tubular body having a
proximal end, a distal end and a tubular passageway extending
therethrough for carrying a cryogen from the proximal end to the
distal end; the proximal end being adapted to receive a cryogen;
the distal end being adapted to dispense the cryogen to the desired
area at a low temperature and low pressure; the tubular body having
a heating element disposed circumferentially around at least a
portion thereof, the heating element extending longitudinally along
at least a substantial length of the tubular body.
2. A catheter for use in a cryosurgical procedure, comprising: an
elongated tubular member having a length, an inside for conveying
cryogen from a proximal end to a distal end, and an outside, the
distal end being open and adapted to spray cryogen at low
temperature and low pressure at selected target tissue; and a
heating element disposed longitudinally on at least a portion of
the tubular member for heating at least a portion of the length of
the catheter.
3. A cryosurgical apparatus for cryogenic spray ablation,
comprising a catheter having an elongated tubular member with a
length, an inside for conveying cryogen from a proximal end to a
distal end, and an outside, the distal end being open and adapted
to spray cryogen at selected target tissue, and a source of cryogen
attached to the catheter by a conduit, wherein the apparatus is
configured such that, in use, cryogen exits the catheter distal end
at low temperature and low pressure, and wherein the distal end of
the catheter is adapted to spray cryogen in a radial direction
substantially perpendicular to the axis of the catheter.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/352,266 filed Jan. 27, 2003, issuing Aug.
14, 2007 as U.S. Pat. No. 7,255,693; which is a
continuation-in-part of U.S. patent application Ser. No. 10/106,985
filed Mar. 26, 2002, now U.S. Pat. No. 7,025,762 issued Apr. 11,
2006; which is a divisional of U.S. patent application Ser. No.
09/477,839 filed Jan. 5, 2000, now U.S. Pat. No. 6,383,181 issued
May 7, 2002; which is a continuation-in-part of U.S. patent
application Ser. No. 09/050,150 filed Mar. 30, 1998, now U.S. Pat.
No. 6,027,499 issued Feb. 22, 2000; which claims benefit of U.S.
patent application Ser. No. 60/047,484 filed May 23, 1997, the
disclosures of which are herein incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention finds applicability in the field of
cryosurgery where a catheter is used to convey a cryogas to ablate
tissue.
BACKGROUND
[0003] In a companion application filed by the inventors, there is
claimed a method for ablation of tissue in the esophagus using a
cryogenic gas. In a specific therapeutic application, Barrett's
esophagus is treated, although other intestinal lesions may also be
treated. While the therapeutic treatment is effective, the cold
cryogenic gas tends to make the catheter stiff and unmanageable,
and at times rupturing the catheter. The herein disclosed invention
is designed to remedy the problem of catheter stiffening. The
inventors have solved this problem by a system by which the
catheter is heated and its flexibility maintained during cryogenic
surgery. Besides the issue of catheter flexibility, the heated
catheter is intended to eliminate the freezing of the catheter to
the lumen of an endoscope. Heating of the catheter will prevent ice
formation which causes sticking.
PRIOR ART U.S. PATENTS
[0004] Crockett (U.S. Pat. No. 5,800,488) teaches a cryoprobe with
a warming feature. The warming feature allows for the quick removal
of the probe after cryosurgery. Crockett does not teach the concept
of an electrically heated catheter.
[0005] Chang et al (U.S. Pat. No. 5,400,602) teaches a cryogenic
transport hose designed facilitate the supply and return of
cryogenic fluid such as a liquefied gas. Flexibility of the hose's
maintained by using multiple layers of reflective metallized
material, surrounded by a layer of foam material which, in turn, is
surrounded on outer cover all covering the gas supply. An electric
means for heating the transport hose is not shown by Chang et
al.
[0006] Lee (U.S. Pat. No. 3,298,371) teaches a cryogenic probe
useful in neurosurgery. The Lee patent also teaches an electric
means for heating the exterior of the probe. This heating means is
provided in the event the insulation on the exterior of the probe
is inadequate to thermally isolate non-target tissue surrounding
the probe. In this way, non-target areas will not be affected by
the cold, and only the cold probe tip will be presented to the
target area. While Lee discloses an external heating means, the
reference is silent as to teaching externally heating a catheter
which is to be used to convey a gas during a cryosurgical
procedure.
[0007] Barken (U.S. Pat. No. 5,531,742) teaches a computer
controlled cryosurgery apparatus. No electrical catheter heating
means is shown by Barken.
[0008] Thomas (U.S. Pat. No. 3,507,283) discloses a cryosurgical
probe whose temperature is precisely controlled to a desired heat
or cold level. Thomas employs heating wire along the external
surface of the instrument. Also shown is a cover of heat shrinkable
polytetrafluoroethylene to protect the user's hand from the cold.
This patent does not disclose the heating of a catheter which is to
be used during cryosurgery in which a gas is to be applied during
cryoablation.
[0009] Griswold (U.S. Pat. No. 5,658,276) teaches a heated
cryosurgical probe with a heated exterior which is able to release
a frozen probe from cryoablated tissue so that areas of the body
not being treated by the probe are not damaged by the cold
instrument. The heat is produced by a battery-energized external
surface of the probe. Griswold does not teach a heated catheter
used to spray a cryogas during internal cryosurgery.
SUMMARY OF THE INVENTION
Principles of Cryotherapy
[0010] The goal of cryotherapy is to freeze a specified volume of
tissue resulting in necrosis without significant damage to the
surrounding "innocent" tissues. Factors that facilitate this are
rapid freezing, slow thawing and repetition of the freeze-thaw
cycle. The cryoburn, the lesion of cryotherapy, is recognizable as
a white, sharply demarcated, frozen, patch of tissue (FIG. 31).
Unlike mucosal ablation with other modalities, ablation is not
immediately apparent after thawing of the cryoburn, which occurs
within seconds to minutes after application of the cryogen ceases.
Once the cryoburn thaws there is mucosal hyperemia. Blistering and
shedding of the mucosal layer does not occur for at least 24 hours.
Immediate cryonecrosis can occur at extremely cold temperatures of
sufficient duration, but does not occur with spray cryotherapy as
described below. Parameters that influence the degree of
cryo-injury are cooling rate, tissue temperature, duration of
freeze, thawing rate and repetition of the freeze-thaw cycle (Gage
et al, Cryobiology 1998; Mazur, Science 1970). Mazur demonstrated
that rapid freezing and slow warming lead to maximum cell death.
Current investigation indicates that the necessary temperature for
cell death is between -40.degree. to -15.degree. C.(10). However,
to achieve immediate cell death via cryonecrosis freezing of
sufficient duration at temperatures between -76.degree. C. and
-158.degree. C. must be attained (Grana et al, Int. Surg.
1981).
[0011] If cell hypothermia is of sufficient duration, cell
organelle and protein damage will occur leading to cell death
through physical breakdown of the cell membrane or through
induction of genetically controlled apoptosis. Apoptosis is a
protective mechanism by which senescent, DNA-damaged, or diseased
cells that could either interfere with normal function or lead to
neoplastic proliferation are induced to die. Cryotherapy at
relatively warm temperatures in the range of -15.degree. C. has
been shown to induce cell death via induction of apoptosis (Clarke
et al, Molec. Urol. 1999). This is potentially a unique mechanism
for the treatment of Barrett's esophagus and dysplasia as some
investigators have identified arrest of apoptosis as one of the
pathologic mechanisms involved in Barrett's (Katada, Arch. Surg.
1997).
[0012] The processes associated with delayed injury begin with the
immediate freeze of targeted and surrounding tissues. Consequent to
this is vasoconstriction and microthrombi formation in the venules
and capillaries resulting in vascular stasis. Tissue ischemia
follows with subsequent cell death (Dawber et al, Prin. and Clin.
Proc. 1992). This mechanism may play a unique role in
gastrointestinal endoscopy in the realm of hemostasis.
[0013] The most delayed cellular mechanism associated with
cryotherapy is the cryo-immune response. When neoplastic or other
tissue is injured through freezing its antigens are released
without being destroyed like in other thermal ablative techniques.
The release of tissue antigen from cryo-injury serves as a nidus
for the development of tumor specific immunity and is unique to
cryotherapy relative to other thermal ablative techniques. Shulman
et al demonstrated that the in situ freezing of tissue constitutes
an antigenic stimulus at least equal to that obtained through the
parenteral administration of antigen which is capable of generating
a specific immunologic response to autologous antigens of the
frozen tissue (Shulman et al, Proc. Soc. Exp. Biol. 1967). Grana et
al demonstrated that in situ freezing of canine esophagus resulted
in a cellular response directed to the antigens present in extracts
of esophageal mucosa and muscularis and that repeated freezing
resulted in an increased response to those antigens suggesting an
anamnestic response (Grana et al, Int. Surg. 1981). The cryoimmune
response may play a unique role in the treatment of mucosal
neoplasms in the gastrointestinal tract such as adenocarcinoma of
the esophagus.
[0014] Certain tissues may have variable sensitivity to cryotherapy
and this difference may be exploited in treatment (Sheski, Clinics
in Chest Med. 1999).
Cryosurgical Procedures
[0015] A completely automated system with sensors and a
microprocessor are employed for performing cryosurgery. It is an
important preferred feature of the present invention that the spray
be conducted in such a manner as to allow constant visualization by
the physician of the tissue treatment as it occurs. If the
temperature of the lens at the distal end of the endoscope drops
precipitously at the start of the liquid nitrogen spray, the moist
air of the esophageal environment or of the air of the catheter
which has been blown out ahead of the nitrogen flow will condense
on the lens, thereby obscuring the physician's view of the
operative site. This can be substantially avoided by means of the
suction pump which will immediately suck out the moist air which is
present prior to the arrival of the liquid nitrogen spray or cold
nitrogen gas. Because of this pumping out of the moist air as the
spray commences and the replacement with extremely dry nitrogen
gas, substantial amounts of moisture will not form on the lens
during the procedure, allowing an excellent view of the operative
site by the physician during the procedure.
[0016] This condensation effect is augmented by the fact that the
catheter itself is preferably not wrapped in additional insulation.
This causes the temperature of the nitrogen gas exiting the
catheter at the distal end to be relatively high at the beginning
of the spraying operation and gradually cooling as the catheter
cools. Indeed, in the tests conducted in the esophagus of pigs
discussed below in the Examples, often 10-20 seconds were necessary
before significant freezing was seen through the endoscope. If the
catheter is substantially insulated, the interior of the catheter
will cool much more quickly as it will not be picking up heat from
the outside. With this insulated catheter, it is to be expected
that the liquid nitrogen would be sprayed onto the tissue almost
immediately, causing much faster freezing and, thus, allowing less
control on the part of the physician.
[0017] Another reason that the lens does not fog or frost in the
present invention is that the esophagus is flushed out with
nitrogen gas, which is extremely dry. The nitrogen gas is moisture
free because the liquid nitrogen is condensed out of atmospheric
gases at a temperature -196.degree. C. colder than the temperature
at which moisture is condensed out.
[0018] The combination of relatively warm, and completely dry
nitrogen gas, together with suction flushes all moist air from the
esophagus. As the temperature of the gas entering the esophagus
falls, so does the surface temperature of the camera lens.
Ordinarily at that time the lens would be cold enough to condense
moisture and fog, however, since the esophagus is dried out (in
contrast to its usual highly moist state) there is no moisture to
condense. Thus, the lens stays un-fogged and un-frosted and
continues to provide a clear view of the operation. On the other
hand, if the esophagus is not vented with suction and/or the
esophagus is not preliminarily flushed with dry nitrogen gas
(perhaps because the catheter is insulated, lowering its heat
capacity, and/or the nitrogen delivery pressure is too high), then
the lens is likely to fog or frost and the physician cannot operate
effectively.
[0019] In order to deal with the moist air problem, there is
supplied in the preferred embodiment of this invention a
nasogastric tube. During the cryosurgical procedure the nasogastric
tube is inserted prior to inserting the endoscope. The nasogastric
tube, when connected to a pump, can serve to evacuate moist air
from the esophagus prior to cryosurgery. With moist air removed,
the TV camera lens is not obscured by fog and the physician can
perform cryosurgery with an unobstructed view. Alternatively, if
fogging occurs during cryosurgery, the nasogastric tube and pump
can be used to evacuate the esophagus.
[0020] In the most preferred embodiment, the composition of the
catheter or the degree of insulating capacity thereof will be
selected so as to allow the freezing of the mucosal tissue to be
slow enough to allow the physician to observe the degree of
freezing and to stop the spray as soon as the surface achieves the
desired whiteness of color (cryoburn). The clear observation
results from the removal of the moist air and sprayed nitrogen by
the vacuum pump; in combination with the period of flushing with
relatively warm nitrogen prior to application of the spray of
liquid nitrogen which is caused by the relative lack of insulation
of the catheter. Preferably, the catheter has a degree of
insulation which permits at least five seconds to pass from the
time said means for controlling is opened to the time that
liquified gas is sprayed onto the mucosa. As a preferred
embodiment, an electrically heated catheter is described
herein.
[0021] An electronic monitoring and recording system is to be used
during cryosurgery. The electronic components of the system
comprise a temperature sensor or probe and timer. Also connected to
the monitoring and recording system are the foot-pedal for
actuating the solenoid and recording console. An electric power
cord runs from solenoid to control box.
[0022] The temperature sensor is thin and can be inserted into the
esophagus beside the catheter. In a preferred embodiment, the
temperature sensor and catheter can be inserted separately or as an
integral unit of sensor and catheter combined, or alternatively the
sensor can be inserted through an extra lumen of the endoscope to
come in contact with the tissue of the esophagus. The temperature
sensor sends temperature readings to the electronic monitoring and
recording system for processing and recordation.
[0023] The liquid gas flow is started by actuating solenoid
foot-pedal and ends with release of the solenoid foot pedal The
electronic monitoring and recording system records the times at
which cryoburn starts and ends. Temperature in the context of time
will be recorded for the cryosurgery. This recordation allows for
better data acquisition and documentation.
[0024] There is an automatic cut-off if a time or temperature
limitation is exceeded. In the event of a cut-off, the electronic
monitoring and recording system can be reactivated by pushing the
reset button. Current time and temperature readings are presented
in the windows as LED numbers. The windows in the system will
indicate total time; shut-down time; cryotime; cryotime set; and
temperature. Within the main console of the electronic monitoring
and recording system is a printing unit which prints and records
the time and temperature during the cryoburn. Every event is
recorded, e.g. time, on and off, temperature, etc.
[0025] The electronic console can be preprogrammed to be patient
specific.
Kit Supplying Components of the Invention
[0026] The components or paraphernalia required to practice the
method of the present invention may be packaged and sold or
otherwise provided to health-care providers in the form of a kit.
The kit is preferably sealed in a sterile manner for opening at the
site of the procedure. The kit will include the catheter, having
the spray means at one end, as well as a means for connecting the
catheter to the source of liquified gas. This means for connecting
may be a simple luer connection on the opposite end of the catheter
from the spray means. However, the term "means for connecting said
catheter to a source of liquified gas" is intended to include any
other device or apparatus which allows the catheter to be connected
to the gas source.
[0027] Many of the components of the cryosurgical system are
conventional medical appliances. For example, the endoscope is a
conventional medical appliance and would not necessarily have to be
supplied as part of a kit. One of the components to be supplied in
a kit or sterilized package is a combined catheter-bleeder vent.
Also, the heated catheter assembly would be supplied in a kit or
sterilized package.
[0028] The inventors envision supplying the heated catheter and
vent unit as a separate item. In this way, the unit can be supplied
in a sterile packet or kit to be used with existing equipment found
in hospital operating rooms. The kit may contain a nasogastric
tube, or the kit could contain only a heated catheter unit.
[0029] The means for controlling the flow of liquified gas to the
catheter is also preferably present in the kit and may be connected
to or may be part of the means for connecting the catheter to the
source of liquified gas. For example, the connector may contain a
valve therein or the valve may be a separate element connected
between the connector and the catheter or between the connector and
the nitrogen source. The connector besides being connected to the
source of gas can also be a connector to the source of
electricity.
[0030] The kit will also optionally contain the means for
withdrawing gas, such as a tube and a means connectable to the tube
for withdrawing gas from the tube. Such means connectable to the
tube for withdrawing gas may be a vacuum pump or any other device
or apparatus which will accomplish the function of withdrawing gas
from the tube. The vacuum pump is optionally omitted from the kit
as a source of vacuum is often found in hospital rooms in which
such a procedure is to take place.
[0031] The means for blocking the lumen is also optionally present
within the kit. Thus, for example, the kit may contain a balloon
catheter or any other device or apparatus which can accomplish the
function of blocking the lumen when in use.
[0032] The term "container" or "package" when used with respect to
the kit is intended to include a container in which the components
of the kit are intended to be transported together in commerce. It
is not intended to comprehend an entire procedure room in which the
individual components may happen to be present, an entire vehicle,
a laboratory cabinet, etc.
Pressure During Cryosurgery
[0033] In an embodiment of the invention, the bleeder valve has
been found to be unnecessary so long as low pressure can be
maintained by other means. In the improved embodiment, a cryoburn
is carried out without the need for a bleeder valve. In this new
embodiment with the tank pressure at 45 psi and the catheter being
a 9 french, the cryo-procedure took 4 minutes and 50 seconds. With
a 10 french catheter using 45 psi, the cryo-procedure took 2
minutes and 50 seconds to achieve a cryoburn temperature. With the
bleeder valve, it takes 10-20 seconds to achieve cryoburn. The
ideal low pressures operative for this invention should be in the
range of 3-45 psi. The most ideal pressure is determinable by those
skilled in the art.
[0034] Regarding pressure 40 psi is preferred, the cryogenic spray
will function at higher pressures. The system could be made to work
at tank pressures as high as 300-400 psi by adjusting the size of
the bleeder line and by using a larger size catheter. Note,
however, that tip pressure is only one factor to be considered for
producing cryoburn. Other factors to consider are size of catheter
and length of time of application. Certain clinical conditions may
require differing pressures and differing time of cryoburn. The
nozzle or tip pressure for cryosurgery should not be so high as to
puncture any internal organ and optimum nozzle pressure can be
determined by those skilled in the art.
[0035] The cryosystem could function at significantly higher nozzle
pressures by adjusting other factors of the protocol. Significantly
higher nozzle pressures would be operative if the treatment exposed
the tissue to shorter cryoburn exposure time. The higher pressures
may necessitate the need for a vacuum line to remove the excess
volume of nitrogen introduced into the body cavity.
[0036] In the future, technology may reduce the size of the
components of the endoscopic. This would allow additional diameter
for the catheter. If the diameter of the catheter is increased, the
flow of the cryogen could also be increased without affecting the
treatment parameters. Potentially, the catheter could be used along
side of the endoscope rather than through the lumens of the
endoscope. Then the size limitation of the catheter could be
modified.
[0037] Additionally, the holding tank could be stored at much
greater pressures. The higher the storage tank pressure, the less
nitrogen bleed off that will occur, resulting in a lower loss of
nitrogen during storage. The temperature of the liquid nitrogen
stored at pressures higher than 22 psi is warmer than that of the
liquid nitrogen stored at 22 psi. At 200 psi (this is the highest
pressure tested) the liquid nitrogen is still cold enough to
deliver a cryoburn.
[0038] The high-pressure tank can be staged in any conceivable
manner. A 700 psi storage tank could be staged down by altering the
size of the bleeder, by altering the size of the catheter, or by
adding additional bleeder lines. A 700 psi flow to 3-5 psi can be
accomplished in a number of ways as understood by those skilled in
the art.
[0039] The inventors have checked nozzle pressures of catheters and
found for tank pressure of 22 psi and a 9-French catheter the
nozzle pressure is 2-3 V.sub.2 psi; and for tank pressure of 22 psi
and a 10-French catheter the nozzle pressure is 3.2-5.9 psi.
[0040] It is clear from experiments performed that a bleeder valve
is not absolutely essential to this invention since low pressure
cryoablation can be carried out through low head pressure in the
storage tank or through selection of the proper inner diameter of
the catheter. Based on experiments carried out with the bleeder
valve embodiment a shorter time period is required for
cryoburn.
[0041] A convenient and preferred means of supplying the cryogenic
gas under pressure and in liquid form would be to employ a
compressor to compress the gas to be used with the catheter before
it is to be used in cryosurgery.
Cryoburn Conditions
[0042] The inventors have concluded from preliminary test results
that a 30 second "cryoburn" time was adequate to ensure the
appropriate tissue destruction, and thus appropriate cellular
healing of damaged tissue (this conclusion was based on a 30 day
follow up period).
[0043] "Cryoburn" is a term defined by the instance that the
normally "pinkish" esophageal tissue turns white (much like freezer
burn). A range for the "cryoburn" time could be 5-10 seconds to 2
minutes or more depending on the substrate to be treated.
[0044] Due to the nature of the system, "cryoburn" does not
immediately occur, but rather requires that the entire fitting and
catheter system become cool. Typically this required approximately
20-30 seconds from the time that the solenoid foot pedal is
depressed, and liquid nitrogen is allowed to flow from the
tank.
[0045] During animal testing the approximate temperature that
cryoburn was first observed was at approximately -10 degrees C. The
temperature range for cryoburn would be approximately -10 to -90
degrees C.
[0046] In carrying out the procedure, a nasogastric tube is first
inserted into the esophagus, after which an endoscope is inserted.
Optionally, attached to the endoscope will be a temperature probe
to sense the temperature and report the temperature to the
recording console. Once the nasogastric tube, endoscope and
temperature probe are in place, the catheter attached to the gas
supply will be inserted into a lumen of the endoscope. Before
liquid gas is supplied, the esophagus is ventilated using the
nasogastric tube to remove moist air from the esophagus (if
required). With the moisture evacuated and the endoscope properly
positioned, gas can be supplied to the catheter by actuating the
solenoid with foot pedal. Once the solenoid is actuated gaseous
nitrogen and then a spray of liquid nitrogen will come from the tip
of the catheter. The cryoburn will generally last for 30 seconds to
two (2) minutes.
[0047] In further developing the cryogenic spray system, the
inventors envision positive advantages in over-exposing the
esophagus to the cryoburn. The scarring that occurs could be
helpful for patients that have chronic reflux. There are currently
a number of techniques that work to "tighten" the lower esophageal
sphincter. The scarring that occurs during over exposure in the
cryosurgical method of the disclosed invention could be an
additional treatment of chronic reflux.
Experiments
[0048] The cryospray was used in experiments to assess the efficacy
and safety of this device in mucosal ablation in the distal
esophagus of swine. The catheter was a long 7Fr ERCP-like catheter
placed through the biopsy channel of an Olympus GIF-100 endoscope.
The swine were sedated using telazol and xylazine given
intravenously. General anesthesia was not necessary. Liquid
nitrogen was sprayed on the distal 2 cm of the esophagus in 16
swine under direct endoscopic observation until a white "cryo-burn"
appeared, usually within 10-20 seconds. Duration and location of
the spray were varied to assess histologic response and depth of
"cryo-burn". The swine were then re-endoscoped on days 2, 7, 14, 21
and 30 to obtain biopsies from the injury site, assess mucosal
ablation and re-epithelialization. All swine were then euthanized
and underwent necropsy.
[0049] Freezing of the esophageal mucosa was recognizable by a
white "cryo-burn" with sharply demarcated margins. This was
followed by slow thawing within minutes and then mucosal erythema.
Sixteen swine underwent hemi-circumferential to circumferential
cryotherapy of their distal esophagus varying the duration of
"cryo-burn" from 10-60 seconds. Blistering and sloughing of the
superficial mucosa occurred within 2 to 7 days of the cryospray.
Mucosal damage occurred only at the cryo site. Biopsies 48 hours
after cryospray consistently demonstrated coagulative necrosis
involving the mucosal layer and biopsies 30 days after cryospray
consistently demonstrated complete re-epithelialization of the
injured area.
[0050] These experiments on living swine, which are a valid model
of the human esophagus, establish that cryotherapy spray of liquid
nitrogen via upper endoscopy is a simple technique capable of
inducing controlled superficial mucosal damage with complete
healing in the esophagus.
[0051] The low-pressure device (FIGS. 28 and 29) described by
Johnston (Gastrointest. Endoscop. 1999) and colleagues, uses liquid
nitrogen in a specially designed system that operates at a maximum
of 30 psi. The catheter, 10F, is multilayered. Its outer sheath is
coated with a special polymer that can be warmed during the cryo
application, thus maintaining catheter pliability and the unique
ability to operate at a very low pressure. This device also uses a
foot pedal for control of gas release and a temperature probe for
monitoring mucosal temperature during the cryo application. With
this delivery system, the depth of injury is controlled by
manipulating 3 parameters: the duration of cryo application, extent
of cryoburn viewed endoscopically, and the temperature of mucosa at
the time of application. These parameters are monitored via a
special software program and device that is part of the cryogenic
system (FIG. 29).
Low Pressure Cryo-therapy Device
[0052] Four separate phases of animal research have been conducted
with the low-pressure device. In the first phase, twenty swine
underwent cryoablation of the distal 2-3 cm of their esophagus with
liquid nitrogen in either a hemi-circumferential or circumferential
pattern and were followed for one month post-cryotherapy (Johnston,
Gastrointest. Endosc. 1999). In the second phase, 8 swine were
treated hemi-circumferentially to the distal 3 cm of the esophagus
and followed for 90 days. In the third phase of experiments, 4
swine underwent endoscopic ultrasound (EUS) of their esophagus
pre-cryo, immediately post cryo and then at 48 hours, 7 days and 14
days to assess the effects on the esophageal wall. In the final
phase, one swine was treated in different locations with Argon
plasma coagulation (APC), Multi-polar electrocoagulation (MPEC) and
cryotherapy. The lesions were then compared both endoscopically and
microscopically.
Phase I
[0053] In twenty swine liquid nitrogen was sprayed
hemi-circumferentially or circumferentially to the distal 2-3 cm of
the esophagus. Duration of spray was varied from 10 to 60 seconds.
The cryoburn appeared at mucosal temperatures between 0 to
-10.degree. C. and was limited to the targeted site. Mucosal
ablation was noted 2 to 7 days post cryo in 19 of the 20 swine. The
swine esophagi were completely normal at 30 days in 17 of the 20
animals. Three developed esophageal strictures and one, aspiration
pneumonia. All strictures occurred in the circumferentially treated
group. The aspiration pneumonia occurred in the first swine ever
treated and occurred secondary to gastric insufflation with air.
Two of the three strictures were minimal with easy passage of the
scope; the third would have required dilation. Complete mucosal
healing was observed in all swine by week 4. There were no deaths
attributable to cryotherapy. This initial study demonstrated
feasibility, efficacy and safety in mucosal ablation relative to
other mucosal ablative techniques (see FIGS. 32 and 33).
Phase II
[0054] In this phase hemi-circumferential cryoablation of the
distal 3 cm of the esophagus was performed in 8 swine using a 45
second treatment cycle. Complete ablation was noted at the targeted
area in all swine at 48 hours. Residual ulceration persisted in all
up to 7 days post-cryo followed by complete healing with no
stricturing by 4 weeks follow-up. There were no complications and
the swine were followed for a total of 90 days with no development
of esophageal stricturing or complications. They gained weight
normally.
Phase III
[0055] Four swine underwent EUS of their distal esophagus to assess
wall thickness and establish baseline anatomy. Following baseline
EUS, each swine underwent a 45 second hemi-circumferential cryoburn
to the distal esophagus which was followed by repeat EUS
immediately and then at 2, 7 and 14 days (FIGS. 36 and 37). The
cryoburn became endoscopically evident at -9.degree. C. The coldest
mucosal temperature measured was -66.degree. C. occurring at the
end of the 45-second treatment. After EUS at 14 days, the swine
were euthanized and underwent esophagectomy to assess the esophagus
histologically. EUS demonstrated edema of the mucosa and submucosa
5 minutes post cryo. At one week there was separation of the
mucosal layer from the underlying structures. Associated with this
was edema throughout the other layers of the esophagus at the cryo
site. In most instances the wall thickness doubled. These findings
resolved by day 14 post cryo. Full thickness biopsies were obtained
on one of the swine to evaluate cryo lesions at two different
stages of evolution, one less than an hour old (FIG. 34) and one
approximately 48 hours old. These biopsies revealed extravasation
of RBCs into the submucosa with normal overlying epithelium at one
hour, while another site 48 hours post cryo (FIG. 35) revealed
complete ablation of the epithelial layer (0.5 to 1.0 mm) with mild
transmural inflammation.
Phase IV
[0056] In this phase one swine had three different ablative
modalities applied to the esophagus. In the very distal esophagus a
cryoburn was applied in a 1-2 cm hemi-circumferential pattern for
45 seconds. The coldest mucosal temperature measured at the end of
the freeze cycle was -25.degree. C. Proximal to this, MPEC was
applied at 24 Watts via 10F Gold probe (Microvasive, Watertown,
Mass., USA) to a 1-2 cm area. Proximal to this, APC was applied at
90 Watts on one side of the esophagus and at 60 Watts on the
opposing side using a flow rate of 2 L/min (ERBE USA, Inc.,
Marietta, Ga.). The swine was then re-endoscoped 48 hours latter
and repeat ablation with all three modalities was performed in
different areas followed by euthanasia and esophagectomy to assess
both the acute and 48 hour lesions. See FIG. 38. Epithelial
ablation was immediate for both APC and MPEC whereas the epithelium
remained intact at the cryo site one hour post-ablation. At 48
hours post-ablation there was an extensive inflammatory response
extending into the esophageal wall for APC and MPEC. It was
transmural for APC at 90 W and less extensive for APC at 60 W. The
MPEC inflammatory response was similar to the APC at 60 W response.
The cryo inflammatory response was significantly less than APC or
MPEC.
Depth of Injury in Cryotherapy
[0057] Barrett's esophagus is a mucosal disease defined as the
presence of specialized intestinal metaplasia in the esophagus.
This includes not only the epithelial elements but also the
glandular structures down to the level of the muscularis mucosa.
Barrett's epithelium is on average 0.5 mm thick with Barrett's
mucosa 1.5 mm thick (Ackroyd, J. Clin. Path. 1999). The esophageal
wall is thickest distally measuring approximately 4 mm by EUS
(Faigel, Gastrointest. Endosc. 2002). Depth of injury reported in
the literature varies considerably for each ablative modality. The
depth for MPEC is between 1.7 to 4.8 mm depending on watt setting,
degree of pressure applied to the probe and duration of application
(Sampliner, Gastroenterology Clinics North America 1997). PDT is
reported to have a depth of 1-2 mm but seems inconsistent with the
high stricture rate that exceeds that of MPEC or APC. Sampliner
reports that depth of injury generally follows this pattern: PDT
and Nd:Yag>MPEC>Argon laser (Sampliner, Gastroenterology
Clinics North America 1997). In our study (APC, MPEC and cryo)
comparing depth of injury side by side in the same living animal we
learned the following. Full depth of injury is not readily apparent
upon completion of an ablative treatment and evolves over time
depending on the technique used. There are both immediate and
delayed injuries contributing to the final depth of ablation. For
APC and MPEC, there is immediate ablation through cautery of the
tissue contacted by the argon gas or MPEC probe accounting for the
immediate destruction of the epithelial layer noted in FIG. 38. For
APC, MPEC and cryo there is also a delayed inflammatory response,
which results in cellular necrosis and extends the depth of injury
depending on the degree of inflammation. For cryo, depending on the
maximum negative temperature achieved (at least -20.degree. C.)
there is immediate ablation of epithelium caused by cryonecrosis,
not observed in this particular comparative treatment protocol.
There is also delayed injury resulting in ablation that occurs as a
result of the processes described above (Gage, Cryobiology 1998).
Epithelial ablation (0.5-1.0 mm) occurred immediately for APC and
MPEC and was easily detected on full thickness biopsy one hour
after application. In the cryotherapy lesion the epithelium
remained intact at one hour. However, significant ablation did
occur over time through the subsequent inflammatory and delayed
responses described in the principles of cryotherapy section of
this chapter. When compared side by side, the inflammatory response
was greatest with APC at 90 W followed by APC at 60 W then MPEC and
then cryo. Microscopically, depth of injury ranged from 4-1 mm and
paralleled that of the inflammatory response in the same order.
From phase one of the cryo studies, assessed via endoscopy, gross
injury was delayed and peaked between 2 to 7 days post cryo.
However, by four weeks healing was complete in all swine. Depth of
ablation based on these studies is approximately 1-2 mm and is very
similar to MPEC.
Heated Catheter Embodiments
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0059] FIG. 1 is a perspective view of the heated catheter
assembly. Part of the catheter is broken away for ease of
illustration.
[0060] FIG. 2 is a cross-section of the heated catheter assembly,
taken along 2-2 of FIG. 1, with the hub portion broken away.
[0061] FIGS. 3, 5 and 6 are views taken along cross-section 5-5 of
FIG. 2 to show components forming the heated catheter. FIG. 4 is a
cross-section taken along 4-4 of FIG. 2.
[0062] FIGS. 7-11 illustrate the steps taken to construct the
heated portion of the catheter. These views are cross-sections
taken longitudinally as 2-2 in FIG. 1.
[0063] FIGS. 12-18 show the method for assembling the hub portion
of the heated catheter.
[0064] FIG. 19 is a perspective view of the gas and electric
connector subassembly.
[0065] FIG. 20 is a cross-section thereof taken along lines 20-20
of FIG. 19.
[0066] FIGS. 21-27 illustrate means by which the catheter is
jointed to the gas and electric connector subassembly, with FIGS.
21-23 being longitudinal cross-sections of the gas and electric
subassembly and top of the hub.
[0067] FIG. 24 is a plan view of the gas and electric connection
joined to the hub. The arrows show the direction for joining the
components.
[0068] FIGS. 25 and 26 are cross-sectional views taken off of 25-25
and 26-26 of FIG. 20.
[0069] FIG. 27 is an enlarged longitudinal cross-section of the
heated catheter.
[0070] FIG. 28 is a photograph of the heated catheter.
[0071] FIG. 29 is a photograph of the complete low pressure spray
cryotherapy device.
[0072] FIG. 30 is a photograph of an endoscope that can be used in
cryotherapy.
[0073] FIG. 31 through 38 are photographs of cryoburns and
histology resulting therefrom.
DETAILED DESCRIPTION
[0074] With reference to FIGS. 1 and 2, a heated catheter assembly
10 has a catheter 18 with a distal end 12 and a proximal end 14. As
part of the catheter assembly 10 there are a hub 40 having a top
portion 42 and a base 43. The top portion 42 of the hub 40 has a
gas and electric connector subassembly 50 for attaching the gas
line and two contact points for making electric contact with the
luer lock and threaded gas nipple 52 (described more fully in FIGS.
19-27).
[0075] Referring to FIGS. 3-6, the order for constructing the
heated catheter is shown in cross-section. Catheter 18 is shown in
FIG. 3. FIG. 4 describes the catheter 18, with internal copper wire
28, the external copper wire 20 outside of the catheter and copper
foil 22. Copper wire 20 being attached to copper foil 22. Wire 28
runs the length of the internal portion of the catheter 18 and
exits at the distal end where it is held in place by a hypodermic
tube or stainless sleeve 38 (see FIG. 9). The stainless sleeve 38
presses over the wire 28 exiting the distal end of the catheter 18
to sandwich the wire between the catheter 18 and stainless sleeve
38. With reference to FIG. 5, an electrodag coating 30 covers part
of the catheter, that is, the electrodag covers a portion of the
catheter contacting a portion of the conductive foil (as explained
more fully below). The electrodag coating is a conductive coating
and is an integral part of the heated catheter. Finally in FIG. 6 a
parylene (dielective insulator coating) coating 34 covers the
electrodag coating 30.
[0076] With reference to FIG. 7 catheter 18 has a flared end 36 and
stainless sleeve 38. The flared end 36 of the catheter allows for a
better seal between the proximal end of the catheter and gas supply
channel as more fully explained in FIGS. 12-15 and 27.
[0077] With particular reference to FIGS. 8-11, the heated catheter
in longitudinal cross section is shown with part of the hub base 43
broken away. Exemplary of the embodiment of this invention is an 84
inch PTFE basic catheter 18 which has an 1/8 inch groove 16 at the
distal end 12 (FIGS. 7 and 8). The catheter 18 is etched (not
shown) for bonding. With reference to FIGS. 9-11, a copper wire 28
runs the length of the catheter on the interior 24. The copper wire
28 runs out through a channel in the groove 16 and is folded over
the distal end 12 of the catheter to the exterior 32 as best shown
in FIG. 9. An 1/8 inch stainless sleeve 38 is press fit over the
wire 28, covering the groove 16 completely and securely holding
wire 28 in place. The proximal end 14 of the catheter 18 is flared
36 to 0.130'' best shown in FIG. 7. Note particularly an insulating
coating 31 covers the foil 22. This insulating coating extends only
over a portion of the catheter and is covered by the parylene
coating which covers the entire catheter. As shown in FIGS. 12-13,
the wire exits the proximal end 14 of the catheter 18 and comes in
contact with the post of the luer 37 and then the compression nut
of the luer 39 is tightened, locking the catheter 18 and the wire
28 in place, as best shown in FIG. 27.
[0078] Note that a copper foil strip 22 is placed longitudinally at
the proximal end 14 of the catheter 18. Referring to FIGS. 10 and
11 once the copper foil 22 is in place on the catheter 18 a short
heat shrink insulating layer 31 goes from the hub base 40 to cover
the copper foil (conductive strip) 22 and a short portion of the
electrodag coating 30. The electrodag coating extends from a short
portion on the copper foil to the distal end of the catheter and
finally a parylene coating (dielectric insulator) covers the hub
and catheter portions of the heated catheter, except for the female
metal gas orfice 45 and hub contact pin 51. The electrodag coating
is a conductive coating containing metal graphite and silver or any
conductive material in an epoxy resin and is an integral part of
the heated catheter. For purposes of this invention conductive foil
22 is copper, but any conductive material would be operative. The
heat conducting strip 22 as disposed on the catheter has proximate
end and a distal end. The distal end of the heat conducting strip
is in contact with the electrodag coating. The proximal end of the
conducting strip is attached to wire 44 (best shown in FIG. 27).
The heat conducting strip, the thin wire and electrodag coating
when attached to the power source produce the heat for the
catheter. In a typical example the outer coating is heat shrink and
will cover the entire foil section. As an example, the electrodag
extends from the distal end of the foil, covering 1.5'' of the
foil, to the tip of the catheter, covering the stainless sleeve on
the end of the catheter and is in turn covered with dielectric
insulator 34.
[0079] With particular reference to FIGS. 12-15, the manner for
attaching the catheter 18 to the hub 40 is illustrated. FIG. 12
describes hub top 42 (in dashed lines) fixedly attached to the
thread male portion 37 of the luer. In FIG. 12 there is illustrated
a tube 47 having at its left end a gas intake orfice or luer 45, in
its middle there is fixedly attached the male thread 37 and its
right end there is a male catheter connector 49 which engages the
flare 36 of the catheter in the female portion 39 of the
compression nut. On tube 47 there is fixedly attached hub top 42
having gas intake orfice 45 and male luer 37 exposed. Specifically
in assembling the catheter to the hub a wire 44 attached to copper
foil 22 at the proximal end 14 of the catheter 18 the male end of
tube 49 and female of luer 39 are joined and the wire is snugged
tight in the luer as best shown in FIG. 27. Referring to FIGS.
14-16 the means for attaching wire 44 from the copper foil 22 to
the post 46 attached to the internal portion of hub top 42 are
shown. Note that wire 44 is attached at one end to the copper foil
and runs from the copper foil through a channel in top 43 to attach
to post 46 (e.g., by solder). Post 46 runs through the top of the
base 42 to form post 51 which contacts electric ring 56 best
described in FIG. 27. With reference to FIGS. 14-16, the top 42 and
base 43 of the hub have hollow compartments 33 for retaining the
luer.
[0080] Referring to FIGS. 15-18: At the proximal end of the
catheter 18, an electrical wire 44 is soldered to the proximal end
of the copper foil 22, the electrical wire 44 wraps a few times
around the catheter 18 and enters the base of the hub 43, and
through channel 35 to contact post 46 at the top of the hub 42.
Note that contact post 46 extends through top 42 and becomes hub
contact pin 51 which contacts ring 56 on hub connector 54
(described in detail in FIGS. 19-24). Electrical contact is made
through metal luer and outside post.
[0081] As an example for assembling the heated catheter, 53 inches
from the distal end 14 of the catheter 18 a short section of copper
foil 22 runs along the exterior of the catheter 18 to the proximal
end 14 and a connecting wire 44 runs from the copper foil through a
channel 35 in the base 43 of the hub 40. Wire 44 attaches to the
copper post 46 of the top section 42 of the hub 40 (FIG. 15). The
copper post 46 is connected to a gold plated contact pin 51 on the
surface of the hub 40. The base 43 mates to the top section 42 and
is secured in place by two screws 48 (FIG. 16). The distal most 55
inches of the catheter is covered with electrodag coating 30, which
covers all of the distal stainless steel hypodermic tube and two
inches of the proximal foil (best shown in FIG. 10). Heat shrink
coating 31 is applied 51 inches from the distal end and extends to
the hub, completely covering the copper foil (FIG. 11). The
Parylene or heat shrink coating covers the exterior of the catheter
over the entire surface including the electrodag coating (FIG. 11).
The outer coating is a dielectric or insulating coating.
Advantageously, a Parylene film is used as the outer insulating
coating because it can be formed in extremely thin layers. The
flare 36 in the catheter tubing creates a positive fluid seal with
the luer, while the hub 40 serves as the electrical connection for
the wire on the interior of the catheter and from the foil 22
running the proximal length on the exterior of the catheter tubing.
The interior of the hub houses a conductive material, while the
outside of the hub is an insulator. The hub and the distal most
portion of the catheter both maintain a zero potential
electrically.
[0082] With reference to FIGS. 19 and 20, there is shown the gas
and electrical connection subassembly 50 having a gas connection
threaded male gas nipple 52 for receiving the cryogenic gas. The
gas nipple is joined at an end to a spring actuated hub connecting
means 54 which contains a spring mechanism 58 for insuring a secure
attachment. Referring specifically to FIGS. 19-20, the spring
actuated hub connecting means 54 has a male member 55 for
connecting to the female gas inlet 60 associated with top of the
hub 42. Connector 54 also had therein an electric contact ring 56
for contacting pin 51 on the hub top 42, as well as a tab 57 on
ring 56.
[0083] An important element of the electric and gas connection is
the spring-loaded hub connector 54 shown in detail in FIGS. 20-24.
Note that the hub connector has an internal spring 58 which is
compressed by pushing on the sides of connector 54; connector 54 is
joined to the female gas inlet 60 of the hub by inserting the male
member 55 of connector 54 into female gas inlet 60, compressing the
spring 58 in the connector by pushing on the side of the connector.
While in the compressed state, male 55 and female 60 are jointed
and tabs 64 on the female inlet 60 are inserted into threaded 65
annular opening 63 and turned a half turn so that the tabs 64 fully
engage thread 65 as shown in FIG. 21-24. Note particularly that in
FIG. 21 springs 58 are not compressed; during engagement the spring
58 is compressed and upon engagement the spring 58 is released
assuring a secure attachment. Tabs 64 are inserted into annular
threaded opening 63; and the spring is released when tabs 64 and
threads 64 are fully engaged. This spring loading insures a secure
fit for both gas and electric connections. Note that the spring is
retained in the hub connector 54 by abutting an end of the nipple
52 and housing 66.
[0084] With reference to FIGS. 21-24, an elegant arrangement for
securely joining the gas and electric subassembly 50 to the female
gas inlet 60 of the hub top 42 is described. This joining depends
upon tabs 64 on either side of female gas inlet 60 entering
threaded annular opening 63. Once tab 64 enters said opening 63,
the hub connector 54 is retracted, and tabs 64 are allowed to enter
the threaded annular opening 63. The tabs 64 which are integral to
hub 40 are turned by twisting the hub 40 a half of a turn so that
the tabs 64 engage thread 65 in annular opening 63. Once the tabs
64 and thread 65 are engaged, hub connector 54 is released allowing
spring 58 within the connector to fixedly attach the hub 40 to the
hub connector 54. In FIGS. 21-23 the arrows are intended to
illustrate the tabs 64 entering annular opening 63 to engage thread
65.
[0085] With reference to FIGS. 21-23, note also that the mating of
the gas and electric subassembly 50 with the hub gas inlet 60 is
described. On the opposite end of the gas inlet 60, there is a gas
outlet 61 having disposed thereon the threaded member 37 of the
luer. There is also fluid seal and electrical components for
contacting the heating components of the catheter to the electric
power supply.
[0086] With reference to FIGS. 25 and 26, a cross section taken
along lines 25-25 and 26-26 are described to show the male portion
55 of connector 54.
[0087] The male fitting connected the solenoid mates with the hub
40 to provide both a fluid seal and an electrical connection. The
center of the fitting is the zero potential contact with the hub.
On the outside of the male fitting, a compressed spring forces the
proximal catheter contact to mate with the male connection.
[0088] The electric leads to heat the catheter are connected
through electric tab 57 and the hex nut 62 of threaded nipple 52.
The leads could be attached by soldering, clipping or other
convenient means.
[0089] As an example, heating of the electrodag coating is achieved
by applying 24 volts at 4.5-6 amps to the leads for 7 seconds, and
then applying 12 volts at 3 amps for the remainder of the heating
cycle which is indicated by the ability to remove the catheter from
the endoscope (approximately 13-15 seconds depending on the
cryo-treatment exposure time). No negative effects will occur if
the heater is applied longer than these time frames. The resistance
of the electrodag generates heat as the current is passed through
the length of the catheter. The initial 24 volts provide a quick
initial thaw, while the remaining heating phase maintains and
finishes the thaw cycle. All materials maintain all structural and
functional properties through the entire heating cycle.
[0090] The herein disclosed invention has been described in terms
of a catheter with an electrodag coating, however, other electrical
means such as a conductive powder coating, a catheter made of
conductive plastic or the like or metal would be operative.
[0091] In a broad aspect, the herein disclosed invention envisions
a heated catheter in combination with an endoscope, with the heated
catheter being fitted into a lumen of the endoscope.
[0092] Following a treatment cycle, the catheter may be warmed by
depressing the right side of the foot pedal. A light on the
solenoid will indicate that the catheter is experiencing a thaw
cycle. The cycle can be interrupted at any time by releasing the
foot pedal. Heat is generated by the resistance in the electrodag
coating applied to the outer surface of the catheter. The hub has
two contacts. The internal contact extends from the hub, through
the catheter's internal surface to the distal fitting by means of
the internal copper wire. This lead maintains a zero potential at
all times. The second contact is located on the top surface of the
hub. This contact extends from the hub, through the copper foil
along the exterior of the catheter and into the proximal electrodag
coating.
Advantages of the Heated Catheter
[0093] The heated catheter provides a number of advantages over a
traditional catheter: [0094] Polyimide or PTFE, the Cryo-catheter
material base, acts as a strong insulator and transports the liquid
nitrogen with minimal thermal temperature loss resulting in a
shorter time to achieve the clinically required cryoburn. [0095]
The heating mechanism allows the catheter to be removed from the
endoscope lumen immediately following the cryo-therapy. More
specifically, using a traditional catheter, the catheter is frozen
into the endoscope lumen for 1-5 minutes following the therapy.
This freezing to the endoscope lumen may result in damage to the
endoscope. Insulated Fittings
[0096] The new fittings on the device will be vacuum insulated.
This will keep the fittings from frosting or feeling super cool to
the human touch.
[0097] In addition, the hub or connective fittings which couple the
catheter to the cryosystem have been redesigned and improved to
accommodate electrical contacts required for the heating
system.
ALTERNATIVE EMBODIMENTS OF THE HEATED CATHETER
[0098] An alternative embodiment contemplated by the inventors is a
heating coil on the heated catheter being energized in "series" or
heated with a continuous length of wire energized from two ends.
Also contemplated is a catheter with the heating element in
parallel. This will result in heating short segments (5-10 segments
per catheter) quickly and with more energy. The inventors may
adjust the wrappings of the heating coil so that the loops touch
one another. A parallel electrical transfer may be necessary. It
may be feasible to employ flat wire (square wire) as opposed to
round wire. Whether to use series or parallel spacing will be
determined based on individual use. The inventors contemplate
coating the gap between the wires with a heat sink which will act
to absorb radiated heat from the heating coil to dispense the heat
to the outside of the catheter. Also contemplated by the inventors
is a spray coat or liquid paint of a nichrome conductor. In this
embodiment the entire catheter could be energized quite quickly.
The inventors envision alternate means for diverting freezing
temperatures from non-target areas. Examples of such diverting
means is a polystyrene tape to function as an insulator.
Alternatively, the catheter may be made of polystyrene or some
other insulating material. During the cryoburn the heat of the
catheter remains active. This prevents the accidental injury to
non-target tissue.
[0099] The inventors have produced a further alternative embodiment
of a heated catheter. The heated catheter in the alternative
embodiment is a composite constructed of three different materials;
in three different layers. The catheter itself (as the first layer)
is made of extruded polyimide. Surrounding the first layer (the
catheter) is a layer of magnetic wire wrapped around the outer
diameter of the polyimide catheter. As a top or final layer, there
is supplied a thin polyester heat shrink.
[0100] More specifically, the heated catheter (cryocatheter) can be
defined as an extruded polyimide tube (O.D. 0.092''). Over the
catheter is wrapped a layer of magnetic copper wire (0.007''
diameter). A number of different diameter wires are available. The
inventors put together prototypes with 0.003'' diameter wire,
0.002'' diameter wire, 0.005'' diameter wire, etc. A 0.007''
diameter wire was the best for the desired voltage, but the
invention does not exclude the use of wires of other diameters.
[0101] The wrappings of wire that functioned the best were 8 wraps
per inch (a single strand was run the length of the catheter, and
the wrapping was applied back over this single strand to complete
the electrical loop. Double strand wrapping with the wrap spacing
(up to 25 wraps per inch) would be operative.
[0102] A selected preferred voltage for application is 12 volts and
1 amp. Voltages of 5, 12, 17 and 24 volts have been tested. The
important thing to keep in mind is that different diameter wires
work well if wrapped to the correct density and heated with the
appropriate amount of voltages.
[0103] The final layer employed is a thin (0.00025'') polyester
heat shrink. This heat shrink serves to hold the wire in place and
to seal the wire from patient contact.
[0104] As an elegant embodiment of this invention, the heated
catheter is disposable (e.g., single-use) and can be used together
with an en endoscope to perform cryosurgical procedures in the
esophagus and as such the catheter will not be allowed to freeze to
the endoscope.
[0105] Obviously, many modifications may be made without departing
from the basic spirit of the present invention. Accordingly, it
will be appreciated by those skilled in the art that within the
scope of the appended claims, the invention may be practiced other
than has been specifically described herein.
* * * * *