U.S. patent application number 10/055762 was filed with the patent office on 2002-06-06 for heat pipe nerve cooler.
This patent application is currently assigned to Innercool Therapies, Inc.. Invention is credited to Dobak, John D. III.
Application Number | 20020068964 10/055762 |
Document ID | / |
Family ID | 27567471 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020068964 |
Kind Code |
A1 |
Dobak, John D. III |
June 6, 2002 |
Heat pipe nerve cooler
Abstract
The invention provides a method and apparatus for producing
reversible focal hypothermia of the nervous system to control
chronic pain. Nerve conduction is blocked by mild cooling (0 to
25.degree. C.), or hypothermia. At these temperatures, nerve tissue
is not destroyed and recovers completely when cooling is
terminated, such that the treatment is reversible. By blocking
conduction in pain nerves, pain sensation is eliminated in a manner
analogous to drugs such as lidocaine that also block nerve
conduction to provide anesthesia. The invention can be applied to a
variety of conditions such as urge incontinence, muscle spasticity,
and epilepsy. Many of these disorders are mediated by nerve and
nervous tissue that could be interrupted by cooling. In addition,
neurologic dysfunction found in multiple sclerosis may improve by
cooling of the nerves. The method and apparatus may be used to cool
areas of the nervous system affected by multiple sclerosis to allow
more normal functions.
Inventors: |
Dobak, John D. III; (La
Jolla, CA) |
Correspondence
Address: |
MARK WIECZOREK
Innercool Therapies, Inc.
3931 Sorrento Valley Boulevard
San Diego
CA
92121
US
|
Assignee: |
Innercool Therapies, Inc.
|
Family ID: |
27567471 |
Appl. No.: |
10/055762 |
Filed: |
January 22, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10055762 |
Jan 22, 2002 |
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09328854 |
Jun 9, 1999 |
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09328854 |
Jun 9, 1999 |
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09012287 |
Jan 23, 1998 |
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09328854 |
Jun 9, 1999 |
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09047012 |
Mar 24, 1998 |
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09328854 |
Jun 9, 1999 |
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09052545 |
Mar 31, 1998 |
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09328854 |
Jun 9, 1999 |
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09103342 |
Jun 23, 1998 |
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09328854 |
Jun 9, 1999 |
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09215038 |
Dec 16, 1998 |
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09328854 |
Jun 9, 1999 |
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09215040 |
Dec 16, 1998 |
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09328854 |
Jun 9, 1999 |
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09262805 |
Mar 4, 1999 |
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Current U.S.
Class: |
607/105 ;
607/113 |
Current CPC
Class: |
A61F 2007/0056 20130101;
A61B 2017/00292 20130101; A61F 2007/126 20130101; A61B 2018/0212
20130101; A61B 2018/0262 20130101; A61F 7/12 20130101; A61B 18/02
20130101 |
Class at
Publication: |
607/105 ;
607/113 |
International
Class: |
A61F 007/00; A61F
007/12 |
Claims
What is claimed is:
1. An apparatus for cooling a portion of tissue, comprising: an
evaporator to be placed in thermal communication with a portion of
tissue; a condenser disposed in thermal communication with a source
or sink of heat, the condenser including an upper chamber and a
lower chamber; and a conduit disposed between the evaporator and
the condenser, the conduit including a wick structure, to
communicate working fluid between the two.
2. The apparatus of claim 1, wherein the lower chamber is separated
from the upper chamber by a porous structure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 09/328,854, filed Jun. 9, 1999, entitled "Heat
Pipe Nerve Cooler", which is a continuation-in-part of the
following U.S. patent applications: U.S. patent application Ser.
No. 09/012,287, filed Jan. 23, 1998, entitled "Selective Organ
Hypothermia Method and Apparatus"; U.S. patent application Ser. No.
09/047,012, filed Mar. 24, 1998, entitled "Improved Selective Organ
Hypothermia Method and Apparatus"; U.S. patent application Ser. No.
09/052,545, filed Mar. 31, 1998, entitled "Circulating Fluid
Hypothermia Method and Apparatus"; U.S. patent application Ser. No.
09/103,342, filed Jun. 23, 1998, entitled "A Selective Organ
Cooling Catheter and Method of Using the Same"; U.S. patent
application Ser. No. 09/215,038, filed Dec. 16, 1998, entitled "An
Inflatable Catheter for Selective Organ Heating and Cooling
Catheter and Method of Using the Same"; U.S. patent application
Ser. No. 09/215,040, filed Dec. 16, 1998, entitled "Method and
Device for Applications of Selective Organ Cooling"; and U.S.
patent application Ser. No. 09/262,805, filed Mar. 4, 1999,
entitled "A Selective Organ Cooling Catheter with Guide Wire
Apparatus", all of which are incorporated herein.
REFERENCE TO FEDERAL FUNDING
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] Pain sensation is mediated by nerve fibers. Nerve fibers
extend to the brain via the spinal cord which forms a portion of
the central nervous system. Referring to FIG. 1, the spinal cord 12
extends from the brain to the level of the second lumbar vertebra,
at which point the spinal cord branches to numerous individual
roots. Throughout the length of the spinal cord, the same is
encased in the vertebral canal. Nerves 14 branch off at regular
intervals.
[0004] A number of types of nerves are disposed within the
posterior gray horn 16. Two types of pain sensing nerves have been
identified: A.sub..delta. and C. Referring to FIGS. 2 and 3,
A.sub..delta. fibers 18 are disposed within regions I and V and the
same produce a rapid initial and intense response to painful
stimuli. C fibers 20 are disposed within region II and produce a
more blunted but prolonged response. C fibers 20 are believed to be
responsible for many chronic pain syndromes.
[0005] A.sub..delta. fibers 18 and C fibers 20 are connected to the
spinal cord 20 via the dorsal root 22 (referring back to FIG. 1).
The dorsal root 22 is a bundle of nerves that enters the dorsal
aspect of the spinal cord 12. The sensory nerves from one
particular body region, such as the right leg, may be split among
several dorsal root nerve bundles spaced along the length of the
spinal cord 12.
[0006] Pain is conducted via fibers of the peripheral nervous
system to the central nervous system, or nerves in the spinal cord.
The pain signal is conducted up nerve tracts of the spinal cord to
the pain sensing areas of the brain (i.e., the thalamus). The
transmission of the pain signal from the peripheral nerves to the
central nerves takes place in the synapses of the posterior gray
horn region 16 of the spinal cord 12. A synapse is a
neuron-to-neuron transmission of a signal by a chemical mediator
that traverses a small gap between two axon terminals.
[0007] As noted above, many A.sub..delta. fibers 18 and C fibers 20
synapse in the most superficial, or dorsal, region of the dorsal
gray horn known as zones 1 and 2. The synaptic region of the C
fibers 20 is also known as the substantia gelatinosa. Various
treatments directed at these fibers and these anatomical locations,
can be and are used to treat pain syndromes.
[0008] An estimated 15 million Americans suffer from chronic
intractable pain. 50% of persons with terminal illness have
significant pain and 10% require a surgical procedure to treat the
pain. $80 billion is spent annually in the United States on chronic
pain.
[0009] Current therapy for chronic pain can be divided into two
categories: medical and surgical. Medical therapy is the
administration of drugs ranging from Tylenol.RTM. to morphine.
Morphine and its analogs are used in cases of severe pain and
terminal illness. These drugs have many serious side effects such
as sedation, confusion, constipation, and depression of
respiration. The more severe the pain, the higher the dosage of the
drug and the more significant the side effects. In addition,
tolerance to these compounds develops, and escalating doses are
required to achieve pain control.
[0010] Surgical therapy can range from the implantation of drug
infusion devices to the ablation, or destruction, of nerves.
Ablation of nervous tissue is irreversible and can cause permanent
loss of function of organs and limbs. One type of surgical
treatment is known as Dorsal Root Entry Zone ("DREZ") ablation. The
DREZ is shown in FIG. 1 as DREZ 24. While DREZ ablation is
effective at treating pain, it can also result in significant limb
and organ dysfunction. Drug infusion into the spinal cord using
implanted devices can reduce drug side effects, however they do not
eliminate side effects entirely nor solve the problem of tolerance.
These approaches require significant surgical procedures; often,
terminally ill patients are not good candidates for surgery.
[0011] Nerve stimulators are also used for pain control. These
electrical devices work indirectly by stimulating nerve fibers that
inhibit conduction pain fibers. It is known to place devices such
as nerve stimulators surgically or percutaneously and they may be
placed directly adjacent to the spinal cord. For example, U.S. Pat.
No. 5,643,330 to Holsheimer et al., issued Jul. 1, 1997, and
entitled "Multichannel Apparatus for Epidural Spinal Cord
Stimulation", discloses placing an epidural spinal cord stimulator
adjacent to spinal cord dura mater.
[0012] Stimulators are relatively ineffective in controlling pain.
This may be in part due to the indirect mechanism of action.
Further, they can cause dysthesias and paresthesias (neurologenic
pain) due to the stimulation of nerve fibers.
[0013] There is a need for a method and apparatus to combat pain,
especially chronic pain, which do not suffer from the drawbacks of
current medical and surgical therapies.
SUMMARY OF THE INVENTION
[0014] In one aspect, the invention is directed to a method of
cooling a portion of a spinal cord of a patient. The method
includes delivering a portion of a heat pipe to a spinal cord of a
patient, the heat pipe including an evaporator and a condenser,
including disposing the evaporator at least in partial thermal
communication with the spinal cord. The evaporator is cooled by
passing a working fluid between the evaporator and the
condenser.
[0015] Implementations of the invention may include one or more of
the following. The delivering may further include disposing the
evaporator at least in partial thermal communication with the
dorsal root entry zone of the spinal cord. The working fluid may be
passed between the evaporator and the condenser through a conduit,
and the conduit may be a tube or wick structure, for example. The
condenser may be implanted within a patient or may be located
externally of a patient. The condenser may have an insulated lower
chamber into which the conduit enters and an upper chamber into
which the return tube enters, the lower and upper chambers
separated by a porous structure, and may further include passing
the working fluid in gaseous form from the evaporator through the
return tube within the conduit to the upper chamber, condensing the
working fluid at least partially from the gaseous form into the
liquid form, passing the working fluid from the upper chamber to
the lower chamber through the porous structure, and passing the
condensed working fluid from the lower chamber to the evaporator
through the conduit. Another implementation may include disposing
the upper chamber in thermal communication with a cold source. The
evaporator may be disposed adjacent the dura mater, or between the
spinal cord and the dura mater, or on the side of the dura mater
opposite the spinal cord.
[0016] In another aspect, the invention is directed to an apparatus
for cooling a portion of tissue. The apparatus includes an
evaporator to be placed in thermal communication with a portion of
tissue; a condenser disposed in thermal communication with a source
or sink of heat, the condenser including an upper chamber and a
lower chamber; and a conduit disposed between the evaporator and
the condenser, the conduit including a wick structure, to
communicate working fluid between the two. An implementation of the
invention may include providing a porous structure to separate the
lower chamber from the upper chamber.
[0017] Advantages of the invention include one or more of the
following. The invention provides for control of chronic pain in an
effective manner. The processes used to achieve hypothermia to
control pain are reversible. Nerve tissue is not destroyed as in
certain other techniques. Nerve tissue recovers completely when the
processes are stopped. The invention allows for treatment of not
only chronic pain but also urge incontinence, muscle spasticity,
epilepsy, and may even be of benefit in treating multiple
sclerosis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic drawing of the spinal cord.
[0019] FIG. 2 is a schematic cross-section of the spinal cord
showing the anterior and posterior gray horn.
[0020] FIG. 3 is more detailed schematic cross-section of a portion
of the spinal cord, showing the posterior horn and layers of nerve
fibers therein.
[0021] FIG. 4 is a schematic cross-sectional side view of an
embodiment of the invention, which may be implanted into a patient
suffering chronic pain.
[0022] FIG. 5 is a schematic cross-sectional side view of an
alternative embodiment of the invention, which may be implanted
into a patient suffering chronic pain.
[0023] FIG. 6 is a schematic cross-sectional side view of another
alternative embodiment of the invention, which may be implanted
into a patient suffering chronic pain.
[0024] FIG. 7 is a schematic view of the embodiments of the
invention shown in FIGS. 4-6 including a schematic of the same's
placement within a patient.
[0025] FIG. 8 is a schematic view of an alternative embodiment of
the invention including a schematic of the same's placement within
a patient.
[0026] FIG. 9 is a more detailed schematic view of the placement of
the invention alongside a patient's spinal cord.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The invention provides, in one embodiment, a cooling
catheter or cooling patch that can be placed on nerve fibers or
tissue. When nerve tissue is cooled (+2.degree. to +20.degree. C.),
conduction therethrough is stopped. Synaptic transmission is
susceptible to termination by cooling, with near complete blockage
of pain transmission occurring at +20.degree. C. A A.sub..delta.
fibers are more susceptible to reduction of conduction via cooling
and will be affected by warmer temperatures than C-fibers. For
example, some A A.sub..delta. fibers will cease to conduct at
+8.degree. C. whereas the conduction of some C-fibers is
substantially blocked at +3.degree. C. This conduction block is
known to be reversible. Normal conduction returns once the nerve
warms.
[0028] In one method of controlling pain, described in more detail
below, the cooling patch or catheter is placed parallel along the
dorsal root entry zone 24 in contact with the spinal cord 12 or on
the dura 26, a membrane that surrounds the cord (see FIGS. 1 and
9). The cooling section of the catheter or patch could be 5 to 10
cm long, or greater, and would stretch along several or many DREZs.
This would substantially ensure the treatment of all pain fibers
for a given body area that is the source of pain.
[0029] By placing the cooling device in the spinal cord 12, the
synapses at the DREZ can be affected. Since these synapses are
susceptible to termination or reduction of conduction at relatively
warm temperatures, the temperature of the cooling device can be
maintained at a reasonably warm temperature. For example, the
surface of the cooling catheter may be maintained at +5.degree. to
+10.degree. C. to produce cooling to +20.degree. C. at the depth of
the substantia gelatinosa 28 (FIG. 2), or 2-3 mm, at the DREZ
24.
[0030] One method of cooling employs a passive two-phase heat
transfer device, or heat pipe. Referring to FIG. 4, a heat pipe 101
includes three basic parts: an evaporator 106, an intervening
connecting conduit 104, and a condenser 102. The evaporator 106 and
the condenser 102 are connected to each other by the conduit
104.
[0031] The conduit 104, which is insulated, allows a coolant to
flow between the evaporator 106 and the condenser 102. The conduit
104 may employ a variety of structures. In FIG. 4, a capillary tube
122 is shown in which coolant flows by capillary forces. In FIG. 5,
a conventional wick structure is shown. In FIG. 6, a cylindrical
wick structure with a central return lumen is shown. In general, as
shown in FIGS. 4-6, the conduit 104 includes a tube 114. Tube 114
defines a return path for gaseous coolant as will be described
below.
[0032] In the heat pipe 101, heat enters from the body tissue and
is absorbed by the evaporator 106. A liquid coolant such as a
freon, within the evaporator 106, boils and absorbs the heat input,
resulting in cooling. The vaporized freon then returns to the
condenser 102 via a return tube 116 defined by tube 114 within the
conduit 104. At the condenser 102, heat is removed, either by
ambient air heat exchange or by cooling from another source. The
cooled coolant condenses the gaseous coolant and the same then
flows back down the conduit 104 to the evaporator 106.
[0033] The condenser 102 may be a small hollow metallic disc made
from titanium, stainless steel, or other similar metals. The disk
acts as a condenser and reservoir for a freon or other such working
fluid. The disc has two chambers, an upper chamber 108 and a lower
chamber 118. The lower chamber 118 may be insulated by an evacuated
space 128 or other such insulation. There is no insulation on the
upper chamber 108 of the disk or condenser 102. A porous/sintered
disk 110 may optionally be used to separate the two halves. The
conduit 104 enters the insulated lower chamber 118 or porous
structure or disc 110. The evaporator conduit 116 enters the upper
chamber 108 (i.e., the uninsulated half of the disk). The
connection of the evaporator conduit 116 into the upper chamber 108
is indicated in FIGS. 4-6, although some details of the connection
are omitted for clarity. At least one heat transfer fin 152 may be
provided within the upper chamber to assist in the conduction of
heat away from porous structure 110 to the cold source described
below (for clarity, this fin 152 is only shown in FIG. 4).
[0034] In FIG. 4, the conduit 104 includes a capillary tube 122.
The capillary tube 122 causes capillary forces to move the liquid
coolant from the condenser 102 to the evaporator 106. The liquid
inlet to the capillary tube 122 may be entirely within a lower
chamber 118, described in more detail below, entirely within a
porous disc 110, described in more detail above, or partly in both.
In FIG. 4, the last embodiment is shown. In other words, liquid
coolant may enter tube 122 through either of the porous disc 110 or
the lower chamber 118.
[0035] In FIG. 5, the conduit 104 includes a wick structure 122'.
The wick structure "wicks" the liquid coolant to the evaporator
106. Of course, it is understood that wick structures also employ
capillary action, but in this embodiment the wick structure is
distinguished from a capillary tube per se. Like the embodiment of
FIG. 4, the wick structure 122' may be connected either to the
lower chamber 118, porous disc 110, or both. Also in this
embodiment, the lower chamber 118 should be sealed so that only
wick structure 122' (and of course porous disc 110) may be inlets
and outlets. In other words, evaporated gaseous coolant should be
prohibited from entering lower chamber 118. The same is true of
capillary tube 122.
[0036] In FIG. 6, a cylindrical wick structure 122" is shown that
provides an additional embodiment of the invention. In this
embodiment, the wick structure 122" approximately matches the inner
diameter of the conduit 104. In this way, the wick structure 122"
is provided with more surface area and volume with which to wick
coolant. The same travels down the wick structure 122" to the
evaporator. Once evaporated, the gaseous coolant may travel in the
central lumen 116 defined by the wick structure 122" itself back to
the condenser 102. Of course, the wick structure 122" in this
embodiment is shaped such that coolant may reach even the upper
portions of the wick structure 122" (adjacent upper chamber 108)
without entering the upper chamber 108. Nevertheless, most of the
coolant may still travel along the portion of the wick structure
adjacent the lower chamber 118. As above, the wick structure may
contact the lower chamber 118 (as shown in FIG. 6) or may
alternatively contact the porous disc 110, or both.
[0037] The evaporator 106 may be, e.g., a 1-2 mm outer diameter
catheter disposed along the spinal cord, and may be, e.g., 10 to 15
cm in length. The evaporator 106 may have metal foil windows 126
that respectively align with the plurality of DREZ 24 thereby
enhancing heat transfer. The evaporator 106 catheter can be made
from polyimide and the metal foil windows 126 may be made of
platinum or platinum iridium. It should be clear to one of skill in
the art that the relative dimensions of the evaporator 106 in FIGS.
4-6 are greatly exaggerated and that most feasible such evaporators
would have a ratio of length to width that is much greater than
that shown in the figures.
[0038] The evaporator 106 is connected to the condenser 102 by the
conduit 104. The conduit may reside in the tissue between the skin
and the spinal cord. An end of the conduit 104 distal of evaporator
106 may be located between the skin and the spinal cord, and more
preferably near the skin so as to allow thermal energy to be passed
from the skin to the conduit and condenser, as well as vice-versa.
In a separate embodiment, described in more detail below, conduit
104 may extend through a percutaneous incision to a region external
of the body. It is also noted that the evaporator 106 may include a
portion of the conduit 104 for better delivery of the coolant to
the heat transfer portions of the evaporator.
[0039] In use, the evaporator 106 is inserted along and adjacent to
the spinal cord 12 percutaneously with a needle introducer. The
needle introducer allows the evaporator 106 to be disposed within
the vertebra so as to be in thermal communication with the spinal
cord 12. In this context, thermal communication refers to the
ability of the evaporator 106 to absorb heat from the spinal cord
12. This thermal communication may arise from conduction,
convection, or radiation. The evaporator 106 is slid along the
spinal cord so as to achieve a high mutual surface area of
contact.
[0040] Referring to FIG. 7, the condenser 102 is implanted just
beneath the skin 30 with the uninsulated side (chamber 108) facing
outward just underneath the skin 30. One way in which to start the
cooling process is to place a cold pack 132 over the skin 30
adjacent the condenser 102. The cold pack 132 may be a
thermoelectric cooler or an ice bag. Because the upper half
(chamber 108) is uninsulated, it is cooled by the cold pack 132.
The coldness condenses the coolant, which subsequently wicks
through the porous separator 110 and enters the lower insulated
half of the disk. Because the lower half (chamber 118) is
insulated, the heat from the body does not allow the coolant to
boil. It is noted that only a portion of the insulation of the
lower chamber is shown in FIG. 7, for clarity. The coolant then
flows down the capillary within conduit 104 to the evaporator 106
where it boils and cools the nerve tissue. The gaseous coolant
returns to the upper chamber 108 of the condenser where it is
cooled and liquefied, restarting the process. Removing the cold
pack 132 terminates the cooling.
[0041] In an alternative embodiment, shown in FIG. 8, the condenser
102 is replaced with a cooling unit 102' that is resident outside
the body. In this embodiment, cooling unit 102' provides and cycles
a working fluid down a conduit to evaporator 106. Evaporator 106
may be similar in most or all aspects to the evaporator in previous
embodiments. The coolant or working fluid flows back to cooling
unit 102' via a return tube. The conduit and return tube may be
similar to the conduit and return tube described above.
[0042] In any of the embodiments, the coolant or working fluid may
be a freon or other such type of refrigerant. In the alternative
embodiment of FIG. 8, the working fluid may also be saline or other
similar coolants. Saline may be employed in this embodiment at
least in part because this embodiment need not rely on evaporation
and condensation to propel the working fluid: rather, the cooling
unit may supply the required pressure.
[0043] FIG. 9 shows one possible placement of the evaporator 106
along the spinal cord 12. In FIG. 9, the evaporator 106 is disposed
along the spinal cord 12 subdurally, i.e., under the dura mater. It
should be noted that the evaporator 106 may additionally be
disposed epidurally, i.e., outside but adjacent to the dura
mater.
[0044] While the invention has been described with respect to
certain embodiments, it will be clear to those skilled in the art
that variations of these embodiments may be employed which still
fall within the scope of the invention. Accordingly, the scope of
the invention is limited only by the claims appended hereto.
* * * * *