U.S. patent application number 09/907782 was filed with the patent office on 2001-11-15 for patient temperature regulation method and apparatus.
This patent application is currently assigned to Innercool Therapies, Inc.. Invention is credited to Dobak, John D. III.
Application Number | 20010041923 09/907782 |
Document ID | / |
Family ID | 23471013 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041923 |
Kind Code |
A1 |
Dobak, John D. III |
November 15, 2001 |
Patient temperature regulation method and apparatus
Abstract
A device and method for providing body cooling. The cooling
device applies cooling to blood flowing in a vena cavae that is
then distributed throughout the body. The cooling can be assisted
by use of thermoregulatory drugs or warming devices to prevent
shivering and vasoconstriction.
Inventors: |
Dobak, John D. III; (La
Jolla, CA) |
Correspondence
Address: |
INNERCOOL THERAPIES
3931 Sorrento Valley Blvd.
San Diego
CA
92121
US
|
Assignee: |
Innercool Therapies, Inc.
|
Family ID: |
23471013 |
Appl. No.: |
09/907782 |
Filed: |
July 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09907782 |
Jul 18, 2001 |
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09373112 |
Aug 11, 1999 |
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Current U.S.
Class: |
607/108 ;
607/113 |
Current CPC
Class: |
A61F 7/12 20130101; A61B
18/02 20130101; A61B 2017/00292 20130101; A61F 2007/126 20130101;
A61P 43/00 20180101; A61B 2018/0212 20130101; A61F 2007/0056
20130101; A61B 2018/0262 20130101 |
Class at
Publication: |
607/108 ;
607/113 |
International
Class: |
A61F 007/00; A61F
007/12 |
Claims
We claim:
1. A cooling system for cooling a patient's body intravascularly,
comprising: a flexible catheter insertable into a vena cavae; a
flexible metallic cooling element attached to a distal end of the
flexible catheter, the flexible metallic cooling element including
a plurality of heat transfer segments connected by flexible joints;
and a heating blanket for applying heat to a selected portion of
the patient's body.
2. The system of claim 1, wherein the heat transfer segments
further comprise a plurality of exterior surface irregularities,
the surface irregularities being shaped and arranged to create
mixing in surrounding fluid.
3. The system of claim 1, wherein the heating blanket employs a
warm-air blower and includes air channels for evenly distributing
warm air to the surface area of the selected portion of the
patient.
4. The system of claim 1, wherein the heating blanket includes an
electrical resistance heater.
5. The system of claim 1, wherein the flexible joint includes a
bellows.
6. The system of claim 1, wherein the flexible joint includes a
flexible tube.
7. The system of claim 2, wherein: the surface irregularities
comprise a helical ridge and a helical groove formed on each heat
transfer segment; and the helical ridge on each heat transfer
segment has an opposite helical twist to the helical ridges on
adjacent heat transfer segments.
8. The system of claim 1, further comprising a plurality of
interior surface irregularities in the cooling element, the
interior surface irregularities being shaped and arranged to create
mixing in fluid within the cooling element.
9. A method for cooling a patient's body intravascularly,
comprising: providing a catheter having a cooling element attached
to a distal end thereof, the cooling element having mixing-inducing
surface features thereon; inserting the catheter through the
vascular system of the patient to place the cooling element in a
vein that drains into the heart of a patient; circulating fluid
through the cooling element; and transferring heat from the blood
in the vein to the cooling element.
10. The method of claim 9, further comprising applying heat via a
warming device to a substantial portion of the surface area of the
patient.
11. The method of claim 9, further comprising applying cooling via
a cooling device to a substantial portion of the surface area of
the patient.
12. The method of claim 9, further comprising administering a
vasoconstrictive drug to the patient.
13. The method of claim 10, wherein the warming device is a heating
blanket.
14. The method of claim 11, wherein the cooling device is a cooling
blanket.
15. The method of claim 9, further comprising inducing mixing in
the blood of the vascular system of the patient.
16. The method of claim 9, further comprising administering a
thermoregulatory drug to the patient.
17. The method of claim 10, further comprising administering a
thermoregulatory drug to the patient.
18. The method of claim 17, wherein the thermoregulatory drug is
selected from the group consisting of clonidine, meperidine,
propofol, magnesium, dexmedetomidine, and combinations thereof.
19. The method of claim 9, wherein the cooling element is disposed
in a vein selected from the group consisting of the superior vena
cava, the inferior vena cava, or both.
20. A method for substantially reducing platelet aggregation in a
blood vessel in which blood is flowing, comprising: providing a
catheter having a cooling element attached to a distal end thereof,
the cooling element employing surface features and thereby inducing
mixing in the blood; inserting the catheter through the vascular
system of the patient to place the cooling element in a blood
vessel in which blood is flowing; circulating fluid through the
cooling element; and transferring heat from the blood in the vessel
to the cooling element, whereby blood is cooled and platelet
aggregation is substantially reduced.
21. A method for substantially reducing dependence on drug
therapies in treating insults or injuries resulting in ischemia,
comprising: providing a catheter having a cooling element attached
to a distal end thereof, the cooling element employing
mixing-inducing surface features; inserting the catheter through
the vascular system of the patient to place the cooling element in
a blood vessel in which blood is flowing; circulating fluid through
the cooling element; and transferring heat from the blood in the
vessel to the cooling element, whereby blood is cooled.
22. A method for substantially reducing cell damage during and
after a myocardial infarction, comprising: providing a catheter
having a cooling element attached to a distal end thereof, the
cooling element employing mixing-inducing surface features;
inserting the catheter through the vascular system of the patient
to place the cooling element in a vein selected from the group
consisting of the superior vena cava, the inferior vena cava, or
both; circulating fluid through the cooling element; and
transferring heat from the blood in the vein to the cooling
element, whereby at least one of platelet aggregation, oxygen
demands, or the metabolic rate of the heart is reduced or
bradycardia is induced.
23. The method of claim 22, further comprising administering a drug
to lower blood pressure.
24. A method for substantially reducing stenoses recurring
following angioplasty, comprising: providing a catheter having a
cooling element attached to a distal end thereof, the cooling
element employing mixing-inducing surface features; performing an
angioplasty or stenting operation on a blood vessel of the patient;
inserting the catheter through the vascular system of the patient
to place the cooling element in the blood vessel; circulating fluid
through the cooling element; and transferring heat from the blood
in the vessel to the cooling element, whereby blood and the blood
vessel wall is cooled.
25. A method for substantially reducing reperfusion injury
following reflow, comprising: performing a catheter having a
cooling element attached to a distal end thereof, the cooling
element employing mixing inducing surface features; performing an
reflow operation on a blood vessel of the patient; inserting the
catheter through the vascular system of the patient to place the
cooling element in the blood vessel; circulating fluid through the
cooling element; and transferring heat from the blood in the vessel
to the cooling element, whereby blood in the vessel is cooled.
26. A method for cooling a patient's body intravascularly,
comprising: providing a catheter having a cooling element attached
to a distal end thereof, the cooling element having mixing-inducing
surface features thereon; inserting the catheter through the
vascular system of the patient to place the cooling element in the
inferior vena cava of a patient; circulating fluid through the
cooling element; and transferring heat from the blood in the
inferior vena cava to the cooling element.
27. A method for cooling a patient's body intravascularly,
comprising: providing a catheter having a cooling element attached
to a distal end thereof, the cooling element having mixing-inducing
surface features thereon; inserting the catheter through the
vascular system of the patient to place the cooling element in the
iliac vein of a patient; circulating fluid through the cooling
element; and transferring heat from the blood in the iliac vein to
the cooling element.
28. A method for cooling a patient's body intravascularly,
comprising: providing a catheter having a cooling element attached
to a distal end thereof, the cooling element having mixing-inducing
surface features thereon; inserting the catheter through the
vascular system of the patient to place the cooling element in the
femoral vein of a patient; circulating fluid through the cooling
element; and transferring heat from the blood in the femoral vein
to the cooling element.
29. A method of treating a human body, comprising: inserting a
flexible conductive heat transfer element into a vein from a distal
location; and circulating a working fluid through the flexible
conductive heat transfer element to modify the temperature of the
blood in the vein, thereby modifying the temperature of the
body.
30. A method of treating a human body, comprising: inserting a
flexible heat transfer element into a vein from a distal location,
the flexible heat transfer element having mixing-inducing surface
features on the exterior thereof; and circulating a working fluid
through the flexible heat transfer element to modify the
temperature of the blood in the vein, thereby modifying the
temperature of the body.
31. A method of treating a human body, comprising: inserting a
flexible heat transfer element into a vein from a distal location,
the flexible heat transfer element having mixing-inducing surface
features on the interior thereof; and circulating a working fluid
through the flexible heat transfer element to modify the
temperature of the blood in the vein, thereby modifying the
temperature of the body.
32. A method of treating a human body, comprising: inserting a
flexible heat transfer element into a vein from a distal location,
the flexible heat transfer element having mixing-inducing features
on the surface thereof; circulating a working fluid through the
flexible heat transfer element to modify the temperature of the
blood in the vein, thereby modifying the temperature of the body;
and modifying the temperature of at least a portion of the surface
of the human body by a surface heater or cooler.
33. A method of modifying the temperature of a human body,
comprising: inserting a heat transfer element into a portion of the
vasculature from a distal location, the heat transfer element
having mixing-inducing features; circulating a working fluid
through the heat transfer element to modify the temperature of the
blood in the vasculature, thereby modifying the temperature of the
body.
34. The method of claim 33, wherein said mixing inducing features
create a turbulence intensity of at least about 0.05.
35. The method of claim 34, wherein said mixing-inducing features
include at least one helical invagination.
36. The method of claim 34, wherein said mixing-inducing features
include at least one protrusion.
37. The method of claim 33, wherein said mixing-inducing features
create a mixing characterized by a Nusselt number of at least about
5.
38. The method of claim 37, wherein said mixing-inducing features
include at least one helical invagination.
39. The method of claim 37, wherein said mixing-inducing features
include at least one protrusion.
40. A method of modifying the temperature of a human body,
comprising: inserting a heat transfer element into a portion of the
vasculature from a distal location, the heat transfer element
having a mixing-inducing shape; circulating a working fluid through
the heat transfer element to modify the temperature of the blood in
the vasculature, thereby modifying the temperature of the body.
41. The method of claim 40, wherein said mixing-inducing shape
creates a turbulence intensity of at least about 0.05.
42. The method of claim 41, wherein said mixing-inducing shape is a
helix.
43. The method of claim 41, wherein said mixing-inducing shape
includes a substantially cylindrical body having protrusions
thereon.
44. The method of claim 40, wherein said mixing-inducing shape
creates a mixing characterized by a Nusselt number of at least
about 5.
45. The method of claim 44, wherein said mixing-inducing shape
includes at least one helical invagination.
46. The method of claim 44, wherein said mixing-inducing shape
includes at least one protrusion.
47. A method of modifying the temperature of a human body,
comprising: inserting a heat transfer element into a portion of the
vasculature from a distal location, the heat transfer element
having a segmented shape; circulating a working fluid through the
segmented heat transfer element to modify the temperature of the
blood in the vasculature, thereby modifying the temperature of the
body.
48. The method of claim 47, wherein the segments of the heat
transfer element are separated by flexible joints.
49. The method of claim 48, wherein the joints are bellows.
50. A cooling system for cooling a patient's body intravascularly,
comprising: a flexible catheter insertable into a blood vessel; a
flexible cooling element attached to a distal end of the flexible
catheter; and a heating blanket for applying heat to a selected
portion of the patient's body, wherein the heating blanket includes
an electrical resistance heater.
51. A method for changing a patient's body temperature
intravascularly while controlling the patient's thermoregulatory
setpoint, comprising: providing a catheter having a heat exchange
element at a portion thereof; inserting the catheter through the
vascular system of the patient to place the heat exchange element
in a blood vessel; circulating fluid through the heat exchange
element; transferring heat from the blood in the vessel to the heat
exchange element; and administering a thermoregulatory drug to the
patient.
52. The method of claim 51, wherein the thermoregulatory drug is
selected from the group consisting of clonidine, meperidine,
propofol, magnesium, dexmedetomidine, and combinations thereof.
53. A method for changing a patient's body temperature
intravascularly while controlling patient shivering, comprising:
providing a catheter having a heat exchange element at a portion
thereof; inserting the catheter through the vascular system of the
patient to place the heat exchange element in a blood vessel;
circulating fluid through the heat exchange element; transferring
heat from the blood in the vessel to the heat exchange element; and
administering an antishivering drug to the patient.
54. The method of claim 53, wherein the antishivering drug is
selected from the group consisting of clonidine, meperidine,
propofol, magnesium, dexmedetomidine, and combinations thereof.
55. A system for modifying the temperature of a patient's body
intravascularly, comprising: a flexible catheter insertable into a
blood vessel; a flexible heat transfer element attached to a distal
end of said flexible catheter; and a heat transfer blanket, wherein
said heat transfer blanket includes a heat transfer device adapted
to transfer heat between said blanket and a portion of the
patient's body.
56. The system recited in claim 55, wherein said heat transfer
element comprises a cooling element.
57. The system recited in claim 55, wherein said heat transfer
element comprises a heating element.
58. The system recited in claim 55, wherein said heat transfer
device comprises a heating device adapted to transfer heat from
said blanket to the portion of the patient's body.
59. The system recited in claim 58, wherein said heating device
comprises an electrical resistance heater.
60. The system recited in claim 55, wherein said heat transfer
device comprises a cooling device adapted to transfer heat from the
portion of the patient's body to said blanket.
61. A method for substantially reducing cell damage during
angioplasty, comprising: providing a catheter having a cooling
element attached to a distal end thereof; inserting the catheter
through the vascular system of the patient to place the cooling
element in a first location in a blood vessel, circulating fluid
through the cooling element; transferring heat from the blood in
the vein to the cooling element; and performing angioplasty on the
blood vessel at a location proximal of the first location.
62. A method for cooling a patient's body intravascularly,
comprising: providing a catheter having a cooling element attached
to a distal end thereof; inserting the catheter through the
vascular system of the patient to place the cooling element in a
vein that drains into the heart of a patient; circulating fluid
through the cooling element; and transferring heat from the blood
in the vein to the cooling element.
63. The method of claim 62, further comprising applying heat via a
warming device to a substantial portion of the surface area of the
patient.
64. The method of claim 62, further comprising applying cooling via
a cooling device to a substantial portion of the surface area of
the patient.
65. The method of claim 62, further comprising administering a
vasoconstrictive drug to the patient.
66. The method of claim 63, wherein the warming device is a heating
blanket.
67. The method of claim 64, wherein the cooling device is a cooling
blanket.
68. The method of claim 62, further comprising administering a
thermoregulatory drug to the patient.
69. The method of claim 63, further comprising administering a
thermoregulatory drug to the patient.
70. The method of claim 69, wherein the thermoregulatory drug is
selected from the group consisting of clonidine, meperidine,
propofol, magnesium, dexmedetomidine, and combinations thereof.
71. The method of claim 62, wherein the cooling element is disposed
in a vein selected from the group consisting of the superior vena
cava, the inferior vena cava, or both.
72. A method for substantially reducing platelet aggregation in a
blood vessel in which blood is flowing, comprising: providing a
catheter having a cooling element attached to a distal end thereof;
inserting the catheter through the vascular system of the patient
to place the cooling element in a blood vessel in which blood is
flowing; circulating fluid through the cooling element; and
transferring heat from the blood in the vessel to the cooling
element, whereby blood is cooled and platelet aggregation is
substantially reduced.
73. A method for substantially reducing dependence on drug
therapies in treating insults or injuries resulting in ischemia,
comprising: providing a catheter having a cooling element attached
to a distal end thereof; inserting the catheter through the
vascular system of the patient to place the cooling element in a
blood vessel in which blood is flowing; circulating fluid through
the cooling element; and transferring heat from the blood in the
vessel to the cooling element, whereby blood is cooled.
74. A method for substantially reducing cell damage during and
after a myocardial infarction, comprising: providing a catheter
having a cooling element attached to a distal end thereof;
inserting the catheter through the vascular system of the patient
to place the cooling element in a vein selected from the group
consisting of the superior vena cava, the inferior vena cava, or
both; circulating fluid through the cooling element; and
transferring heat from the blood in the vein to the cooling
element, whereby at least one of platelet aggregation, oxygen
demands, or the metabolic rate of the heart is reduced or
bradycardia is induced.
75. The method of claim 74, further comprising administering a drug
to lower blood pressure.
76. A method for substantially reducing stenoses recurring
following angioplasty, comprising: providing a catheter having a
cooling element attached to a distal end thereof; performing an
angioplasty or stenting operation on a blood vessel of the patient;
inserting the catheter through the vascular system of the patient
to place the cooling element in the blood vessel; circulating fluid
through the cooling element; and transferring heat from the blood
in the vessel to the cooling element, whereby blood and the blood
vessel wall is cooled.
77. A method for substantially reducing reperfusion injury
following reflow, comprising: providing a catheter having a cooling
element attached to a distal end thereof; performing an reflow
operation on a blood vessel of the patient; inserting the catheter
through the vascular system of the patient to place the cooling
element in the blood vessel; circulating fluid through the cooling
element; and transferring heat from the blood in the vessel to the
cooling element, whereby blood in the vessel is cooled.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part patent application of
co-pending U.S. patent application Ser. No. 09/292,532, filed on
Apr. 15, 1999, and entitled "Isolated Selective Organ Cooling
Method and Apparatus", which is a continuation-in-part patent
application of copending U.S. patent application Ser. No.
09/211,076, filed on Dec. 14, 1998, and entitled "Selective Organ
Cooling Apparatus and Method", which is a continuation patent
application of co-pending U.S. patent application Ser. No.
09/103,342, filed on Jun. 23, 1998, and entitled "Selective Organ
Cooling Catheter and Method of Using the Same".
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates generally to the lowering and
control of the temperature of the human body. More particularly,
the invention relates to a method and intravascular apparatus for
cooling the body without the adverse consequences associated with
prior methods of total body cooling. The invention also relates to
a method and intravascular apparatus for cooling the body without
causing thermoregulatory suppression of the cooling.
[0005] 2. Background Information Organs in the human body, such as
the brain, kidney and heart, are maintained at a constant
temperature of approximately 37.degree. C. Hypothermia can be
clinically defined as a core body temperature of 35.degree. C. or
less. Hypothermia is sometimes characterized further according to
its severity. A body core temperature in the range of 33.degree. C.
to 35.degree. C. is described as mild hypothermia. A body
temperature of 28.degree. C. to 32.degree. C. is described as
moderate hypothermia. A body core temperature in the range of
24.degree. C. to 28.degree. C. is described as severe
hypothermia.
[0006] Hypothermia is uniquely effective in reducing brain injury
caused by a variety of neurological insults and may eventually play
an important role in emergency brain resuscitation. Experimental
evidence has demonstrated that cerebral cooling improves outcome
after global ischemia, focal ischemia, or traumatic brain injury.
For this reason, hypothermia may be induced in order to reduce the
effect of certain bodily injuries to the brain as well as other
organs.
[0007] Cerebral hypothermia has traditionally been accomplished
through whole body cooling to create a condition of total body
hypothermia in the range of 20.degree. C. to 30.degree. C. The
currently-employed techniques and devices used to cause total body
hypothermia lead to various side effects. In addition to the
undesirable side effects, present methods of administering total
body hypothermia are cumbersome.
[0008] Catheters have been developed which are inserted into the
bloodstream of the patient in order to induce total body
hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes
a method and apparatus of lowering and raising the temperature of
the human body. Dato induces moderate hypothermia in a patient
using a rigid metallic catheter. The catheter has an inner
passageway through which a fluid, such as water, can be circulated.
The catheter is inserted through the femoral vein and then through
the inferior vena cava as far as the right atrium and the superior
vena cava. The Dato catheter has an elongated cylindrical shape and
is constructed from stainless steel. By way of example, Dato
suggests the use of a catheter approximately 70 cm in length and
approximately 6 mm in diameter. Thus, the Dato device cools along
the length of a very elongated device. Use of the Dato device is
highly cumbersome due to its size and lack of flexibility.
[0009] U.S. Pat. No. 5,837,003 to Ginsburg also discloses a method
and apparatus for controlling a patient's body temperature. In this
technique, a flexible catheter is inserted into the femoral artery
or vein or the jugular vein. The catheter may be in the form of a
balloon to allow an enhanced surface area for heat transfer. A
thermally conductive metal foil may be used as part of a
heat-absorbing surface. This device fails to disclose or teach use
of any ability to enhance heat transfer. In addition, the disclosed
device fails to disclose temperature regulation.
[0010] Therefore, a practical method and apparatus that lowers and
controls the temperature of the human body satisfies a long-felt
need.
BRIEF SUMMARY OF THE INVENTION
[0011] In one aspect, the apparatus of the present invention can
include a heat transfer element that can be used to apply cooling
to the blood flowing in a large vein feeding the heart. An optional
heating element may be used to supply warming to a portion of the
remainder of the body to provide comfort to the patient and to
allow a low target hypothermic temperature to be achieved. The
heating element may be applied before or after a target temperature
is achieved. The warming operation can be accomplished by means of
local heating of the vein or artery with an external heat
applicator or by means of substantially whole body warming with a
heating blanket. The warming operation can be accomplished per se
or in combination with thermoregulatory drugs.
[0012] The heat transfer element, by way of example only, includes
first and second elongated, articulated segments, each segment
having a mixing-inducing exterior surface. A flexible joint can
connect the first and second elongated segments. An inner lumen may
be disposed within the first and second elongated segments and is
capable of transporting a pressurized working fluid to a distal end
of the first elongated segment. In addition, the first and second
elongated segments may have a mixing-inducing interior surface for
inducing mixing within the pressurized working fluid. The
mixing-inducing exterior surface may be adapted to induce mixing
within a blood flow when placed within an artery or vein. In one
embodiment, the flexible joint includes a bellows section that also
allows for axial compression of the heat transfer element as well
as for enhanced flexibility. In alternative embodiments, the
bellows section may be replaced with flexible tubing such as small
cylindrical polymer connecting tubes.
[0013] In one embodiment, the mixing-inducing exterior surfaces of
the heat transfer element include one or more helical grooves and
ridges. Adjacent segments of the heat transfer element can be
oppositely spiraled to increase mixing. For instance, the first
elongated heat transfer segment may include one or more helical
ridges having a counterclockwise twist, while the second elongated
heat transfer segment includes one or more helical ridges having a
clockwise twist. Alternatively, of course, the first elongated heat
transfer segment may include one or more clockwise helical ridges,
and the second elongated heat transfer segment may include one or
more counter-clockwise helical ridges. The first and second
elongated, articulated segments may be formed from highly
conductive materials such as metals.
[0014] The heat transfer device may also have a supply catheter
with an inner catheter lumen coupled to the inner lumen within the
first and second elongated heat transfer segments. A working fluid
supply configured to dispense the pressurized working fluid may be
coupled to the inner catheter lumen or alternatively to the supply
catheter. The working fluid supply may be configured to produce the
pressurized working fluid at a temperature of about 0.degree. C.
and at a pressure below about 5 atmospheres of pressure.
[0015] In yet another alternative embodiment, the heat transfer
device may have three or more elongated, articulated, heat transfer
segments each having a mixing-inducing exterior surface, with
additional flexible joints connecting the additional elongated heat
transfer segments. In one such embodiment, by way of example only,
the first and third elongated heat transfer segments may include
clockwise helical ridges, and the second elongated heat transfer
segment may include one or more counter-clockwise helical ridges.
Alternatively, of course, the first and third elongated heat
transfer segments may include counter-clockwise helical ridges, and
the second elongated heat transfer segment may include one or more
clockwise helical ridges.
[0016] The mixing-inducing exterior surface of the heat transfer
element may optionally include a surface coating or treatment to
inhibit clot formation. A surface coating may also be used to
provide a degree of lubricity to the heat transfer element and its
associated catheter.
[0017] The present invention is also directed to a method of
inducing hypothermia in the body by inserting a flexible,
conductive cooling element into a vein that is in pressure
communication with the heart, e.g., the superior or inferior vena
cavae or both. The vena cavae may be accessed via known techniques
from the jugular vein or from the subclavian or femoral veins, for
example. The heat transfer element in one or both vena cavae may
then cool virtually all the blood being returned to the heart. The
cooled blood enters the right atrium at which point the same is
pumped through the right ventricle and into the pulmonary artery to
the lungs where the same is oxygenated. Due to the heat capacity of
the lungs, the blood does not appreciably warm during oxygenation.
The cooled blood is returned to the heart and pumped to the entire
body via the aorta. Thus, cooled blood may be delivered indirectly
to a chosen organ such as the brain. This indirect cooling is
especially effective as high blood flow organs such as the heart
and brain are preferentially supplied blood by the vasculature. A
warming blanket or other warming device may be applied to portions
of the body to provide comfort to the patient and to inhibit
thermoregulatory responses such as vasoconstriction.
Thermoregulatory drugs may also be so provided for this reason.
[0018] The method further includes circulating a working fluid
through the flexible, conductive cooling element in order to lower
the temperature of the blood in the vena cava. The flexible,
conductive heat transfer element preferably absorbs more than about
150 or 300 Watts of heat.
[0019] The method may also include inducing mixing within the free
stream blood flow within the vena cava. It is noted that a degree
of turbulence or mixing is generally present within the vena cava
anyway. The step of circulating may include inducing mixing in the
flow of the working fluid through the flexible, conductive heat
transfer element. The pressure of the working fluid may be
maintained below about 5 atmospheres of pressure.
[0020] The present invention also envisions a method for inducing
therapeutic hypothermia in the body of a patient which includes
introducing a catheter, with a cooling element, into a vena cava
supplying the heart, the catheter having a diameter of about 18 mm
or less, inducing mixing in blood flowing over the cooling element,
and lowering the temperature of the cooling element to remove heat
from the blood to cool the blood. In one embodiment, the cooling
step removes at least about 150 Watts of heat from the blood. In
another embodiment, the cooling step removes at least about 300
Watts of heat from the blood.
[0021] The mixing induced may result in a Nusselt number
enhancement of the flow of between about 5 and 80.
[0022] In another aspect of the method, the invention is directed
to a method of lowering the temperature of the body while
prohibiting intervention of the body's thermoregulatory responses.
Steps of the method may include delivering a drug to lower the
thermoregulatory setpoint of the body such that thermoregulatory
responses, including shivering and vasoconstriction, are not
triggered above a certain temperature, wherein the certain
temperature is lower than normal body temperature. The temperature
of the blood in a major vein such as the vena cavae is then lowered
to induce hypothermia in the body. The thermoregulatory drugs
provide patient comfort. If even lower body temperatures are
desired or required, heating blankets may be provided to further
ensure patient comfort. Generally, for one degree of body core
cooling, the heating blanket should be 5.degree. C. above the skin
temperature to provide patient comfort. However, the temperature of
the blanket should generally not exceed 42.degree. C.
[0023] Advantages of the invention are numerous. Patients can be
provided with the beneficial aspects of hypothermia without
suffering the deleterious consequences of the prior art. The
procedure can be administered safely and easily. Numerous cardiac
and neural settings can benefit by the hypothermic therapy. For
example, ischemia and restenosis can be minimized. Other advantages
will be understood from the following.
[0024] The novel features of this invention, as well as the
invention itself, will be best understood from the attached
drawings, taken along with the following description, in which
similar reference characters refer to similar parts, and in
which:
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0025] FIG. 1 is an elevation view of one embodiment of a heat
transfer element according to the invention;
[0026] FIG. 2 is a longitudinal section view of the heat transfer
element of FIG. 1;
[0027] FIG. 3 is a transverse section view of the heat transfer
element of FIG. 1;
[0028] FIG. 4 is a perspective view of the heat transfer element of
FIG. 1 in use within a blood vessel;
[0029] FIG. 5 is a cut-away perspective view of an alternative
embodiment of a heat transfer element according to the
invention;
[0030] FIG. 6 is a transverse section view of the heat transfer
element of FIG. 5;
[0031] FIG. 7 is a schematic representation of the heat transfer
element being used in one embodiment to provide hypothermia to a
patient by causing total body cooling and then rewarming the
body;
[0032] FIG. 8 is a schematic representation of the heat transfer
element being used in another embodiment to provide hypothermia to
a patient by causing total body cooling and then rewarming the
body;
[0033] FIG. 9 is a schematic representation of the heat transfer
element being used in an embodiment within the superior vena
cava;
[0034] FIG. 10 is a graph showing preferential cooling of the high
flow organs of the body under a hypothermic therapy; and
[0035] FIG. 11 is a flowchart showing an exemplary method of the
invention employing heating blankets and thermoregulatory
drugs.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Overview
[0037] A one or two-step process and a one or two-piece device may
be employed to intravascularly lower the temperature of a body in
order to induce therapeutic hypothermia. A cooling element may be
placed in a high-flow vein such as the vena cavae to absorb heat
from the blood flowing into the heart. This transfer of heat causes
a cooling of the blood flowing through the heart and thus
throughout the vasculature. Such a method and device may
therapeutically be used to induce an artificial state of
hypothermia.
[0038] A heat transfer element that systemically cools blood should
be capable of providing the necessary heat transfer rate to produce
the desired cooling effect throughout the vasculature. This may be
up to or greater than 300 watts, and is at least partially
dependent on the mass of the patient and the rate of blood flow.
Surface features may be employed on the heat transfer element to
enhance the heat transfer rate. The surface features and other
components of the heat transfer element are described in more
detail below.
[0039] One problem with hypothermia as a therapy is that the
patient's thermoregulatory defenses initiate, attempting to defeat
the hypothermia. Methods and devices may be used to lessen the
thermoregulatory response. For example, a heating blanket may cover
the patient. In this way, the patient may be made more comfortable.
Thermoregulatory drugs may also be employed to lower the trigger
point at which the patient's thermoregulatory system begins to
initiate defenses. Such drugs are described in more detail below. A
method employing thermoregulatory drugs, heating blankets, and heat
transfer elements is also disclosed below.
[0040] Anatomical Placement
[0041] The internal jugular vein is the vein that directly drains
the brain. The external jugular joins the internal jugular at the
base of the neck. The internal jugular veins join the subclavian
veins to form the brachiocephalic veins that in turn drain into the
superior vena cava. The superior vena cava drains into the right
atrium of the heart as may be seen by referring ahead to FIG. 9.
The superior vena cava supplies blood to the heart from the upper
part of the body.
[0042] A cooling element may be placed into the superior vena cava,
inferior vena cava, or otherwise into a vein which feeds into the
superior vena cava or otherwise into the heart to cool the body. A
physician percutaneously places the catheter into the subclavian or
internal or external jugular veins to access the superior vena
cava. The blood, cooled by the heat transfer element, may be
processed by the heart and provided to the body in oxygenated form
to be used as a conductive medium to cool the body. The lungs have
a fairly low heat capacity, and thus the lungs do not cause
appreciable rewarming of the flowing blood.
[0043] The vasculature by its very nature provides preferential
blood flow to the high blood flow organs such as the brain and the
heart. Thus, these organs are preferentially cooled by such a
procedure as is also shown experimentally in FIG. 10. FIG. 10 is a
graph of measured temperature plotted versus cooling time. This
graph show the effect of placing a cooling element in the superior
vena cavae of a sheep. The core body temperature as measured by an
esophageal probe is shown by curve 82. The brain temperature is
shown by curve 86. The brain temperature is seen to decrease more
rapidly than the core body temperature throughout the experiment.
The inventors believe this effect to be due to the preferential
supply of blood provided to the brain and heart. This effect may be
even more pronounced if thermoregulatory effects, such as
vasoconstriction, occur that tend to focus blood supply to the core
vascular system and away from the peripheral vascular system.
[0044] Heat Transfer
[0045] When a heat transfer element is inserted approximately
coaxially into an artery or vein, the primary mechanism of heat
transfer between the surface of the heat transfer element and the
blood is forced convection. Convection relies upon the movement of
fluid to transfer heat. Forced convection results when an external
force causes motion within the fluid. In the case of arterial or
venous flow, the beating heart causes the motion of the blood
around the heat transfer element.
[0046] The magnitude of the heat transfer rate is proportional to
the surface area of the heat transfer element, the temperature
differential, and the heat transfer coefficient of the heat
transfer element.
[0047] The receiving artery or vein into which the heat transfer
element is placed has a limited diameter and length. Thus, the
surface area of the heat transfer element must be limited to avoid
significant obstruction of the artery or vein and to allow the heat
transfer element to easily pass through the vascular system. For
placement within the superior vena cava via the external jugular,
the cross sectional diameter of the heat transfer element may be
limited to about 5-6 mm, and its length may be limited to
approximately 10-15 cm. For placement within the inferior vena
cava, the cross sectional diameter of the heat transfer element may
be limited to about 6-7 mm, and its length may be limited to
approximately 25-35 cm.
[0048] Decreasing the surface temperature of the heat transfer
element can increase the temperature differential. However, the
minimum allowable surface temperature is limited by the
characteristics of blood. Blood freezes at approximately 0.degree.
C. When the blood approaches freezing, ice emboli may form in the
blood, which may lodge downstream, causing serious ischemic injury.
Furthermore, reducing the temperature of the blood also increases
its viscosity, which results in a small decrease in the value of
the convection heat transfer coefficient. In addition, increased
viscosity of the blood may result in an increase in the pressure
drop within the artery, thus compromising the flow of blood to the
brain. Given the above constraints, it is advantageous to limit the
minimum allowable surface temperature of the cooling element to
approximately 5.degree. C. This results in a maximum temperature
differential between the blood stream and the cooling element of
approximately 32.degree. C. For other physiological reasons, there
are limits on the maximum allowable surface temperature of the
warming element.
[0049] The mechanisms by which the value of the convection heat
transfer coefficient may be increased are complex. However, it is
well known that the convection heat transfer coefficient increases
with the level of "mixing" or "turbulent" kinetic energy in the
fluid flow. Thus it is advantageous to have blood flow with a high
degree of mixing in contact with the heat transfer element.
[0050] The blood flow has a considerably more stable flux in the
superior vena cava than in an artery. However, the blood flow in
the superior vena cava still has a high degree of inherent mixing
or turbulence. Reynolds numbers in the superior vena cava may
range, for example, from 2,000 to 5,000. Thus, blood cooling in the
superior vena cava may benefit from enhancing the level of mixing
with the heat transfer element but this benefit may be
substantially less than that caused by the inherent mixing.
[0051] Boundary Layers
[0052] A thin boundary layer has been shown to form during the
cardiac cycle. Boundary layers develop adjacent to the heat
transfer element as well as next to the walls of the artery or
vein. Each of these boundary layers has approximately the same
thickness as the boundary layer that would have developed at the
wall of the artery in the absence of the heat transfer element. The
free stream flow region is developed in an annular ring around the
heat transfer element. The heat transfer element used in such a
vessel should reduce the formation of such viscous boundary
layers.
[0053] Heat Transfer Element Characteristics and Description
[0054] The intravascular heat transfer element should be flexible
in order to be placed within the vena cavae or other veins or
arteries. The flexibility of the heat transfer element is an
important characteristic because the same is typically inserted
into a vein such as the external jugular and accesses the superior
vena cava by initially passing though a series of one or more
branches. Further, the heat transfer element is ideally constructed
from a highly thermally conductive material such as metal in order
to facilitate heat transfer. The use of a highly thermally
conductive material increases the heat transfer rate for a given
temperature differential between the working fluid within the heat
transfer element and the blood. This facilitates the use of a
higher temperature coolant, or lower temperature warming fluid,
within the heat transfer element, allowing safer working fluids,
such as water or saline, to be used. Highly thermally conductive
materials, such as metals, tend to be rigid. Therefore, the design
of the heat transfer element should facilitate flexibility in an
inherently inflexible material.
[0055] It is estimated that the cooling element should absorb at
least about 300 Watts of heat when placed in the superior vena cava
to lower the temperature of the body to between about 30.degree. C.
and 34.degree. C. These temperatures are thought to be appropriate
to obtain the benefits of hypothermia described above. The power
removed determines how quickly the target temperature can be
reached. For example, in a stroke therapy in which it is desired to
lower brain temperature, the same may be lowered about 4.degree. C.
per hour in a 70 kg human upon removal of 300 Watts.
[0056] One embodiment of the invention uses a modular design. This
design creates helical blood flow and produces a level of mixing in
the blood flow by periodically forcing abrupt changes in the
direction of the helical blood flow. The abrupt changes in flow
direction are achieved through the use of a series of two or more
heat transfer segments, each included of one or more helical
ridges. The use of periodic abrupt changes in the helical direction
of the blood flow in order to induce strong free stream turbulence
may be illustrated with reference to a common clothes washing
machine. The rotor of a washing machine spins initially in one
direction causing laminar flow. When the rotor abruptly reverses
direction, significant turbulent kinetic energy is created within
the entire wash basin as the changing currents cause random
turbulent motion within the clothes-water slurry. These surface
features also tend to increase the surface area of the heat
transfer element, further enhancing heat transfer.
[0057] FIG. 1 is an elevation view of one embodiment of a cooling
element 14 according to the present invention. The heat transfer
element 14 includes a series of elongated, articulated segments or
modules 20, 22, 24. Three such segments are shown in this
embodiment, but two or more such segments could be used without
departing from the spirit of the invention. As seen in FIG. 1, a
first elongated heat transfer segment 20 is located at the proximal
end of the heat transfer element 14. A mixing-inducing exterior
surface of the segment 20 includes four parallel helical ridges 28
with four parallel helical grooves 26 therebetween. One, two,
three, or more parallel helical ridges 28 could also be used
without departing from the spirit of the present invention. In this
embodiment, the helical ridges 28 and the helical grooves 26 of the
heat transfer segment 20 have a left hand twist, referred to herein
as a counter-clockwise spiral or helical rotation, as they proceed
toward the distal end of the heat transfer segment 20.
[0058] The first heat transfer segment 20 is coupled to a second
elongated heat transfer segment 22 by a first bellows section 25,
which provides flexibility and compressibility. The second heat
transfer segment 22 includes one or more helical ridges 32 with one
or more helical grooves 30 therebetween. The ridges 32 and grooves
30 have a right hand, or clockwise, twist as they proceed toward
the distal end of the heat transfer segment 22. The second heat
transfer segment 22 is coupled to a third elongated heat transfer
segment 24 by a second bellows section 27. The third heat transfer
segment 24 includes one or more helical ridges 36 with one or more
helical grooves 34 therebetween. The helical ridge 36 and the
helical groove 34 have a left hand, or counter-clockwise, twist as
they proceed toward the distal end of the heat transfer segment 24.
Thus, successive heat transfer segments 20, 22, 24 of the heat
transfer element 14 alternate between having clockwise and
counterclockwise helical twists. The actual left or right hand
twist of any particular segment is immaterial, as long as adjacent
segments have opposite helical twist.
[0059] In addition, the rounded contours of the ridges 28, 32, 36
allow the heat transfer element 14 to maintain a relatively
atraumatic profile, thereby minimizing the possibility of damage to
the blood vessel wall. A heat transfer element according to the
present invention may include two, three, or more heat transfer
segments.
[0060] The bellows sections 25, 27 are formed from seamless and
nonporous materials, such as metal, and therefore are impermeable
to gas, which can be particularly important, depending on the type
of working fluid that is cycled through the heat transfer element
14. The structure of the bellows sections 25, 27 allows them to
bend, extend and compress, which increases the flexibility of the
heat transfer element 14 so that it is more readily able to
navigate through blood vessels. The bellows sections 25, 27 also
provide for axial compression of the heat transfer element 14,
which can limit the trauma when the distal end of the heat transfer
element 14 abuts a blood vessel wall. The bellows sections 25, 27
are also able to tolerate cryogenic temperatures without a loss of
performance. In alternative embodiments, the bellows may be
replaced by flexible polymer tubes, which are bonded between
adjacent heat transfer segments.
[0061] The exterior surfaces of the heat transfer element 14 can be
made from metal, and may include very high thermal conductivity
materials such as nickel, thereby facilitating heat transfer.
Alternatively, other metals such as stainless steel, titanium,
aluminum, silver, copper and the like, can be used, with or without
an appropriate coating or treatment to enhance biocompatibility or
inhibit clot formation. Suitable biocompatible coatings include,
e.g., gold, platinum or polymer paralyene. The heat transfer
element 14 may be manufactured by plating a thin layer of metal on
a mandrel that has the appropriate pattern. In this way, the heat
transfer element 14 may be manufactured inexpensively in large
quantities, which is an important feature in a disposable medical
device.
[0062] Because the heat transfer element 14 may dwell within the
blood vessel for extended periods of time, such as 24-48 hours or
even longer, it may be desirable to treat the surfaces of the heat
transfer element 14 to avoid clot formation. In particular, one may
wish to treat the bellows sections 25, 27 because stagnation of the
blood flow may occur in the convolutions, thus allowing clots to
form and cling to the surface to form a thrombus. One means by
which to prevent thrombus formation is to bind an antithrombogenic
agent to the surface of the heat transfer element 14. For example,
heparin is known to inhibit clot formation and is also known to be
useful as a biocoating. Alternatively, the surfaces of the heat
transfer element 14 may be bombarded with ions such as nitrogen.
Bombardment with nitrogen can harden and smooth the surface and
thus prevent adherence of clotting factors. Another coating that
provides beneficial properties may be a lubricious coating.
Lubricious coatings, on both the heat transfer element and its
associated catheter, allow for easier placement in the, e.g., vena
cava.
[0063] FIG. 2 is a longitudinal sectional view of the heat transfer
element 14 of an embodiment of the invention, taken along line 2-2
in FIG. 1. Some interior contours are omitted for purposes of
clarity. An inner tube 42 creates an inner lumen 40 and an outer
lumen 46 within the heat transfer element 14. Once the heat
transfer element 14 is in place in the blood vessel, a working
fluid such as saline or other aqueous solution may be circulated
through the heat transfer element 14. Fluid flows up a supply
catheter into the inner lumen 40. At the distal end of the heat
transfer element 14, the working fluid exits the inner lumen 40 and
enters the outer lumen 46. As the working fluid flows through the
outer lumen 46, heat is transferred from the working fluid to the
exterior surface 37 of the heat transfer element 14. Because the
heat transfer element 14 is constructed from a high conductivity
material, the temperature of its exterior surface 37 may reach very
close to the temperature of the working fluid. The tube 42 may be
formed as an insulating divider to thermally separate the inner
lumen 40 from the outer lumen 46. For example, insulation may be
achieved by creating longitudinal air channels in the wall of the
insulating tube 42. Alternatively, the insulating tube 42 may be
constructed of a non-thermally conductive material like
polytetrafluoroethylene or another polymer.
[0064] It is important to note that the same mechanisms that govern
the heat transfer rate between the exterior surface 37 of the heat
transfer element 14 and the blood also govern the heat transfer
rate between the working fluid and the interior surface 38 of the
heat transfer element 14. The heat transfer characteristics of the
interior surface 38 are particularly important when using water,
saline or other fluid that remains a liquid as the working fluid.
Other coolants such as Freon undergo nucleate boiling and create
mixing through a different mechanism. Saline is a safe working
fluid, because it is non-toxic, and leakage of saline does not
result in a gas embolism, which could occur with the use of boiling
refrigerants. Since mixing in the working fluid is enhanced by the
shape of the interior surface 38 of the heat transfer element 14,
the working fluid can be delivered to the cooling element 14 at a
warmer temperature and still achieve the necessary cooling rate.
Similarly, since mixing in the working fluid is enhanced by the
shape of the interior surface of the heat transfer element, the
working fluid can be delivered to the warming element 14 at a
cooler temperature and still achieve the necessary warming
rate.
[0065] This has a number of beneficial implications in the need for
insulation along the catheter shaft length. Due to the decreased
need for insulation, the catheter shaft diameter can be made
smaller. The enhanced heat transfer characteristics of the interior
surface of the heat transfer element 14 also allow the working
fluid to be delivered to the heat transfer element 14 at lower flow
rates and lower pressures. High pressures may make the heat
transfer element stiff and cause it to push against the wall of the
blood vessel, thereby shielding part of the exterior surface 37 of
the heat transfer element 14 from the blood. Because of the
increased heat transfer characteristics achieved by the alternating
helical ridges 28, 32, 36, the pressure of the working fluid may be
as low as 5 atmospheres, 3 atmospheres, 2 atmospheres or even less
than 1 atmosphere.
[0066] FIG. 3 is a transverse sectional view of the heat transfer
element 14 of the invention, taken at a location denoted by the
line 3-3 in FIG. 1. FIG. 3 illustrates a five-lobed embodiment,
whereas FIG. 1 illustrates a four-lobed embodiment. As mentioned
earlier, any number of lobes might be used. In FIG. 3, the
construction of the heat transfer element 14 is clearly shown. The
inner lumen 40 is defined by the insulating tube 42. The outer
lumen 46 is defined by the exterior surface of the insulating tube
42 and the interior surface 38 of the heat transfer element 14. In
addition, the helical ridges 32 and helical grooves 30 may be seen
in FIG. 3. Although FIG. 3 shows four ridges and four grooves, the
number of ridges and grooves may vary. Thus, heat transfer elements
with 1, 2, 3, 4, 5, 6, 7, 8 or more ridges are specifically
contemplated.
[0067] FIG. 4 is a perspective view of a heat transfer element 14
in use within a blood vessel, showing only one helical lobe per
segment for purposes of clarity. Beginning from the proximal end of
the heat transfer element (not shown in FIG. 4), as the blood moves
forward, the first helical heat transfer segment 20 induces a
counter-clockwise rotational inertia to the blood. As the blood
reaches the second segment 22, the rotational direction of the
inertia is reversed, causing mixing within the blood. Further, as
the blood reaches the third segment 24, the rotational direction of
the inertia is again reversed. The sudden changes in flow direction
actively reorient and randomize the velocity vectors, thus ensuring
mixing throughout the bloodstream. During such mixing, the velocity
vectors of the blood become more random and, in some cases, become
perpendicular to the axis of the vessel. Thus, a large portion of
the volume of warm blood in the vessel is actively brought in
contact with the heat transfer element 14, where it can be cooled
by direct contact rather than being cooled largely by conduction
through adjacent laminar layers of blood.
[0068] Referring back to FIG. 1, the heat transfer element 14 has
been designed to address all of the design criteria discussed
above. First, the heat transfer element 14 is flexible and is made
of a highly conductive material. The flexibility is provided by a
segmental distribution of bellows sections 25, 27 that provide an
articulating mechanism. Bellows have a known convoluted design that
provide flexibility. Second, the exterior surface area 37 has been
increased through the use of helical ridges 28, 32, 36 and helical
grooves 26, 30, 34. The ridges also allow the heat transfer element
14 to maintain a relatively atraumatic profile, thereby minimizing
the possibility of damage to the vessel wall. Third, the heat
transfer element 14 has been designed to promote mixing both
internally and externally. The modular or segmental design allows
the direction of the grooves to be reversed between segments. The
alternating helical rotations create an alternating flow that
results in mixing the blood in a manner analogous to the mixing
action created by the rotor of a washing machine that switches
directions back and forth. This action is intended to promote
mixing to enhance the heat transfer rate. The alternating helical
design also causes beneficial mixing, or turbulent kinetic energy,
of the working fluid flowing internally.
[0069] FIG. 5 is a cut-away perspective view of an alternative
embodiment of a heat transfer element 50. An external surface 52 of
the heat transfer element 50 is covered with a series of axially
staggered protrusions 54. The staggered nature of the outer
protrusions 54 is readily seen with reference to FIG. 6 which is a
transverse cross-sectional view taken at a location denoted by the
line 6-6 in FIG. 5. As the blood flows along the external surface
52, it collides with one of the staggered protrusions 54 and a
turbulent wake flow is created behind the protrusion. As the blood
divides and swirls alongside of the first staggered protrusion 54,
its turbulent wake encounters another staggered protrusion 54
within its path preventing the re-lamination of the flow and
creating yet more mixing. In this way, the velocity vectors are
randomized and mixing is created not only in the boundary layer but
also throughout a large portion of the free stream. As is the case
with the preferred embodiment, this geometry also induces a mixing
effect on the internal working fluid flow.
[0070] A working fluid is circulated up through an inner lumen 56
defined by an insulating tube 58 to a distal tip of the heat
transfer element 50. The working fluid then traverses an outer
lumen 60 in order to transfer heat to the exterior surface 52 of
the heat transfer element 50. The inside surface of the heat
transfer element 50 is similar to the exterior surface 52 in order
to induce turbulent flow of the working fluid. The inner
protrusions can be aligned with the outer protrusions 54 as shown
in FIG. 6 or they can be offset from the outer protrusions 54 as
shown in FIG. 5.
[0071] Method of Use
[0072] FIG. 7 is a schematic representation of the invention being
used to cool the body of a patient and to warm a portion of the
body. The hypothermia apparatus shown in FIG. 7 includes a first
working fluid supply 10, preferably supplying a chilled liquid such
as water, alcohol or a halogenated hydrocarbon, a first supply
catheter 12 and the cooling element 14. The first supply catheter
12 may have a substantially coaxial construction. An inner lumen
within the first supply catheter 12 receives coolant from the first
working fluid supply 10. The coolant travels the length of the
first supply catheter 12 to the cooling element 14 which serves as
the cooling tip of the catheter. At the distal end of the cooling
element 14, the coolant exits the insulated interior lumen and
traverses the length of the cooling element 14 in order to decrease
the temperature of the cooling element 14. The coolant then
traverses an outer lumen of the first supply catheter 12 so that it
may be disposed of or recirculated. The first supply catheter 12 is
a flexible catheter having a diameter sufficiently small to allow
its distal end to be inserted percutaneously into an accessible
vein such as the external jugular vein of a patient as shown in
FIG. 7. The first supply catheter 12 is sufficiently long to allow
the cooling element 14 at the distal end of the first supply
catheter 12 to be passed through the vascular system of the patient
and placed in the superior vena cava 62, inferior vena cava (not
shown), or other such vein.
[0073] The method of inserting the catheter into the patient and
routing the cooling element 14 into a selected vein is well known
in the art. Percutaneous placement of the heat transfer element 14
into the jugular vein is accomplished directly, since the jugular
vein is close to the surface. The catheter would reside in the
internal jugular and into the superior vena cava or even the right
atrium.
[0074] Although the working fluid supply 10 is shown as an
exemplary cooling device, other devices and working fluids may be
used. For example, in order to provide cooling, freon,
perflourocarbon, water, or saline may be used, as well as other
such coolants.
[0075] The cooling element can absorb up to or more than 300 Watts
of heat from the blood stream, resulting in absorption of as much
as 100 Watts, 150 Watts, 170 Watts or more from the brain.
[0076] Heating Blankets
[0077] FIG. 7 also shows a heating element 66, shown as a heating
blanket. Heating blankets 66 generally are equipped with forced
warm-air blowers that blow heated air through vents in the blanket
in a direction towards the patient. This type of heating occurs
through the surface area of the skin of the patient, and is
partially dependent on the surface area extent of the patient. As
shown in FIG. 7, the heating blanket 66 may cover most of the
patient to warm and provide comfort to the patient. The heating
blanket 66 need not cover the face and head of the patient in order
that the patient may more easily breathe.
[0078] The heating blanket 66 serves several purposes. By warming
the patient, vasoconstriction is avoided. The patient is also made
more comfortable. For example, it is commonly agreed that for every
one degree of core body temperature reduction, the patient will
continue to feel comfortable if the same experiences a rise in
surface area (skin) temperature of five degrees. Spasms due to
total body hypothermia may be avoided. Temperature control of the
patient may be more conveniently performed as the physician has
another variable (the amount of heating) which may be adjusted.
[0079] As an alternative, the warming element may be any of the
heating methods proposed in U.S. patent application Ser. No.
09/292,532, filed on Apr 15, 1999, and entitled "Isolated Selective
Organ Cooling Method and Apparatus", and incorporated by reference
above.
[0080] The practice of the present invention is illustrated in the
following non-limiting example.
Exemplary Procedure
[0081] 1. The patient is initially assessed, resuscitated, and
stabilized.
[0082] 2. The procedure may be carried out in an angiography suite
or surgical suite equipped with fluoroscopy.
[0083] 3. An ultrasound or angiogram of the superior vena cava and
external jugular can be used to determine the vessel diameter and
the blood flow; a catheter with an appropriately sized heat
transfer element can be selected.
[0084] 5. After assessment of the veins, the patient is sterilely
prepped and infiltrated with lidocaine at a region where the
femoral artery may be accessed.
[0085] 6. The external jugular is cannulated and a guide wire may
be inserted to the superior vena cava. Placement of the guide wire
is confirmed with fluoroscopy.
[0086] 7. An angiographic catheter can be fed over the wire and
contrast media injected into the vein to further to assess the
anatomy if desired.
[0087] 8. Alternatively, the external jugular is cannulated and a
10-12.5 french (f) introducer sheath is placed.
[0088] 9. A guide catheter is placed into the superior vena cava.
If a guide catheter is placed, it can be used to deliver contrast
media directly to further assess anatomy.
[0089] 10. The cooling catheter is placed into the superior vena
cava via the guiding catheter or over the guidewire.
[0090] 11. Placement is confirmed if desired with fluoroscopy.
[0091] 12. Alternatively, the cooling catheter shaft has sufficient
pushability and torqueability to be placed in the superior vena
cava without the aid of a guide wire or guide catheter.
[0092] 13. The cooling catheter is connected to a pump circuit also
filled with saline and free from air bubbles. The pump circuit has
a heat exchange section that is immersed into a water bath and
tubing that is connected to a peristaltic pump. The water bath is
chilled to approximately 0.degree. C.
[0093] 14. Cooling is initiated by starting the pump mechanism. The
saline within the cooling catheter is circulated at 5 cc/sec. The
saline travels through the heat exchanger in the chilled water bath
and is cooled to approximately 1.degree. C.
[0094] 15. The saline subsequently enters the cooling catheter
where it is delivered to the heat transfer element. The saline is
warmed to approximately 5-7.degree. C. as it travels along the
inner lumen of the catheter shaft to the end of the heat transfer
element.
[0095] 16. The saline then flows back through the heat transfer
element in contact with the inner metallic surface. The saline is
further warmed in the heat transfer element to 12-15.degree. C.,
and in the process, heat is absorbed from the blood, cooling the
blood to 30.degree. C. to 35.degree. C. During this time, the
patient may be warmed with an external heat source such as a
heating blanket.
[0096] 17. The chilled blood then goes on to chill the body. It is
estimated that less than an hour will be required to cool the brain
to 30.degree. C. to 35.degree. C.
[0097] 18. The warmed saline travels back the outer lumen of the
catheter shaft and is returned to the chilled water bath where the
same is cooled to 1.degree. C.
[0098] 19. The pressure drops along the length of the circuit are
estimated to be between 1 and 10 atmospheres.
[0099] 20. The cooling can be adjusted by increasing or decreasing
the flow rate of the saline. Monitoring of the temperature drop of
the saline along the heat transfer element will allow the flow to
be adjusted to maintain the desired cooling effect.
[0100] 21. The catheter is left in place to provide cooling for,
e.g., 6-48 hours.
[0101] Referring to FIG. 8, an alternative embodiment is shown in
which the heat transfer element 14 is disposed in the superior vena
cava 62 from the axillary vein rather than from the external
jugular. It is envisioned that the following veins may be
appropriate to percutaneously insert the heat transfer element:
femoral, internal jugular, subclavian, and other veins of similar
size and position. It is also envisioned that the following veins
may be appropriate in which to dispose the heat transfer element
during use: inferior vena cava, superior vena cava, femoral,
internal jugular, and other veins of similar size and position.
[0102] FIG. 9 shows a cross-section of the heart in which the heat
transfer element 14 is disposed in the superior vena cava 62. The
heat transfer element 14 has rotating helical grooves 22 as well as
counter-rotating helical grooves 24. Between the rotating and the
counter-rotating grooves are bellows 27. It is believed that a
design of this nature would enhance the Nusselt number for the flow
in the superior vena cava by about 5 to 80.
[0103] Thermoregulatory Drugs
[0104] The above description discloses mechanical methods of
rewarming a patient, or portions of a patient, to minimize the
deleterious consequences of total body hypothermia. Another
procedure which may be performed, either contemporaneous with or in
place of mechanical warming, is the administration of
anti-vasoconstriction and anti-shivering drugs. Such drugs minimize
the effect of vasoconstriction which may otherwise hinder heat
transfer and thus cooling of the patient. In general, hypothermia
tends to trigger aggressive thermoregulatory defenses in the human
body. Such drugs also prohibit responses such as shivering which
may cause damage to cardiac-compromised patients by increasing
their metabolic rate to dangerous levels.
[0105] To limit the effectiveness of thermoregulatory defenses
during therapeutic hypothermia, drugs that induce thermoregulatory
tolerance may be employed. A variety of these drugs have been
discovered. For example, clonidine, meperidine, a combination of
clonidine and meperidine, propofol, magnesium, dexmedetomidine, and
other such drugs may be employed.
[0106] It is known that certain drugs inhibit thermoregulation
roughly in proportion to their anesthetic properties. Thus,
volatile anesthetics (isoflurane, desflurane, etc.), propofol, etc.
are more effective at inhibiting thermoregulation than opioids
which are in turn more effective than midazolam and the central
alpha agonists. It is believed that the combination drug of
clonidine and meperidine synergistically reduces vasoconstriction
and shivering thresholds, synergistically reduces the gain and
maximum intensity of vasoconstriction and shivering, and produces
sufficient inhibition of thermoregulatory activity to permit
central catheter-based cooling to 32.degree. C. without excessive
hypotension, autonomic nervous system activation, or sedation and
respiratory compromise.
[0107] These drugs may be particularly important given the rapid
onset of thermoregulatory defenses. For example, vasoconstriction
may set in at temperatures of only {fraction (1/2)} degree below
normal body temperature. Shivering sets in only a fraction of a
degree below vasoconstriction.
[0108] The temperature to which the blood is lowered may be such
that thermoregulatory responses are not triggered. For example,
thermoregulatory responses may be triggered at a temperature of
1-11/2 degrees below normal temperature. Thus, if normal body
temperature is 37.degree. C., thermoregulatory responses may set in
at 35.degree. C. Thermoregulatory drugs may used to lower the
temperature of the thermoregulatory trigger threshold to 33.degree.
C. Use of the heating blankets described above may allow even
further cooling of the patient. For example, to lower the patient's
temperature from 33.degree. C. to 31.degree. C., a 2.degree. C.
temperature difference, a 2 times 5.degree. C. or 10.degree. C.
rise is surface temperature may be employed on the skin of the
patient to allow the patient to not "feel" the extra 2.degree. C.
cooling.
[0109] A method which combines the thermoregulatory drug
methodology and the heating blanket methodology is described with
respect to FIG. 11. This figure is purely exemplary. Patients'
normal body temperatures vary, as do their thermoregulatory
thresholds.
[0110] As shown in FIG. 11, the patient may start with a normal
body temperature of 37.degree. C. and a typical thermoregulatory
threshold of 35.degree. C. (step 102). In other words, at
35.degree. C., the patient would begin to shiver and vasoconstrict.
A thermoregulatory drug may be delivered (step 104) to suppress the
thermoregulatory response, changing the threshold temperature to,
e.g., 35.degree. C. This new value is shown in step 106. The heat
transfer element may then be placed in a high flow vein, such as
the superior or inferior vena cavae or both (step 108). Cooling may
occur to lower the temperature of the blood (step 110). The cooling
may be in a fashion described in more detail above. The cooling
results in the patient undergoing hypothermia and achieving a
hypothermic temperature of, e.g., 33.degree. C. (step 112). More
cooling may be performed at this stage, but as the thermoregulatory
threshold has only been suppressed to 33.degree. C. (step 112),
shivering and vasoconstriction would deleteriously result. This may
complete the procedure. Alternatively, an additional drug therapy
may be delivered to further lower the thermoregulatory
threshold.
[0111] An alternate way to lower the thermoregulatory threshold is
to use a heating blanket. As noted above, a common rule-of-thumb is
that a patient's comfort will stay constant, even if their body
temperature is lowered 1.degree. C., so long as a heating blanket,
5.degree. C. warmer than their skin, is applied to a substantial
portion of the surface area of the patient (step 114). For a
2.degree. C.-body temperature reduction, a 10.degree. C. (warmer
than the skin temperature) blanket would be applied. Of course, it
is also known that blankets warmer than about 42.degree. C. can
damage patient's skins, this then being an upper limit to the
blanket temperature. The patient's body temperature may then
continue to be lowered by use of a heating blanket. For each
1.degree. C. reduction in body temperature (step 116), the heating
blanket temperature may be raised 5.degree. C. (step 118). After
each reduction in body temperature, the physician may decide
whether or not to continue the cooling process (step 120). After
cooling, other procedures may be performed if desired (step 122)
and the patient may then be rewarmed (step 124).
[0112] It is important to note that the two alternate methods of
thermoregulatory response reduction may be performed independently.
In other words, either thermoregulatory drugs or heating blankets
may be performed without the use of the other. The flowchart given
in FIG. 11 may be used by omitting either step 104 or steps 114 and
118.
[0113] Vasoconstrictive Therapies
[0114] FIG. 10 showed the more rapid response of the high blood
flow organs to hypothermia than that of the peripheral circulation.
This response may be maintained or enhanced by applying, as an
alternative method of performing hypothermia, a cooling blanket
rather than a heating blanket. The cooling blanket may serve to
vasoconstrict the vessels in the peripheral circulation, further
directing blood flow towards the heart and brain.
[0115] An alternate method of performing the same function is to
provide separate vasoconstrictive drugs which affect the posterior
hypothalamus in such a way as to vasoconstrict the peripheral
circulation while allowing heart and brain circulation to proceed
unimpeded. Such drugs are known and include alpha receptor type
drugs. These drugs, as well as the cooling blankets described
above, may also enhance counter-current exchange, again forcing
cooling towards the heart and brain. Generally, any drug or cooling
blanket that provides sufficient cooling to initiate a large scale
cutaneous peripheral vasoconstrictive response would be capable of
forcing the cooling blood flow towards the brain and heart (i.e.,
the "central" volumes). In this application, the term "peripheral
circulation" or "peripheral vasculature" refers to that portion of
the vasculature serving the legs, arms, muscles, and skin.
[0116] Additional Therapies
[0117] Turning now from thermoregulatory drugs to additional
therapies, the method and device according to the embodiments of
the invention may also play a significant role in treating a
variety of maladies involving cell damage.
[0118] Stroke
[0119] A patent application incorporated by reference above
discloses devices and methods for enhancing fibrinolysis of a clot
by cooling blood flowing in an artery. The present invention may
also use blood cooling to substantially reduce platelet aggregation
as there is a significant reduction in platelet activity at reduced
temperatures. Such reduction may take place by inhibiting enzyme
function, although the actual methodology is unclear. This
reduction in platelet aggregation, as well as the enhanced
fibrinolysis noted above, may reduce or eliminate current
dependence on such drugs as tPA or Rheopro.
[0120] Myocardial Infarction
[0121] The above-described venous cooling may also provide a number
of benefits for patients undergoing myocardial infarction.
[0122] Current therapies for treating myocardial infarction involve
three areas. Thrombolysis or stenting are used to establish reflow.
The oxygen supply is increased by directly supplying the patient
with oxygen and by vasodilation with nitrates. And the oxygen
demand is lessened by decreasing the heart rate and the blood
pressure.
[0123] Devices and methods according to the present invention can
work well in combination with these current therapies. For example,
the device and method may lessen the heart's demand for oxygen by
providing cooled blood to the heart. The cooled blood in turn cools
the inner chambers of the heart, essentially from the inside.
Hearts undergoing myocardial infarction may beat very fast due to
an agitated state of the victim. However, cooled blood may induce a
state of bradycardia that reduces the demand for oxygen by the
heart per se.
[0124] To establish reflow and the oxygen supply, the enhanced
fibrinolysis, discussed above, may also dissolve the clot, allowing
more blood flow and more oxygen delivered to the heart. As
mentioned above, platelet aggregation may be reduced. Additionally,
conduction through the subendocardium, cooling the heart, may
reduce the overall metabolic activity of the heart as well as
protect the subendocardium from cell damage.
[0125] It is additionally noted that reflow is often accompanied by
reperfusion injury which can further damage cells. Neutrophil
activation occurs as part of reperfusion injury. Hypothermia can
limit such activation and thus can limit reperfusion injury.
[0126] Thus, numerous therapies may be delivered by one device.
Therefore, e.g., currently-employed "beta-blocker" drugs used to
reduce heart rate in patients undergoing infarcts may not need to
be employed in patients undergoing these hypothermic therapies.
[0127] Re-stenosis
[0128] Another application of the device and method may be in the
treatment of stenotic arteries. Stenotic arteries are vessels that
have narrowed due to a build-up of tissue and/or plaque atheroma.
Stenotic vessels are treated by angioplasty or stenting, which
opens the artery. During treatment the vessel wall may be injured.
Such injuries often (20-50%) cause an inflammatory reaction that
eventually causes the vessel to undergo restenosis after a period
of time, which may range from 6-12 months or even several years
later.
[0129] Hypothermia is known to mitigate inflammatory responses. For
example, one of the initial steps in the process of re-stenosis is
the migration of macrophages or white blood cells to the injured
area. Hypothermia can limit this migration. Hypothermia can also
inhibit reactions and processes initiated by molecules acting in an
autocrine or paracrine fashion. Hypothermia may also limit the
release of several growth factors (at the site of injury) such as
PDGF and EGF that act in these fashions.
[0130] While the invention herein disclosed is capable of obtaining
the objects hereinbefore stated, it is to be understood that this
disclosure is merely illustrative of the presently preferred
embodiments of the invention and that no limitations are intended
other than as described in the appended claims.
* * * * *