U.S. patent application number 09/915482 was filed with the patent office on 2002-02-07 for lumen design for catheter.
This patent application is currently assigned to Innercool Therapies, Inc.. Invention is credited to Dobak, John D. III, Gilmartin, Kevin P., Lasheras, Juan C., Werneth, Randell L., Yon, Steven A..
Application Number | 20020016621 09/915482 |
Document ID | / |
Family ID | 24066443 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020016621 |
Kind Code |
A1 |
Werneth, Randell L. ; et
al. |
February 7, 2002 |
Lumen design for catheter
Abstract
The invention provides a device for heating or cooling a
surrounding fluid in a feeding vessel and a method of manufacturing
the same. The device includes a catheter assembly capable of
insertion to a selected blood vessel in the vascular system of a
patient. The assembly includes an elongated catheter body, a heat
transfer element located at a distal portion of the catheter body
and including an interior, an elongated supply lumen adapted to
deliver a working fluid to the interior of the heat transfer
element and having a hydraulic diameter, an elongated return lumen
adapted to return a working fluid from the interior of the heat
transfer element and having a hydraulic diameter, and wherein the
ratio of the hydraulic diameter of the return lumen to the
hydraulic diameter of the supply lumen is substantially equal to
0.75. The method of manufacturing the catheter assembly involves
extruding an elongated catheter body; locating a heat transfer
element including an interior at a distal portion of the catheter
body; extruding an integrated elongated bi-lumen member including a
first lumen adapted to receive a guide wire and a second lumen
having a hydraulic diameter, the second lumen comprising either a
supply lumen to deliver a working fluid to an interior of the heat
transfer element or a return lumen to return a working fluid from
the interior of the heat transfer element; and providing the
integrated bi-lumen member substantially within the elongated
catheter body so that a third lumen having a hydraulic diameter is
formed, the third lumen comprising either a supply lumen to deliver
a working fluid to an interior of the heat transfer element or a
return lumen to return a working fluid from the interior of the
heat transfer element and the ratio of the second lumen hydraulic
diameter to the third lumen hydraulic diameter is substantially
equal to 0.75.
Inventors: |
Werneth, Randell L.; (San
Diego, CA) ; Gilmartin, Kevin P.; (Encinitas, CA)
; Yon, Steven A.; (San Diego, CA) ; Lasheras, Juan
C.; (La Jolla, CA) ; Dobak, John D. III; (La
Jolla, CA) |
Correspondence
Address: |
INNERCOOLTherapies
3931 Sorrento Valley Blvd.
San Diego
CA
92121
US
|
Assignee: |
Innercool Therapies, Inc.
|
Family ID: |
24066443 |
Appl. No.: |
09/915482 |
Filed: |
July 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09915482 |
Jul 25, 2001 |
|
|
|
09519022 |
Mar 3, 2000 |
|
|
|
Current U.S.
Class: |
607/105 ;
607/96 |
Current CPC
Class: |
A61F 7/12 20130101; A61F
2007/126 20130101 |
Class at
Publication: |
607/105 ;
607/96 |
International
Class: |
A61F 007/00; A61F
007/12 |
Claims
What is claimed is:
1. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element located at a distal portion of the catheter body and
including an interior; an elongated supply lumen having a
cross-sectional area located within the catheter body and adapted
to deliver a working fluid to the interior of the heat transfer
element; an elongated return lumen having a cross-sectional area
located within the catheter body and adapted to return a working
fluid from the interior of the heat transfer element; and the ratio
of the hydraulic diameter of the return lumen to the hydraulic
diameter of the supply lumen being substantially equal to 0.75.
2. The device of claim 1, wherein the supply lumen is disposed
substantially within the return lumen.
3. The device of claim 1, wherein one of the supply lumen and
return lumen has a cross-sectional shape that is substantially
luniform.
4. The device of claim 1, wherein one of the supply lumen and the
return lumen has a cross-sectional shape that is annular.
5. The device of claim 1, wherein said heat transfer element
includes an interior portion adapted to induce mixing of the
working fluid and means for further enhancing mixing of said
working fluid.
6. The device of claim 1, wherein the heat transfer element
includes an interior distal portion, the supply lumen includes
first means for delivering working fluid to the interior distal
portion of the heat transfer element and second means for
delivering working fluid to the interior of the heat transfer
element at one or more points point proximal to the distal portion
of the heat transfer element.
7. The device of claim 1, wherein the supply lumen has a general
cross-sectional shape and the return lumen has a general
cross-sectional shape different from the general cross-sectional
shape of the supply lumen.
8. The device of claim 1, wherein said catheter assembly includes
an integrated elongated bi-lumen member including a first lumen
adapted to receive a guide wire and a second lumen, the second
lumen comprising either said supply lumen or said return lumen.
9. The device of claim 8, wherein said bi-lumen member has a
cross-sectional shape that is substantially in the shape of a
figure eight.
10. The device of claim 8, wherein said first lumen has a
cross-sectional shape that is substantially circular and the second
lumen has a cross-sectional shape that is annular.
11. The device of claim 1, wherein the heating element includes
means for inducing mixing in a surrounding fluid.
12. A catheter assembly capable of insertion into a selected blood
vessel in the vascular system of a patient, comprising: an
elongated catheter body including an operative element having an
interior at a distal portion of the catheter body; an elongated
supply lumen adapted to deliver a working fluid to the interior of
said distal portion and having a hydraulic diameter; an elongated
return lumen adapted to return a working fluid from the interior of
said operative element and having a hydraulic diameter; and the
ratio of the hydraulic diameter of the return lumen to the
hydraulic diameter of the supply lumen being substantially equal to
0.75.
13. The catheter assembly of claim 12, wherein the supply lumen is
disposed substantially within the return lumen.
14. The catheter assembly of claim 12, wherein one of the supply
lumen and return lumen has a cross-sectional shape that is
substantially luniform.
15. The catheter assembly of claim 12, wherein one of the supply
lumen and the return lumen has a cross-sectional shape that is
annular.
16. The catheter assembly of claim 12, wherein the supply lumen has
a general cross-sectional shape and the return lumen has a general
cross-sectional shape different from the general cross-sectional
shape of the supply lumen.
17. The catheter assembly of claim 12, wherein said catheter
assembly includes an integrated bi-lumen member including a first
lumen adapted to receive a guide wire and a second lumen, the
second lumen comprising either said supply lumen or said return
lumen.
18. The catheter assembly of claim 17, wherein said bi-lumen member
has a cross-sectional shape that is substantially in the shape of a
figure eight.
19. The catheter assembly of claim 17, wherein said first lumen has
a cross-sectional shape that is substantially circular and the
second lumen has a cross-sectional shape that is substantially
luniform.
20. The catheter assembly of claim 12, wherein said operative
element includes a heat transfer element adapted to transfer heat
to or from said working fluid.
21. The catheter assembly of claim 20, wherein said heat transfer
element includes means for inducing mixing in a surrounding
fluid.
22. The catheter assembly of claim 12, wherein said operative
element includes a catheter balloon adapted to be inflated with
said working fluid.
23. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element located at a distal portion of the catheter body and
including an interior; an integrated elongated bi-lumen member
located within said catheter body and including a first lumen
adapted to receive a guide wire and a second lumen, the second
lumen comprising either a supply lumen to deliver a working fluid
to an interior of the heat transfer element or a return lumen to
return a working fluid from the interior of the heat transfer
element; and a third lumen comprising either a supply lumen to
deliver a working fluid to an interior of the heat transfer element
or a return lumen to return a working fluid from the interior of
the heat transfer element.
24. The device of claim 23, wherein the catheter body includes an
internal wall and the integrated bi-lumen member includes an
exterior wall, the third lumen substantially defined by said
internal wall of the catheter body and the exterior wall of the
bi-lumen member.
25. The device of claim 23, wherein both the catheter body and the
bi-lumen member are extruded.
26. The device of claim 23, wherein the bi-lumen member is disposed
substantially within the third lumen.
27. The device of claim 23, wherein said second lumen has a
cross-sectional shape that is substantially luniform.
28. The device of claim 23, wherein said third lumen has a
cross-sectional shape that is annular.
29. The device of claim 23, wherein said heat transfer element
includes an interior portion adapted to induce mixing of the
working fluid and means for further enhancing mixing of said
working fluid.
30. The device of claim 23, wherein the heat transfer element
includes an interior distal portion, the supply lumen includes
first means for delivering working fluid to the interior distal
portion of the heat transfer element and second means for
delivering working fluid to the interior of the heat transfer
element at one or more points proximal to the distal portion of the
heat transfer element.
31. The device of claim 23, wherein the second lumen has a general
cross-sectional shape and the third lumen has a general
cross-sectional shape different from the general cross-sectional
shape of the second lumen.
32. The device of claim 23, wherein said bi-lumen member has a
cross-sectional shape that is substantially in the shape of a
figure eight.
33. The device of claim 23, wherein said first lumen has a
cross-sectional shape that is substantially circular and the second
lumen has a cross-sectional shape that is substantially
luniform.
34. The device of claim 23, wherein the heat transfer element
includes means for inducing mixing in a surrounding fluid.
35. A catheter assembly capable of insertion into a selected blood
vessel in the vascular system of a patient, including: an elongated
catheter body including an operative element having an interior at
a distal portion of the catheter body; an integrated elongated
bi-lumen member located within said catheter body and including a
first lumen adapted to receive a guide wire and a second lumen, the
second lumen comprising either a supply lumen to deliver a working
fluid to the interior of the operative element or a return lumen to
return a working fluid from the interior of the operative element;
and a third lumen within said catheter body and comprising either a
supply lumen to deliver a working fluid to an interior of the
operative element or a return lumen to return a working fluid from
the interior of the operative element.
36. The catheter assembly of claim 35, wherein the catheter body
includes an internal wall and the integrated bi-lumen member
includes an exterior wall, the third lumen defined at least
partially by said internal wall of the catheter body and the
exterior wall of the bi-lumen member.
37. The catheter assembly of claim 35, wherein both the catheter
body and the bi-lumen member are extruded.
38. The catheter assembly of claim 35, wherein the bi-lumen member
is disposed substantially within the third lumen.
39. The catheter assembly of claim 35, wherein said second lumen
has a cross-sectional shape that is substantially luniform.
40. The catheter assembly of claim 35, wherein said third lumen has
a cross-sectional shape that is annular.
41. The catheter assembly of claim 35, wherein the second lumen has
a general cross-sectional shape and the third lumen has a general
cross-sectional shape different from the general cross-sectional
shape of the second lumen.
42. The catheter assembly of claim 35, wherein said bi-lumen member
has a cross-sectional shape that is substantially in the shape of a
figure eight.
43. The catheter assembly of claim 35, wherein said first lumen has
a cross-sectional shape that is substantially circular and the
second lumen has a cross-sectional shape that is substantially
luniform.
44. A method of manufacturing a catheter assembly for heating or
cooling a surrounding fluid in a vascular feeding vessel,
comprising: extruding an elongated catheter body; locating a heat
transfer element including an interior at a distal portion of the
catheter body; extruding an integrated elongated bi-lumen member
including a first lumen adapted to receive a guide wire and a
second lumen, the second lumen comprising either a supply lumen to
deliver a working fluid to an interior of the heat transfer element
or a return lumen to return a working fluid from the interior of
the heat transfer element; providing said integrated bi-lumen
member substantially within said elongated catheter body so that a
third lumen is formed, said third lumen comprising either a supply
lumen to deliver a working fluid to an interior of the heat
transfer element or a return lumen to return a working fluid from
the interior of the heat transfer element.
45. The method of claim 44, wherein said second lumen has a
hydraulic diameter and said third lumen has a hydraulic diameter,
and the ratio of the hydraulic diameter of the second lumen to the
hydraulic diameter of the third lumen is substantially equal to
0.75.
46. The method of claim 44, wherein the step of providing said
integrated bi-lumen member substantially within said elongated
catheter body includes simultaneously extruding said integrated
bi-lumen member substantially within said elongated catheter
body.
47. A method of manufacturing a catheter assembly, comprising:
extruding an elongated catheter body; locating an operative element
including an interior at a distal portion of the catheter body;
extruding an integrated elongated bi-lumen member including a first
lumen adapted to receive a guide wire and a second lumen, the
second lumen comprising either a supply lumen to deliver a working
fluid to an interior of the operative element or a return lumen to
return a working fluid from the interior of the operative element;
providing said integrated bi-lumen member substantially within said
elongated catheter body so that a third lumen is formed, said third
lumen comprising either a supply lumen to deliver a working fluid
to an interior of the operative element or a return lumen to return
a working fluid from the interior of the operative element.
48. The method of claim 47, wherein said second lumen has a
hydraulic diameter and said third lumen has a hydraulic diameter,
and the ratio of the hydraulic diameter of the second lumen to the
hydraulic diameter of the third lumen is substantially equal to
0.75.
49. The method of claim 47, wherein the step of providing said
integrated bi-lumen member substantially within said elongated
catheter body includes simultaneously extruding said integrated
bi-lumen member substantially within said elongated catheter
body.
50. A method of manufacturing a catheter assembly, comprising:
extruding an elongated catheter body; locating an operative element
including an interior at a distal portion of the catheter body;
extruding an integrated elongated bi-lumen member including a first
lumen adapted to receive a guide wire and a second lumen, the
second lumen comprising either a supply lumen to deliver a working
fluid to an interior of the operative element or a return lumen to
return a working fluid from the interior of the operative element,
the integrated elongated bi-lumen member including a circular outer
surface; providing said integrated bi-lumen member substantially
within said elongated catheter body so that a third lumen is
formed, said third lumen comprising either a supply lumen to
deliver a working fluid to an interior of the operative element or
a return lumen to return a working fluid from the interior of the
operative element.
51. The method of claim 50, wherein said second lumen has a
hydraulic diameter and said third lumen has a hydraulic diameter,
and the ratio of the hydraulic diameter of the second lumen to the
hydraulic diameter of the third lumen is substantially equal to
0.75.
52. The method of claim 50, wherein the step of providing said
integrated bi-lumen member substantially within said elongated
catheter body includes simultaneously extruding said integrated
bi-lumen member substantially within said elongated catheter
body.
53. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element including at least a first heat transfer segment and a
second heat transfer segment located at a distal portion of the
catheter body and including an interior distal portion and an
interior portion; and at least one elongated supply lumen located
within the catheter body, the at least one elongated supply lumen
including first means for delivering working fluid to the interior
distal portion of the first heat transfer segment and second means
for delivering working fluid to the interior portion of the second
heat transfer segment.
55. The device of claim 53, wherein the first working fluid
delivering means is adapted to deliver working fluid to the
interior distal portion of the heat transfer element and the second
working fluid delivering means is adapted to deliver working fluid
to the interior portion of the heat transfer element near a
midpoint of the heat transfer element.
56. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element located at a distal portion of the catheter body and
including an interior distal portion and an interior portion; and
at least one elongated supply lumen located within the catheter
body, the at least one elongated supply lumen including first means
for delivering working fluid to the interior distal portion of the
heat transfer element and second means for delivering working fluid
to the interior portion of the heat transfer element at one or more
points proximal to the distal portion of the heat transfer
element.
57. The device of claim 56, wherein the second working fluid
delivering means is adapted to deliver working fluid to the
interior portion of the heat transfer element near a midpoint of
the heat transfer element.
58. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element including at least a first heat transfer segment and a
second heat transfer segment located at a distal portion of the
catheter body and including an interior distal portion and an
interior portion; and a first elongated supply lumen located within
the catheter body and terminating at the interior distal portion of
the heat transfer element into first means for delivering working
fluid to the interior distal portion of the heat transfer element;
and a second elongated supply lumen located within the catheter
body and terminating at a point proximal to the distal portion of
the heat transfer element into second means for delivering working
fluid to the interior portion of the heat transfer element at a
point proximal to the distal portion of the heat transfer
element.
59. The device of claim 58, wherein the first working fluid
delivering means is adapted to deliver working fluid to the
interior distal portion of the heat transfer element and the second
working fluid delivering means is adapted to deliver working fluid
to the interior portion of the heat transfer element near a
midpoint of the heat transfer element.
60. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element including at least a first heat transfer segment and a
second heat transfer segment located at a distal portion of the
catheter body and including an interior distal portion and an
interior portion; and a first elongated supply lumen located within
the catheter body and terminating at the interior distal portion of
the first heat transfer segment into first means for delivering
working fluid to the interior of the first heat transfer segment;
and a second elongated supply lumen located within the catheter
body and terminating at a point proximal to the distal portion of
the heat transfer element into second means for delivering working
fluid to the interior portion of the second heat transfer
segment.
61. The device of claim 60, wherein the second working fluid
delivering means is adapted to deliver working fluid to the
interior portion of the heat transfer element near a midpoint of
the heat transfer element.
62. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element located at a distal portion of the catheter body and
including an interior portion adapted to induce mixing of a working
fluid to effect heat transfer between the heat transfer element and
working fluid, the heat transfer element including at least a first
heat transfer segment, a second heat transfer segment, and an
intermediate segment between the first heat transfer segment and
the second heat transfer segment; an elongated supply lumen member
located within the catheter body and adapted to deliver the working
fluid to the interior of the heat transfer element, said supply
lumen member including a circular outer surface; an elongated
return lumen defined in part by the outer surface of the supply
lumen member and the interior portion of the heat transfer element
and adapted to return the working fluid from the interior of the
heat transfer element; and wherein the distance between the
interior portion of the heat transfer element and the outer surface
of the supply lumen member adjacent the intermediate segment is
less than the distance between the interior portion of the heat
transfer element and the outer surface of the supply lumen member
adjacent the first heat transfer segment.
63. The device of claim 62, wherein the distance between the
interior portion of the heat transfer element and the outer surface
of the supply lumen member adjacent the intermediate segment is
such that the characteristic flow resulting from a flow of working
fluid is at least of a transitional nature.
64. The device of claim 62, wherein the intermediate segment
includes an interior diameter that is less than the interior
diameter of the first heat transfer segment or the second heat
transfer segment.
65. The device of claim 62, wherein the supply lumen member
includes an outer diameter adjacent the intermediate segment that
is greater than its outer diameter adjacent the first heat transfer
segment or the second heat transfer segment.
66. The device of claim 62, wherein the supply lumen member
comprises a multiple-lumen member.
67. The device of claim 62, wherein the supply lumen member
includes a supply lumen having a hydraulic diameter and the return
lumen has a hydraulic diameter substantially equal to 0.75 of the
hydraulic diameter of the supply lumen.
68. The device of claim 62, wherein the intermediate segment
includes a flexible bellows joint.
69. The device of claim 62, wherein the intermediate segment
includes a flexible tube.
70. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element located at a distal portion of the catheter body and
including an interior portion adapted to induce mixing of a working
fluid to effect heat transfer between the heat transfer element and
working fluid; an elongated supply lumen member located within the
catheter body and adapted to deliver the working fluid to the
interior of the heat transfer element; an elongated return lumen
member located within the catheter body and adapted to return the
working fluid from the interior of the heat transfer element; and
means located within said heat transfer element for further
enhancing mixing of said working fluid to effect further heat
transfer between the heat transfer element and working fluid.
71. The device of claim 70, wherein the supply lumen member
comprises a multiple-lumen member having a circular outer
surface.
72. The device of claims 70, wherein the supply lumen member
includes a supply lumen having a hydraulic diameter and the return
lumen has a hydraulic diameter substantially equal to 0.75 of the
hydraulic diameter of the supply lumen.
73. A device for heating or cooling a surrounding fluid in a blood
vessel, comprising: an elongated catheter body; a heat transfer
element located at a distal portion of the catheter body and
including an interior portion adapted to induce mixing of a working
fluid to effect heat transfer between the heat transfer element and
working fluid; an elongated supply lumen member located within the
catheter body and adapted to deliver the working fluid to the
interior of the heat transfer element; an elongated return lumen
member located within the catheter body and adapted to return the
working fluid from the interior of the heat transfer element; and a
mixing-enhancing mechanism located within said heat transfer
element and adapted to further mix said working fluid to effect
further heat transfer between the heat transfer element and working
fluid.
74. The device of claim 73, wherein the supply lumen member
comprises a multiple-lumen member having a circular outer
surface.
75. The device of claims 73, wherein the supply lumen member
includes a supply lumen having a hydraulic diameter and the return
lumen has a hydraulic diameter substantially equal to 0.75 of the
hydraulic diameter of the supply lumen.
76. A method of heating or cooling a surrounding fluid in a blood
vessel, comprising: providing a device for heating or cooling a
surrounding fluid in a blood vessel within the blood stream of a
blood vessel, the device including an elongated catheter body, a
heat transfer element located at a distal portion of the catheter
body and including an interior portion adapted to induce mixing of
a working fluid to effect heat transfer between the heat transfer
element and working fluid, an elongated supply lumen member located
within the catheter body and adapted to deliver the working fluid
to the interior of the heat transfer element, an elongated return
lumen member located within the catheter body and adapted to return
the working fluid from the interior of the heat transfer element,
and a mixing-enhancing mechanism located within said heat transfer
element and adapted to further mix said working fluid to effect
further heat transfer between the heat transfer element and working
fluid; causing a working fluid to flow to and along the interior
portion of the heat transfer element of the device using the supply
lumen and return lumen; facilitating the transfer of heat between
the working fluid and the heat transfer element by effecting mixing
of the working fluid with the interior portion adapted to induce
mixing of a working fluid; facilitating additional transfer of heat
between the working fluid and the heat transfer element by
effecting further mixing of the working fluid within the interior
portion with said mixing-enhancing mechanism; causing heat to be
transferred between the blood stream and the heat transfer element
by the heat transferred between the heat transfer element and
working fluid.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention-The present invention relates
generally to lumen designs for catheters. More particularly, the
invention relates to lumen designs for catheters that modify and
control the temperature of a selected body organ.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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 metallic catheter. The metallic 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.
[0006] Due to certain problems sometimes associated with total body
hypothermia, attempts have been made to provide more selective
cooling. For example, cooling helmets or headgear have been used in
an attempt to cool only the head rather than the patient's entire
body. However, such methods rely on conductive heat transfer
through the skull and into the brain. One drawback of using
conductive heat transfer is that the process of reducing the
temperature of the brain is prolonged. Also, it is difficult to
precisely control the temperature of the brain when using
conduction due to the temperature gradient that must be established
externally in order to sufficiently lower the internal temperature.
In addition, when using conduction to cool the brain, the face of
the patient is also subjected to severe hypothermia, increasing
discomfort and the likelihood of negative side effects. It is known
that profound cooling of the face can cause similar cardiovascular
side effects as total body cooling. From a practical standpoint,
such devices are cumbersome and may make continued treatment of the
patient difficult or impossible.
[0007] Selected organ hypothermia has been accomplished using
extracorporeal perfusion, as detailed by Arthur E. Schwartz, M.D.
et al., in Isolated Cerebral Hypothermia by Single Carotid Artery
Perfusion of Extracorporeally Cooled Blood in Baboons, which
appeared in Vol. 39, No. 3, NEUROSURGERY 577 (September, 1996). In
this study, blood was continually withdrawn from baboons through
the femoral artery. The blood was cooled by a water bath and then
infused through a common carotid artery with its external branches
occluded. Using this method, normal heart rhythm, systemic arterial
blood pressure and arterial blood gas values were maintained during
the hypothermia. This study showed that the brain could be
selectively cooled to temperatures of 20.degree. C. without
reducing the temperature of the entire body. However, external
circulation of blood is not a practical approach for treating
humans because the risk of infection, need for anticoagulation, and
risk of bleeding is too great. Further, this method requires
cannulation of two vessels making it more cumbersome to perform
particularly in emergency settings. Even more, percutaneous
cannulation of the carotid artery is difficult and potentially
fatal due to the associated arterial wall trauma. Finally, this
method would be ineffective to cool other organs, such as the
kidneys, because the feeding arteries cannot be directly cannulated
percutaneously.
[0008] Selective organ hypothermia has also been attempted by
perfusion of a cold solution such as saline or perflourocarbons.
This process is commonly used to protect the heart during heart
surgery and is referred to as cardioplegia. Perfusion of a cold
solution has a number of drawbacks, including a limited time of
administration due to excessive volume accumulation, cost, and
inconvenience of maintaining the perfusate and lack of
effectiveness due to the temperature dilution from the blood.
Temperature dilution by the blood is a particular problem in high
blood flow organs such as the brain.
[0009] Catheters adapted for delivering heat transfer fluids at
temperatures above or below normal body temperatures to selected
internal body sites have been devised in the past (See, for
example, U.S. Pat. No. 5,624,392 to Saab). These catheters often
have a concentric, coaxial configuration of multiple lumens. The
configurations often have a first central lumen adapted to receive
a guide surrounded by a concentric second supply lumen adapted to
supply a working fluid to a distal portion of the catheter and an
outer concentric third return lumen, which surrounds the second
lumen, adapted to return a working fluid to a fluid source. A
problem with this configuration is that the working fluid in the
supply lumen makes surface area contact with both an outer wall,
which partially defines the outer limits of the second lumen, and
an inner wall, which defines the first lumen, leading to increased
heat transfer between the walls and the working fluid. Thus, if the
second supply lumen in the catheter is designed to deliver a
cooling fluid to the distal portion of the catheter, the increased
surface area contact caused by this configuration unnecessarily
warms the cooling fluid prior to delivery to the distal portion of
the catheter. Another problem with these catheters is that the
supply lumen(s) and return lumen(s) are not sized relative to each
other to maximize the flow rate through the catheter. Hence, they
do not optimize heating and/or cooling catheter performance.
BRIEF SUMMARY OF THE INVENTION
[0010] The present invention involves a device for heating or
cooling a surrounding fluid in a blood vessel that addresses and
solves the problems discussed above with multiple lumen
arrangements of catheters in the past. The device includes an
elongated catheter body, a heat transfer element located at a
distal portion of the catheter body and including an interior, an
elongated supply lumen adapted to deliver a working fluid to the
interior of the heat transfer element and having a hydraulic
diameter, an elongated return lumen adapted to return a working
fluid from the interior of the heat transfer element and having a
hydraulic diameter, and wherein the ratio of the hydraulic diameter
of the return lumen to the hydraulic diameter of the supply lumen
is substantially equal to 0.75.
[0011] Implementations of the above aspect of the invention may
include one or more of the following. The supply lumen may be
disposed substantially within the return lumen. One of the supply
lumen and return lumen may have a cross-sectional shape that is
substantially luniform. One of the supply lumen and the return
lumen has a cross-sectional shape that is substantially annular.
The supply lumen has a general cross-sectional shape and the return
lumen has a general cross-sectional shape different from the
general cross-sectional shape of the supply lumen. The catheter
assembly includes an integrated elongated bi-lumen member having a
first lumen adapted to receive a guide wire and a second lumen
comprising either the supply lumen or the return lumen. The
bi-lumen member has a cross-sectional shape that is substantially
in the shape of a figure eight. The first lumen has a
cross-sectional shape that is substantially circular and the second
lumen has a cross-sectional shape that is substantially annular.
The heat transfer element includes means for inducing mixing in a
surrounding fluid. The device further includes means for inducing
wall jets or means for further enhancing mixing of the working
fluid to effect further heat transfer between the heat transfer
element and working fluid. The heat transfer element includes an
interior distal portion and the supply lumen includes first means
for delivering working fluid to the interior distal portion of the
heat transfer element and second means for delivering working fluid
to the interior of the heat transfer element at one or more points
point proximal to the distal portion of the heat transfer
element.
[0012] A second aspect of the invention involves a catheter
assembly capable of insertion into a selected blood vessel in the
vascular system of a patient. The catheter assembly includes an
elongated catheter body including an operative element having an
interior at a distal portion of the catheter body, an elongated
supply lumen adapted to deliver a working fluid to the interior of
the distal portion and having a hydraulic diameter, an elongated
return lumen adapted to return a working fluid from the interior of
the operative element and having a hydraulic diameter, and wherein
the ratio of the hydraulic diameter of the return lumen to the
hydraulic diameter of the supply lumen being substantially equal to
0.75.
[0013] Any of the implementations described above with respect to
the first aspect of the invention also apply to the second aspect
of the invention. Further, implementations of the second aspect of
the invention may include one or more of the following. The
operative element may include a heat transfer element adapted to
transfer heat to or from the working fluid. The heat transfer
element may include means for inducing mixing in a surrounding
fluid. The operative element may include a catheter balloon adapted
to be inflated with the working fluid.
[0014] A third aspect of the invention involves a device for
heating or cooling a surrounding fluid in a vascular blood vessel.
The device includes an elongated catheter body, a heat transfer
element located at a distal portion of the catheter body and
including an interior, an integrated elongated bi-lumen member
located within the catheter body and including a first lumen
adapted to receive a guide wire and a second lumen, the second
lumen comprising either a supply lumen to deliver a working fluid
to an interior of the heat transfer element or a return lumen to
return a working fluid from the interior of the heat transfer
element, and a third lumen comprising either a supply lumen to
deliver a working fluid to an interior of the heat transfer element
or a return lumen to return a working fluid from the interior of
the heat transfer element.
[0015] Implementations of the third aspect of the invention may
include one or more of the following. The catheter body includes an
internal wall and the integrated bi-lumen member includes an
exterior wall, and the third lumen is substantially defined by the
internal wall of the catheter body and the exterior wall of the
bi-lumen member. Both the catheter body and the bi-lumen member are
extruded. The bi-lumen member is disposed substantially within the
third lumen. The second lumen has a cross-sectional shape that is
substantially luniform. The third lumen has a cross-sectional shape
that is substantially annular. The second lumen has a general
cross-sectional shape and the third lumen has a general
cross-sectional shape different from the general cross-sectional
shape of the second lumen. The bi-lumen member has a
cross-sectional shape that is substantially in the shape of a
figure eight. The first lumen has a cross-sectional shape that is
substantially circular and the second lumen has a cross-sectional
shape that is substantially luniform. The heat transfer element
includes means for inducing mixing in a surrounding fluid. The
device further includes means for inducing wall jets or means for
further enhancing mixing of the working fluid to effect further
heat transfer between the heat transfer element and working fluid.
The heat transfer element includes an interior distal portion and
the supply lumen includes first means for delivering working fluid
to the interior distal portion of the heat transfer element and
second means for delivering working fluid to the interior of the
heat transfer element at one or more points point proximal to the
distal portion of the heat transfer element.
[0016] A fourth aspect of the present invention involves a catheter
assembly capable of insertion into a selected blood vessel in the
vascular system of a patient. The catheter assembly includes an
elongated catheter body including an operative element having an
interior at a distal portion of the catheter body, an integrated
elongated bi-lumen member located within the catheter body and
including a first lumen adapted to receive a guide wire and a
second lumen, the second lumen comprising either a supply lumen to
deliver a working fluid to the interior of the operative element or
a return lumen to return a working fluid from the interior of the
operative element, and a third lumen within the catheter body and
comprising either a supply lumen to deliver a working fluid to an
interior of the operative element or a return lumen to return a
working fluid from the interior of the operative element.
[0017] Any of the implementations described above with respect to
the third aspect of the invention also apply to the fourth aspect
of the invention.
[0018] A fifth aspect of the invention involves a method of
manufacturing a catheter assembly for heating or cooling a
surrounding fluid in a blood vessel. The method involves extruding
an elongated catheter body; locating a heat transfer element
including an interior at a distal portion of the catheter body;
extruding an integrated elongated bi-lumen member including a first
lumen adapted to receive a guide wire and a second lumen, the
second lumen comprising either a supply lumen to deliver a working
fluid to an interior of the heat transfer element or a return lumen
to return a working fluid from the interior of the heat transfer
element; and providing the integrated bi-lumen member substantially
within the elongated catheter body so that a third lumen is formed,
the third lumen comprising either a supply lumen to deliver a
working fluid to an interior of the heat transfer element or a
return lumen to return a working fluid from the interior of the
heat transfer element.
[0019] Implementations of the fifth aspect of the invention may
include one or more of the following. The second lumen has a
hydraulic diameter and the third lumen has a hydraulic diameter,
and the ratio of the hydraulic diameter of the second lumen to the
hydraulic diameter of the third lumen is substantially equal to
0.75. The step of providing the integrated bi-lumen member
substantially within the elongated catheter body includes
simultaneously extruding the integrated bi-lumen member
substantially within the elongated catheter body.
[0020] A sixth aspect of the present invention involves a method of
manufacturing a catheter assembly. The method includes extruding an
elongated catheter body; locating an operative element including an
interior at a distal portion of the catheter body; extruding an
integrated elongated bi-lumen member including a first lumen
adapted to receive a guide wire and a second lumen, the second
lumen comprising either a supply lumen to deliver a working fluid
to an interior of the operative element or a return lumen to return
a working fluid from the interior of the operative element; and
providing the integrated bi-lumen member substantially within the
elongated catheter body so that a third lumen is formed, the third
lumen comprising either a supply lumen to deliver a working fluid
to an interior of the operative element or a return lumen to return
a working fluid from the interior of the operative element.
[0021] Any of the implementations described above with respect to
the fifth aspect of the invention also apply to the sixth aspect of
the invention.
[0022] A seventh aspect of the present invention involves a device
for heating or cooling a surrounding fluid in a blood vessel. The
device includes an elongated catheter body, a heat transfer element
located at a distal portion of the catheter body and including an
interior distal portion and an interior portion defining at least a
first heat transfer segment and a second heat transfer segment, and
at least one elongated supply lumen located within the catheter
body, the at least one elongated supply lumen including first means
for delivering working fluid to the interior distal portion of the
first heat transfer segment and second means for delivering working
fluid to the interior portion of the second heat transfer
segment.
[0023] In an implementation of the seventh aspect of the invention,
the second working fluid delivering means is adapted to deliver
working fluid to the interior portion of the heat transfer element
near a midpoint of the heat transfer element.
[0024] An eighth aspect of the present invention involves a device
for heating or cooling a surrounding fluid in a blood vessel. The
device includes an elongated catheter body, a heat transfer element
located at a distal portion of the catheter body and including an
interior distal portion and an interior portion, and at least one
elongated supply lumen located within the catheter body, the at
least one elongated supply lumen including first means for
delivering working fluid to the interior distal portion of the heat
transfer element and second means for delivering working fluid to
the interior portion of the heat transfer element at one or more
points proximal to the distal portion of the heat transfer
element.
[0025] In an implementation of the eighth aspect of the invention,
the second working fluid delivering means is adapted to deliver
working fluid to the interior portion of the heat transfer element
near a midpoint of the heat transfer element.
[0026] A ninth aspect of the present invention involves a device
for heating or cooling a surrounding fluid in a blood vessel. The
device includes an elongated catheter body, a heat transfer element
located at a distal portion of the catheter body and including an
interior distal portion and an interior portion defining at least a
first heat transfer segment and a second heat transfer segment, a
first elongated supply lumen located within the catheter body and
terminating at the interior distal portion of the heat transfer
element into first means for delivering working fluid to the
interior distal portion of the heat transfer element, and a second
elongated supply lumen located within the catheter body and
terminating at a point proximal to the distal portion of the heat
transfer element into second means for delivering working fluid to
the interior portion of the heat transfer element at a point
proximal to the distal portion of the heat transfer element.
[0027] In an implementation of the ninth aspect of the invention,
the second working fluid delivering means is adapted to deliver
working fluid to the interior portion of the beat transfer element
near a midpoint of the heat transfer element.
[0028] A tenth aspect of the present invention involves a device
for heating or cooling a surrounding fluid in a blood vessel. The
device includes an elongated catheter body, a heat transfer element
located at a distal portion of the catheter body and including an
interior distal portion and an interior portion defining at least a
first heat transfer segment interior portion and a second heat
transfer segment interior portion, a first elongated supply lumen
located within the catheter body and terminating at the interior
distal portion of the first heat transfer segment into first means
for delivering working fluid to the interior of the first heat
transfer segment, and a second elongated supply lumen located
within the catheter body and terminating at a point proximal to the
distal portion of the heat transfer element into second means for
delivering working fluid to the interior portion of the second heat
transfer segment.
[0029] In an implementation of the tenth aspect of the invention,
the second working fluid delivering means is adapted to deliver
working fluid to the interior portion of the heat transfer element
near a midpoint of the heat transfer element.
[0030] An eleventh aspect of the present invention involves a
device for heating or cooling a surrounding fluid in a blood
vessel. The device includes an elongated catheter body, a heat
transfer element located at a distal portion of the catheter body
and including an interior portion adapted to induce mixing of a
working fluid to effect heat transfer between the heat transfer
element and working fluid, the heat transfer element including at
least a first heat transfer segment, a second heat transfer
segment, and an intermediate segment between the first heat
transfer segment and the second heat transfer segment, an elongated
supply lumen member located within the catheter body and adapted to
deliver the working fluid to the interior of the heat transfer
element, the supply lumen member including a circular outer
surface, an elongated return lumen defined in part by the outer
surface of the supply lumen member and the interior portion of the
heat transfer element and adapted to return the working fluid from
the interior of the heat transfer element, and wherein the distance
between the interior portion of the heat transfer element and the
outer surface of the supply lumen member adjacent the intermediate
segment is less than the distance between the interior portion of
the heat transfer element and the outer surface of the supply lumen
member adjacent the first heat transfer segment.
[0031] Implementations of the eleventh aspect of the invention may
include one or more of the following. The distance between the
interior portion of the heat transfer element and the outer surface
of the supply lumen member adjacent the intermediate segment is
such that the characteristic flow resulting from a flow of working
fluid is at least of a transitional nature. The intermediate
segment includes an interior diameter that is less than the
interior diameter of the first heat transfer segment or the second
heat transfer segment. The supply lumen member includes an outer
diameter adjacent the intermediate segment that is greater than its
outer diameter adjacent the first heat transfer segment or the
second heat transfer segment. The supply lumen member comprises a
multiple-lumen member. The supply lumen member includes a supply
lumen having a hydraulic diameter and the return lumen has a
hydraulic diameter substantially equal to 0.75 the hydraulic
diameter of the supply lumen. The intermediate segment includes a
flexible bellows joint.
[0032] A twelfth aspect of the present invention involves a device
for heating or cooling a surrounding fluid in a blood vessel. The
device includes an elongated catheter body, a heat transfer element
located at a distal portion of the catheter body and including an
interior portion adapted to induce mixing of a working fluid to
effect heat transfer between the heat transfer element and working
fluid, an elongated supply lumen member located within the catheter
body and adapted to deliver the working fluid to the interior of
the heat transfer element, an elongated return lumen member located
within the catheter body and adapted to return the working fluid
from the interior of the heat transfer element, and means located
within the heat transfer element for further enhancing mixing of
the working fluid to effect further heat transfer between the heat
transfer element and working fluid.
[0033] Implementations of the twelfth aspect of the invention may
include one or more of the following. The supply lumen member
comprises a multiple-lumen member having a circular outer surface.
The supply lumen member includes a supply lumen having a hydraulic
diameter and the return lumen has a hydraulic diameter
substantially equal to 0.75 of the hydraulic diameter of the supply
lumen.
[0034] A thirteenth aspect of the present invention involves a
device for heating or cooling a surrounding fluid in a blood
vessel. The device includes an elongated catheter body, a heat
transfer element located at a distal portion of the catheter body
and including an interior portion adapted to induce mixing of a
working fluid to effect heat transfer between the heat transfer
element and working fluid, an elongated supply lumen member located
within the catheter body and adapted to deliver the working fluid
to the interior of the heat transfer element, an elongated return
lumen member located within the catheter body and adapted to return
the working fluid from the interior of the heat transfer element,
and a mixing-enhancing mechanism located within the heat transfer
element and adapted to further mix the working fluid to effect
further heat transfer between the heat transfer element and working
fluid.
[0035] Implementations of the thirteenth aspect of the invention
may include one or more of the following. The supply lumen member
comprises a multiple-lumen member having a circular outer surface.
The supply lumen member includes a supply lumen having a hydraulic
diameter and the return lumen has a hydraulic diameter
substantially equal to the hydraulic diameter of the supply
lumen.
[0036] A fourteenth aspect of the present invention involves a
method of heating or cooling a surrounding fluid in a blood vessel.
The method includes providing a device for heating or cooling a
surrounding fluid in a blood vessel within the blood stream of a
blood vessel, the device including an elongated catheter body, a
heat transfer element located at a distal portion of the catheter
body and including an interior portion adapted to induce mixing of
a working fluid to effect heat transfer between the heat transfer
element and working fluid, an elongated supply lumen member located
within the catheter body and adapted to deliver the working fluid
to the interior of the heat transfer element, an elongated return
lumen member located within the catheter body and adapted to return
the working fluid from the interior of the heat transfer element,
and a mixing-enhancing mechanism located within the heat transfer
element and adapted to further mix the working fluid to effect
further heat transfer between the heat transfer element and working
fluid; causing a working fluid to flow to and along the interior
portion of the heat transfer element of the device using the supply
lumen and return lumen; facilitating the transfer of heat between
the working fluid and the heat transfer element by effecting mixing
of the working fluid with the interior portion adapted to induce
mixing of a working fluid; facilitating additional transfer of heat
between the working fluid and the heat transfer element by
effecting further mixing of the working fluid with the interior
portion with the mixing-enhancing mechanism; causing heat to be
transferred between the blood stream and the heat transfer element
by the heat transferred between the heat transfer element and
working fluid.
[0037] 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
[0038] FIG. 1 is a graph showing the relationship between the
Nusselt number (Nu) and the Reynolds number (Re) for air flowing
through a long heated pipe at uniform wall temperature.
[0039] FIG. 2 is a front view of a first embodiment of a
mixing-inducing heat transfer element according to the principles
of the invention within an artery;
[0040] FIG. 3 is a more detailed front view of the heat transfer
element of FIG. 1;
[0041] FIG. 4 is a front sectional view of the heat transfer
element of FIG. 1;
[0042] FIG. 5 is a transverse sectional view of the heat transfer
element of FIG. 1;
[0043] FIG. 6 is a front perspective view of the heat transfer
element of FIG. 1 in use within a partially broken away blood
vessel;
[0044] FIG. 7 is a partially broken away front perspective view of
a second embodiment of a mixing-inducing heat transfer element
according to the principles of the invention;
[0045] FIG. 8 is a transverse sectional view of the heat transfer
element of FIG. 7;
[0046] FIG. 9 is a schematic representation of the invention being
used to cool the brain of a patient;
[0047] FIG. 10 is a front sectional view of a guide catheter
according to an embodiment of the invention which may be employed
for applications of the heat transfer element according to the
principles of the invention;
[0048] FIG. 11 is a front sectional view of a third embodiment of a
catheter employing a heat transfer element according to the
principles of the invention further employing a return tube/guide
catheter;
[0049] FIG. 12 is a front sectional view of a fourth embodiment of
a catheter employing a heat transfer element according to the
principles of the invention further employing a delivery
catheter;
[0050] FIG. 13 is a front sectional view of the fourth embodiment
of FIG. 12 further employing a working fluid catheter;
[0051] FIG. 14 is a front sectional view of a fifth embodiment of a
catheter employing a heat transfer element according to the
principles of the invention further employing a guide wire;
[0052] FIG. 15 is a front sectional view of a sixth embodiment of a
catheter employing a heat transfer element according to the
principles of the invention further employing a delivery lumen;
[0053] FIG. 16 is a front sectional view of an seventh embodiment
of a catheter employing a heat transfer element according to the
principles of the invention further employing a delivery lumen;
[0054] FIG. 17 is a front sectional view of an eighth embodiment of
a catheter employing a heat transfer element according to the
principles of the invention further employing a delivery lumen,
this delivery lumen non-coaxial with the central body of the
catheter;
[0055] FIG. 18 is a front sectional view of a ninth embodiment of a
catheter employing a heat transfer element according to the
principles of the invention further employing multiple lumens;
[0056] FIG. 19 is a cross-sectional view of the ninth embodiment of
FIG. 18, taken a long lines 19-19 of FIG. 18;
[0057] FIG. 20 is a front sectional view of a tenth embodiment of a
catheter employing a heat transfer element according to the
principles of the invention;
[0058] FIG. 21 is a front sectional view of a further embodiment of
a catheter employing a heat transfer element according to the
principles of the invention further employing a side-by-side lumen
arrangement constructed in accordance with an embodiment of the
invention;
[0059] FIG. 22 is a cross-sectional view of the catheter of FIG. 21
taken along line 22-22 of FIG. 21;
[0060] FIG. 23 is a front sectional view of a catheter employing a
heat transfer element and lumen arrangement constructed in
accordance with a further embodiment of the invention;
[0061] FIG. 24 is a front sectional view of a catheter employing a
heat transfer element and lumen arrangement constructed in
accordance with a still further embodiment of the invention;
and
[0062] FIG. 25 is a front sectional view of a another embodiment of
a catheter employing a heat transfer element according to the
principles of the invention further employing a side-by-side lumen
arrangement constructed in accordance with another embodiment of
the invention; and
[0063] FIG. 26 is a cross-sectional view of the heat transfer
element illustrated in FIG. 25 taken along line 26-26 of FIG.
25.
DETAILED DESCRIPTION OF THE INVENTION
[0064] The temperature of a selected organ may be intravascularly
regulated by a heat transfer element placed in the organ's feeding
artery to absorb or deliver heat to or from the blood flowing into
the organ. While the method is described with respect to blood flow
into an organ, it is understood that heat transfer within a volume
of tissue is analogous. In the latter case, heat transfer is
predominantly by conduction.
[0065] The heat transfer may cause either a cooling or a heating of
the selected organ. A heat transfer element that selectively alters
the temperature of an organ should be capable of providing the
necessary heat transfer rate to produce the desired cooling or
heating effect within the organ to achieve a desired temperature.
If placed in the venous system, whole body cooling may also be
effected.
[0066] On the arterial side, the heat transfer element should be
small and flexible enough to fit within the feeding artery while
still allowing a sufficient blood flow to reach the organ in order
to avoid ischemic organ damage. Feeding arteries, like the carotid
artery, branch off the aorta at various levels. Subsidiary arteries
continue to branch off these initial branches. For example, the
internal carotid artery branches off the common carotid artery near
the angle of the jaw. The heat transfer element is typically
inserted into a peripheral artery, such as the femoral artery,
using a guide catheter or guide wire, and accesses a feeding artery
by initially passing though a series of one or more of these
branches. Thus, the flexibility and size, e.g., the diameter, of
the heat transfer element are important characteristics. This
flexibility is achieved as is described in more detail below.
[0067] These points are illustrated using brain cooling as an
example. Other organs, as well as the whole body, may also be
cooled. The common carotid artery supplies blood to the head and
brain. The internal carotid artery branches off the common carotid
artery to supply blood to the anterior cerebrum. The heat transfer
element may be placed into the common carotid artery or into both
the common carotid artery and the internal carotid artery.
[0068] The benefits of hypothermia described above are achieved
when the temperature of the blood flowing to the brain is reduced
to between 30.degree. C. and 32.degree. C. A typical brain has a
blood flow rate through each carotid artery (right and left) of
approximately 250-375 cubic centimeters per minute (cc/min). With
this flow rate, calculations show that the heat transfer element
should absorb approximately 75-175 watts of heat when placed in one
of the carotid arteries to induce the desired cooling effect.
Smaller organs may have less blood flow in their respective supply
arteries and may require less heat transfer, such as about 25
watts.
[0069] The method employs conductive and convective heat transfers.
Once the materials for the device and a working fluid are chosen,
the conductive heat transfers are solely dependent on the
temperature gradients. Convective heat transfers, by contrast, also
rely on the movement of fluid to transfer heat. Forced convection
results when the heat transfer surface is in contact with a fluid
whose motion is induced (or forced) by a pressure gradient, area
variation, or other such cause. In the case of arterial flow, the
beating heart provides an oscillatory pressure gradient to force
the motion of the blood in contact with the heat transfer surface.
One of the aspects of the device uses turbulence to enhance this
forced convective heat transfer.
[0070] The rate of convective heat transfer Q is proportional to
the product of S, the area of the heat transfer element in direct
contact with the fluid, .DELTA.T=T.sub.b-T.sub.s, the temperature
differential between the surface temperature T.sub.s of the heat
transfer element and the free stream blood temperature T.sub.b, and
{overscore (h)}.sub.c, the average convection heat transfer
coefficient over the heat transfer area. {overscore (h)}.sub.c is
sometimes called the "surface coefficient of heat transfer" or the
"convection heat transfer coefficient".
[0071] The magnitude of the heat transfer rate Q to or from the
fluid flow can be increased through manipulation of the above three
parameters. Practical constraints limit the value of these
parameters and how much they can be manipulated. For example, the
internal diameter of the common carotid artery ranges from 6 to 8
mm. Thus, the heat transfer element residing therein may not be
much larger than 4 mm in diameter to avoid occluding the vessel.
The length of the heat transfer element should also be limited. For
placement within the internal and common carotid artery, the length
of the heat transfer element is limited to about 10 cm. This
estimate is based on the length of the common carotid artery, which
ranges from 8 to 12 cm.
[0072] Consequently, the value of the surface area S is limited by
the physical constraints imposed by the size of the artery into
which the device is placed. Surface features can be used to
increase the surface area of the heat transfer element; however,
these features alone generally cannot provide enough surface area
enhancement to meet the required heat transfer rate to effectively
cool the brain.
[0073] One may also attempt to vary the magnitude of the heat
transfer rate by varying .DELTA.T. The value of
.DELTA.T=T.sub.b-T.sub.s can be varied by varying the surface
temperature T.sub.s of the heat transfer element. The allowable
surface temperature of the heat transfer element is limited by the
characteristics of blood. The blood temperature is fixed at about
37.degree. C., and 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
{overscore (h)}.sub.c. Increased viscosity of the blood may further
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 surface temperature of
the heat transfer element to approximately 1.degree. C.-5.degree.
C., thus resulting in a maximum temperature differential between
the blood stream and the heat transfer element of approximately
32.degree. C.-36.degree. C.
[0074] One may also attempt to vary the magnitude of the heat
transfer rate by varying {overscore (h)}.sub.c. Fewer constraints
are imposed on the value of the convection heat transfer
coefficient {overscore (h)}.sub.c. The mechanisms by which the
value of {overscore (h)}.sub.c may be increased are complex.
However, one way to increase {overscore (h)}.sub.c for a fixed mean
value of the velocity is to increase the level of turbulent kinetic
energy in the fluid flow.
[0075] The heat transfer rate Q.sub.no-flow in the absence of fluid
flow is proportional to .DELTA.T, the temperature differential
between the surface temperature T.sub.s of the heat transfer
element and the free stream blood temperature T.sub.b times k, the
diffusion constant, and is inversely proportion to distance D
across which heat is being transferred.
[0076] The magnitude of the enhancement in heat transfer by fluid
flow can be estimated by taking the ratio of the heat transfer rate
with fluid flow to the heat transfer rate in the absence of fluid
flow N=Q.sub.flow/Q.sub.no-flow={overscore (h)}.sub.c/(k/.delta.).
This ratio is called the Nusselt number ("Nu"). For convective heat
transfer between blood and the surface of the heat transfer
element, Nusselt numbers of 50-80 have been found to be appropriate
for selective cooling applications of various organs in the human
body. Nusselt numbers are generally dependent on several other
numbers: the Reynolds number, the Womersley number, and the Prandtl
number.
[0077] For example, FIG. 1 illustrates the dependency of the
Nusselt number on the Reynolds number for a fluid flowing through a
long duct, i.e., air flowing though a long heated pipe at a uniform
wall temperature. Although FIG. 1 illustrates this relationship for
a different fluid through a different structure, the inventors of
the present invention believe a similar relationship exists for
blood flow through a blood vessel. FIG. 1 illustrates that flow is
laminar when the Reynolds number is below some number, in this case
about 2100. In the range of Reynolds numbers between another set of
numbers, in this case 2100 and 10,000, a transition from laminar to
turbulent flow takes place. The flow in this regime is called
transitional. The mixing caused by the heat transfer element of the
present invention produces a flow that is at least transitional. At
another Reynolds number, in the case above, about 10,000, the flow
becomes fully turbulent.
[0078] The type of flow that occurs is important because in laminar
flow through a duct, there is no mixing of warmer and colder fluid
particles by eddy motion. Thus, the only heat transfer that takes
place is through conduction. Since most fluids have small thermal
conductivities, the heat transfer coefficients in laminar flow are
relatively small. In transitional and turbulent flow, mixing occurs
through eddies that carry warmer fluid into cooler regions and vice
versa. Since the mixing motion, even if it is only on a small scale
compared to fully turbulent flow, accelerates the transfer of heat
considerably, a marked increase in the heat transfer coefficient
occurs above a certain Reynolds number, which in the graph of FIG.
1 is about 2100. It can be seen from FIG. 1 that it is at
approximately this point where the Nusselt number increases more
dramatically. A different set of numbers may be measured for blood
flow through an artery or vein. However, the inventors believe that
a Nusselt number at least in the transitional region is important
for enhanced heat transfer.
[0079] Stirring-type mechanisms, which abruptly change the
direction of velocity vectors, may be utilized to induce at least
transitional flow, increasing the heat transfer rate by this eddy
creation. The level of turbulence or mixing so created is
characterized by the turbulence intensity .THETA.. Turbulence
intensity .THETA. is defined as the root mean square of the
fluctuating velocity divided by the mean velocity. Such mechanisms
can create high levels of turbulence intensity in the free stream,
thereby increasing the heat transfer rate. This turbulence
intensity should ideally be sustained for a significant portion of
the cardiac cycle, and should ideally be created throughout the
free stream and not just in the boundary layer.
[0080] Turbulence does occur for a short period in the cardiac
cycle anyway. In particular, the blood flow is turbulent during a
small portion of the descending systolic flow. This portion is less
than 20% of the period of the cardiac cycle. If a heat transfer
element is placed co-axially inside an artery, the heat transfer
rate will be enhanced during this short interval. For typical of
these fluctuations, the turbulence intensity is at least 0.05. In
other words, the instantaneous velocity fluctuations deviate from
the mean velocity by at least 5%. In some embodiments, lower
fluctuations may be employed, such as 3% or even 2%. Although
ideally turbulence is created throughout the entire period of the
cardiac cycle, the benefits of turbulence are obtained if the
turbulence or mixing is sustained for 75%, 50% or even as low as
30% or 20% of the cardiac cycle. Of course, such turbulence or
mixing is much less, or is even non-existent, in veins or in very
small arteries.
[0081] One type of mixing-inducing heat transfer element which may
be advantageously employed is a heat transfer element made of a
high thermal conductivity material, such as metal. The use of a
high thermal conductivity material increases the heat transfer rate
for a given temperature differential between the coolant within the
heat transfer element and the blood. This facilitates the use of a
higher temperature coolant within the heat transfer element,
allowing safer coolants, such as water, to be used. Highly
thermally conductive materials, such as metals, tend to be rigid.
Bellows provided a high degree of articulation that compensated for
the intrinsic stiffness of the metal. In another embodiment, the
bellows may be replaced with a straight metal tube having a
predetermined thickness to allow flexibility via bending of the
metal. Alternatively, the bellows may be replaced with a polymer
tube, e.g., a latex rubber tube, a plastic tube, or a flexible
plastic corrugated tube.
[0082] The device size may be minimized, e.g., less than 4 mm, to
prevent blockage of the blood flowing in the vessel. The design of
the heat transfer element should facilitate flexibility in an
inherently inflexible material.
[0083] To create the desired level of turbulence intensity in the
blood free stream during the whole cardiac cycle, one embodiment of
the device uses a modular design. This design creates helical blood
flow and produces a high level of mixing in the free stream by
periodically forcing abrupt changes in the direction of the helical
blood flow. FIG. 2 is a perspective view of such a mixing-inducing
heat transfer element within an artery. Transitional to turbulent
flow would be found at point 114, in the free stream area. The
abrupt changes in flow direction are achieved through the use of a
series of two or more heat transfer segments, each comprised of one
or more helical ridges.
[0084] The use of periodic abrupt changes in the helical direction
of the blood flow in order to induce strong free stream turbulence
or mixing 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 mixing is created within the entire
wash basin as the changing currents cause random turbulent motion
within the clothes-water slurry.
[0085] FIG. 3 is an elevation view of one embodiment of a heat
transfer element 14. The heat transfer element 14 is comprised of a
series of elongated, articulated segments or modules 20, 22, 24.
Three such segments are shown in this embodiment, but one or more
such segments could be used. As seen in FIG. 3, 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 comprises 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. 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.
[0086] The first heat transfer segment 20 is coupled to a second
elongated heat transfer segment 22 by a first tube section 25,
which provides flexibility. The second heat transfer segment 22
comprises 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 tube section 27. The third heat transfer segment 24
comprises 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.
[0087] In addition, the rounded contours of the ridges 28, 32, 36
also 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 may be comprised of
one, two, three, or more heat transfer segments.
[0088] The tube 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 tube 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 tube sections 25, 27 are also able to
tolerate cryogenic temperatures without a loss of performance. The
tube sections 25, 27 may have a predetermined thickness of their
walls, such as between about 0.5 and 0.8 mils. The predetermined
thickness is to a certain extent dependent on the diameter of the
overall tube. Thicknesses of 0.5 to 0.8 mils may be appropriate
especially for a tubal diameter of about 4 mm. For smaller
diameters, such as about 3.3 mm, larger thicknesses may be employed
for higher strength. In another embodiment, tube sections 25, 27
may be formed from a polymer material such as rubber, e.g., latex
rubber.
[0089] The exterior surfaces of the heat transfer element 14 can be
made from metal except in flexible joint embodiments where the
surface may be comprised of a polymer material. The metal may be a
very high thermal conductivity material such as nickel, thereby
facilitating efficient 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.
[0090] 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. 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 to the surface.
[0091] FIG. 4 is a longitudinal sectional view of the heat transfer
element 14, taken along line 4-4 in FIG. 3. Some interior contours
are omitted for purposes of clarity. An inner tube 42 creates an
inner coaxial lumen 40 and an outer coaxial 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 coaxial
lumen 40. At the distal end of the heat transfer element 14, the
working fluid exits the inner coaxial lumen 40 and enters the outer
lumen 46. As the working fluid flows through the outer lumen 46,
heat is transferred between the working fluid and 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 approach
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 some other polymer.
[0092] 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 which remains a liquid as the coolant. Other
coolants such as freon undergo nucleate boiling and create
turbulence through a different mechanism. Saline is a safe coolant
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 turbulence or mixing in the coolant is enhanced
by the shape of the interior surface 38 of the heat transfer
element 14, the coolant can be delivered to the heat transfer
element 14 at a warmer temperature and still achieve the necessary
heat transfer rate.
[0093] 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.
[0094] FIG. 5 is a transverse sectional view of the heat transfer
element 14, taken at a location denoted by the line 5-5 in FIG. 3.
FIG. 5 illustrates a five-lobed embodiment, whereas FIG. 3
illustrates a four-lobed embodiment. As mentioned earlier, any
number of lobes might be used. In FIG. 5, the coaxial construction
of the heat transfer element 14 is clearly shown. The inner coaxial
lumen 40 is defined by the insulating coaxial tube 42. The outer
lumen 46 is defined by the exterior surface of the insulating
coaxial 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. 5. In the preferred embodiment, the depth of
the grooves, d.sub.i, may be greater than the boundary layer
thickness which would have developed if a cylindrical heat transfer
element were introduced. For example, in a heat transfer element 14
with a 4 mm outer diameter, the depth of the invaginations,
d.sub.i, may be approximately equal to 1 mm if designed for use in
the carotid artery. Although FIG. 5 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.
[0095] FIG. 6 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. 6), as the blood moves
forward during the systolic pulse, the first helical heat transfer
segment 20 induces a counter-clockwise rotational inertia to the
blood. As the blood reaches the second segment 22, an unstable
shear layer is produced that causes 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
transitional to turbulent flow, the velocity vectors of the blood
become more random and, in some cases, become perpendicular to the
axis of the artery. In addition, as the velocity of the blood
within the artery decreases and reverses direction during the
cardiac cycle, additional mixing is induced and sustained
throughout the duration of each pulse through the same mechanisms
described above.
[0096] 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. As noted above, the depth of the grooves 26, 30, 34 (FIG.
3) is greater than the depth of the boundary layer that would
develop if a straight-walled heat transfer element were introduced
into the blood stream. In this way, mixing is induced. In the
preferred embodiment, in order to create the desired level of
mixing in the entire blood stream during the whole cardiac cycle,
the heat transfer element 14 creates a turbulence intensity greater
than about 0.05. The turbulence intensity may be greater than 0.05,
0.06, 0.07 or up to 0.10 or 0.20 or greater.
[0097] Referring back to FIG. 3, 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 tube sections 25, 27 which provide an
articulating mechanism. The tube sections have a predetermined
thickness which provides sufficient 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
invaginations to be reversed between segments. The alternating
helical rotations create an alternating flow that results in a
mixing of 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 mixing action is intended to promote a high
level of mixing or turbulent kinetic energy to enhance the heat
transfer rate. The alternating helical design also causes
beneficial mixing, or turbulent kinetic energy, of the working
fluid flowing internally.
[0098] FIG. 7 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. 8 which is a
transverse cross-sectional view taken at a location denoted by the
line 8-8 in FIG. 7. In order to induce free stream turbulence, the
height, d.sub.p, of the staggered outer protrusions 54 is greater
than the thickness of the boundary layer which would develop if a
smooth heat transfer element had been introduced into the blood
stream. 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 along side 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 the free stream. As is the case with the preferred
embodiment, this geometry also induces a mixing effect on the
internal coolant flow.
[0099] A working fluid is circulated up through an inner coaxial
lumen 56 defined by an insulating coaxial tube 58 to a distal tip
of the heat transfer element 50. The working fluid then traverses
an outer coaxial 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 mixing flow of the working fluid. The inner
protrusions can be aligned with the outer protrusions 54, as shown
in FIG. 8, or they can be offset from the outer protrusions 54, as
shown in FIG. 7.
[0100] FIG. 9 is a schematic representation of an embodiment of the
invention being used to cool the brain of a patient. A selective
organ hypothermia apparatus shown in FIG. 9 includes a working
fluid supply 10, preferably supplying a chilled liquid such as
water, alcohol or a halogenated hydrocarbon, a supply catheter 12
and the heat transfer element 14. The supply catheter 12 has a
coaxial construction. An inner coaxial lumen within the supply
catheter 12 receives coolant from the working fluid supply 10. The
coolant travels the length of the supply catheter 12 to the heat
transfer element 14 which serves as the cooling tip of the
catheter. At the distal end of the heat transfer element 14, the
coolant exits the insulated interior lumen and traverses the length
of the heat transfer element 14 in order to decrease the
temperature of the heat transfer element 14. The coolant then
traverses an outer lumen of the supply catheter 12 so that it may
be disposed of or recirculated. The supply catheter 12 is a
flexible catheter having a diameter sufficiently small to allow its
distal end to be inserted percutaneously into an accessible artery
such as the femoral artery of a patient as shown in FIG. 9. The
supply catheter 12 is sufficiently long to allow the heat transfer
element 14 at the distal end of the supply catheter 12 to be passed
through the vascular system of the patient and placed in the
internal carotid artery or other small artery. The method of
inserting the catheter into the patient and routing the heat
transfer element 14 into a selected artery is well known in the
art. A mentioned above, the device may also be placed in the venous
system to cause total body cooling. The device's helices, which are
one way of increasing the surface area as well as to induce mixing
or turbulence, enhance heat transfer.
[0101] 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,
perflourocarbons, water, or saline may be used, as well as other
such coolants.
[0102] The heat transfer element can absorb or provide over 75
Watts of heat to the blood stream and may absorb or provide as much
as 100 Watts, 150 Watts, 170 Watts or more. For example, a heat
transfer element with a diameter of 4 mm and a length of
approximately 10 cm using ordinary saline solution chilled so that
the surface temperature of the heat transfer element is
approximately 5.degree. C. and pressurized at 2 atmospheres can
absorb about 100 Watts of energy from the bloodstream. Smaller
geometry heat transfer elements may be developed for use with
smaller organs which provide 60 Watts, 50 Watts, 25 Watts or less
of heat transfer. For venous cooling, as much as or more than 250
Watts may be extracted.
[0103] An exemplary practice of the present invention, for arterial
applications, is illustrated in the following non-limiting
example.
Exemplary Procedure
[0104] 1. The patient is initially assessed, resuscitated, and
stabilized.
[0105] 2. The procedure is carried out in an angiography suite or
surgical suite equipped with fluoroscopy.
[0106] 3. Because the catheter is placed into the common carotid
artery, it is important to determine the presence of stenotic
atheromatous lesions. A carotid duplex (Doppler/ultrasound) scan
can quickly and non-invasively make this determination. The ideal
location for placement of the catheter is in the left carotid so
this may be scanned first. If disease is present, then the right
carotid artery can be assessed. This test can be used to detect the
presence of proximal common carotid lesions by observing the slope
of the systolic upstroke and the shape of the pulsation. Although
these lesions are rare, they could inhibit the placement of the
catheter. Examination of the peak blood flow velocities in the
internal carotid can determine the presence of internal carotid
artery lesions. Although the catheter is placed proximally to such
lesions, the catheter may exacerbate the compromised blood flow
created by these lesions. Peak systolic velocities greater that 130
cm/sec and peak diastolic velocities>100 cm/sec in the internal
indicate the presence of at least 70% stenosis. Stenosis of 70% or
more may warrant the placement of a stent to open up the internal
artery diameter.
[0107] 4. The ultrasound can also be used to determine the vessel
diameter and the blood flow and the catheter with the appropriately
sized heat transfer element are selected.
[0108] 5. After assessment of the arteries, the patient's inguinal
region is sterilely prepped and infiltrated with lidocaine.
[0109] 6. The femoral artery is cannulated and a guide wire may be
inserted to the desired carotid artery. Placement of the guide wire
is confirmed with fluoroscopy.
[0110] 7. An angiographic catheter can be fed over the wire and
contrast media injected into the artery to further to assess the
anatomy of the carotid.
[0111] 8. Alternatively, the femoral artery is cannulated and a
10-12.5 french (f) introducer sheath is placed.
[0112] 9. A guide catheter is placed into the desired common
carotid artery. If a guiding catheter is placed, it can be used to
deliver contrast media directly to further assess carotid
anatomy.
[0113] 10. A 10 f-12 f (3.3-4.0 mm) (approximate) cooling catheter
is subsequently filled with saline and all air bubbles are
removed.
[0114] 11. The cooling catheter is placed into the carotid artery
via the guiding catheter or over the guidewire. Placement is
confirmed with fluoroscopy.
[0115] 12. The cooling catheter is connected to a refrigerated pump
circuit also filled with saline and free from air bubbles.
[0116] 13. Cooling is initiated by starting the refrigerated pump
circuit. The saline within the cooling catheter is circulated at
3-8 cc/sec. The saline travels through the refrigerated pump
circuit and is cooled to approximately 1.degree. C.
[0117] 14. 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.
[0118] 15. 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 32.degree. C.
[0119] 16. The chilled blood then goes on to chill the brain. It is
estimated that 15-30 minutes will be required to cool the brain to
30 to 32.degree. C.
[0120] 17. The warmed saline travels back down the outer lumen of
the catheter shaft and back to the chilled water bath where it is
cooled to 1.degree. C.
[0121] 18. The pressure drops along the length of the circuit are
estimated to be, e.g., 6 atmospheres.
[0122] 19. The cooling can be adjusted by increasing or decreasing
the flow rate of the saline, or by changing the temperature 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.
[0123] 20. The catheter is left in place to provide cooling for up
to or more than 12 to 24 hours.
[0124] 21. If desired, warm saline can be circulated to promote
warming of the brain at the end of the procedure.
[0125] The invention may also be used in combination with other
techniques. For example, one technique employed to place working
lumens or catheters in desired locations employs guide catheters,
as mentioned above. Referring to FIG. 10, a guide catheter 102 is
shown which may be advantageously employed in the invention. The
guide catheter 102 has a soft tapered tip 104 and a retaining
flange 124 at a distal end 101. The soft tapered tip 104 allows an
atraumatic entrance of the guide catheter 102 into an artery as
well as a sealing function as is described in more detail below.
The retaining flange 124 may be a metallic member adhered to the
guide catheter interior wall or may be integral with the material
of the tube. The retaining flange 124 further has a sealing
function described in more detail below.
[0126] The guide catheter 102 may have various shapes to facilitate
placement into particular arteries. In the case of the carotid
artery, the guide catheter 102 may have the shape of a hockey
stick. The guide catheter 102 may include a Pebax.RTM. tube with a
Teflon.RTM. liner. The Teflon.RTM. liner provides sufficient
lubricity to allow minimum friction when components are pushed
through the tube. A metal wire braid may also be employed between
the Pebax.RTM. tube and the Teflon.RTM. liner to provide
torqueability of the guide catheter 102.
[0127] A number of procedures may be performed with the guide
catheter 102 in place within an artery or vein. For example, a
stent may be disposed across a stenotic lesion in the internal
carotid artery. This procedure involves placing a guide wire
through the guide catheter 102 and across the lesion. A balloon
catheter loaded with a stent is then advanced along the guide wire.
The stent is positioned across the lesion. The balloon is expanded
with contrast, and the stent is deployed intravascularly to open up
the stenotic lesion. The balloon catheter and the guide wire may
then be removed from the guide catheter.
[0128] A variety of treatments may pass through the guide catheter.
For example, the guide catheter, or an appropriate lumen disposed
within, may be employed to transfer contrast for diagnosis of
bleeding or arterial blockage, such as for angiography. The same
may further be employed to deliver various drug therapies, e.g., to
the brain. Such therapies may include delivery of thrombolytic
drugs that lyse clots lodged in the arteries of the brain.
[0129] A proximal end 103 of the guide catheter 102 has a male luer
connector for mating with a y-connector 118 attached to a supply
tube 108. The supply tube 108 may include a braided Pebax.RTM. tube
or a polyimide tube. The y-connector 118 connects to the guide
catheter 102 via a male/female luer connector assembly 116. The
y-connector 118 allows the supply tube 108 to enter the assembly
and to pass through the male/female luer connector assembly 116
into the interior of the guide catheter 102. The supply tube 108
may be disposed with an outlet at its distal end. The outlet of the
supply tube 108 may also be used to provide a working fluid to the
interior of a heat transfer element 110. The guide catheter 102 may
be employed as the return tube for the working fluid supply in this
aspect of the invention. In this embodiment, a heat transfer
element 110 is delivered to the distal end 101 of the guide
catheter 102 as is shown in FIG. 11.
[0130] In FIG. 11, the heat transfer element 110 is shown, nearly
in a working location, in combination with the return tube/guide
catheter 102. In particular, the heat transfer element 110 is shown
near the distal end 101 of the return tube/guide catheter ("RTGC")
102. The heat transfer element 110 may be kept in place by a flange
106 on the heat transfer element 10 that abuts the retaining flange
124 on the RTGC 102. Flanges 124 and 106 may also employ o-rings
such as an o-ring 107 shown adjacent to the flange 106. Other such
sealing mechanisms or designs may also be used. In this way, the
working fluid is prevented from leaking into the blood.
[0131] The supply tube 108 may connect to the heat transfer element
110 (the connection is not shown) and may be employed to push the
heat transfer element 110 through the guide catheter 102. The
supply tube should have sufficient rigidity to accomplish this
function. In an alternative embodiment, a guide wire may be
employed having sufficient rigidity to push both the supply tube
108 and the heat transfer element 110 through the guide catheter
102. So that the supply tube 108 is preventing from abutting its
outlet against the interior of the heat transfer element 110 and
thereby stopping the flow of working fluid, a strut 112 may be
employed on a distal end of the supply tube 108. The strut 112 may
have a window providing an alternative path for the flowing working
fluid.
[0132] The heat transfer element 110 may employ any of the forms
disclosed above, as well as variations of those forms. For example,
the heat transfer element 110 may employ alternating helical ridges
separated by flexible joints, the ridges creating sufficient mixing
to enhance heat transfer between a working fluid and blood in the
artery. Alternatively, the heat transfer element 110 may be
inflatable and may have sufficient surface area such that the heat
transfer due to conduction alone is sufficient to provide the
requisite heat transfer. Details of the heat transfer element 10
are omitted in FIG. 11 for clarity.
[0133] FIG. 12 shows an alternate embodiment of the invention in
which a heat transfer element 204 employs an internal supply
catheter 216. The heat transfer element 204 is shown with
mixing-inducing invaginations 218 located thereon. Similar
invaginations may be located in the interior of the heat transfer
element 204 but are not shown for clarity. Further, it should be
noted that the heat transfer element 204 is shown with merely four
invaginations. Other embodiments may employ multiple elements
connected by flexible joints as is disclosed above. A single heat
transfer element is shown in FIG. 12 merely for clarity.
[0134] A return supply catheter 202 is shown coupled to the heat
transfer element 204. The return supply catheter may be coupled to
the heat transfer element 204 in known fashion, and may provide a
convenient return path for working fluid as may be provided to the
heat transfer element 204 to provide temperature control of a flow
or volume of blood.
[0135] A delivery catheter 216 is also shown in FIG. 12. The
delivery catheter 216 may be coupled to a y-connector at its
proximal end in the manner disclosed above. The delivery catheter
216 may be freely disposed within the interior of the return supply
catheter 202 except where it is restrained from further
longitudinal movement (in one direction) by a retaining flange 210
disposed at the distal end 208 of the heat transfer element 204.
The delivery catheter 216 may be made sufficiently flexible to
secure itself within retaining flange 210, at least for a short
duration. The delivery catheter 216 may have a delivery outlet 212
at a distal end to allow delivery of a drug or other such material
for therapeutic purposes. For example, a radioopaque fluid may be
dispensed for angiography or a thrombolytic drug for thrombolytic
applications.
[0136] For applications in which it is desired to provide drainage
of the artery, e.g., laser ablation, the delivery catheter may be
pulled upstream of the retaining flange 210, exposing an annular
hole in fluid communication with the return supply catheter 202.
The return supply catheter 202 may then be used to drain the volume
adjacent the retaining flange 210.
[0137] The assembly may also perform temperature control of blood
in the artery where the same is located. Such temperature control
procedures may be performed, e.g., before or after procedures
involving the delivery catheter 216. Such a device for temperature
control is shown in FIG. 13. In this figure, a working fluid
catheter 222 is disposed within the return supply catheter 202 and
the heat transfer element 204. In a manner similar to the delivery
catheter 216, the working fluid catheter may be freely disposed
within the interior of the return supply catheter 202 and may
further be coupled to a y-connector at its proximal end in the
manner disclosed above. The working fluid catheter 222 may further
be made sufficiently flexible to secure itself within retaining
flange 210, at least for a short duration. The working fluid
catheter 222 may have a plurality of outlets 214 to allow delivery
of a working fluid. The outlets 214 are located near the distal end
224 of the working fluid catheter 222 but somewhat upstream. In
this way, the outlets 214 allow dispensation of a working fluid
into the interior of the heat transfer element 204 rather than into
the blood stream. The working fluid catheter 222 may also be
insulated to allow the working fluid to maintain a desired
temperature without undue heat losses to the walls of the working
fluid catheter 222.
[0138] One method of disposing a heat transfer device within a
desired artery, such as the carotid artery, involves use of a guide
wire. Referring to FIG. 14, a guide wire 232 is shown disposed
within the interior of the heat transfer element 204. The heat
transfer element 204 may conveniently use the hole defined by
retaining flange 210 to be threaded onto the guide wire 232.
[0139] Numerous other therapies may then employ the return supply
catheter and heat transfer element as a "guide catheter". For
example, various laser and ultrasound ablation catheters may be
disposed within, as well as microcatheters. In this way, these
therapeutic techniques may be employed at nearly the same time as
therapeutic temperature control, including, e.g., neuroprotective
cooling.
[0140] The use of an additional lumen was disclosed above in
connection with passing a variety of treatments through the guide
catheter. For example, an additional lumen may be employed to
transfer contrast for diagnosis of bleeding or arterial blockage,
such as for angiography. Such an additional lumen may be defined by
a drug delivery catheter which forms a part of the overall catheter
assembly. The same may be employed to deliver various drug
therapies, e.g., to the brain. The use of an additional lumen was
further mentioned in connection with expansion of a balloon that
may be used to occlude a drug delivery lumen outlet.
[0141] FIG. 15 depicts an implementation of an embodiment of the
invention employing just such a third lumen. In FIG. 15, a third
lumen 316 is a small central lumen defined by a drug delivery
catheter substantially parallel to the supply and return catheters.
A return catheter 302 defining an outlet lumen 320 is coupled to a
heat transfer element 304 as before. The heat transfer element 304
may have mixing or turbulence-inducing invaginations 306 thereon.
Within the heat transfer element 304 and the return catheter 302 is
an inlet lumen 318 defined by a supply catheter 310. The inlet
lumen 318 may be used to deliver a working fluid to the interior of
the heat transfer element 304. The outlet lumen 320 may be used to
return or exhaust the working fluid from the heat transfer element
304. As above, their respective functions may also be reversed. The
radius of the return catheter may be greater or less (in the case
where their roles are reversed) than the radius of the supply
catheter. The working fluid may be used to heat or cool the heat
transfer element which in turn heats or cools the fluid surrounding
the heat transfer element.
[0142] A drug delivery catheter 312 defines the third lumen 316 and
as shown may be coaxial with the inlet lumen 318 and the outlet
lumen 320. Of course, the delivery catheter 312 may be also be
off-axis or non-coaxial with respect to the inlet lumen 318 and the
outlet lumen 320.
[0143] For example, as shown in FIG. 16, the drug delivery catheter
may be a lumen 316' within the return catheter and may be further
defined by a catheter wall 312'. As another example, as shown in
FIG. 17, the drug delivery catheter may be a lumen 316" adjacent to
and parallel to the return catheter and may be further defined by a
catheter wall 312". In an alternative embodiment, more than one
lumen may be provided within the return catheter to allow delivery
of several types of products, e.g., thrombolytics, saline
solutions, etc. Of course, the supply catheter may also be used to
define the drug delivery catheter. The drug delivery catheter may
be substantially parallel to the return catheter or supply catheter
or both, or may alternatively be at an oblique angle. The drug
delivery catheter includes an outlet at a distal end thereof. The
outlet may be distal or proximal of the distal end of the return or
supply catheters. The outlet may be directed parallel to the return
and supply catheters or may alternatively be directed transverse of
the return and supply catheters.
[0144] The device may be inserted in a selected feeding vessel in
the vascular system of a patient. For example, the device may be
inserted in an artery which feeds a downstream organ or which feeds
an artery which, in turn, feeds a downstream organ. In any of the
embodiments of FIGS. 15-17, the drug delivery catheter lumen may be
used to deliver a drug, liquid, enzyme or other material to the
approximate location of the heat transfer element. Such delivery
may occur before, after, or contemporaneous with heat transfer to
or from the blood. For example, materials, e.g., drugs, liquids,
enzymes, which operate at temperatures other than normal body
temperature may be used by first altering the local blood
temperature with the heat transfer element and then delivering the
temperature specific material, e.g., a temperature-specific
thrombolytic, which then operates at the altered temperature.
Alternatively, such "third" lumens (with the supply and return
catheters for the working fluid defining "first" and "second"
lumens) may be used to remove particles, debris, or other desired
products from the blood stream.
[0145] FIGS. 18 and 19 show another embodiment of the invention
that is related to the embodiment of FIG. 16. In this embodiment,
several additional sealed lumens are disposed in the return
catheter. Some of the lumens may be for drug delivery and others
may be used to enhance mixing in a manner described below. The
sealed lumens are in pressure communication with a supply of air to
inflate the same. In FIG. 18, a return catheter 302' has one lumen
316'" C as shown for drug delivery. Another, lumen 316'" I, is
shown which may be employed to alter the geometry and shape of the
overall catheter. That is, inflating lumen 316'" I causes the lumen
to expand in the same way that inflating a balloon causes it to
expand. In order to allow for the expansion, appropriately reduced
return catheter wall thicknesses may be employed. Also, inflatable
lumens 316'" A-B and 316'" D-N may be distributed in a
substantially symmetric fashion around the circumference of the
catheter for a uniform inflation if desired. Of course, less
distortion under inflation may occur at or adjacent lumens such as
316'" C used for drug delivery, as these do not inflate.
[0146] The inflatable lumens 316'" A-B and 316'" D-N may be caused
to inflate under influence of, e.g., an air compressor with a
variable air delivery flow. Rapid pulses of air may be used to
inflate the lumens 316'" A-B and 316'" D-N in a rapid and repeated
fashion. By so doing, the outer walls defining these lumens move
rapidly into and out of the bloodstream around the catheter,
inducing turbulence. Preferably, the amplitude of the vibrations is
large enough to move the outer walls defining the lumens out of the
boundary layer and into the free stream of blood. This effect
produces mixing which is used to enhance heat transfer. As it is
important to induce mixing primarily near the heat transfer
element, the area of appropriate wall thickness to allow for
inflation need only be at, near, or adjacent the portion of the
return catheter exterior wall adjacent the heat transfer element.
In other words, the return catheter wall only requires substantial
reduction near the heat transfer element. The remainder of the
catheter wall may remain thick for strength and durability.
[0147] The supply catheter 310 may be constructed such that the
same does not contact the interior of the distal end 308 of the
heat transfer element, which may cause a subsequent stoppage of
flow of the working fluid. Such construction may be via struts
located in the return catheter 302 that extend radially inwards and
secure the supply catheter 310 from longitudinal translations.
Alternatively, struts may extend longitudinally from the distal end
of the supply catheter 310 and hold the same from contacting the
heat transfer element. This construction is similar to strut 112
shown in FIG. 11.
[0148] FIG. 20 shows an alternate method of accomplishing this
goal. In FIG. 20, a heat transfer element 304' has an orifice 326
at a distal end 308. A supply catheter 310' is equipped with a drug
delivery catheter 312' extending coaxially therein. The drug
delivery catheter 312 may be formed of a solid material integral
with supply catheter 310', or the two may be bonded after being
constructed of separate pieces, or the two may remain separate
during use, with a friction fit maintaining their positions with
respect to each other. The supply catheter 310' is "in position"
when a tapered portion 324 of the same is lodged in the hole 326 in
the heat transfer element 304'. The tapered portion 324 should be
lodged tightly enough to cause a strong friction fit so that
working fluid does not leak through the hole 326. However, the
tapered portion 324 should be lodged loosely enough to allow the
supply catheter 310' to be removed from the heat transfer element
304' if continued independent use of the return catheter is
desired.
[0149] The supply catheter 310' has a plurality of outlets 322.
Outlets 322 are provided at points generally near or adjacent the
distal end of the supply catheter 310'. The outlets are provided
such that, when the supply catheter 310' is in position, the
outlets generally face the heat transfer element 304'. In this way,
the working fluid, emerging from the outlets 322, more directly
impinges on the interior wall of the heat transfer element 304'. In
particular, the working fluid exits the interior of the supply
catheter and flows into a volume defined by the exterior of the
supply catheter and the interior of the heat transfer element.
[0150] For clarity, FIG. 20 does not show the invaginations on the
interior wall of the heat transfer element 304'. However, it will
be understood that such invaginations may be present and may allow
for enhanced heat transfer in combination with the emerging working
fluid.
[0151] In the embodiments of FIGS. 10, 12, and 14-20, various types
of catheter assemblies employing drug delivery catheters are
described. In those embodiments, and particularly in the
embodiments such as FIGS. 12, 15 and 20, in which a distal end of
the drug delivery catheter protrudes substantially from the distal
end of the remainder of the catheter assembly, a therapy may be
performed in which the distal end of the catheter is embedded into
a clot to be dissolved. An enzyme solution, such as a warm or cool
enzyme solution, may then be sent directly into the clot to locally
enhance the fibrinolytic activity.
[0152] In particular, the catheter may be placed as described
above. In this procedure, however, the catheter is placed such that
the tip of the protruding drug delivery catheter touches, is
substantially near, or becomes embedded within the clot. An enzyme
solution or other such drug is then delivered down the drug
delivery catheter directly into the clot or into the volume of
blood surrounding the clot. The enzyme solution may include tPA,
streptokinase, urokinase, pro-urokinase, combinations thereof, and
may be heated to enhance fibrinolytic activity. In a related
embodiment, the solution may be a simple heated saline solution.
The heated saline solution warms the clot, or the volume
surrounding the clot, again leading to enhanced fibrinolytic
activity.
[0153] In these procedures, it is advantageous to use embodiments
of the invention in which the distal tip of the drug delivery
catheter is substantially protruding, or is distal, from the
remainder of the catheter assembly. In this way, the distal tip may
be disposed adjacent to or within a clot without being obstructed
by the remainder of the catheter assembly.
[0154] The heat transfer element 110 (FIG. 11) may employ any of
the forms disclosed above, as well as variations of these forms.
For example, the heat transfer element 110 may employ alternating
helical ridges separated by flexible joints, the ridges creating
sufficient mixing and/or surface area to enhance heat transfer
between a working fluid and blood in the artery or vein.
Alternatively, the heat transfer element 110 may be inflatable and
may have sufficient surface area such that the heat transfer due to
conduction alone is sufficient to provide the requisite heat
transfer. Details of the heat transfer element 110 are omitted in
FIG. 11 for clarity.
[0155] With reference to FIGS. 21 and 22, a catheter 400
constructed in accordance with an alternative embodiment of the
invention will now be described. The catheter 400 includes an
elongated catheter body 402 with a heat transfer element 404
located at a distal portion 406 of the catheter body 402. The
catheter 400 includes a multiple lumen arrangement 408 to deliver
fluid to and from an interior 410 of the heat transfer element 404
and allow the catheter 400 to be placed into a blood vessel over a
guidewire. The heat transfer element 404 includes
turbulence-inducing invaginations 412 located on an exterior
surface 414. Similar invaginations may be located on an interior
surface 416 of the heat transfer element 404, but are not shown for
clarity. Further, it should be noted that the heat transfer element
404 is shown with only four invaginations 412. Other embodiments
may employ multiple elements connected by flexible joints or
bellows as disclosed above. A single heat transfer element is shown
in FIG. 21 merely for clarity. In an alternative embodiment of the
invention, any of the other heat-transfer elements described herein
may replace heat transfer element 406. Alternatively, the
multi-lumen arrangement may be used to deliver fluid to and from
the interior of an operative element(s) other than a
heat-transfer-element such as, but without limitation, a catheter
balloon, e.g., a dilatation balloon.
[0156] The catheter 400 includes an integrated elongated multiple
lumen member such as a bi-lumen member 418 having a first lumen
member 420 and a second lumen member 422. The bi-lumen member 418
has a substantially figure-eight cross-sectional shape (FIG. 22)
and an outer surface 419 with the same general shape. The first
lumen member 420 includes an interior surface 424 defining a first
lumen or guide wire lumen 426 having a substantially circular
cross-sectional shape. The interior surface 424 may be coated with
a lubricious material to facilitate the sliding of the catheter 400
over a guidewire. The first lumen member 420 further includes a
first exterior surface 428 and a second exterior surface 430. The
first lumen 426 is adapted to receive a guide wire for placing the
catheter 400 into a blood vessel over the guidewire in a well-known
manner.
[0157] In FIGS. 21 and 22, the guide wire lumen 426 is not coaxial
with the catheter body 402. In an alternative embodiment of the
invention, the guide wire lumen 426 may be coaxial with the
catheter body 402.
[0158] The second lumen member 422 includes a first interior
surface 432 and a second interior surface 434, which is the same as
the second exterior surface 430 of the first lumen member 420, that
together define a second lumen or supply lumen 436 having a
substantially luniform cross-sectional shape. The second lumen
member 422 further includes an exterior surface 438. The second
lumen 436 has a cross-sectional area A.sub.2. The second lumen 436
is adapted to supply working fluid to the interior of the heat
transfer element 404 to provide temperature control of a flow or
volume of blood in the manner described above.
[0159] The second lumen member 422 terminates short of a distal end
440 of the catheter 400, leaving sufficient space for the working
fluid to exit the supply lumen 436 so it can contact the interior
surface 416 of the heat transfer element 404 for heat transfer
purposes.
[0160] Although the second lumen member 422 is shown as a single
supply lumen terminating adjacent the distal end 440 of catheter
400 to deliver working fluid at the distal end of the catheter 200,
with reference to FIG. 23, in an alternative embodiment of the
invention, a single supply lumen member 435 may include one or more
outlet openings 437 adjacent the distal end 440 of the catheter 400
and one or more outlet openings 439 adjacent a mid-point along the
interior length of the heat transfer element 404. This arrangement
improves the heat transfer characteristics of the heat-transfer
element 404 because fresh working fluid at the same temperature is
delivered separately to each segment 22, 24 of the interior of the
heat-transfer element 404 instead of in series.
[0161] Although two heat transfer segments 22, 24 are shown, it
will be readily apparent that a number of heat transfer segments
other than two, e.g., one, three, four, etc., may be used.
[0162] It will be readily apparent to those skilled in the art that
in another embodiment of the invention, in addition to the one or
more openings 437 in the distal portion of the heat transfer
element 404, one or more openings at one or more locations may be
located anywhere along the interior length of the heat transfer
element 404 proximal to the distal portion.
[0163] With reference to FIG. 24, in an alternative embodiment of
the invention, first and second supply lumen members 441, 443
define respective first and second supply lumens 445, 447 for
supplying working fluid to the interior of the heat transfer
element 404. The first supply lumen 441 terminates just short of
the distal end 440 of the catheter 400 to deliver working fluid at
the distal portion of the heat transfer element 404. The second
supply lumen 443 terminates short of the distal portion of the
catheter 400, for example, at approximately a mid-length point
along the interior of the heat transfer element 404 for delivering
working fluid to the second heat transfer segment 22. In an
alternative embodiment of the invention, the second lumen member
443 may terminate anywhere along the interior length of the heat
transfer element 404 proximal to the distal portion of the heat
transfer element 404. Further, a number of supply lumens 443
greater than two may terminate along the interior length of the
heat transfer element 404 for delivering a working fluid at a
variety of points along the interior length of the heat transfer
element 404.
[0164] With reference back to FIGS. 21 and 22, the bi-lumen member
418 is preferably extruded from a material such as polyurethane or
Pebax. In an embodiment of the invention, the bi-lumen member is
extruded simultaneously with the catheter body 402. In an
alternative embodiment of the invention, the first lumen member 420
and second lumen member 422 are formed separately and welded or
fixed together.
[0165] A third lumen or return lumen 442 provides a convenient
return path for working fluid. The third lumen 442 is substantially
defined by the interior surface 416 of the heat transfer element
404, an interior surface 444 of the catheter body 402, and the
exterior surface 419 of the bi-lumen member 418. The inventors have
determined that the working fluid pressure drop through the lumens
is minimized when the third lumen 442 has a hydraulic diameter
D.sub.3 that is equal to 0.75 of the hydraulic diameter D.sub.2 of
the second lumen 436. However, the pressure drop that occurs when
the ratio of the hydraulic diameter D.sub.3 to the hydraulic
diameter D.sub.2 is substantially equal to 0.75, i.e.,
0.75.+-.0.10, works well. For flow through a cylinder, the
hydraulic diameter D of a lumen is equal to four times the
cross-sectional area of the lumen divided by the wetted perimeter.
The wetted perimeter is the total perimeter of the region defined
by the intersection of the fluid path through the lumen and a plane
perpendicular to the longitudinal axis of the lumen. The wetted
perimeter for the return lumen 442 would include an inner wetted
perimeter (due to the outer surface 419 of the bi-lumen member 418)
and an outer wetted perimeter (due to the interior surface 444 of
the catheter body 402). The wetted perimeter for the supply lumen
436 would include only an outer wetted perimeter (due to the first
and second interior surfaces 432, 434 of the bi-lumen member 418).
Thus, the wetted perimeter for a lumen depends on the number of
boundary surfaces that define the lumen.
[0166] The third lumen 442 is adapted to return working fluid
delivered to the interior of the heat transfer element 404 back to
an external reservoir or the fluid supply for recirculation in a
well-known manner.
[0167] In an alternative embodiment, the third lumen 442 is the
supply lumen and the second lumen 436 is the return lumen.
Accordingly, it will be readily understood by the reader that
adjectives such as "first," "second," etc. are used to facilitate
the reader's understanding of the invention and are not intended to
limit the scope of the invention, especially as defined in the
claims.
[0168] In a further embodiment of the invention, the member 418 may
include a number of lumens other than two such as, for example, 1,
3, 4, 5, etc. Additional lumens may be used as additional supply
and/or return lumens, for other instruments, e.g., imaging devices,
or for other purposes, e.g., inflating a catheter balloon or
delivering a drug.
[0169] Heating or cooling efficiency of the heat transfer element
404 is optimized by maximizing the flow rate of working fluid
through the lumens 436, 442 and minimizing the transfer of heat
between the working fluid and the supply lumen member. Working
fluid flow rate is maximized and pressure drop minimized in the
present invention by having the ratio of the hydraulic diameter
D.sub.3 of the return lumen 442 to the hydraulic diameter D.sub.2
of the supply lumen 436 equal to 0.75. However, a ratio
substantially equal to 0.75, i.e., 0.75.+-.10-20%, is acceptable.
Heat transfer losses are minimized in the supply lumen 436 by
minimizing the surface area contact made between the bi-lumen
member 418 and the working fluid as it travels through the supply
lumen member. The surface area of the supply lumen member that the
supplied working fluid contacts is much less than that in co-axial
or concentric lumens used in the past because the supplied working
fluid only contacts the interior of one lumen member compared to
contacting the exterior of one lumen member and the interior of
another lumen member. Thus, heat transfer losses are minimized in
the embodiments of the supply lumen in the multiple lumen member
418 of the present invention.
[0170] It will be readily apparent to those skilled in the art that
the supply lumen 436 and the return lumen 442 may have
cross-sectional shapes other than those shown and described herein
and still maintain the desired hydraulic diameter ratio of
substantially 0.75. With reference to FIGS. 25 and 26, an example
of a catheter 400 including a supply lumen and a return lumen
constructed in accordance with an alternative preferred embodiment
of the invention, where the hydraulic diameter ratio of the return
lumen to the supply lumen is substantially equal to 0.75 is
illustrated. It should be noted, the same elements as those
described above with respect to FIGS. 21 and 22 are identified with
the same reference numerals and similar elements are identified
with the same reference numerals, but with a (`) suffix.
[0171] The catheter 400 illustrated in FIGS. 25 and 26 includes a
multiple lumen arrangement 408' for delivering working fluid to and
from an interior 410 of the heat transfer element 404 and allowing
the catheter to be placed into a blood vessel over a guide wire.
The multiple lumen arrangement 408' includes a bi-lumen member 418'
with a slightly different construction from the bi-lumen member 418
discussed above with respect to FIGS. 21 and 22. Instead of an
outer surface 419 that is generally figure-eight shaped, the
bi-lumen member 418' has an outer surface 419' that is circular.
Consequently, the third lumen 442' has an annular cross-sectional
shape.
[0172] As discussed above, maintaining the hydraulic diameter ratio
of the return lumen 436' to the supply lumen 442' substantially
equal to 0.75 maximizes the working fluid flow rate through the
multiple lumen arrangement 408'.
[0173] In addition, the annular return lumen 442' enhances the
convective heat transfer coefficient within the heat transfer
element 404, especially adjacent an intermediate segment or bellows
segment 449. Working fluid flowing through the annular return lumen
442', between the outer surface 419' of the bi-lumen member 418'
and the inner surface 416 of the heat transfer element, encounters
a restriction 450 caused by the impingement of the bellows section
449 into the flow path. Although the impingement of the bellows
section 449 is shown as causing the restriction 450 in the flow
path of the return lumen 442', in an alternative embodiment of the
invention, the bi-lumen member 418' may create the restriction 450
by being thicker in this longitudinal region of the bi-lumen member
418'. The distance between the bi-lumen member 418' and the bellows
section 449 is such that the characteristic flow resulting from a
flow of working fluid is at least of a transitional nature.
[0174] For a specific working fluid flux or flow rate (cc/sec), the
mean fluid velocity through the bellows section restriction 450
will be greater than the mean fluid velocity obtained through the
annular return lumen 442' in the heat transfer segment 22, 24 of
the heat transfer element 404. Sufficiently high velocity through
the bellows section restriction 450 will result in wall jets 451
directed into the interior portion 416 of the heat transfer segment
22. The wall jets 451 enhance the heat transfer coefficient within
the helical heat transfer segment 22 because they enhance the
mixing of the working fluid along the interior of the helical heat
transfer segment 22. Increasing the velocity of the jets 451 by
increasing the working fluid flow rate or decreasing the size of
the restriction 450 will result in a transition closer to the jet
exit and greater mean turbulence intensity throughout the helical
heat transfer segment 22. Thus, the outer surface 419' of the
bi-lumen member 418', adjacent the bellows 449, and the inner
surface of the bellows 449 form means for further enhancing the
transfer of heat between the heat transfer element 404 and the
working fluid, in addition to that caused by the interior portion
416 of the helical heat transfer segment 22.
[0175] In an alternative embodiment of the invention, as described
above, the heat transfer element may include a number of heat
transfer segments other than two, i.e., 1, 3, 4, etc., with a
corresponding number of intermediate segments, i.e., the number of
heat transfer segments minus one.
[0176] The embodiment of the multiple lumen arrangement 418
discussed with respect to FIGS. 21 and 22 would not enhance the
convective heat transfer coefficient as much as the embodiment of
the multiple lumen arrangement 418' discussed with respect to FIGS.
25 and 26 because working fluid would preferentially flow through
the larger areas of the return lumen 442, adjacent the junction of
the first lumen member 420 and second lumen member 422. Thus,
high-speed working fluid would have more contact with the outer
surface 419 of the bi-lumen member 418 and less contact with the
interior portion of 416 heat transfer element 404. In contrast, the
annular return lumen 442' of the multiple lumen arrangement 418'
causes working fluid flow to be axisymmetric so that significant
working fluid flow contacts all areas of the helical segment
equally.
[0177] The invention has been described with respect to certain
embodiments. It will be clear to one of skill in the art that
variations of the embodiments may be employed in the method of the
invention. Accordingly, the invention is limited only by the scope
of the appended claims.
* * * * *