Method and device for patient temperature control employing optimized rewarming

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Method and device for patient temperature control employing optimized rewarming

Abstract
Embodiments of the invention provide a system for temperature control of the human body. The system includes an indwelling catheter with a tip-mounted heat transfer element. The catheter is fluidically coupled to a console that provides a heated or cooled heat transfer working fluid to exchange heat with the heat transfer element, thereby heating or cooling blood. The heated or cooled blood then heats or cools the patient's body or a selected portion thereof. In particular, strategies for optimizing the rewarming of patients for various medical procedures are provided, including stroke, neurosurgery, and myocardial infarction.

Inventors: Magers; Michael (Encinitas, CA)
Assignee: Innercool Therapies, Inc. (San Diego, CA)
Appl. No.: 11/003,220
Filed: December 3, 2004

Parent Case Text


CONTINUING INFORMATION

This application is a continuation of U.S. application Ser. No. 10/216,487, entitled "Method And Device For Patient Temperature Control Employing Optimized Rewarming", filed on Aug. 9, 2002, now U.S. Pat. No. 6,830,581, which is a continuation-in-part of U.S. application Ser. No. 09/650,940, entitled "Selective Organ Hypothermia Method And Apparatus," filed on Aug. 30, 2000 now U.S. Pat. No. 6,482,226; U.S. Ser. No. 09/785,243, entitled "Circulating Fluid Hypothermia Method And Apparatus," filed on Feb. 16, 2001 now U.S. Pat. No. 6,818,011; U.S. Ser. No. 09/566,531, entitled "Method Of Making Selective Organ Cooling Catheter," filed on May 8, 2000 now ABN; U.S. Ser. No. 09/757,124, entitled "Inflatable Catheter For Selective Organ Heating And Cooling And Method Of Using The Same," filed on Jan. 8, 2001 now U.S. Pat. No. 6,540,771; U.S. Ser. No. 09/714,749, entitled "Method For Low Temperature Thrombolysis And Low Temperature Thrombolytic Agent With Selective Organ Temperature Control," filed on Nov. 16, 2000 now U.S. Pat. No. 6,468,296; U.S. Ser. No. 09/621,051, entitled "Method And Device For Applications Of Selective Organ Cooling," filed on Jul. 21, 2000 now U.S. Pat. No. 6,582,455; U.S. Ser. No. 09/800,159, entitled "Method And Apparatus For Location And Temperature Specific Drug Action Such As Thrombolysis," filed on Mar. 6, 2001 now ABN; U.S. Ser. No. 09/292,532, entitled "Isolated Selective Organ Cooling Method And Apparatus," filed on Apr. 15, 1999 now ABN; U.S. Ser. No. 09/379,295, entitled "Method Of Manufacturing A Heat Transfer Element For In Vivo Cooling," filed on Aug. 23, 1999 now ABN; U.S. Ser. No. 09/885,655, entitled "Inflatable Heat Transfer Apparatus," filed on Jun. 20, 2001 now U.S. Pat. No. 6,676,690; U.S. Ser. No. 09/246,788, entitled "Method And Device For Applications Of Selective Organ Cooling," filed on Feb. 9, 1999 now U.S. Pat. No. 6,491,716; U.S. Ser. No. 09/797,028, entitled "Selective Organ Cooling Catheter With Guidewire Apparatus And Temperature-Monitoring Device," filed on Feb. 27, 2001 now ABN; U.S. Ser. No. 09/607,799, entitled "Selective Organ Cooling Apparatus And Method," filed on Jun. 30, 2000 now U.S. Pat. No. 6,464,716; U.S. Ser. No. 09/519,022, entitled "Lumen Design For Catheter," filed on Mar. 3, 2000 now U.S. Pat. No. 6,379,378; U.S. Ser. No. 10/082,964, entitled "Method For Determining The Effective Thermal Mass Of A Body Or Organ Using A Cooling Catheter," filed on Feb. 25, 2002 now U.S. Pat. No. 6,660,028; U.S. Ser. No. 09/539,932, entitled "Medical Procedure," filed on Mar. 31, 2000 now U.S. Pat. No. 6,491,039; U.S. Ser. No. 09/658,950, entitled "Medical Procedure," filed on Sep. 11, 2000 now ABN; U.S. Ser. No. 09/373,112, entitled "Patient Temperature Regulation Method And Apparatus," filed on Aug. 11, 1999 now U.S. Pat. No. 6,843,800; U.S. Ser. No. 10/007,545, entitled "Circulation Set For Temperature-Controlled Catheter And Method Of Using The Same," filed on Nov. 6, 2001 now U.S. Pat. No. 6,719,779; U.S. Ser. No. 10/005,416, entitled "Fever Regulation Method And Apparatus," filed on Nov. 7, 2001 now U.S. Pat. No. 6,585,752; U.S. Ser. No. 10/117,733, entitled "Method Of Manufacturing A Heat Transfer Element For In Vivo Cooling," filed on Apr. 4, 2002 now U.S. Pat. No. 6,702,841; and is a conversion of U.S. Patent Application Ser. No. 60/311,589, entitled "Optimal Rewarming Strategies," filed on Aug. 9, 2001; 60/312,409, entitled "Controlling The Application Of Hypothermia," filed on Aug. 15, 2001; 60/316,057, entitled "Controlling Hypothermia," filed on Aug. 29, 2001; 60/316,922, entitled "Novel Antishiver Drugs And Regimens," filed on Aug. 31, 2001; 60/322,945, entitled "Novel Antishiver Drugs And Regimens," filed on Sep. 14, 2001; 60/328,259, entitled "Single Operator Exchange Coaxially Cooling Catheter," filed on Oct. 9, 2001; and 60/328,320, entitled "Temperature Projection Method In A Catheter Mounted Temperature Sensor," filed on Oct. 9, 2001; all of the above are incorporated by reference herein in their entirety.
Claims


The invention claimed is:

1. A method of rewarming a patient following neurosurgery comprising: draping a patient with a blanket; inserting a heat transfer element into a vein of the patient, wherein the heat transfer element includes at least two heat transfer segments separated by a bellows; circulating a working fluid through the heat transfer element, the working fluid heated by a heat exchanger to a temperature sufficient to raise the temperature of a blood stream to a temperature less than about 42.degree. C.; sensing a patient temperature; controlling the patient temperature to a target temperature of less than about 35.degree. C.; and rewarming the patient to normothermia using a heating blanket, wherein the heat transfer element includes a straight lumen surrounded by a helical lumen.

2. The method of claim 1, wherein the heat transfer element is flexible and is made of a polymer.

3. The method of claim 1, wherein the sensing a patient temperature includes sensing a patient temperature with an esophageal probe.

4. A method of rewarming a patient following a stroke comprising: covering a patient with a heating blanket set to a temperature of between about 38.degree. C. and 43.degree. C.; inserting a heat transfer element into a vein of the patient, wherein the heat transfer element includes at least two heat transfer segments separated by a bellows; circulating a working fluid through the heat transfer element; sensing a patient temperature; controlling the patient temperature such that the patient temperature rises to greater than about 36.degree. C. over a period of time between about 6 hours to about 24 hours; if the patient is experiencing shivering during the controlled rewarm, administering an antishivering drug; and rewarming the patient to normothermia using the active heating blanket, wherein the heat transfer element includes a straight lumen surrounded by a helical lumen.

5. The method of claim 4, wherein the heat transfer element is flexible and is made of a polymer.

6. A method of rewarming a patient following a cardiovascular surgery, comprising: inserting a heat transfer element into a vein of the patient wherein the heat transfer element includes at least two heat transfer segments separated by a bellows; performing a cardiac surgery; following the cardiac surgery, circulating a working fluid through the heat transfer element, the working fluid heated by a heat exchanger to a temperature sufficient to raise the blood temperature to a blood temperature less than about 42.degree. C.; sensing a patient temperature; controlling the patient temperature such that the patient temperature rises to greater than about 36.5.degree. C.

7. The method of claim 6, wherein the sensing a patient temperature includes sensing a patient temperature with an esophageal probe.

8. The method of claim 6, wherein the sensing a patient temperature includes sensing a patient temperature with a bladder probe.
Description


FIELD OF THE INVENTION

The present invention relates generally to the lowering, raising, and control of the temperature of the human body. More particularly, the invention relates to a method and intravascular apparatus for controlling the temperature of the human body.

BACKGROUND

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.

Hypothermia is uniquely effective in reducing ischemia. For example, it is 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 ischemic injuries to other organs.

SUMMARY OF THE INVENTION

The apparatus of the present invention can include a heat transfer element which can be used to apply cooling to the blood flowing in a vessel. The heat transfer element, by way of example only, comprises first and second elongated, articulated segments, each segment having a turbulence-inducing exterior surface. A flexible joint can connect the first and second elongated segments. An inner coaxial lumen may be disposed within the first and second elongated segments and is capable of transporting a working fluid to a distal end of the first elongated segment. In addition, the first and second elongated segments may have a turbulence-inducing interior surface for inducing turbulence within the pressurized working fluid. The turbulence-inducing exterior surface may be adapted to induce turbulence within a free stream of blood flow when placed within an artery or vein. The turbulence-inducing exterior surface may be adapted to induce a turbulence intensity greater than 0.05 within a free stream blood flow. In one embodiment, the flexible joint comprises a bellows section which also allows for axial compression of the heat transfer element.

In an embodiment, the turbulence-inducing exterior surfaces of the heat transfer element comprise one or more helical ridges. Adjacent segments of the heat transfer element can be oppositely spiraled to increase turbulence. For instance, the first elongated heat transfer segment may comprise one or more helical ridges having a counter-clockwise twist, while the second elongated heat transfer segment comprises one or more helical ridges having a clockwise twist. Alternatively, of course, the first elongated heat transfer segment may comprise one or more clockwise helical ridges, and the second elongated heat transfer segment may comprise one or more counter-clockwise helical ridges. The first and second elongated, articulated segments may be formed from highly conductive materials.

The heat transfer device may also have a coaxial supply catheter with an inner catheter lumen coupled to the inner coaxial lumen within the first and second elongated heat transfer segments. A working fluid supply configured to dispense the pressurized working fluid may be coupled to the inner catheter lumen. The working fluid supply may be configured to produce the pressurized working fluid at a temperature of about 0.degree. C. and at a pressure below about 5 atmospheres of pressure. The working fluid may be isolyte, saline, D5W, etc.

In yet another alternative embodiment, the heat transfer device may have three or more elongated, articulated, heat transfer segments having a turbulence-inducing exterior surface, with additional flexible joints connecting the additional elongated heat transfer segments. In one such embodiment, by way of example, the first and third elongated heat transfer segments may comprise clockwise helical ridges, and the second elongated heat transfer segment may comprise one or more counter-clockwise helical ridges. Alternatively, of course, the first and third elongated heat transfer segments may comprise counter-clockwise helical ridges, and the second elongated heat transfer segment may comprise one or more clockwise helical ridges.

The turbulence-inducing exterior surface of the heat transfer element may optionally include a surface coating or treatment to inhibit clot formation.

The present invention also envisions a method of cooling the body which comprises inserting a flexible, conductive cooling element into the inferior vena cava from a distal location, and providing a means of warming the body to prevent shivering by means of a cooling blanket. The method further includes circulating a working fluid through the flexible, conductive cooling element in order to lower the temperature of the body. The flexible, conductive heat transfer element absorbs more than about 25, 50 or 75 Watts of heat.

The method may also comprise inducing turbulence within the free stream blood flow within an artery or vein. In one embodiment, the method includes the step of inducing blood turbulence with a turbulence intensity greater than about 0.05 within the vascular system. The circulating may comprise inducing mixing flow of the working fluid through the flexible, conductive heat transfer element. The pressure of the working fluid may be maintained below about 5 atmospheres of pressure.

The cooling or warming may comprise circulating a working fluid in through an inner lumen in the catheter and out through an outer, coaxial lumen. In one embodiment, the working fluid remains a liquid throughout the cycle. The working fluid may be aqueous.

The present invention also envisions a cooling or warming catheter comprising a catheter shaft having first and second lumens therein. The catheter also comprises a cooling or warming tip adapted to transfer heat to or from a working fluid circulated in through the first lumen and out through the second lumen, and turbulence-inducing structures on the tip capable of inducing free stream turbulence when the tip is inserted into a blood vessel. The tip may be adapted to induce turbulence within the working fluid. The catheter is capable of removing at least about 25 Watts of heat from an organ when inserted into a vessel supplying that organ, while cooling the tip with a working fluid that remains a liquid in the catheter. Alternatively, the catheter is capable of removing at least about 50 or 75 Watts of heat from an organ when inserted into a vessel supplying that organ, while cooling the tip with an aqueous working fluid.

In another embodiment, a cooling or warming catheter may comprise a catheter shaft having first and second lumens therein, a cooling or warming tip adapted to transfer heat to or from a working fluid circulated in through the first lumen and out through the second lumen, and turbulence-inducing structures on the tip capable of inducing turbulence when the tip is inserted into a blood vessel.

The present invention may also provide a temperature control apparatus comprising a flexible catheter which can be inserted through the vascular system of a patient to an artery or vein, with an inflatable balloon heat exchanger near the distal end of the catheter. The present invention also encompasses a method for using such a device to perform cooling, heating, or temperature management. After placement in a vessel, an embodiment of the invention includes an apparatus where the heat exchanger balloon is inflated by pressurization with a working fluid, such as saline, isolyte, D5W, or other similar fluids, or combinations of these, via a supply lumen in the catheter. The heat exchanger balloon has one or more blood passageways passing through it, from a proximal aspect of the balloon to a distal aspect of the balloon. When the heat exchanger balloon is inflated to contact the wall of the artery in which it is placed, each of the blood passageways comprises a tube having an inlet in one face of the heat exchanger balloon and an outlet in another face of the heat exchanger balloon, thereby allowing blood to continue flowing through the artery after inflation of the balloon. The blood passageway tubes can be constructed of a material having a relatively high thermal conductivity, such as a thin metallized polymer, such as a film with one or more metallized surfaces. Alternatively, the blood passageway tubes can be constructed of a metal-loaded polymer film. Further, the entire heat exchanger balloon can be constructed of such a material, in order to maximize the cooling capacity of the heat exchanger.

After inflation of the heat exchanger balloon, the saline solution, which is chilled by an external chiller, continues circulating through the interior of the heat exchanger balloon, around the blood passageway tubes, and back out of the balloon through a return lumen in the catheter. This cools the blood passageway tubes, which in turn cool the blood flowing through them. This cooled blood then flows through the selected organ and cools the organ.

The device can also incorporate a lumen for a guidewire, facilitating the navigation of the catheter through the vascular system of the patient.

In one aspect, the invention is directed to a catheter system to change the temperature of blood by heat transfer to or from a working fluid. The system includes an inflatable inlet lumen and outlet lumen. The outlet lumen is coupled to the inlet lumen so as to transfer working fluid between the two. The outlet lumen has a structure when inflated to induce turbulence in the blood and/or in the working fluid.

Variations of the system may include one or more of the following. The inlet lumen and the outlet lumen may be made of a flexible material such as latex rubber. The outlet lumen may have a structure to induce turbulence in the working fluid when inflated, such as a helical shape which may be tapered in a segmented or non-segmented manner. The radii of the inlet and outlet lumens may decrease in a distal direction such that the inlet and outlet lumens are tapered when inflated. A wire may be disposed in the inlet or outlet lumens to provide shape and strength when deflated.

The thickness of the outlet lumen, when inflated, may be less than about 1/2 mil. The length of the inlet lumen may be between about 5 and 30 centimeters. If the outlet lumen has a helical shape, the diameter of the helix may be less than about 8 millimeters when inflated. The outer diameter of the helix of the outlet lumen, when inflated, may be between about 2 millimeters and 8 millimeters and may taper to between about 1 millimeter and 2 millimeters. In segmented embodiments, a length of a segment may be between about 1 centimeter and 10 centimeters. The radii of the inlet and outlet lumens when inflated may be between about 0.5 millimeters and 2 millimeters.

The outlet lumen may further include at least one surface feature and/or interior feature, the surface feature inducing turbulence in the fluid adjacent the outlet lumen and the interior feature inducing turbulence in the working fluid. The surface feature may include one or more helical turns or spirals formed in the outlet lumen. Adjacent turns may employ opposite helicity. Alternatively or in combination, the surface feature may be a series of staggered protrusions formed in the outlet lumen.

The turbulence-inducing outlet lumen may be adapted to induce turbulence when inflated within a free stream of blood when placed within an artery. The turbulence intensity may be greater than about 0.05. The turbulence-inducing outlet lumen may be adapted to induce turbulence when inflated throughout the period of the cardiac cycle when placed within an artery or during at least 20% of the period.

The system may further include a coaxial supply catheter having an inner catheter lumen coupled to the inlet lumen and a working fluid supply configured to dispense the working fluid and having an output coupled to the inner catheter lumen. The working fluid supply may be configured to produce a pressurized working fluid at a temperature of between about -3.degree. C. and 36.degree. C. and at a pressure below about 5 atmospheres of pressure. Higher temperatures may be employed if blood heating is desired.

The turbulence-inducing outlet lumen may include a surface coating or treatment such as heparin to inhibit clot formation. A stent may be coupled to the distal end of the inlet lumen. The system may be employed to cool or heat volumes of tissue rather than blood.

In embodiments employing a tapered helical outlet lumen, the taper of the outlet lumen allows the outlet lumen to be placed in an artery having a radius less than the first radius. The outlet lumen may be tapered in segments. The segments may be separated by joints, the joints having a radius less than that of either adjacent segment.

In another aspect, the invention is directed to a method of changing the temperature of blood by heat transfer. The method includes inserting an inflatable heat transfer element into an artery or vein and inflating the same by delivering a working fluid to its interior. The temperature of the working fluid is generally different from that of the blood. The method further includes inducing turbulence in the working fluid by passing the working fluid through a turbulence-inducing path, such that turbulence is induced in a substantial portion of a free stream of blood. The inflatable heat transfer element may have a turbulence-inducing structure when inflated.

In another aspect, the invention is directed towards a method of treating the brain which includes inserting a flexible heat transfer element into an artery from a distal location and circulating a working fluid through the flexible heat transfer element to inflate the same and to selectively modify the temperature of an organ without significantly modifying the temperature of the entire body. The flexible, conductive heat transfer element preferably absorbs more than about 25, 50 or 75 watts of heat. The artery may be the common carotid or a combination of the common carotid and the internal carotid.

In another aspect, the invention is directed towards a method for selectively cooling an organ in the body of a patient which includes introducing a catheter into a blood vessel supplying the organ, the catheter having a diameter of 5 mm or less, inducing free stream turbulence in blood flowing over the catheter, and cooling the catheter to remove heat from the blood to cool the organ without substantially cooling the entire body. In one embodiment, the cooling removes at least about 75 watts of heat from the blood. In another embodiment, the cooling removes at least about 100 watts of heat from the blood. The organ being cooled may be the human brain.

The circulating may further include passing the working fluid in through an inlet lumen and out through an outlet, coaxial lumen. The working fluid may be a liquid at or well below its boiling point, and furthermore may be aqueous.

Advantages of the invention include one or more of the following. The design criteria described above for the heat transfer element: small diameter when deflated, large diameter when inflated, high flexibility, and enhanced heat transfer rate through increases in the surface of the heat transfer element and the creation of turbulent flow, facilitate creation of a heat transfer element which successfully achieves selective organ cooling or heating. Because the blood is cooled intravascularly, or in situ, problems associated with external circulation of the blood are eliminated. Also, only a single puncture and arterial vessel cannulation are required which may be performed at an easily accessible artery such as the femoral, subclavian, or brachial arteries. By eliminating the use of a cold perfusate, problems associated with excessive fluid accumulation are avoided. In addition, rapid cooling to a precise temperature may be achieved. Further, treatment of a patient is not cumbersome and the patient may easily receive continued care during the heat transfer process. The device and method may be easily combined with other devices and techniques to provide aggressive multiple therapies. Other advantages will

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. 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.

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.

Another 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.

Any of the implementations described above with respect to one aspect of the invention may also apply to other aspects of the invention. Further, implementations 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.

Another 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.

Implementations 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.

Another 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.

Another 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.

Implementations 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.

Another 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.

Another 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.

In an implementation 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.

Another 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.

In an implementation 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.

Another 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.

In an implementation 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.

Another 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.

In an implementation 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.

Another 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.

Implementations 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.

Another 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.

Implementations 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.

Another 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.

Implementations 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. 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.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a schematic representation of the heat transfer element being used in an embodiment within the superior vena cava;

FIG. 2 is a graph showing preferential cooling of the high flow organs of the body under a hypothermic therapy; and

FIG. 3 is a graph illustrating the velocity of steady state turbulent flow as a function of time;

FIG. 4 is a graph showing the velocity of the blood flow within an artery as a function of time;

FIG. 5 is a graph illustrating the velocity of steady state turbulent flow under pulsatile conditions as a function of time, similar to arterial blood flow;

FIG. 6 is an elevation view of a turbulence inducing heat transfer element within an artery;

FIG. 7 is a velocity profile diagram showing a typical steady state Poiseuillean flow driven by a constant pressure gradient;

FIG. 8 is a velocity profile diagram showing blood flow velocity within an artery, averaged over the duration of the cardiac pulse;

FIG. 9 is a velocity profile diagram showing blood flow velocity within an artery, averaged over the duration of the cardiac pulse, after insertion of a smooth heat transfer element within the artery;

FIG. 10 is a schematic diagram of a heat transfer element according to an embodiment of the invention.

FIG. 11 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.

FIG. 12 is an elevation view of one embodiment of a heat transfer element according to the invention;

FIG. 13 is a longitudinal section view of the heat transfer element of FIG. 1;

FIG. 14 is a transverse section view of the heat transfer element of FIG. 1;

FIG. 15 is a perspective view of the heat transfer element of FIG. 1 in use within a blood vessel;

FIG. 16 is a perspective view of another embodiment of a heat transfer element according to the invention, with aligned longitudinal ridges on adjacent segments;

FIG. 17 is a perspective view of another embodiment of a heat transfer element according to the invention, with somewhat offset longitudinal ridges on adjacent segments; and

FIG. 18 is a transverse section view of the heat transfer element of FIG. 16 or FIG. 17.

FIG. 19 is a cut-away perspective view of an alternative embodiment of a heat transfer element according to the invention;

FIG. 20 is a transverse section view of the heat transfer element of FIG. 5;

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;

FIG. 22 is a cross-sectional view of the catheter of FIG. 21 taken along line 22-22 of FIG. 21;

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;

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

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

FIG. 26 is a cross-sectional view of the heat transfer element illustrated in FIG. 25 taken along line 26-26 of FIG. 25.

FIG. 27 is a side schematic view of an inflatable turbulence-inducing heat transfer element according to an embodiment of the invention, as the same is disposed within an artery.

FIG. 28 illustrates an inflatable turbulence-inducing heat transfer element according to an alternative embodiment of the invention employing a surface area enhancing taper and a turbulence-inducing shape.

FIG. 29 illustrates a tapered joint which may be employed in the embodiment of FIG. 23.

FIG. 30 illustrates a turbulence-inducing heat transfer element according to a second alternative embodiment of the invention employing a surface area enhancing taper and turbulence-inducing surface features.

FIG. 31 illustrates a type of turbulence-inducing surface feature which may be employed in the heat transfer element of the embodiment of FIG. 28. In FIG. 31 a spiral feature is shown.

FIG. 32 illustrates a heat transfer element according to an alternative embodiment of the invention employing a surface area enhancing taper.

FIG. 33 illustrates another type of turbulence-inducing surface feature which may be employed in the heat transfer element of the embodiment of FIG. 27. In FIG. 33, a series of staggered protrusions are shown.

FIG. 34 is a transverse cross-sectional view of the heat transfer element of the embodiment of FIG. 33.

FIG. 35 is a perspective view of the device of the present invention in place in a common carotid artery of a patient;

FIG. 36 is a perspective view of the device shown in FIG. 35, with additional details of construction;

FIG. 37 is a transverse section view of the device shown in FIG. 36, along the section line 3-3; and

FIG. 38 is a partial longitudinal section view of the device shown in FIG. 30, showing the flow path of the cooling fluid.

FIG. 39 is a schematic representation of the heat transfer element being used in one embodiment to provide hypothermia to a patient by causing total body cooling and then rewarming the body;

FIG. 40 is a schematic representation of the heat transfer element being used in one embodiment to cool the brain of a patient and to warm the blood returning from the brain in the jugular vein;

FIG. 41 is a schematic representation of the heat transfer element being used in one embodiment to cool the brain of a patient, while a warm saline solution is infused to warm the blood returning from the brain in the jugular vein; and

FIG. 42 is a schematic representation of one embodiment of an external warming device which can be used to warm the blood returning from an organ in a vein.

FIG. 43 is a schematic representation of the heat transfer element being used in another embodiment to provide hypothermia to a patient by causing total body cooling and then rewarming the body;

FIG. 44 is a flowchart showing an exemplary method of the invention employing heating blankets and thermoregulatory drugs.

FIG. 45 shows a meperidine molecule

FIG. 46 shows a morphine molecule.

FIG. 47 shows a prodine (+) isomer molecule.

FIG. 48 shows a prodine (-) isomer molecule.

FIG. 49 shows a fentanyl molecule.

FIG. 50 shows a hydroxy allyl prodine (+) isomer molecule.

FIG. 51 shows a picenadol (+) isomermolecule.

FIG. 52 shows a picenadol (-) isomer molecule.

FIG. 53 shows a tramadol molecule.

FIG. 54 shows a nefopam molecule.

FIG. 55 is a schematic representation of the use of a heat transfer element to cool the body, according to an embodiment of the invention.

FIG. 56 is a flowchart showing an exemplary method of the invention.

FIG. 57 shows a catheter having a manifold constructed in accordance with the present invention.

FIG. 58 is an enlarged sectional view of a fragmentary portion of the catheter shown in FIG. 57.

FIG. 59 is a perspective view of a heat transfer catheter system including a circulation set constructed in accordance with an embodiment of the invention;

FIG. 60 is a cross-sectional view of an embodiment of a distal portion of a heat transfer catheter along with a side-elevational view of an embodiment of a proximal portion of the catheter that may be used with the circulation set illustrated in FIG. 59;

FIG. 61 is a schematic view of a valve that may be employed in an embodiment of the present invention.

FIG. 62 is a schematic diagram of the circulation set illustrated in FIG. 48;

FIG. 63 is an exploded perspective view of an embodiment of a disposable heat exchanger that may be used in the circulation set of the present invention.

FIG. 64 is a cross sectional view of the heat exchanger illustrated in FIG. 52.

FIGS. 65 and 66 are perspective views of the manifold portions of the heat exchanger illustrated in FIG. 63.

FIG. 67 is a perspective view of a temperature and pressure sensor assembly constructed in accordance with an embodiment of the invention;

FIG. 68 is an exploded perspective view of the temperature and pressure sensor assembly illustrated in FIG. 67.

FIG. 69 is an exploded side-elevational view of the temperature and pressure sensor assembly illustrated in FIG. 67.

FIG. 70 is an exploded perspective view of the temperature and pressure sensor assembly illustrated in FIG. 67, but from a different vantage point from that of FIG. 68.

FIG. 71 is an exemplary graph of a pump motor speed versus time for a pump of the circulation set illustrated in FIG. 59.

FIG. 72 is an exemplary graph of pressure versus pump motor speed for a 10 F heat transfer catheter and a 14 F heat transfer catheter used with the circulation set illustrated in FIG. 59.

FIG. 73 is a schematic representation of layers constituting a wall of the heat transfer element according to an embodiment of the invention and formed by a method according to the invention;

FIG. 74 is a schematic representation of layers constituting a wall of the heat transfer element according to a second embodiment of the invention and formed by a method according to the invention; and

FIG. 75 is an exploded schematic representation of layers constituting a wall of the heat transfer element according to a third embodiment of the invention and formed by a method according to the invention.

DETAILED DESCRIPTION

Overview

In the following description, the term "pressure communication" is used to describe a situation between two points in a flow or in a standing fluid. If pressure is applied at one point, the second point will eventually feel effects of the pressure if the two points are in pressure communication. Any number of valves or elements may be disposed between the two points, and the two points may still be in pressure communication if the above test is met. For example, for a standing fluid in a pipe, any number of pipe fittings may be disposed between two pipes and, so long as an open path is maintained, points in the respective pipes may still be in pressure communication.

A one or two-step process and a one or two-piece device may be employed to intravascularly lower the temperature of a body in order to induce therapeutic hypothermia. A cooling element may be placed in a high-flow vein such as the vena cavae to absorb heat from the blood flowing into the heart. This transfer of heat causes a cooling of the blood flowing through the heart and thus throughout the vasculature. Such a method and device may therapeutically be used to induce an artificial state of hypothermia.

A heat transfer element that systemically cools blood should be capable of providing the necessary heat transfer rate to produce the desired cooling effect throughout the vasculature. This may be up to or greater than 300 watts, and is at least partially dependent on the mass of the patient and the rate of blood flow. Surface features may be employed on the heat transfer element to enhance the heat transfer rate. The surface features and other components of the heat transfer element are described in more detail below.

One problem with hypothermia as a therapy is that the patient's thermoregulatory defenses initiate, attempting to defeat the hypothermia. Methods and devices may be used to lessen the thermoregulatory response. For example, a heating blanket may cover the patient. In this way, the patient may be made more comfortable. Thermoregulatory drugs may also be employed to lower the trigger point at which the patient's thermoregulatory system begins to initiate defenses. Such drugs are described in more detail below. A method employing thermoregulatory drugs, heating blankets, and heat transfer elements is also disclosed below.

Anatomical Placement

The internal jugular vein is the vein that directly drains the brain. The external jugular joins the internal jugular at the base of the neck. The internal jugular veins join the subclavian veins to form the brachiocephalic veins that in turn drain into the superior vena cava. The superior vena cava drains into the right atrium of the heart as may be seen by referring ahead to FIG. 1. The superior vena cava supplies blood to the heart from the upper part of the body.

A cooling element may be placed into the superior vena cava, inferior vena cava, or otherwise into a vein which feeds into the superior-vena cava or otherwise into the heart to cool the body. A physician percutaneously places the catheter into the subclavian or internal or external jugular veins to access the superior vena cava. The blood, cooled by the heat transfer element, may be processed by the heart and provided to the body in oxygenated form to be used as a conductive medium to cool the body. The lungs have a fairly low heat capacity, and thus the lungs do not cause appreciable rewarming of the flowing blood.

The vasculature by its very nature provides preferential blood flow to the high blood flow organs such as the brain and the heart. Thus, these organs are preferentially cooled by such a procedure as is also shown experimentally in FIG. 2. FIG. 2 is a graph of measured temperature plotted versus cooling time. This graph show the effect of placing a cooling element in the superior vena cavae of a sheep. The core body temperature as measured by an esophageal probe is shown by curve 14. The brain temperature is shown by curve 12. The brain temperature is seen to decrease more rapidly than the core body temperature throughout the experiment. The inventors believe this effect to be due to the preferential supply of blood provided to the brain and heart. This effect may be even more pronounced if thermoregulatory effects, such as vasoconstriction, occur that tend to focus blood supply to the core vascular system and away from the peripheral vascular system.

Heat Transfer

When a heat transfer element is inserted approximately coaxially into an artery or vein, the primary mechanism of heat transfer between the surface of the heat transfer element and the blood is forced convection. Convection relies upon the movement of fluid to transfer heat. Forced convection results when an external force causes motion within the fluid. In the case of arterial or venous flow, the beating heart causes the motion of the blood around the heat transfer element.

The magnitude of the heat transfer rate is proportional to the surface area of the heat transfer element, the temperature differential, and the heat transfer coefficient of the heat transfer element.

The receiving artery or vein into which the heat transfer element is placed has a limited diameter and length. Thus, the surface area of the heat transfer element must be limited to avoid significant obstruction of the artery or vein and to allow the heat transfer element to easily pass through the vascular system. For placement within the superior vena cava via the external jugular, the cross sectional diameter of the heat transfer element may be limited to about 5-6 mm, and its length may be limited to approximately 10-15 cm. For placement within the inferior vena cava, the cross sectional diameter of the heat transfer element may be limited to about 6-7 mm, and its length may be limited to approximately 25-35 cm.

Decreasing the surface temperature of the heat transfer element can increase the temperature differential. However, the minimum allowable surface temperature is limited by the characteristics of blood. Blood freezes at approximately 0.degree. C. When the blood approaches freezing, ice emboli may form in the blood, which may lodge downstream, causing serious ischemic injury. Furthermore, reducing the temperature of the blood also increases its viscosity, which results in a small decrease in the value of the convection heat transfer coefficient. In addition, increased viscosity of the blood may result in an increase in the pressure drop within the artery, thus compromising the flow of blood to the brain. Given the above constraints, it is advantageous to limit the minimum allowable surface temperature of the cooling element to approximately 5.degree. C. This results in a maximum temperature differential between the blood stream and the cooling element of approximately 32.degree. C. For other physiological reasons, there are limits on the maximum allowable surface temperature of the warming element.

The mechanisms by which the value of the convection heat transfer coefficient may be increased are complex. However, it is well known that the convection heat transfer coefficient increases with the level of "mixing" or "turbulent" kinetic energy in the fluid flow. Thus it is advantageous to have blood flow with a high degree of mixing in contact with the heat transfer element.

The blood flow has a considerably more stable flux in the superior vena cava than in an artery. However, the blood flow in the superior vena cava still has a high degree of inherent mixing or turbulence. Reynolds numbers in the superior vena cava may range, for example, from 2,000 to 5,000. Thus, blood cooling in the superior vena cava may benefit from enhancing the level of mixing with the heat transfer element but this benefit may be substantially less than that caused by the inherent mixing.

A thin boundary layer has been shown to form during the cardiac cycle. Boundary layers develop adjacent to the heat transfer element as well as next to the walls of the artery or vein. Each of these boundary layers has approximately the same thickness as the boundary layer that would have developed at the wall of the artery in the absence of the heat transfer element. The free stream flow region is developed in an annular ring around the heat transfer element. The heat transfer element used in such a vessel should reduce the formation of such viscous boundary layers.

Heat Transfer Element Characteristics

The intravascular heat transfer element should be flexible in order to be placed within the vena cavae or other veins or arteries. The flexibility of the heat transfer element is an important characteristic because the same is typically inserted into a vein such as the external jugular and accesses the superior vena cava by initially passing though a series of one or more branches. Further, the heat transfer element is ideally constructed from a highly thermally conductive material such as metal in order to facilitate heat transfer. The use of a highly thermally conductive material increases the heat transfer rate for a given temperature differential between the working fluid within the heat transfer element and the blood. This facilitates the use of a higher temperature coolant, or lower temperature warming fluid, within the heat transfer element, allowing safer working fluids, such as water or saline, to be used. Highly thermally conductive materials, such as metals, tend to be rigid. Therefore, the design of the heat transfer element should facilitate flexibility in an inherently inflexible material.

It is estimated that the cooling element should absorb at least about 300 Watts of heat when placed in the superior vena cava to lower the temperature of the body to between about 30.degree. C. and 34.degree. C. These temperatures are thought to be appropriate to obtain the benefits of hypothermia described above. The