BACKGROUND OF THE INVENTION
Field of the Invention. The present invention relates generally to medical apparatus and methods. More particularly, the present invention relates to the construction and use of heat exchange catheters having elastically inflatable heat exchange surfaces.
Under ordinary circumstances, the thenroregulatory system of the human body maintains a near constant temperature of about 37° C. (98.6° F.), a temperature referred to as normothermia. For various reasons, however, a person may develop a body temperature that is below normal temperature, a condition know as hypothermia, or a temperature that is above normal temperature, a condition known as hyperthermia. Hypothermia and hyperthermia are generally harmful, and if severe, the patient is generally treated to reverse the condition and return the patient to normothermia. Accidental hypothermia significant enough to require treatment may occur in patients exposed to overwhelming cold stress in the environment or whose thermoregulatory ability has been lessened due to injury, illness or anesthesia. For example, this type of hypothermia sometimes occurs in patients suffering from trauma or as a complication in patients undergoing surgery. Likewise, examples of hyperthermia include exposure to overwhelming exposure to hot environmental stimulation, injury or illness, or complications of anesthesia.
In certain situations, however, hyperthermia and especially hypothermia may be desirable and may even be intentionally induced. For instance, hypothermia is generally recognized as being neuroprotective, and may, therefore, be induced in conjunction with treatments for ischemic or hemorrhagic stroke, blood deprivation such as caused by cardiac arrest, intracerebral or intracranial hemorrhage, and head and spinal trauma. In each of these instances, damage to neural tissue may occur because of ischemia, increased intracranial pressure, edema or other processes, often resulting in a loss of cerebral function and permanent neurological deficits. Intentionally induced hypothermia may reduce or avoid the damage that would otherwise occur if the patient temperature was normothermic or hyperthermic.
Other examples where hypothermia may be neuroprotective include periods of cardiac arrest in myocardial infarction and heart surgery, neurosurgical procedures such as aneurysm repair surgeries, endovascular aneurysm repair procedures, spinal surgeries, procedures where the patient is at risk for brain, cardiac or spinal ischemia such as beating heart by-pass surgery or any surgery where the blood supply to the heart, brain or spinal cord may be temporarily interrupted. Hypothermia has also been found to be advantageous as a treatment to protect both neural tissue and cardiac muscle tissue during or after a myocardial infract (MI).
Body heating and cooling can be achieved in a variety of ways. Body heating is most simply achieved by wrapping a patient in blankets and/or heated jackets in order to raise body temperature over time. Body cooling can be similarly achieved using cooling jackets. The ability to cool patients using external cooling, however, is problematic. Induced cooling will trigger a patient's thermoregulatory responses, causing patient's body to generate more heat in order to maintain body temperature. It has also been found that external cooling can cause the patient to “shiver,” and that shivering not only causes discomfort but also induces the patient's body to generate still more heat in response.
In order to overcome the deficiencies of external body heating and cooling, it has been proposed to heat or cool blood in a patient's circulation, thus effecting an internal modification of body temperature. For example, it has been proposed to remove blood in a patient, e.g., from the inferior vena cava, externally heat or cool the blood, and then return the blood to patient circulation. Such external cooling of patient blood is performed, for example, during cardiopulmonary bypass surgery where the heart is stopped and the blood is also oxygenated. Such external blood cooling, however, suffers from a number of deficiencies. It is quite invasive to the patient, is damaging to the blood (causing significant hemolysis over time), generally must be performed in a sophisticated operating room and by highly trained and expensive medical specialists, and can only be performed for up to several hours before it must be discontinued. Thus, external blood heating or cooling is not appropriate for many circumstances.
Of particular interest to the present invention, an improved method for adding or removing heat from patient circulation uses a heat exchange catheter placed in the bloodstream of a patient, as described in U.S. Pat. No. 5,486,208 to Ginsburg, the complete disclosure of which is incorporated herein by reference. The Ginsburg patent discloses a method of controlling the temperature of a body by adding or removing heat to the blood by inserting a heat exchange catheter having a heat exchange region into the vascular system and exchanging heat between the heat exchange region and the blood to affect the temperature of a patient. One method disclosed for doing so includes inserting a catheter having a heat exchange region comprising a balloon into the vasculature of a patient and circulating warm or cold heat exchange fluid through the balloon while the balloon is in contact with the blood. Other patents and applications describing heat exchange catheters are listed below.
Heretofore, the balloons of heat exchange catheters have generally been formed from polyethylene terephthalate (PET) and other substantially non-distensable materials, i.e., materials which are essentially non-elastic and do not stretch when the balloon is filled with heat exchange medium. Distensible or elastomeric heat exchange structures, however, may have certain advantages over non-distensible heat exchange structures in many situations. For example, when the balloon is non-elastic, it needs to be folded or otherwise constrained on the distal end of the heat exchange catheter in order to facilitate introduction. After use and deflection prior to withdrawal, the heat exchange balloon becomes loose and floppy, rendering withdrawal of the catheter more difficult. In its loose and floppy condition, it may be more prone to damage upon withdrawal from the patient. Further, responsiveness to various ranges of pressures is sometimes an advantage, for example when pulsing or fluctuating motion desirable to induce mixing for enhanced heat exchange in flowing fluid such as blood. The control of size by control of pressure in the elastomeric heat exchange structure may be an advantage, for example, when a range of heat exchange surface sized can be obtained for different sized patients using the same type of device by controlling the pressure of the heat exchange fluid. Moreover, manufacturing of heat exchange catheters with PET and other non-distensible balloon materials may be more difficult and expensive than manufacturing the device with elastomeric material.
For these reasons, it would be desirable to provide improved heat exchange catheters, and in particular improved balloon structures on such heat exchange catheters. Such balloon structures will preferably conform closely to the exterior surface of the heat exchange catheter when introduced and will return to such a closely conforming configuration when withdrawn after use. Such balloon structures should provide adequate or improved heat transfer characteristics when compared with the PET and other non-distensible balloon materials of prior art. Moreover, such balloon structures should be fabricated from materials which are bio-compatible and which induce little or no clot formation (are non-thrombogenic). At least some of these objectives will be met by the inventions described hereinafter.
DESCRIPTION OF THE BACKGROUND ART
Patents and published applications assigned to the assignee of the present invention include U.S. Pat. Nos. 6,306,161; 6,264,679; 6,231,594; 6,149,676; 6,149,673; 6,110,168; 5,989,238; 5,879,329; and 5,837,003; U.S. Patent Publication US 2001/005791; and Published PCT Applications WO 01/64164; WO 01/58397; WO 01/152781; WO 01/43661; WO 01/13809; WO 01/10323; WO 00/10494; WO 98/31312; and WO 98/26831. Other patents relating to body cooling include U.S. Pat. Nos. 6,325,818; 6,312,452; 6,261,312; 6,254,626; 6,251,130; 6,251,129; 6,245,095; 6,238,428; 6,235,048; 6,231,595; 6,224,624; 6,149,677; 6,096,068; 6,042,559; 6,299,599; 6,290,717; 6,287,326; 6,165,207; 6,149,670; 6,146,411; 6,126,684; 6,019,703; and 5,269,758. The full disclosures of each of these patents and published applications are incorporated herein.
BRIEF SUMMARY OF THE INVENTION
This section describes what may be typical features and characteristics of a medical device of the invention, but unless the feature is specifically stated to be necessary, the references are not limiting of the invention despite their inclusion in this section.
The present invention provides improved heat exchange catheters having elastic heat exchange structures, referred to hereinafter as “balloons” or “chambers.” The heat exchange structures are elastically expansible so that they inflate or enlarge when a suitable heat exchange medium, such as heated or cooled saline, is introduced to the heat exchange structure under pressure. The heat exchange medium will usually, although not necessarily be non-compressible. The pressure-induced expansion enlarges the heat exchange structure, thus increasing the surface area of the heat exchange structure which is available for transferring heat to or from the circulating blood in a patient's vasculature.
Many aspects of the construction of the heat exchange catheters may be conventional and may, for example, incorporate many elements of the heat exchange catheters described in the patents and applications, which have been incorporated by reference above. For example, the heat exchange structures of the present invention will be incorporated on a catheter body having a proximal end, a distal region, and usually at least two fluid flow lumens therethrough. The catheter body will be suitable for percutaneous introduction to the patient's vasculature through a variety of access sites, such as introduction into the femoral vein and advancement into the inferior vena cave (IVC) or introduction into one of the carotid veins or the subclavian vein and advancement into the superior vena cava (SVC). Any other appropriate site may be used; for example placement in the arterial vasculature may be made by introduction into the femoral artery and advancement into the aorta. Other placement as may be appropriate for the particular purpose is within the contemplation of this patent, for example into the renal arteries to cool the kidneys, into the hepatic arteries to cool the liver or into the carotid arteries to cool the bead or brain.
The catheter bodies will typically have a length in the range from 15 cm to 100 cm, typically from 25 cm to 75 cm, and a diameter from 1 mm to 4 mm, usually from 2 mm to 4 mm. The catheter bodies will typically be formed from a relatively hard, non-elastic polymer, typically having a hardness in the range from 75 A to 82 D, usually from 85 A to 72 D. Suitable polymeric materials include polyurethanes, C-Flex®, and the like. Specific catheter body designs are disclosed, for example, in U.S. Pat. No. 6,264,679, assigned to the assignee in the present application, and WO 00/10494, the full disclosures which are incorporated herein by reference, as well as PCT application PCT/U.S. 01/03828, assigned to the assignee in the present application, and WO 00/10494, the full disclosures of which are incorporated herein by reference.
As used herein, the term “elastic” includes heat exchange structures which are formed from a suitable elastomer, as well as structures which are formed from non-elastomeric sheets or membranes and which incorporate elastic reinforcement or constraining materials so that the structures may elastically expand and deflate as the heat exchange medium is introduced and removed. Suitable elastomers will usually be softer and often thinner than the material from which the catheter body has been formed, but may be composed of the same polymeric resin. Suitable elastomeric balloon or chamber materials will have hardness in the range from 65 A to 45 D, usually from 75 A to 100 A. Suitable elastomers include polyurethanes, silicone ruber, natural and synthetic latex (although generally not preferred), polyvinyls, plastisized PVC and the like. An exemplary and presently preferred material is styrene-ethylene-butylene-modified block copolymer with silicone oil, available under the C-Flex® tradename. The use of a heat exchange structure material which is the same as (although softer and more elastic than) the catheter body material is advantageous since it facilitates heat sealing of the materials together, as will be described in more detail below.
The catheter bodies of the heat exchange catheters of the present invention will usually have at least two lumens to provide for inflow and outflow of the heat exchange medium, respectively. Optionally, additional lumens may be provided for supply of heat exchange medium to different compartments within the heat exchange structure or for other purposes.
In a first aspect of the present invention, heat exchange catheters comprise a catheter body having a proximal end and a distal end. A heat exchange balloon structure is disposed over the distal region, and the balloon structure is constructed or composed of the elastic material selected so that the structure initially conforms to the distal region of the catheter body (preferably without folding as is characteristic of non-distensible balloons such as angioplasty balloons) and expands elastically in response to the introduction of the heat exchange medium under pressure. When the treatment is done, and the supply of the heat exchange medium terminated, the heat exchange balloon structure will deflate elastically so that it again conforms to the catheter body to facilitate removal of the catheter. While the heat exchange structures will be highly elastic, it will be appreciated that some hysteresis, i.e., loss of the elasticity, is acceptable. It is preferred, however, that the elongation of the balloon structure in any one direction be less than 10% after use, preferably being less than 5%.
Preferred balloons and other heat exchange structures will be relatively small when deflated, having a diameter or width which does not significantly exceed that of round catheter body. The functional deflated cross-sectional size is sometimes called profile. If the catheter is not round, this still gives a functional measure of the size since this is the size of puncture introducer hole that is necessary in order to insert the catheter. Profile is generally measured in French size (Fr) with one Fr equal to 0.33 mm. The Fr size of the preferred catheters including balloons will generally be between 4 Fr and 14 Fr with a size between about 6 Fr and 10 Fr being preferable. Generally, a smaller French size for insertion is preferable to a larger size, and one advantage of the elastomeric heat exchange region is the potential of having a very large heat exchange surface when inflated despite a small French size when deflated for insertion. When inflated at a typical heat exchange medium pressure in the range from 0.5 psig to 50 psig, however, the heat exchange balloons or other structures will have a surface area which is significantly greater, typically increasing by at least 10% more typically by at least 25%.
In a second aspect of the present invention, the heat exchange catheter comprises a catheter body having a proximal end, a distal region, an inflow lumen, and an outflow lumen. The heat exchange balloon or other structure comprises a plurality of elastic polymer chambers disposed over the distal region and fluidly connected at an inlet end to the inflow lumen and at an outlet end to the outflow lumen. By dividing the inflow of heat exchange medium among a plurality of heat exchange chambers, the heat transfer rate can be improved. Polymeric chambers may be arranged axially, helically, or in other patterns over the distal region of the catheter body. The number of chambers may vary, typically be in the range from two to twelve, usually from two to eight, and preferably from four to eight. In order to further enhance heat transfer, it is sometimes desirable to circumferentially space-apart the axial or spiral chambers which are formed over the distal region. The surface areas when inflated and deflated, material properties, and other characteristics of these catheters will generally be the same as described with respect to the first embodiment of the catheter set forth above.
In a third embodiment, a heat exchange catheter constructed in accordance with the principles of the present invention comprises a catheter body having a proximal end, a distal region, an inflow lumen, and an outflow lumen. An elastomer tube (either consisting of an elastomeric material or reinforced or constrained by elastomeric components) is coaxially positioned over the distal region, and the tube is sealed to the catheter body along a multiplicity of lines to define at least one, and usually a plurality of separate inflatable chambers, each of which is fluidly connected at an inlet end to the inflow lumen and at an outlet end to the outflow lumen. The surface areas of the chambers, materials of the balloon and catheter body, catheter dimensions, and the like, may all be the same as described with the first and second embodiments of the present invention as set forth above.
In a fourth aspect, the present invention comprises a method for fabricating a catheter. A tubular catheter body is first positioned over a mandrel where the catheter body has at least an inflow lumen and an outflow lumen. An elastomer tube (as defined above) is placed over the distal region of the catheter body, and the elastomer tube is then attached to the catheter body in order to define a plurality of separate, elastically expandable chambers between the outside of the catheter body and the inside of the elastomer tube. The chambers are arranged so that an inlet end of each chamber is fluidly connected to the inflow lumen and an outlet end of each chamber is fluidly connected to the outflow lumen. The dimensions, materials, and other characteristics of the catheter body and elastomer tube may generally be the same as set forth above for the catheter body and elastic heat exchange region.
In the preferred embodiments, the elastomer tube is attached to the catheter body using heat staking in which case it further preferred that the elastomer tube be “heat sealable” with the material of the catheter body, typically being the same material but having a different hardness. By “heat sealable” it is meant that the materials of the catheter body and the elastomer tube will, when exposed to heat, at least partially melt and meld together along lines formed by a suitable heating tool. Such heat staking or other sealing will preferably be performed over a multiplicity of lines to define the plurality of chambers therebetween. Chambers may be formed axially, helically, or in other patterns as desired. In a preferred aspect of the fabrication method, the heat stake or other attachment lines will be formed to have a width in the circumferential direction in the range from 0.01 mm to 2 mm, preferably from 0.1 mm to 0.5, in order to circumferentially separate adjacent heat exchange chambers.
In a fifth aspect of the present invention, a method for exchanging heat with vascular circulation of a patient comprises percutaneously introducing a catheter to a blood vessel of the patient. The catheter includes at least one elastic chamber conformed over a surface thereof while it is introduced. After introduction, the chamber is elastically inflated with a heat exchange medium, typically heated or cooled saline, whereby heat is exchanged between the heat exchange medium and the vascular circulation. Typically, the catheter may be introduced into a blood vessel, such as the femoral vein, an advanced so that the heat exchange region is at a desired location in the vasculature such as the IVC. The heat exchange chamber is inflated with heat exchange medium at a pressure in the range from 0.5 psi to 50 psi, preferably from 1 psi to 30 psi, and a flow rate in the range from 5 ml/min to 1000 ml/min, preferably from 100 ml/min to 500 ml/min. For heating, the temperature of the medium will typically be in the range from 33° C. to 48° C., usually from 38° C. to 42° C. For cooling, the temperature of the medium will typically be from −10° C. to 34° C., usually from 0° C. to 10° C. In a particular aspect of the present invention, the heat exchange medium may be pulsed within the elastic heat exchange structure in order to cause the heat exchange surface to move or pulse, as generally described in commonly assigned patent application Ser. No. 09/872,818, the full disclosure which has previously been incorporated herein by reference.