Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
2000-10-03
2003-03-11
Gibson, Roy D. (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
C607S106000, C607S107000, C606S027000
Reexamination Certificate
active
06530946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to apparatus and methods for producing heat exchange with body tissue, and more specifically to methods and apparatus for the initiation of hypothermic treatment of a body fluid in a body conduit or maintaining normothermia within the body conduit.
2. Discussion of the Prior Art
Many of the advantages of hypothermia, as well as maintaining normothermia, are well known. By way of example, it has been found particularly desirable to lower the temperature of body tissue in order to reduce the metabolism of the body. In stroke and several other pathological conditions, hypothermia also reduces the permeability of the blood/brain barrier. It inhibits release of damaging neurotransmitters and also inhibits calcium-mediated effects. Hypothermia inhibits brain edema and lowers intracranial pressure.
In the past, hypothermic treatment has been addressed systemically, meaning that the overall temperature of the entire body has been lowered to achieve the advantages noted above. This has been particularly desirable in surgical applications where the reduced metabolism has made it possible to more easily accommodate lengthy operative procedures. An example of this systemic approach includes catheters for transferring heat to or from blood flowing within a patient's vessel, as disclosed by Ginsburg in U.S. Pat. No. 5,486,208. A closed loop heat exchange catheter is also disclosed by Saab in U.S. Pat. No. 5,624,392.
Some of the disadvantages of systemic hypothermia include cardiac arrhythmia, pulmonary edema and coagulopathies. Systemic hypothermia also results in hypotension and various immunodeficiencies.
The systemic approach is not always advantageous when the beneficial effects are desired locally at the focus of the operative procedure and only the disadvantages of hypothermia are felt throughout the remainder of the body.
More recent focus has been directed to producing hypothermia in localized areas of the body, leaving the remainder of the body to function at a normal body temperature. These localized applications of hypothermia have been external, relying for example on cooling helmets or cooling neck collars to produce localized hypothermia for the brain.
Another area of catheter construction involves heat pipe technology. Heat pipes are ideally packaged in thin metal envelopes (or tubes) due to the nature of good thermal conductivity and high pressure vessel strength. The heat pipe is ideal from the standpoint that no moving parts are required and no pumping mechanisms are needed to move the working fluid. An example of a heat pipe used as a catheter for precise temperature control for treating diseased tissue is disclosed by Fletcher in U.S. Pat. No. 5,591,162. However Fletcher does not teach a catheter with flexible bellows to allow for insertion into the human bloodstream. Nor does Fletcher disclose a catheter which can be used in the ambulatory setting.
In many of the neurological injury scenarios, time to treatment or the onset of hyperthermia is critical to the patient and ultimate recovery. It would be ideal if treatment could be initiated as soon as the patient presents or is reached. This can often be outside of a hospital setting. Therefore, a means to initiate hypothermia or maintain normothermia in an ambulatory environment would be greatly beneficial. The current state of technology, (i.e. recirculating catheters, water blankets, etc.) requires significant pieces of equipment to provide a cooling source along with tubing and heat exchangers to couple the cold source to the patient.
Current ambulatory methods of initiating hypothermia are ice baths, alcohol wipes, eliminating clothing and fanning. In hospital management, tools include water blankets and drug therapy. Such ambulatory methods listed are all topical or superficial cooling methods. Topical cooling is slow and labor intensive. In cases of brain injury, the patient does not necessarily have an elevated temperature at the time of injury. However, if the patient's temperature can be managed from the time of insult, the better the chances are of maintaining normothermia or preventing severe elevated temperatures or fever spikes. Some applications such as heat exposure, burn victims, systemic infections, etc., may already be febrile and could benefit from immediate cooling. Systemic intravascular cooling is more effective than topical cooling since the body core temperature is directly effected by bloodstream temperature. Topical cooling does not always accomplish core cooling as desired. Therefore there has been a long felt need for an indwelling catheter which is portable for use in the ambulatory setting and flexible to navigate through the tortuosity of the blood vessels atraumatically.
SUMMARY OF THE INVENTION
A heat exchange catheter and method of operation are included in the present invention. The method is adapted to produce hypothermia, hyperthermia or maintain normothermia in a selected portion of the body without substantially varying the temperature of the remaining portions of the body. The selected body portion will typically be associated with a body conduit which conveys a body fluid to the selected body portion. Of particular interest are the organs of the body which are commonly nourished and maintained by a flow of blood in the arterial system. For example, a flow of blood is introduced to the brain through the carotid artery. Of course the temperature of this blood is usually at the normal body temperature.
By positioning a heat exchange catheter in the body conduit, heat can be added to or removed from the body fluid to heat or cool the selected body portion. For example, the heat exchange catheter can be disposed in the carotid artery where the arterial blood flowing to the brain can be cooled. The flow of cooled blood to the brain reduces the temperature of the brain thereby resulting in cerebral hypothermia. Importantly, this temperature reduction occurs primarily and selectively in the brain; the remaining portions of the body maintain a generally normal body temperature. In accordance with this method, the selected body portion, such as the brain, can be cooled thereby providing the advantages associated with hypothermia for this body portion. The remainder of the body, such as the portions other than the brain, do not experience the reduction in temperature and therefore are not susceptible to the disadvantages of hypothermia. Furthermore, the invention is intended to remotely alter temperature in a region other than the point of introduction into the body. This is different than devices intended for systemic temperature control.
Several factors are of interest in effecting heat transfer in a heat exchanger. These factors include, for example, the convection heat transfer coefficient of the two fluids involved in the heat exchange, as well as the thermal conductivity and thickness of the barrier between the two fluids. Other factors include the relative temperature differential between the fluids, as well as the contact area and residence time of heat transfer. The Reynolds number for each fluid stream affects boundary layers, turbulence and laminar flow.
With concern for these factors, the heat exchange catheter of the present invention includes a shaft having an axis, a fluid inlet lumen and a fluid outlet lumen each extending generally between a proximal end and a distal end of the shaft. A hub disposed at the proximal end provides access to the fluid lumens. At least one balloon is provided in a heat exchange region at the distal end of the shaft, the balloon wall providing the barrier between the two fluids. With the catheter positioned in contact with the body fluid within the conduit, heat transfer occurs across the balloon wall. The relative temperature differential is facilitated with countercurrent flow between the two fluids.
In one aspect of the invention, a first balloon is disposed at the distal end of the shaft and defines with the shaft an inflatable first cavity. Portio
Evans Scott
Jones Mike
Noda Wayne
Alsius Corporation
Burns Doane Swecker & Mathis L.L.P.
Gibson Roy D.
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