Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
2001-12-03
2003-06-10
Gibson, Roy D. (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
C607S105000, C604S043000, C604S264000
Reexamination Certificate
active
06576001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to lumen designs for catheters. More particularly, the invention relates to lumen designs for catheters that modify and control the temperature of a selected body organ.
2. Background Information
Organs in the human body, such as the brain, kidney and heart, are maintained at a constant temperature of approximately 37° C. Hypothermia can be clinically defined as a core body temperature of 35° C. or less. Hypothermia is sometimes characterized further according to its severity. A body core temperature in the range of 33° C. to 35° C. is described as mild hypothermia. A body temperature of 28° C. to 32° C. is described as moderate hypothermia. A body core temperature in the range of 24° C. is described as severe hypothermia.
Hypothermia is uniquely effective in reducing brain injury caused by a variety of neurological insults and may eventually play an important role in emergency brain resuscitation. Experimental evidence has demonstrated that cerebral cooling improves outcome after global ischemia, focal ischemia, or traumatic brain injury. For this reason, hypothermia may be induced in order to reduce the effect of certain bodily injuries to the brain as well as other organs.
Cerebral hypothermia has traditionally been accomplished through whole body cooling to create a condition of total body hypothermia in the range of 20° C. to 30° C.
Catheters have been developed which are inserted into the bloodstream of the patient in order to induce total body hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes a method and apparatus of lowering and raising the temperature of the human body. Dato induces moderate hypothermia in a patient using a metallic catheter. The metallic catheter has an inner passageway through which a fluid, such as water, can be circulated. The catheter is inserted through the femoral vein and then through the inferior vena cava as far as the right atrium and the superior vena cava. The Dato catheter has an elongated cylindrical shape and is constructed from stainless steel. By way of example, Dato suggests the use of a catheter approximately 70 cm in length and approximately 6 mm in diameter.
Due to certain problems sometimes associated with total body hypothermia, attempts have been made to provide more selective cooling. For example, cooling helmets or headgear have been used in an attempt to cool only the head rather than the patient's entire body. However, such methods rely on conductive heat transfer through the skull and into the brain. One drawback of using conductive heat transfer is that the process of reducing the temperature of the brain is prolonged. Also, it is difficult to precisely control the temperature of the brain when using conduction due to the temperature gradient that must be established externally in order to sufficiently lower the internal temperature. In addition, when using conduction to cool the brain, the face of the patient is also subjected to severe hypothermia, increasing discomfort and the likelihood of negative side effects. It is known that profound cooling of the face can cause similar cardiovascular side effects as total body cooling. From a practical standpoint, such devices are cumbersome and may make continued treatment of the patient difficult or impossible.
Selected organ hypothermia has been accomplished using extracorporeal perfusion, as detailed by Arthur E. Schwartz, M.D. et al., in
Isolated Cerebral Hypothermia by Single Carotid Artery Perfusion of Extracorporeally Cooled Blood in Baboons,
which appeared in Vol. 39, No. 3, NEUROSURGERY 577 (September, 1996). In this study, blood was continually withdrawn from baboons through the femoral artery. The blood was cooled by a water bath and then infused through a common carotid artery with its external branches occluded. Using this method, normal heart rhythm, systemic arterial blood pressure and arterial blood gas values were maintained during the hypothermia. This study showed that the brain could be selectively cooled to temperatures of 20° C. without reducing the temperature of the entire body. However, external circulation of blood is not a practical approach for treating humans because the risk of infection, need for anticoagulation, and risk of bleeding is too great. Further, this method requires cannulation of two vessels making it more cumbersome to perform particularly in emergency settings. Even more, percutaneous cannulation of the carotid artery is difficult and potentially fatal due to the associated arterial wall trauma. Finally, this method would be ineffective to cool other organs, such as the kidneys, because the feeding arteries cannot be directly cannulated percutaneously.
Selective organ hypothermia has also been attempted by perfusion of a cold solution such as saline or perflourocarbons. This process is commonly used to protect the heart during heart surgery and is referred to as cardioplegia. Perfusion of a cold solution has a number of drawbacks, including a limited time of administration due to excessive volume accumulation, cost, and inconvenience of maintaining the perfusate and lack of effectiveness due to the temperature dilution from the blood. Temperature dilution by the blood is a particular problem in high blood flow organs such as the brain.
Catheters adapted for delivering heat transfer fluids at temperatures above or below normal body temperatures to selected internal body sites have been devised in the past (See, for example, U.S. Pat. No. 5,624,392 to Saab). These catheters often have a concentric, coaxial configuration of multiple lumens. The configurations often have a first central lumen adapted to receive a guide surrounded by a concentric second supply lumen adapted to supply a working fluid to a distal portion of the catheter and an outer concentric third return lumen, which surrounds the second lumen, adapted to return a working fluid to a fluid source. A problem with this configuration is that the working fluid in the supply lumen makes surface area contact with both an outer wall, which partially defines the outer limits of the second lumen, and an inner wall, which defines the first lumen, leading to increased heat transfer between the walls and the working fluid. Thus, if the second supply lumen in the catheter is designed to deliver a cooling fluid to the distal portion of the catheter, the increased surface area contact caused by this configuration unnecessarily warms the cooling fluid prior to delivery to the distal portion of the catheter. Another problem with these catheters is that the supply lumen(s) and return lumen(s) are not sized relative to each other to maximize the flow rate through the catheter. Hence, they do not optimize heating and/or cooling catheter performance.
BRIEF SUMMARY OF THE INVENTION
The present invention involves a device for heating or cooling a surrounding fluid in a blood vessel that addresses and solves the problems discussed above with multiple lumen arrangements of catheters in the past. The device includes an elongated catheter body, a heat transfer element located at a distal portion of the catheter body and including an interior, an elongated supply lumen adapted to deliver a working fluid to the interior of the heat transfer element and having a hydraulic diameter, an elongated return lumen adapted to return a working fluid from the interior of the heat transfer element and having a hydraulic diameter, and wherein the ratio of the hydraulic diameter of the return lumen to the hydraulic diameter of the supply lumen is substantially equal to 0.75.
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 shap
Dobak, III John D
Gilmartin Kevin P.
Lasheras Juan C
Werneth Randell L.
Yon Steven A.
Gibson Roy D.
Innercool Therapies, Inc.
Procopio Cory Hargreaves & Savitch LLP
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