Abstract:
An apparatus for cooling the brain of a patient includes a housing for engagement on a neck of the patient and one or more nozzles for receiving a coolant fluid from an external coolant source and providing a directed mist of the coolant. The nozzles are mounted within the housing and are aligned such that the mist of coolant is directed to the neck of the patient. The apparatus can include a brain temperature sensor operatively coupled to a controller to regulate the discharge of the mist of coolant to maintain a desired brain temperature.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to medical apparatus and more particularly relates to a medical apparatus for cooling the brain of patient undergoing a medical procedure 
     BACKGROUND OF THE INVENTION 
     It is well known in the medical community that brain cells are susceptible to damage and ultimately death, when subjected to temperature extremes. The body normally is capable of regulating the temperature at a safe level, such as 98.6° Fahrenheit. However, if the body is subjected to an illness which induces extreme fever or if a medical procedure is taking place which elevates the temperature of the blood flowing in the patient, brain damage may result unless measures are taken to ensure that the brain temperature remains below 108° Fahrenheit. For example, if a patient is undergoing microwave therapy, as described in U.S. Pat. No. 5,922,013, a patient&#39;s body is subjected to local heating. This local heating may result in excess brain temperature unless the brain temperature is independently controlled from the region undergoing microwave heating. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an apparatus for cooling the brain of a patient in a rapid and controlled manner. 
     It is a further object of the present invention to provide a method for cooling the brain of a patient in a rapid and controlled manner. 
     An apparatus for cooling the brain of a patient includes a housing for engagement on a neck of the patient and one or more nozzles for receiving a coolant fluid from an external coolant source and providing a directed mist of the coolant. The nozzles are mounted within the housing and are aligned such that the mist of coolant is directed to the neck of the patient. 
     The brain cooling apparatus can include a pump interposed between the nozzles and the external coolant. 
     The brain cooling apparatus can also include a brain temperature sensor for measuring the temperature of the brain of the patient and a controller which is coupled to the brain temperature sensor and provides a signal to the pump to adjust the coolant discharge rate in response to a measured brain temperature. Generally, the signal from the controller directs the pump to increase the coolant discharge rate when the measured brain temperature exceeds a maximum brain temperature value and directs the pump to decrease the coolant discharge rate when the measured brain temperature is below a minimum brain temperature value. 
     The housing can also include a fluid discharge port to establish fluid communication with a fluid collection vessel. 
     A method for cooling the brain of a patient includes the steps of directing a fluid mist discharge onto the neck of a patient, measuring the temperature of the brain, and altering the fluid mist discharge in response to the measured brain temperature to maintain a desired brain temperature. The altering step can increase a discharge rate of the fluid mist if the measured brain temperature exceeds a maximum brain temperature value and decrease the discharge rate of the fluid mist if the measured brain temperature is below a minimum brain temperature value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention, in which 
     FIG. 1 is a block diagram of an embodiment of the present brain cooling system; 
     FIG. 2 is a top cross-sectional view of the housing portion of the brain cooling system of FIG. 1, engaged upon the neck of a patient; and 
     FIG. 3 is a flow chart illustrating a method of cooling a brain in a controlled manner. 
    
    
     Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the subject invention will now be described in detail with reference to the figures, it is done so in connection with the illustrative embodiments. It is intended that changes and modifications can be made to the described embodiments without departing from the true scope and spirit of the subject invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In general, the term patient, as used herein, refers to a human being or other animal undergoing treatment with the present apparatus and methods. Referring to FIG.  1  and FIG. 2, the present brain cooling apparatus includes a housing  100  which is adapted to engage the neck of a patient and provide a substantially fluid tight seal therewith. Within the housing  100  are a first cool mist nozzle  102  and a second cool mist nozzle  104 . The cool mist nozzles  102 ,  104  are in fluid communication with a pump  106  through conduit  108 . The pump  106  is coupled via fluid conduit  110  to a coolant fluid supply vessel  112 . The pump  106  preferably provides a variable flow rate and operates in response to control signals provided by controller  114  which in turn is responsive to a signal from a brain temperature sensor  116 . Alternatively, the coolant fluid supply vessel  112  can contain a pressurized coolant and pump  106  can be replaced with an electronically controllable fluid regulator valve. 
     The coolant provided in coolant supply vessel  112  can be any fluid known to provide significant cooling. This can include refrigerants, such as liquid nitrogen, which rapidly evaporate to effect cooling or fluids which exhibit a very low freezing point and are chilled to an appropriately low temperature by a refrigerator unit within the coolant supply vessel  112  or downstream therefrom. For example, a chilled alcohol solution may provide sufficient cooling. 
     The brain temperature sensor  116  can take any form known in the art for measuring the temperature of brain tissue. The brain temperature sensor  116  provides a signal indicative of the brain temperature of the patient to the controller  114 . In response, the controller  114  processes the brain temperature sensor signal to determine whether the brain is within an acceptable range of temperatures (T D ±Δ), which can be predetermined or set by an operator using a suitable interface device (not shown) to the controller  114 . The controller  114  provides a signal to the pump  106  to control the fluid flow from the coolant supply vessel  112  through conduits  110  and  108  to the cool mist nozzles  102 ,  104 . If the brain temperature exceeds a desired temperature range (T D ±Δ), the controller  114  can direct the pump  106  to increase the fluid flow. Similarly, if the brain temperature is below a desired temperature, the controller  114  can direct the pump  106  to reduce the fluid flow. The desired brain temperature can be any temperature below 108° F., including temperatures which induce safe levels of brain hypothermia. 
     The housing  100  has a front face  100   a  and a back face  100   b  which are separated by a side wall  100   c  and bottom wall sections  100   d  to establish a fluid containing chamber when the housing is engaged on the neck of a patient. Both the front face  100   a  and the back face  100   b  have substantially semicircular cutaways which are sized and shaped to form a sealing engagement with the neck of a patient. The resulting housing can be described as an inverted U-shaped housing. Compliant diaphragm member  126  can be used along the perimeter of the openings to facilitate a comfortable, yet fluid tight seal with the neck of the patient. 
     The first cool mist nozzle  102  and second cool mist nozzle  104  are mounted in the housing  100  such that a fine mist from each nozzle is directed onto a region of the neck over the carotid arteries of the patient when the housing is properly engaged on the neck of the patient. The nozzle should provide a minimum practicable droplet size for the selected coolant. It is also desirable that the nozzle provide an elongate spray pattern, such as a fan shaped pattern  202 , which substantially extends along the neck region over the carotid arteries. The nozzle attributes contribute to provide a maximum cooling effect as the surface area of the coolant impinging upon the neck of the patient is maximized Preferably, the nozzles  102 ,  104  are mounted on adjustable brackets  204  such that the angular direction of the nozzle, as well as the distance of the nozzle from the patient&#39;s neck, can be adjusted to suit an individual patient. 
     A fluid discharge port  130  can also be included in the housing  100  to provide a return path for coolant which is discharged from the first cool mist nozzle  102  and second cool mist nozzle  104 . The recovered coolant can be in the form of a vapor, a liquid, or both depending on the coolant selected. The state of the recovered coolant will determine the location of the discharge port. In the case where the discharge is heavier than air, the discharge port  130  can be located on a lower portion of the housing  100 . In the case where the discharge is lighter than air, the discharge port  130  can be located on an upper portion of the housing  100 . The discharge port  130  is preferably in fluid communication with a pump  132  via conduit  134 . The pump  132  forces the coolant collected in the housing  100  into a collection vessel  136  via fluid conduit  138 . Alternatively, the collection vessel  136  can be placed below the housing  100  and a gravity feed system can be used to transfer fluid from the housing  100  to the collection vessel  136 . Preferably, the fluid collection vessel can be further coupled to a coolant reclamation unit  138  which can condense, chill and otherwise restore the coolant to its original state and return the restored coolant fluid to the coolant supply vessel  112 . In this way, a closed system is established whereby a majority of the coolant fluid is continuously re-circulated. 
     By directly impinging the carotid arteries with a fine mist of a coolant fluid, the blood flowing to the brain is rapidly cooled, resulting in cooling of the brain tissue or maintaining the brain tissue at a safe temperature. The rate of cooling is determined by the temperature of the coolant, the rate of evaporation of the coolant and the volume of the coolant being applied to the surface of the neck proximate the carotid arteries. The thermal resistance of the tissue interposed between the surface of the patient&#39;s neck and the carotid artery will also effect the cooling rate. The orifice diameter and spray pattern of the nozzles  102 ,  104  can be selected in cooperation with the flow rate range of the pump  106  and the selected coolant provided in coolant supply  112  to effect an effective cool mist application. The flow of coolant, within the discharge range of the selected pump  106 , is controlled by the controller  114  in response to a signal from the brain temperature sensor  116 . Thus, a closed loop control system is established whereby the brain temperature is positively regulated despite the aforementioned variables, such as tissue thermal resistance. 
     FIG. 3 is a flow chart illustrating a method of maintaining the brain of a patient in a desired temperature range (T D ⊥Δ), where T D  is the nominal desired brain temperature and Δ is a constant which provides a range of hystereses in the control system. After initialization  300 , the controller  114  sets the pump  106  to a flow rate approximately in the center of the range of operation of the pump (step  305 ). A brain temperature measurement is taken to determine the current brain temperature (T B ) (step  310 ). This can be an instantaneous measurement or an average of several samples taken over a known time period. 
     The measured brain temperature (T B ) is then compared against the desired temperature range (T D ±Δ)(step  315 ). If the brain temperature is within the desired range, the coolant flow rate is acceptable and control is returned to step  310  for a new brain temperature measurement. If the brain temperature is below the minimum desired brain temperature value (step  320 ), the flow of coolant is reduced (step  325 ) and the process returns to step  310 . If the brain temperature is above the maximum desired brain temperature value (step  330 ), the coolant flow rate is increased (step  335 ) and the process returns to step  310 . If the condition of steps  315 ,  320  and  330  all fail, this indicates an error and control is terminated (step  340 ). 
     The apparatus and methods described herein use direct impingement of a fine mist of coolant to effect a rapid and controlled cooling the brain of a patient. Such rapid and controlled cooling of the brain provides for maintaining the brain at a temperature lower than a portion of a patient&#39;s body which is undergoing medical microwave, or other local heating treatment. Such rapid and controlled cooling of the brain can also be used to induce brain hypothermia, and unconsciousness, without medication. 
     Although the present invention has been described in connection with specific exemplary embodiments, it should be understood that various changes, substitutions and alterations can be made to the disclosed embodiments without departing from the spirit and scope of the invention as set forth in the appended claims.