Abstract:
Medical devices for inducing hypothermia are disclosed. Induced hypothermia is a treatment used to reduce secondary complications caused by reduced oxygen and blood flow during traumatic injuries and surgeries. However, induced hypothermia also has negative side effects such as shivering and lowered immune system. These devices incorporate Highly-Oriented Pyrolytic Graphite (HOPG) for solid conduction to lower the temperature at targeted locations on and inside the body. The benefits of incorporating HOPG include: highly efficient heat conduction, flexibility in design and manufacture, reduction of dependence on inefficient and unstable fluid-filled implants and catheters, and anti-thrombotic effects.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority of U.S. Provisional Application 62/262,501, filed on Dec. 3, 2015, and is a continuation-in-part of U.S. patent application Ser. No. 14/257,135, which claims the benefit of priority of U.S. Provisional Application 61/814,964, filed on Apr. 23, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to devices for inducing hypothermia. 
         [0004]    2. Description of the Related Art 
         [0005]    Induced therapeutic hypothermia and other medically-induced cooling methods are promising treatments with wide-ranging applications. The reduction of patients&#39; body temperature during strokes, heart attacks and brain or spine injuries has been shown to reduce secondary complications caused by ischemia and other impairments to oxygen and blood flow. Induction of mild hypothermia has been hypothesized to significantly decrease intracranial pressure and secondary neurological injury. The Hypothermia after Cardiac Arrest Study Group. “Mild Therapeutic Hypothermia to Improve the Neurologic Outcome after Cardiac Arrest.” New England Journal of Medicine 346.8 (2002): 549-56. 
         [0006]    Hypothermia can be applied in many circumstances, including in emergency settings to mitigate damage, and during surgeries to reduce the risk of ischemia. Currently known methods of induced hypothermia include external cooling baths and blankets, and internal circulation of fluids and gasses, whether directly into the body or within delivery means such as balloon catheters. Many methods are aimed at inducing systemic hypothermia, i.e. hypothermia induced to the whole body. In fact, induction of systemic hypothermia is now the standard of care in the management of patients who survive cardiac arrest. 
         [0007]    More specific applications of applied cooling methods include, but are not limited to, pain relief, prevention of chemotherapy induced hair loss, and reduction of discomfort of braces and casts. In addition, some devices seek to induce systemic hypothermia using localized techniques, because systemic hypothermia is associated with a host of negative side effects such as bleeding diathesis, shivering, arrhythmias, suppression of the immune system, and electrolyte imbalance. Some such devices focus on cooling the brain, for instance using cooling helmets. Others purport to deliver cooling directly to circulating fluids, for instance, the bloodstream (see U.S. Pub. No. 2002/0030717 A1), or cerebrospinal fluid (see U.S. Pat. No. 2007/0005121 A1). Inserts such as catheters are cooled using the circulation of fluid to the inserted device. These devices, however, are limited by the freezing point of the fluid, and they can rupture or leak fluid, resulting in dangerous contamination. Furthermore, balloon catheter use has been associated with increased risk of deep vein thrombosis (DVT) and clotting. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Disclosed herein are devices for inducing therapeutic hypothermia using solid-to-solid conduction. These devices include garments that apply cooling to the body, both local and general, and insertable devices such as catheters, which use the flow of blood or cerebrospinal fluid to distribute cooling throughout the body. The devices use solid thermal conductive elements, safe to use in and on the human body, to transmit cooling temperatures from an external cooling element to sections of the device in contact with the body. In particular, the preferred solid thermal conductive and body-safe elements are comprised of Highly Oriented Pyrolytic Graphite sheets (HOPG), which have known anti-clotting effects. 
         [0009]    HOPG, also known as graphite sheets, graphene, and PGS (Pyrolytic Graphite Sheets), is currently used in electronic applications for heat conductive properties. Hereinafter, the term “HOPG” will be used to refer to those currently known forms of synthetic graphite comprised of highly aligned graphite crystallites resulting in high thermal conductivity. The thermal conductivity of the HOPG is much higher than aluminum, steel, and even copper. For instance, 25 μm sheets demonstrate conductivity of up to 1700 W/m K, versus 300 W/m K for pure copper. Furthermore, HOPG can be produced in thin, flexible sheets and other shapes suitable to all kinds of medical devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the following drawings, like reference numbers have been used wherever possible to indicate like parts in different views: 
           [0011]      FIG. 1  is a side view of a first catheter lumen with HOPG sheets. 
           [0012]      FIG. 2  is a front cross-sectional view of the first catheter lumen with HOPG sheets. 
           [0013]      FIG. 3  is a perspective schematic of an implantable device with HOPG sheets. 
           [0014]      FIG. 4  is a perspective view of a hypothermia-induction catheter implantable into the brain ventricles. 
           [0015]      FIG. 5  is a perspective view of a second catheter lumen with HOPG sheets. 
           [0016]      FIG. 6  is a perspective view of a cooling garment worn on the head in an environment of use. 
           [0017]      FIG. 7  is a perspective view of a cooling garment in an environment of use. 
           [0018]      FIG. 8  is a schematic of a hypothermia-induction catheter implantable into the bloodstream in an environment of use. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    In a first embodiment, shown in environment of use in  FIG. 4  and  FIG. 8 , the lumen of a catheter for implantation into the body is comprised of HOPG, described in further detail below. A HOPG transmission member  101  or  121  is in solid thermal conductive contact with the HOPG of the lumen, as well as with an external cooling element  102  or  122 . When the external cooling element is operated, the cooling temperature is rapidly transmitted along the HOPG transmission element to the catheter. 
         [0020]    As shown in  FIGS. 1, 2, 3 and 5 , the catheter lumen comprises sections of HOPG  300 . HOPG is biocompatible and bioinert, i.e. elicits little to no response from the body, and furthermore is known to have antithrombotic effects within the body, reducing the risk of clotting. Due to the flexibility of the HOPG, many configurations are possible. For instance, the HOPG  300  stretches axially along the length of the lumen, as shown in  FIGS. 1 and 2 . Or, as depicted in  FIG. 4 , the HOPG  300  is deposited in cross-sectional rings along the lumen. Alternatively, the HOPG  300  shown in  FIG. 4  may be a thermally conductive frame attachable to a standard catheter, disposable or sterilizable and reusable. 
         [0021]    A second embodiment, which is a generalized HOPG implant  303 , is shown schematically in  FIG. 3 . Like the catheter lumens depicted in  FIGS. 1, 2, and 4 , the general HOPG implant can be implanted anywhere in the body. The general HOPG implant  303  can be a solid piece of HOPG, rather than a flexible and hollow lumen, and is shaped to maximize surface area. As shown in  FIG. 3 , the HOPG sheets of the implant have been folded in a fan or accordion-like structure. Other alternatives include: the HOPG may be rolled into a tube that is built into the catheter or multiple flexible “ribbons” of the graphite sheet may be affixed to the distal end of the catheter (like a horse&#39;s tail or cauda equina) which would float in the body cavity, cerebrospinal fluid or blood vessel. Although numerous designs are possible, the aforementioned designs would maximize exposed surface area and therefore the effects of heat conduction. Implant  303  is in solid thermal conductive connection with HOPG transmission member  301 , which in turn is in thermal connection with external cooling element  302 . 
         [0022]    Similarly, as shown in  FIGS. 4 and 8 . The HOPG of the catheters  100  or  120  is in solid thermal conductive connection with an HOPG transmission member  101  or  121  which is in turn in thermal conductive connection with an external cooling element  102  or  122 . It should here be noted that the views depicted are schematics and do not limit the length or size of the HOPG transmission members. In other words, HOPG transmission members  101 ,  121 ,  301 ,  131 , and  142  may be any length. Because of the high thermal conductivity of the HOPG, heat is rapidly conducted from the external cooling elements to the implants. Furthermore, due to the flexibility of HOPG and the freedom to design almost any shape, the HOPG transmission member and the HOPG of the catheters may be one and same. The external cooling element may be any cooling device, as simple as chilled liquid or gas such as frozen CO2, or more complex electronic devices such as heat pipes, Peltier machines, or other heat exchangers known in the art. 
         [0023]    Preferably, the cooling catheter is implanted where circulation maximizes the induction of hypothermia. In the preferred embodiment, the cooling catheter is implanted into cerebrospinal fluid (CSF) during standard of care ventricle drainage procedures. The drainage catheter  100  is typically inserted into lateral ventrical  500  of the brain, as depicted in  FIG. 4 , and may comprise any combination of known monitoring sensors, such as pressure transducer, oxygen monitor, and temperature gauge. Openings  200  allow pressure to be alleviated as CSF enters catheter  100  through the openings and out of the skull. Due to the circulation of CSF throughout the brain and spinal cord, effective cooling may take place throughout the body, and especially in the brain and spinal cord where it is most needed. As such, the CSF cooling catheter both regulates intracranial pressure and induces hypothermia to further prevent ischemic injury. The cooling catheter may also be implanted into the bloodstream, as shown in  FIG. 8 . Not only is graphite biocompatible, but anti-thrombotic effects of HOPG further prevent clotting and strokes. Like the lumens shown in  FIGS. 1, 2, 3 and 5 , vascular cooling catheters may comprise openings for infusions of drugs and other fluids. The cooling catheter or cooling implant may also be inserted into the nasal or oral cavity, or natural orifices (such as, but not limited to, the oronasopharynx, esophagus, trachea, or colon/rectum) or elsewhere throughout the body. 
         [0024]    The concept of the present invention can also be applied to other cooling devices such as helmets, vests and blankets. For instance, as shown in  FIG. 6 , a cooling cap for placement over the head is comprised of HOPG  130 , which is in solid thermal conductive connection with HOPG transmission member  131 . Using an external cooling element  132 , cooling temperatures are transferred via cooling member  131  to the graphite garment  130 . In another embodiment, depicted in  FIG. 7 , a cooling garment or vest  140  is comprised of HOPG  140 , which is in solid thermal conductive connection with HOPG transmission member  142 . Using an external cooling element  143 , cooling temperatures are transferred via transmission member  142  to the graphite garment  140 . Due to the flexibility of the synthetic HOPG, the HOPG transmission member and the graphite of the catheters may be one and same. As in the case of the catheter devices, the external cooling element may be any cooling device, as simple as chilled liquid or gas such as frozen CO2, or electronic devices such as heat pipes, Peltier machines, or other heat exchangers known in the art. 
         [0025]    Because the HOPG is biocompatible, it is suitable for contact with any section of the human body. Furthermore, the flexibility of the HOPG allows it to be incorporated into any type of garment or shape. The high thermal conductivity of the HOPG can also be utilized within braces, collars, immobilization devices, and casts to conduct away heat in order to maintain a more comfortable temperature for the patient. It is further contemplated that HOPG can be used in any garment for the purpose of cooling, and therefore has applications in clothing generally, such as leisure, athletics and other physical work. Optionally, electronic control may be connected to the cooling mechanism by wired or wireless connection.