Apparatus and methods for cooling a region within the body

This application is a continuation of U.S. patent application Ser. No. 11/096,980 filed Apr. 1, 2005, which is a continuation of U.S. patent application Ser. No. 10/841,160 filed May 7, 2004 (now U.S. Pat. No. 7,232,458), which is a continuation of U.S. patent application Ser. No. 10/159,713 filed May 31, 2002 (now U.S. Pat. No. 6,746,474), each of which is incorporated herein by reference in its entirety.

The present invention relates to the controlled cooling of selected regions within a body for the purpose of controlling pain. The present invention relates to the cooling of selected regions within the body, such as the vagus nerves, by implantable apparatus for reducing pain sensation or stimulating the nerves.

It is generally known that cooling an injured region of the body typically helps to abate the associated pain. For example, cooling painful joints, inflamed tissue, or burned areas of skin can help with reducing the pain and inflammation. However, this type of treatment is generally limited to cooling via the surface of the skin, e.g., by applying a cold compress or ice, and is not optimal in limiting the area to be treated.

Other methods of pain management usually include the ingestion or intake of analgesics or other anodynes. For instance, chronic pain typically associated with conditions such as muscle spasms, tendonitis, sciatica, etc., is not only very painful to the individual, but is usually very difficult to treat and can lead to debilitating conditions.

Such conditions, e.g., muscle spasms, may be painful, violent, and involuntary and affect a large segment of the population. This type of pain is often also chronic, i.e., lasts for one day or longer. Other conditions may result from injury or trauma to affected region within the body, such as to the muscles or to the nerves that innervate the muscles.

Examples of other painful conditions include sciatica and tendonitis. Sciatica is a condition characterized by pain radiating from the muscles in the back into the buttocks and may be a result of trauma to the spinal cord or to the sciatic nerve.

The debilitating effects of chronic pain are not only a source of anxiety and distress for the individual, but also represent a tremendous cost to society. For instance, workers suffering from chronic pain are frequently absent from work for weeks or even longer. This poses a great expense not only to the employer in sick-time coverage and disability pay, but also to society in lost productivity.

A variety of medicines are typically used in an attempt to alleviate the conditions associated with chronic pain. These have included muscle relaxants, such as methocarbamol, carisoprodol, mephenesin, etc. Nonsteroidal anti-inflammatory agents, such as ibuprofen, aspirin, and indomethacin are also used in conjunction with muscle relaxants for treating muscle spasms, tendonitis and sciatica. However, these methods provide, at most, partial relief and do not provide the type of relief considered adequate by most people. Accordingly, there exists a need for a method of effectively alleviating chronic pain and doing so in a manner which least impacts a person\'s normal daily activities.

These types of conditions may potentially be treated by the stimulation of certain regions within the brain or certain nerve fibers leading to and from the brain. One such nerve is the vagus nerve, which is located in the side of the neck and acts as a highway of information for carrying messages to and from the brain. The vagus nerve is connected to many areas of the brain which are involved in detecting chronic pain as well as areas which are instrumental in producing seizures and spasms, such as those symptoms associated with Parkinson\'s disease and epilepsy.

The treatment of internal organs and regions within the body to bring relief have sometimes involved electrical or hyperthermic treatments. For instance, treatment modalities have included delivering energy, usually in the form of RF or electrical energy, for the heating of, e.g., malignant tumors. But many of these treatments are performed through invasive surgery (laparoscopic or otherwise) that may require repeated procedures to achieve the desired effect.

Methods used in treating epilepsy include vagal nerve stimulation, where the vagal nerve is electrically stimulated to disrupt abnormal brain activity. This may include implanting an electrical stimulation device within a patient that is electrically connected to a portion of the vagal nerve. However, this method of treatment is limited to epilepsy and does may not be effective in the treatment of other types of disorders.

Various devices and methods for cooling selected regions within a body are described herein. For example, an implantable cooling system used to cool regions of the brain, regions of the spinal cord, fibrous nerve bodies such as the vagus nerve which relay impulses from the brain which may take part in epilepsy, Parkinson\'s disease, chronic pain impulses, etc. Other regions of the body for cooling may include tissue and fibrous material as well. Cooling these certain regions within the body from about 37° C. down to about 30° C. aids in diminishing or masking these impulses to control seizures or chronic pain.

Such an implantable cooling system may comprise an implantable unit that may contain a pumping mechanism and/or various control electronics. It may also include a heat exchanger connected to a heat sink contained within the body or that may be a part of the body. Such a heat sink preferably includes tubular body organs through which heat may be effectively dissipated, such as the superior vena cava (SVC) or the inferior vena cava (IVC) because of the relatively high blood flow rate therein.

Additionally, the cooling system may comprise a variety of cooling devices, but it is preferably an electrically controllable thermoelectric module that may essentially function as a heat pump. Such modules are typically known as Peltier junctions and are generally comprised of a sandwich of at least two dissimilar metals. When an electric current is applied to such a module, heat is moved from one side of the module to the other, thereby creating a “cool” side due to the Peltier Effect and a converse “hot” side due to the Seebeck Effect. Despite the reversible polarity of the current and the resulting reversible heating and cooling effect, the side contacting the nerve body below is called the cooled region, and conversely the side which is heated is called the heated region for simplicity. It is the cooled region which may be placed into intimate contact with the various regions within the body to effect the cooling of the appropriate tissue.

The heated region may be placed in thermal contact with a heat exchanging chamber filled with a liquid heat transfer medium. The liquid heat transfer medium is preferably a fluid which has a high specific heat capacity and is also biocompatible. Such fluids may include chilled saline, fluorinated hydrocarbon (Fluorinert™), liquid chlorodifluoromethane, water, etc., among others. As the heat transfer medium absorbs the heat from the heated region, the medium may be urged by a pump to pass through a controllable outlet and through a feedline to the second heat exchanger, where the absorbed heat may be discharged to the SVC, IVC, or other body organ.

The cooling device or unit may comprise a variety of configurations. One configuration is a semi-circular configuration where the cooled region is circumferentially surrounded by the heated region. Each of the cooled and heated regions may define an opening through which the vagus nerve or other nerve body to be cooled may pass through to enable the junction to fixedly attach about the nerve. To effect a better heat transfer coefficient between the junction and the nerve body, biocompatible adhesives having a sufficient thermal conductivity, i.e., does not impede the heat transfer, may be used as a thermal interface between the two. Other configurations may include clamping members which may be urged open to allow for placement onto the nerve body, and helical variations which may be unraveled temporarily by an external force to allow for placement around the nerve body. Upon releasing the external force, the device may preferably reconfigure itself to reform its helical configuration and wrap around the nerve body.

The pump may be a conventional implantable pump with an integrated power supply and/or control electronics. Alternatively, the power supply to actuate the pump and cooling unit may be supplied by an implantable transcutaneous charger. Such a charger may have its power supply recharged by an external charging unit which may be placed over the skin in proximity of the charger. Other types of pumps may be subcutaneously implanted and externally actuated and driven. Such pumps may have a diaphragm attached to an actuator, which may comprise a permanent magnet, in the pumping chamber. The diaphragm and pump may then be actuated by an external alternating electromagnet placed over the skin. Other types of pumps may also include rotational pumps that are subcutaneously implanted and also externally actuated.