Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2002-01-25
2004-04-13
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06721603
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to methods and apparatus for treating or controlling medical, psychiatric or neurological disorders by application of modulating electrical signals to a selected nerve or nerve bundle of a patient, and more particularly to techniques for treating pain syndromes in patients by selective electrical stimulation of at least one of the trigeminal, glossopharyngeal, vagus and sympathetic nerves.
The most commonly experienced form of pain is attributable to a stimulus on nerve endings, which transmits impulses to the cerebrum. In this nociception or nociceptive pain, a somatic sensation of pain, the organism is informed of impending tissue damage. The pain signals are initially processed by somatic and visceral free nerve endings—nociceptors. A pathway for nociceptive pain exists within the central nervous system (CNS) through neurons that are the basic excitable cell units of the nerve tissue in the CNS. Each neuron transmits impulse information about the stimulus on the nerve endings along portions of the pathway.
Other types of pain, such as neuropathic pain and psychogenic pain, may develop without actual impending tissue damage. Neuropathic pain involves a disease of the nervous system, usually from an underlying disease process or injury, typically arising after injury to elements of the nervous system involved in nociception. For example, peripheral nerve injury may occur in which the lesions de-afferent the nociceptive pathway, that is, produce a state of loss of afferent input by removal of the incoming signal fiber functions of the pathway.
The nociceptive pathway serves to protect the organism from pain, such as that experienced from a burn. This pathway is inactive unless danger to the organism exists. It begins with activation of peripheral receptors, the signal traveling up the peripheral nerve and into the spinal cord where synapses are made on second order neurons. The latter transmit the pain signal up the spinal cord in the spinothalamic tract ending in the thalamus. The prevailing view is that pain is recognized or perceived in the thalamus. Ventrolateral and ventromedial thalamic nuclei project to the cortex, where the pain is processed respecting localization and other integrative characteristics.
The neuropathic or psychogenic pain pathways are not associated with immediate action to prevent injury. For example, pain experienced following amputation of a limb is neuropathic—no danger of injury exists to the missing limb. Psychogenic pain is a chronic condition of pain without definite organic pathology.
Pain signals originate from peripheral neural receptors, the sensory nerve endings responsive to stimulation, typically from free nerve endings in the skin or the organs. When activated, a graded receptor potential is generated which causes an axon in the nerve fibers to fire action potentials. Action potentials are electrical impulses that self-propagate in a series of polarizations and depolarizations transmitted down the axon. Whether specific pain fibers exist or the sensation of pain comes from recognition of a pattern of impulses, the pain sensations are usually carried by small diameter nerve fibers. Initially, the receptor potential varies in amplitude and may dissipate rapidly with time despite a continuing stimulus, with consequent reduction in the firing frequency in the nerve fiber.
A descending pathway that can inhibit the incoming pain signals is important in the body's endogenous control of pain. It includes the periaqueductal grey, the dorsal raphe nuclei, locus ceruleus, and nuclei of the medullary reticular formation. Spontaneous activation of the pathway, which may involve activation of the endogenous opiate system, tends to suppress pain transmission.
Other projections from the periphery may also assist to gate pain, for example pain transmission is inhibited with the activation of large diameter A afferents activated by vibration, such as when the individual's hand is burned and is involuntarily shaken in response. Transcutaneous electrical nerve stimulation (TENS) analgesia also applies this technique, using a non-invasive procedure to submit electrical impulses from an external stimulator through electrodes on the skin to reduce transmission of pain signals to the brain.
Some pain syndromes are associated with an overactive sympathetic nervous system. This occurs following peripheral nerve injury, with resulting pain and sympathetic activity known as causalgia. There is evidence, for example, that norepinephrine—a transmitter of the sympathetic system—excites nociceptive fibers to produce this abnormal pain. It is possible, however, that aberrant nerve transmission results in activation of sympathetic afferents and to the overactivity.
The sensation of pain is subjective, the clinical reaction differing from patient to patient. The patient's interpretation of the sensation and its potential sources can lead to apprehension and distress that exacerbates the pain itself. Concentrations of excitatory and inhibitory neurotransmitters in the spinal cord and the brain may vary from individual to individual in response to different stimuli. This may be part of the basis for differences in the tolerance for pain among individuals, and even in the same individual over time. The tolerance for or threshold of pain is, in any case, a dynamic process that depends on the state of the organism, as, for example, instances of minimal pain being experienced for some injuries suffered by soldiers in battle.
The physician's diagnosis of the site and nature of the underlying pathology of pain depends substantially on historical information provided by the patient. This information includes location of the pain, the extent that it tends to radiate, its intensity, whether it is continual or recurring, the conditions or medications that tend to reduce or increase its severity, in addition to other factors. However, different patients describe pain and its apparent sources in different ways, and some are unable to describe it adequately as to specific site or nature. Prescribing the proper treatment requires an understanding of the underlying organic basis of the pain, and is particularly difficult with patients who experience chronic pain syndromes.
Common complaints include existence of spinal pain, usually in the cervical or lower spine, headache, facial pain, neck pain, and pain in the extremities. Chronic pain that lacks pathological basis is psychogenic, and may be symptomatic of patients suffering from tension, anxiety, depression, hysteria, hypochondria, or simply malingering. But persistent or recurring pain may be neuropathic, attributable to a condition such as arthritis, peripheral nerve pain such as causalgia, or peripheral neuropathy. Hyperpathia and hyperalgesia patients suffer excessive painful reaction to what may constitute normal pain sensations in most individuals.
Drug therapy remains the principal form of treatment for pain, including prescription of analgesics, corticosteroids, antidepressants, topical anesthetics and local anesthetic injections. In acute settings, as after surgery, it is common to prescribe narcotics and anti-inflammatory drugs. For chronic pain, anti-inflammatory drugs are generally the preferred prescription. Other drug therapies in use include tricyclic antidepressants for activating the descending pathways that provide analgesia. Local or systemic administration of anesthetic agents may be used in some cases. Opiates delivered by programmed administration to the cerebrospinal fluid by external drug pumps have been prescribed for patients with intractable pain, especially cancer patients.
TENS analgesia has been most often used for pain following peripheral nerve injury (deafferentation), or for back pain which is chronic and refractory to surgical therapy, or in other cases where surgery is not indicated. Other therapies include dorsal column stimulation and CNS stimulation. The former requires implantation of electrodes in the dorsa
Barrett Burke T.
Parnis Steven M.
Zabara Jacob
Blank Rome LLP
Cyberonics, Inc.
Layno Carl
LandOfFree
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